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ThiS publication ·IS number 90 THE PRODUCTION and MARKETING of in the Techn·lcal Report Series TRAY- CULTURED RAFT OYSTERS "In of the Fishermens Service Branch

(formerly Industrial Development Branch) BRITISH COLUMBIA

British Columbia 1976

Prepared by M. Humphries

Sabine Seafoods Ltd.

Report on a

FEDERAL - PROVINCIAL

Shared Cost Project

Financed jointly by

Industrial Development Branch

Fisheries and Marine Service Environment Canada

and

Marine Resources Branch

Department of Recreation and Travel Industry

British Columbia

Opi.nions expressed and conclusions reached by the author are not necessarily

endorsed by the sponsors of this project

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I.

II.

III.

IV.

V.

VI.

VII.

VIII.

IX.

X.

XI.

TABLE OF CONTENTS

INTRODU CTION

DESCRlFTION OF RAFT-CULTURE METHOD

DETAILED DESCRIPTION OF THE SUSPENSION SYSTEM a) Cedar Floats b) Stee1-Dru:m Floats c} Long-Line Syste:m

GROW-OUT TRAYS

SEED ACQUISITION a) Seed-on-Cultch Shells b) Seed on Plywood J-'anels c) Seed on Ce:ment Chips d) Hatchery Seed

PROCESSING AND PACKING PLANT

FOULThTG

HARVESTING, PACKING, AND SHIPPING

MARKETING

ECONOMIC ANALYSIS a) Two-Year Production Cycle b) One- Year Production Cyle c) Sequential Analysis of Total Costs and Yield d) Effect of Increasing Production on Total Costs

and Net Profit

GROWTH STUDIES 1. Growth in Nestier Trays as a Function

of Initial Size 2. Growth as a Function of Type of Seed 3. Growth in Weight as a Function of Size and

Density 4. Com.parison of the Growth Rates for Three Seed

Types at Tucker Bay and Ten-Mile Point

Page

1

2

3 3 5 7

10

13 13 13 15 16

19

22

25

27

29 29 35 36

41

43

43 46

49

51

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Page

XII. CONCLUSIONS 54

XIII. RECOA11.1ENDATIONS 58

XIV. REFERENCES 60

, ;

..

LIST OF PHOTOGRAPHS

Number Title

l. CEDAR LOG FLOATS

2. CEDAR LOG FLOATS

3. TRAY SUSPENDED FROM CABLE

4. STEEL DRUM FLOATS

5. NESTlER GROW-OUT TRAYS

6. NESTlER GROW-OUT TRAYS

7. SEED ON PLYWOOD PANELS

8. SEED ON CEMENT CHIP

9. HATCHERY SEED

10. PACKING PLANT

1l. PACKING PLANT

f 12. ENCRUSTING SPONGE

13. ENCRUSTING SPONGE

14. TYPICAL TRAY-CULTURED OYSTERS

15. TYPICAL TRAY-CULTURED OYSTERS

I J

1. INTRODUCTION

Sabine Seafoods Ltd. of Lasqueti Island~ B.C. has just completed a

I I two-year project to investigate the feasibility of the large-scale use of , I trays as a means of raising oysters by raft culture in British Columbia.

The imn~ediate objectives of the project included the following: the

construction of a tray-suspension system and a packing plant; the depl~)y-

ITlent of 3,000 Nestier trays with sufficient seed to fill theITl; the production

and ITlarketing of the oysters produced in the two-year period; the com-

pletion of eITlpirical studies of growth and mortality; the preparation of

a cost analysis of the operation; and the preparation of progress and final

reports.

In 1974, a progress report described the construction of the first

floatation SystCIU, the packing plant, the acquisition of seed, some initial

observations on growth, and the initial attempts to market the product. A

second progress report (April, 1975) summ.arized the data on production,

ITlarketing, and a preliminary growth study.

The present papcr, constituting the Final Report, prescnts a summ.ary

of the previously reported findings and developments, along with additional

data on construction, procedures, production, cost analysis, growth data,

marketing, and major problems encountered during the project. Recom-

:mendations are :made that should be of value to others contemplating the

production of raft oysters in British Columbia.

- 2 -

II. DESCRIPTION OF THE BASIC RAFT CULTURE METHOD

The system used by Sabine Seafoods is essentially a two-year cycle

in which trays are used throughout. In the spring of the first year. small

seed acquired from the previous season's spat is placed in trays which are

then suspended from rafts. During the first growing season the seed is

frequently thinned and cleaned. until toward the end of the season each

tray contains between 100 and 200 oysters. in the 5 to 6 em size-class.

The trays are left suspended during the fall and winter months. although

very little growth. if any. occurs during that period. During the spring,

the seed is again thinned so ·that each tray contains about 160 oysters.

Cleaning and thinning continue during the second growing season, at the

end of which each tray will contain about four-dozen oysters of marketable

size - about 9.0 em in length and 75 grams in weight.

When the oysters have achieved marketable "size, they are spray

cleaned with salt water and then packed in wax-dipped cardboard cartons.

Oysters being shipped by air are packed inside poly bags, to conform to

airline regulations. All the oysters produced so far have been sold directly

to restaurants, and have been used for fresh oysters on the half shell. The

shelf life of the product when kept at or about 50 C is at least two weeks,

provided that they have been carefully packed with the cup side down, so that

body fluids are retained. In 1974, the best price we could obtain was. $1.75

per dozen, FOB Vancouver. Since that time we have been able to raise the

price to $3.15 per dozen. FOB Qualicum.

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Ill. DETAILED DESCRIFTION OF THE SUSPENSION SYSTEM

Two methods of suspending trays have been tried, and a third is now

being designed.

a) Cedar Log Floats

The first method entailed the use of 60' cedar logs banded to-

gether in pairs, each pair constituting an individual float with its

ovvn cedar. decking. Six such floats were built in 1974 and are

still in use. The six floats were connected to a main 100' boom

log in such a way that each float was separated from its neighbour

by about 8 feet. In addition to ensuring some separation between

floats, the boom log acted as a breakwater. At the other end, the

floats were connected to an underwater cable so as to permit the

entrance of a boat or work raft between floats {Fhotos 1 and 2}.

Four steel drums loaded with rocks and concrete served as anchors

for the system, one out from each of the four co~ners.

Stainless steel cables were strung along each side of the floats

(Photo 3). These cables, two for each float, provided the

supports from which the trays were suspended. Such a system

is capable of suspending about 500 Nestier trays per float, or

3000 trays in total.

The most successful method of attaching t h e tray sets to the

cable seemed to be means of a simple rope bridle to the top

tray in each set, terminating with a standard halibut snap. The

snaps provided a r apid m e thod of attaching and detaching the

- 4 -

bundle of tra ys, and yet they provide enough tension on the cable

to prevent the tray sets from shifting along the cable, even in

very high winds.

Although the life expectancy of this system is limited, because

of the action of teredo and gribb1es, it turned out to be struc-

turally strong, and a very stable work surface, even in fair.1y

high v.rinds. The dam.ping action provided by the m.as s also

minimizes the wear on support cables, halibut snaps and con-

--necting rope bridles.

If the logs could be treated in som.e way, or if they could be

placed in fresh water during the winter m.onths, the life expec-

tancy could no doubt be extended. As it is, we suspect that

three years is the best we can expect.

If we were to use this system. again, the cable support system

would be strung from. the raft in such a way that the- rope bridles

were held clear of the logs to reduce the wear on the bridles,

and sufficiently far above the surface of the water to reduce the

corrosion of halibut snaps. With the present system., halibut

snaps have to be replaced every six months, and bridles need to

be checked after every severe storm.

The cost of the suspension system, including logs, decking,

cables, chain and anchors was about $3,600.00, or about $5.00

per linear foot of suspension, both sides of the rafts being

available for suspension of trays. With a life expectancy of

- 5 -

three years, this type of suspension costs about $1.70 per linear

foot per year. (Note: Total linear feet available on the six - 60'

long floats is 720'.)

One possible disadvantage of cedar logs, if untreated, is the

rather incredible quantity of feces and other detritus produced

by the borers and other fouling organisms. This material tended

to drift down onto the upper trays of the sets beneath. Although

we have no· data on the quantity produced, nor any estimates of

the effects on oyster growth, we suspect that this fall-out must

hamper circulation if nothing else. Some Japanese studies sug-

gest that such feces, while acting as a stimulus to shell growth,

may reduce the quality and weight of the meat.

b) Steel Drum Floats

The second method of floatation was designed and built during the

spring of 1975 • . This system used 45 gallon steel drums as the

source of floatation (Photo 4). The drums were treated inside

with rust inhibitor, and were then coated with hot tar to reduce

the effects of corrosipn. The basic structure consisted of a

series of 4" x 4'1 cedar cross pieces connected to one another by

2" X 6" cedar decking. The steel drums were attached to the

decking by means of stainless steel strapping. As in the earlier

system steel cables were used to support the trays.

Six such floats were connected to a boom log that provided some

- 6 -

protection from storm action and ensured separation between

floats. At the open end of the float system the individual floats

were connected to an underwater rope cable. The systenl as a

whole was anchored by means of chains to steel drum anchors,

and to steel rings cemented into the rocks on shore.

As originally designed the drum system proved to be highly un-

stable. A series of cross walks and stabilizing members were

bolted across the floats at the break-water end. Even so~ although

nicely flexible in a storm~ they are somewhat hazardous to walk

along in rough weather.

-. ~.

The cost of the drum system, using second-hand drums obtained

at a very reasonable price~ turned out to be the same as for the

cedar float system - - about $5.00 per linear foot~ or $2~ 400.00 --. --

for the six - 40 1 long floats. The life expectancy of the system

should be much greater than for the cedar log system~ particu-

larly as individual drums can be replaced quite easily as the need

arises. {Note: the total linear feet available on the six - 40'

floats is 4801 .}

It was also quite apparent that the amount of feces and detritus

falling into the trays was much less for this system than for the • cedar logs. Although we have no data yet on the differential

effect of this difference~ it should be easy to obtain during the

next growing season.

--_._----- ._------- -~-

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c) Long-Line System

One criticism of the previously described floatation systems is

that a good deal of capital is tied up in providing floatation for

work crews who use it only periodically. In addition, both t he log

and the steel drum systems are vulnerable to storms. A better

system might be one that is not exposed to storm action, and does

not entail expensive floatation for activities that occur only in-

frequently. These considerations prompted us to explore the use

of long-lines, as developed by the Japanese and Koreans, and as

used on the East Coast by growers such as McNichol. 1

There would appear to be at least two approaches to long-lines that

may be applicable to tray culture. One entails a series of floats

along a line to which the tray sets are attached. The tray sets

themselves would have no floatation -- this is provided by the

buoys distributed along the line. In. this case, the long-line wo~d

have to be lifted in order to gain access to individual sets of trays,

which would mean a somewhat specialized vessel or work raft,

or at least som.c specialized gear by means of which the line could

be lifted and the trays reached. Should anything cause the tray

sets to become disconnected from the line, they would, of course,

sink to the bottom, which would pose no great problem, if one were

working in relatively shallow water (six fathoms or so), or if one

had the services of a diver. One great adva...l'ltage of such a system

IvicNichol, Personal COITununication.

- 8 -

would be the relatively low profile in the face of storms. The

n1.ajor disadvantage may arise from the need frequently to lift,

clean and sort individual sets of trays. The solution to the pro­

blem of keeping track of seed or coding the contents of tray sets

which are submerged may become a bit complicated.

The second approach, the one used by McNichol, entails providing

floatation for each set of trays. This could be done by filling the

top tray with sufficient foam or similar material to support the

set, or by means of a small buoy or float attached to each tray

set. In this system, the long-line itself need not be very strong

as it sim.ply acts as a restraint on the line of individually supported

sets of trays. Presun1.Q.bi~ ground tackle could similarly be scaled

down in strength and weight. As each tray- set floats on or near

the surface, the problem of m.arking or coding each set, and

gaining access to particular sets is simplified. Being on or near

the s:urface however, this system would be more vulnerable to

the effects of storm. action than the former, particularly to the

effects of floating debris, to boats and curious water skiers. In

this case, if sets were to become disconnected from the line, they

might well drift away.

A reasonable solution may be to combine these two approaches.

Sufficient floatation by means of buoys could be provided to keep

the long-line at or near the surface. Individual sets of trays could

have marker buoys a.t the junction with the: long-line, but the

- 9 -

buoyancy so provided would not be sufficient to float the set by

itself. In this case" if sets become disconnected they would sink"

but when connected they would be close enough to the surface to be

individually identified and reached as required without complex

gear. The area containing long-lines would have to be clearly

marked~ and perhaps protected by boom logs or floats around the

pe rimete r •

The initial cost of these systems should be quite low~ and the life

expectancy quite high. It will take some experimenting to devise

an efficient way of servicing the trays" and keeping track of thein"

but the savings in initial capital costs~ the extension of life expec­

tancy and the reduction in maintenance costs should more than

compensate for the relatively minor changes in equipment and

procedures.

- 10 -

IV. GROW-OUT TRAYS

The company began the project in 1974 with about 3,000 Nestier trays

{Model 5-4660). Although we had hoped to acquire some trays of other

designs this proved to be im.possible. Consequently, all the observations

entailed in this report are based on the use of the Nestier tray. (Photo­

graphs 5 and 6)

At the start of the project in .1974,. the Nestier trays were banded to­

gether in sets of ten. Later, it was discovered that the growth rate in the

upper and lower trays was considerably greater than in the middle trays.

It was also found that a 10-tray set loaded with 60mm oysters was too heavy

for one person to lift with any ease. For these reasons, the sets were

reduced to five trays. By alternating long and short bridles so that when

suspended the short ones were almost directly over the long ones,. it was

still pos sible to carry as many trays on each float as with 10-tray sets.

This process does entail a doubling of the number of bridles, halibut snaps

and top trays,. so the cost of suspension is increased slightly.

In general, the Nestier tray is ideal to handle. It is easy to load and

to stack, and. in 5-tray bundles they are easy to lift and move around.

They are strong and durable, and a life expectancy of ten years would seem

quite reasonab] e. ·The plastic banding and buckles are reusable, and even

·when fouled with nlUssels, barnacles and hydroids,. the sets can be opened

easily for cleaning and grading. It also appears that when fouling occurs,.

it ta.kes place ;mainly on the outside of the trays, leaving the oysters ·within

~:c 3.sonably dc;o.D. ane: f::ee from much of the fouling organism.s.

- .:.

-, .

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There is one major drawback to these trays however - the holes are

too small. Water circulation through the trays is less than it could be,

hence the growth rate is reduced, particularly in the middle trays of a set.

The small size of the holes also means that a relatively small amount of

fouling, particularly in the form of algae and hydroid growth, has a very

great effect on the reduction in circulation. This tray design, therefore

even when the tray is clean, limits the growth rate, and when fouling is

present, imposes a requirement that the trays be cleaned every three to

four weeks.

A partial solution to this problem can be achieved by drilling 3/4" holes

in t..~e sides of the trays. Sixteen such holes were drilled in a large num.ber

of our trays and it was found that the effect of fouling on circUlation was re-

duced, and the trays required less frequeht cleaning.

A far better solution would be to find or design a tray that m.ore ade-

quately meets the needs of tray culture. In the near future, the com.pany

will be experimenting with a tray designed by Doug McNichol in Nova Scotia;

however, even this tray is not ideal for several reasons. For one thing the

1v1cNichol tray is too small; its carrying capacity is only about 18 mature

oysters, compared with 48 for the Nestier tray. Also, as McNichol him-

self indicated, the grower really needs two tray designs -- one for seed

and one for larger oysters, or a single tray that can be :modified easily and

ine:h.."}Jensively to be ideal for both sizes. This simply means that a tray de-

signed to contain seed oysters, such as the Nestier and the McNichol, will

}i dit C holes that are smaller than needed for large oysters, thus reducing

- 12 -

the available food supply for the larger. Nevertheless, because of the

design of the tray (like a donut) and the shape of the holes, the circulation

in the McNichol tray should be greater than in the Nestier. As there is no

available data on the cOlnparative growth rates in McNichol and Nestier

trays~ a study will be conducted to test this prediction. The final solution,

however~ will still entail the design and manufacture of an inexpe,nsive tray

for the specialized need of half- shell oyster culture.

- 13 -

v. SEED ACQUISITION

One of the most important factors determining the success of a tray-

culture operation has to do with the acquisition of sufficient seed in a form

that economically enables the grower to load trays with individual oysters

as early in the growing process as possible. The major problems are

associated "vith survival rate and labour. As the goal is to produce attrac-

tive, single oysters for the half- shell market, the best seed is that which

can be separated into individual oysters as early as possible with the mini-

mum of labour and mortality. Of the several varieties of seed available

to growers in British ColUlnbia, we tried four: seed on cultch shells; seed

on. plywood panels; seed on cement chips; and hatchery seed from the U.S.A.

a) Seed on Cultch Shells

The company tried two types of seed on shell and found both to be

unsatisfactory for tray culture. One type made use of West Coast

oyster shell as the medium. of collection, and the other used rela-

tively small, thin Philippine shell as the mediUln. In both cases,

the labour and the mortality involved in separating the seed from

one another and frOln the collector shell proved to be too great.

It may be that an operation involving both shucked and unshucked

oyster production could make use of such seed, as is done on the

East Coast, but such seed is not effective for tray culture itself.

b) Seed on Plywood Panels (Photograph 7)

The second type of seed used by the company was collected on

cenlcnt-coated plywood panels. Normally, this seed is collected

- 14

during the late summer of one year and is sold after the growing

season has ended, at which time the seed will have reached a length

of 5 to 15 mm, depending on the amount of growth after the set.

The task for the grower is then to remove the seed from the

panels, and separate the seed from one another, and then place

the seed in trays for subsequent growth.

The ease with which the seed can be removed from the panels

depends on the size of the seed, the thickness of the cement

veneer, and the pattern of growth. In general, the larger the size,

the more easily it can be removed without damage. The thicker

the veneer the better, at least within limits, as a very thin coating

seems to adhere to the wood excessively. When the oys.ters are

crowded they tend to grow out from the panel and are more easily

separated than in areas where the set is thin and the oysters grow

along the panel. The best strategy is to permit the oysters to grow

for several weeks in the spring, dry the panels for a day or so,

and then by a twisting action of the panels remove those that seem

to come away most easily. Those remaining can be left on the

panels for a few more \-leeks of growth after which they too can be

removed. Although this process entails a fair amount of labouT,

the mortality is kept to a minimum, and the return is reasonable.

Our experience has been that the grower needs to order from 20

to 30% more seed than he predicts he will need to cover the losses

incurred during the separation process. It has also been our ex-

- 15 -

perience that seed from panels will require a full two seasons in

trays before most reach marketable length and weight. The initial

cost of panel seed in 1974 was about $34.00 per case with an esti-

mated yield of about 20~ OOO~ or about 1/5 cent each. In 1976, panel

seed is available for $54.00 per case with an estimated yield of

22~ 000 per case. =:e

c) Seed on Cement Chip (Photograph 8)

The third type of seed used was collected on cement discs which

produce individual diamond shaped chips about 1" in width. The

seed provided had an estimated count of 2.5 seed oysters per chip.

The chips are large enough to be placed directly in Nestier trays

without having to use fine mesh screens~ as .may be necessary for

some panel and some hatchery seed.

We found that although several hundred chips could be placed in

each Nestier tray, they had to be thinned and separated every two

weeks or so at first, otherwise the seed tended to fuse with adjacent

cement chips and with other oysters, and the labour and mortality

associated with this process was excessive. Provided the seed

was thinned early enough, the mortality was low.

After six m.onths in trays m.any of the oysters seemed to come away

from the chips, or they could be separated manually rather easily

in many cases. In other cases the chip itself could be reduced in

size by breaking, leaving a relatively unobtrusive chip of cement.

~; : When deliv ered in F ebruary, 1976, the actual count was about 11, 000 per case.

- 16 -

It was considered that Diamond Chip seed would be an acceptable

form of seed for tray culture, provided the initial count \"as high

enough -- at least two per chip. The cost of this seed was about

In cent apiece, but the labour involved in producing individual

seed initially was a good deal less than for panel seed.

d) Hatchery Seed (Photograph 9)

The fourth type of seed was obtained from Bay Center Mariculture

in Washington. This seed is produced in a hatchery, and is

collected from the spawning tanks on small chips of shell with usually

one or two oysters surviving on each chip. We ordered several

sizes of seed from the hatchery, the first being about 3 mID. The

very small seed was placed initially in special trays with a fine

mesh screen, or in Nestier trays with similar screen inserts.

As soon as this seed reached 5 mID, it was placed in standard

Nestier trays. Subsequent thinning and cleaning were done at two

week intervals, or until the seed reached 30 mm. The larger seed

was placed directly in trays, and over a period of months thinned

to about 50 oysters per tray.

The hatchery seed was delivered in good condition; sorting and

thinning was relatively easy to do . The major dral .. back to this

type of seed was the initial cost about 1 cent apiece for small

seed, and 2 cents for the larger.

It had been hoped that the hatchery would be able to provide a

A.

- 17 -

fairly large quantity of the large seed as it was felt that although

the initial cost was highl the fact that mortality would be low and

the time to maturity reduced to one growing season would more

than compensate. The hatche ry in question was not able, with

present methods, to guarantee a supply of the larger seed in the

quantities required. In the future, however, this approach to

tray culture n"lay become possible, either from hatcheries, or

from seed producers of wild seed who are willing to cater to the

needs of tray culture.

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TABLE I

S~~ARY OF SEED AVAILABLE FOR TRAY CULTURE

Type

Seed on Cultch

Basic Cost/l,OOO

Panel Seed $3.00 (Plus about $1.00/ 1,000 labour)

Diamond $5.00 Chip

Hatchery a) $10.00 for 5mm or less

b) $20.00 for seed larger than 10mm

.Comments

Unacceptab 1 e Due to loss and labour

Acceptable Initial labour high Mortality initially 20%-30%

Acceptable Initial Labour medium to Low Mortality Low (5%)

Acceptable Initial Labour low Mortality low (5%)

Sources

Various

Wes Parry, White Rock. B.C.

Ken Lawrence. Prince George,B.C.

Dennis Wilson Bay Center. Washington U.S.A.

- . 19 -

VI. PROCESSING AND PACKING PLANT

A combination cleaning and packing plant, designed as a floating struc-

ture, was completed and anchored close to the floats during the sum.JTler

1974. The plant was designed to provide a sheltered work space close to

the growing area, so that the problems and costs of transporting trays and

oysters would be reduced. It was also designed to meet the specifications

for a packing plant to permit the company to pack and sell oysters without

having to go through a wholesale~ or some other packing plant.

The plant is a single structure consisting of two sections located on

a concrete slab aboard a steel barge. (photographs 10 and 11) The barge

is about 50' x 181, while the dimensions of the plant are 28' x 151. The

outer covered section of the plant (10' x 1St) is used as a preliminary

washing and grading area, all that is needed in fine weather for most of

the routine operations. It is in this area that all the dirty work is nor-

rnally done: cleaning trays and oysters by means of a high pressure hose;

grading and selecting oysters; repairing tray bridles, etc. The inner

section of the plant (18' x 1St) was designed to meet the specifications for

a packing plant and is used mainly for final inspection and packing of oysters

of marketable size. As only oysters for the half-shell market are pro-

cessed, some of the requiren"lents for conventional shucking sheds were

considered inappropriate, and were not required. The processing area

provides for the sanitary requirements of a packing plant: concrete floor,

stove, sin..1<1 storage facility for cartons, washroom and adequate lighting.

The concept of a floating plant located close to thc floats was generated

- 20 -

to facilitate and centralize the cleaning, grading and packing operations. It

has proved to be a great time saver in terms of transportation, and ensures

that the oysters can be reached and processed regardless of tides. It has

also provided the operator with a sheltered place to \'lOrk and a more than

adequate place to store equipment and tools close to the area where they

are required. Portable gasoline power pumps and generators are more

than adequate to provide water pressure and electricity needed for this

type of operation.

One major problem with such plants concerns the provision of toilet

and washroom facilities. In this case the problem was solved by providing

a portable toilet such as is used in campers. All fresh water used for

hand washing is stored in covered containers. All refuse and grey water

is removed from the plant and dumped into a sewage disposal system on

shore. Sanitary conditions within the packing area are achieved and main­

tained by the use of diluted household bleach added to the water used to wash

down the walls, work surfaces and the concrete floor.

The location of the plant close to the floats also means that the oysters

can be left in the water until the last moment. Even in rough weather trays

can be lifted and moved to the washing area where, protected from the· ele­

ments, the operator can clean and select. Packing occurs immediately.

In this way, the condition of the oysters is maintained and the probability

of contamination reduced to a minimum.

The cost of the floating processing and packing plant was rather high

($10,000) but, in our opini.on, it is justified in our location where there

- 21 -

is no deep water access to the shore. In situations where a packing plant

on shore could be reached at all tides, it may be much cheaper to have a

shore-based plant, and a relatively inexpensive work barge to provide a

work platform near the floats. In other areas all facilities could be

shore-based, particularly if the floats can be located close to the plant

and work sheds. If arrangernents of a satisfactory economic nature can

be rnade wi'f:h a certified plant, it may not be necessary to have a separate

one.

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VI1. FOULING

As with all forms of mariculture, fouling is a factor with which the

grower must contend. The amount and the nature of the fouling will vary

from year to year and from one area to another. The effects of fouling

can be separated into those forms that directly damage or destroy the

oyster, those that simply reduce grmvth rate by competition for food, or

through the reduction in water circulation, and those that primarily dis-

figure the oyster so as to make it a somewhat less marketable product for

the half-shell market.

The major forms of fouling around Lasqueti Island appear to be the

following: mussels, barnacles, hydroids, algae in various forms, sponge

of three types, starfish and at least two forms of seaworms. Although all

forms of fouling and of other organisms associated with oysters have been

thoroughly described by Quayle (1969), some mention should be made here

of the ones that are likely to affect tray cultured raft oysters.

In the Lasqueti area one form of fouling that appears to damage the

oyster is the boring sponge (Cliona). This appears as a yellow ~pot within

small circular holes that are drilled into a shell. Although it is not very

common on the West Coast apparently, we have found a total of five oysters

in two years that have been infested sufficiently to kill them. Normally,

most of our trays have been spray cleaned~ inside and out, every two

months, but even so some mortality from this source has been encountered.

What mortality would result if trays were not spray cleaned, of course, we

h~ve no way of estimating. Whether any of the other methods of defouling

- 23 -

to be discussed later would be effective we cannot say, as we have never

detected the presence of this sponge before the damage was irreversible.

The other major form of fouling to produce mortality in raft oysters is

the sea star or starfish. This organism apparently gets into the trays, .

usually in the late sum.m.er or early fall whilst in the larvae stage. We have

found as many as several hundred minute starfish in a set of trays during

the month of October, at which time they are 5 to 10 rnm. in diameter. At

this stage they seem to be killed quite easily if the trays are air dried for

a day or so. Others can be removed by spraying and flushing the trays.

As they are very small, although they are harmless at this stage, they are

hard to see and may be left in the trays until they become large enough to

attack oysters, particularly seed oysters. For this reason, it is particu-

larly important to establish frequent and regular cleaning of trays during

the spring months.

The other forms of fouling encounted in the waters off Lasqueti are

troublesome, primarily because they reduce growth rate, or disfigure the

shell. Mussels and barnacles, if caught at an early stage, can be removed

by hand or by spraying. This is also true of the other forms of fouling -

algae, seaworms, hydroids and sponge. One of the encrusting sponges,

yellow-orange in colour, has proved to be particularly troublesome, as it

not only can smother the oyster, but some chemical it produces flavours

the meat in a most unpleasant way, enough to make it unpalatable and

hence unmarketable. The other type of encrusting sponge, grey-bro"vn

in colour, seems not to affect the flavour of the meat. L'1. both cases

- 24 -

however, unless the sponge has become well established, spray cleaning

seems sufficient to remove the sponge. Otherwise, the oysters need to be

air dried for a day or so, and then sprayed. (Photos 12 and 13)

One method of defouling used on the East Coast \vith the relatively thick­

shelled eastern variety may have application to West Coast tray c.ulture.

As described by McNichol, this method entails dipping tray-sets into a

bath of fresh water heated to 600

C for a period of 10 seconds. This ex­

posure would appear to kill the fouling organisms without doing harm to

the oysters. It has been suggested however, that the very thin-shelled,

raft-grown Pacific oyster may not be able to survive that temperature for

that length of time. To discover an acceptable combination of tempera­

tures and exposure times, we shall be carrying out a series of simple

experiments. If this procedure proves effective, it could gre atly reduce

the labour costs and the time presently being used to reduce the effects

of fouling. '

- 25 -

VIII. HARVESTING, PACKING, AND SHIPPING

The method of production used by Sabine Seafoods entails frequent and

regular cleaning and grading of oysters throughout the growing process. As

each type of seed is thinned and graded~ the tray- sets are coded~ and records

are kept of the quantity of ea::h type and size. Thus, at any time the grower

is able to determine the number of marketable oysters available~ and using

previously established growth patterns, he is able to predict what quantities

will be available at any given time in the future. This process enables the

grower to maintain an up-to-date inventory, and to adjust the marketing

process accordingly. He is able to inform his markets when oysters will

become available, and in what quantities, and when shipments will have to

cease, either because stocks have ;run out, or because of the condition of

the oysters.

The previously described procedures greatly facilitated the process

of harve sting. Usually, on the day when a shipment is to go out, the

oysters ready for market are removed from the water in the morning, and

are spray cleaned with salt water and allowed to drain. They are then

screened for size and weight, and counted into previously cleaned trays.

After they have been counted, they are packed in wax-dipped cartons.

Those going by air are placed in poly bags in order to comply with airline

regulations covering the shipment of seafood products. We have found that

if the oysters are carefully packed 'with the cupside down, they lose very

little moisture, and have had a shelf-life under refrigerated conditions

(350 F) of several weeks ,vith no adverse effects on condition. (photo 14)

- 26 -

In general, we have found that it takes about 10 man-hours to

clean, grade and pack 200 dozen oysters by the method described. UsiT'g

wax-dipped cartons and the poly bags the cost of packaging amounts to

approximately .06¢ per dozen.

-=:-

- 27 -

IX. :MARKETING

At the present time Sabine Seafoods is shipping to three local res-

taurants and to one large restaurant chain in the United States. At the

peak of our production we have shipped over 300 dozen per week. At the

present time we are shipping during two periods of the year, fro~ Sep-

ternber to January, and from May to mid-July. The major constraint on

our winter shipments has been our inability to produce enough marketable

oysters, although there is some indication that the quality of the oysters

produced here tends to decline in January -- they become rather thin and

watery. The major constraint on summer shipments has been ,that as the

water temperature rises in July, the conversion to gonad material makes

the oysters unacceptable for the half-shell market. Since the start of our

marketing operations in September 1974, we have shipped 6,055 dozen for

a total value of $15,685.00.

As yet, we have not needed to find additional markets. In anticipation

of increased production however, we have approached several restaurants

in the local area and in the United States. At the present time, and with

no great effort, we feel sure that' we could obtain markets in excess of "

~:. 15,000 dozen per year. What is yet untested is the market in other parts <,

of B. C., Alberta and Saskatchewan. We suspect that to penetrate much

further to the east would not be com,petitive against East Coast oysters at

this time. Also worthy of exploration are the markets in the United

States, particularly in California, and the mid-western states.

At the present time we are able to obtain a little over $3.00 a dozen,

- 28 -

FOB Vancouver. The restaurants served by us seem to be selling the

product for about $3.75 per half-dozen, served on the half- shell.

The reaction of the restaurants' custOITlers has been most favourable.

Some have claimed that these raft-grown Pacific oysters taste as good or

better than l!bluepoints ll • Others have said that they are better than any

they have had, even in Europe. These llGolden Mantle" oysters, a~ we

call them, have been the subject of reports m the radio, and of newspaper

articles. Restaurants that initially refused even to try 'West Coast oysters

were finally convinced that there is a difference between the raft- grown

version and those grown on the bottom. Many people who had previously

tried raw oysters and disliked them were able to acquire a taste for these.

It is our opinion that if the quality can be maintained, and if production

can be increased, there will very shortly be a greatly expanded market for

West Coast raft-cultured oysters, at a price that will make the production

of them economic on a large scale.

- 29 -

x. ECONOlvllC ANALYSIS

Using the data collected during the two-year period of the project, the

attempt will be made to arrive at some realistic estimate of the various

costs involved in the production of tray-cultured raft oysters. A number

of alternative estimates are provided to reflect the probable effect Qf

several production strategies.

a) Two- Year Production Cycle

For most growers starting a tray-culture operation~ the most

probable situation will be one in which they acquire seed during

the winter months~ and arrange for the acquisition of trays and

the construction of floats in preparation for the start of the growing

season~ which for most areas of British Columbia commences in

April. If panel seed is used~ the first operation will be to remove

the seed from panels. This is a rather laborious process~ which~

if hurried~ will lead to a very high mortality. As the seed tends

not to grow at a uniform rate~ it is usually necessary to carry out

the separation of seed in two phases: in the first~ the largest are

removed, and then the panels are returned to the water to permit

the smaller oysters to gro"\" to a size large enough to allow their

removal.

During each month of the first gro"\ving season (April to October)

the nlajor work-load is associated with the process of thinning and

cleaning. If the only seed available is 10 mm. panel, Diam.ond or

hatchery seed, the munbcr of trays and the floatation required

- 30 -

initially will be minirnal. The number of trays, and the amount of

floatation and labour will increase rapidly as the season progresses.

During the second year the number of trays, the floatation space,

and the alnount of labour will rapidly approach the maximum re­

quired for a given number of marketable oysters.

For the: purpose of the analysis of the two-year cycle, it is assumed

that floatation can be provided on the average for $5.00 per linear

foot of a two- sided float, and can be amortized over a three-year

period {$l. 70 per foot per year}. It is also assumed that a Nestier­

type tray capable of carrying four-dozen mature oysters can be

made available at a cost of .50f per year. Labour is assessed

at $3.00 per hour. Materials for banding and hanging of trays

average about .10f per set per month. Table II sununarizes the

activity and basic components involved in the first of a two-year

cycle. Table III summarizes similar inforInation for the second

of the two years of production.

At the end of the first growing season, assuming that about 120,000

oysters survive, the grower will have about 120 sets (600 trays

plus 120 caps -- 720 trays) suspended from floatation t~talling

180 linear feet, or the equivalent of one 90 foot long float. The

total1abour cost "viil be about $1, 005.00 for the' monthly cleaning

and thinning operations. Materials for the banding and hanging of

trays. will have cost about $50.00.

r I ; - 31 -

TABIE II

SUMMARY OF THE ACTIVITY CYCIE DT.JRING YEAR ONE OF A TWO-YEAR PRODlJCTION PERIOD (GOAL: 10, OO.::.O....:D::...O::.:ZE=_:.:.:~~) ____________ _

Oysters/ No. of Feet of Hours of Month Activity 5-Tray Set Sets Floatation Labour

March Placing seed in 10,000 * 16 24 15 traYflJ banding, &t.c. (160,000)

April Thinning & Cleaning 8,000 20 30 20

May II II 7,000 20 30 20

June Thinning & Cleaning 6,000 23 36 25 (140,000)

July Thinning & Cleaning 5,000 28 42 30

August II " 3,000 45 68 45

September Thinning & Cl~aning 2,000 60 90 60 (120,000)

October Thinning & Cleaning 1,000 120 180 120

TOTAlS 120 180 335

*Note: Assume the grower starts with 160,000 separate seed and that about 40,000 are lost for one reason or another.

TABIE III

SUMMARY OF THE ACTIVITY CYCIE DURING YEAR TWO OF A TI'rO-YEAR PRODUCTION PERIOD (GOAL: 10,000 DOZEN)

Oysters/ No. of Feet of Hours of Month Activity 5-Tray Set Sets Floatation Labour

February Cleaning 1,000 120 180 120

April Thinning & Cleaning 800 150 225 150

May II " 700 170 255 170

June " " 500 240 360 240

July " " 300 400 600 400

August " " 250 480 720 480

§ept.ernber " " · 250 480 720 480

TOTALS 480 720 2,040 ---.

- 32 -

The ren"laining factor detern"lining the cost of production during

the first year is the type of seed used. At the present tin"le, panel

seed is available for about $60. 00 per case, each case having an

estimated count of 20, 000 seed. In our experience it has taken as

n1.uch as three n"lan-hours to ren"love the seed fron"l one case of

panels, and in order to reduce n"lortality and to n"laximize the

yield, the process has to be done twice. Our experience also

suggests that about 25% mortality is to be expected ultimately.

Consequently, if panel seed is used, the cost of filling the trays

initially with enough seed to produce 10, 000 dozen oysters will be

about $750.00.

If hatchery seed is used, to cover costs of transportation and

allowance of 20% for mortality and variations in yield, the grower

should expect to pay about $1,500.00. Similar costs would appear

to be valid for Diamond Chip seed. In the case of hatchery seed

the grower is advised to place his order during SUn"ln"ler to ensure

his supply. An order placed during the winter months may not be

deliverable until May, and even then the size of the seed may be

3n"ln"l,orless.

Prior to the start of the second year the grower should have pro­

vided him.sel£ v.rith sufficient trays and floatation to handle the

predicted yield from the first season's gro"\vth. If about 120,000

seed do survive into the second season, he will need about 2,900

Nesticr-typ(' trays (2~ 400 trays plus 480 ca.ps), and 720 feet 6f

I

~ t'

- 33 -

floatation (the equivalent of 360 feet of two- sided rafts). His

labour will probably cost about $6,120.00 and materials for

banding and hanging about $200. 00. ~Nith this information "ve can

now estimate the direct costs of production for a two-year opera-

tion, as is shown in Table IV.

TABIE IV

PRODUCTION COOTS FOR 10,000 DOZEN OYSTERS - TWO-YEAR GROWING CYCIE

Year One Year Two Total

Seed Panel Type $ 750.00 $ 750 0 00 (other Types) (1,500000) (1,500.00)

Trays 720 x .50¢ 360 000 2,880 x .50¢ $1,440.00 1,800.00

Labour 335 x $3.00 1,005.00 2,040 x $3.00 6,120.00 7,125000

Floatation 180 x $1.67 300.00 720 x $1.67 1,200.00 1,500,,00

Materials 50.00 200.00 250.00

TO'I'AL

(If other seed is used)

$2,465.00

(S3,215 0 00)

S8,960.00 $11,425.00

(S12 ,175)

If the previously mentioned as sumptions are reasonably valid,

alLd if the costs of trays and floatation can be arnmortized as

ShO\Vll, then the direct cost of producing 10,000 dozen oysters

- 34 -

will be between $11,425.00 and $12,175.00 or somewhere in the

region of $1. IS and $1.25 per dozen.

Included in the total costs of producing and selling 10,000 dozen

oysters should be the costs of harvesting and packaging. On the

basis of our figures, it takes about lOman-hours to select, cl~an

and pack 200 dozen, a labour cost of about $1,000 to process for

market 10,000 dozen. Our packaging costs have averaged about

$1.00 per 15 dozen, which would amount to $670.00 for 10,000

dozen.

From these figures we would estimate the total cost of producing

and marketing 10,000 dozen as follows:

Production

Harvesting

Packaging

TOTAL

$ll, 425. 00

1,000.00

670.00

$13,095.00

On a continuing basis, however, the grower will order and process

new seed each year and thus have a work and cost load in anyone

year which ,"vill be the sum of the previously described first and

second-year cycles. This will mean for example that starting

in the second year he "lill have to provide a total of SO~1e 900' of

floatation, about 3, 600 trays, and will need about 2,375 man-hour s

of labour. Thus, starting with the second gro'\v-ing season, the t"tal

direct co~ts of production will become about $13,000.00 annually.

- 35 -

The total cost of producing, harvesting and packaging at the rate

of 10,000 dozen a year will bring the average cost to $1.30 per

dozen.

In addition to the direct costs summarized above are those asso-

ciated with leases, permits and general business costs. These costs

m.ay vary somewhat from one company to another, and from one

location to another (due to transportation charges for example)

but, in general, when once established they should not vary sig-

nificantiy with the quantity produced. If they can be held to about

$5,000.00 a year, and are charged against each successive crop,

this would bring the total costs, excluding capital equipment, to ,

about $18,000.00 per year, or about $1.80 per dozen.

b) One-Year Production Cycle

Another approach to the use of tray culture. might be to use a one-

year production cycle to reduce the amount of labour, floatation

and the number of trays needed in anyone year. This approach

is dependent upon a reliable supply of 40 mm seed well before the

start of each growing season. By eliminating the first":year cycle,

the grower could operate vvi.th about 720' of floatation, and 2,880

trays, for a total arrunortized cost of about $9,000.00.

If a reliable source could be found that ",;ould provide 40 mm seed

for about. 03 ~ each, allov-ring about 20% for los s from various

sources, thE' seed would cost about $4,350.00, thus bringing the

;f " !. it ,

I I

j j

"\' r

"

j

- 36 -

total direct costs including harvesting and packaging to about

$15,000.00, or about $1.50 a dozen. If the prev-iously mentioned

overhead of $5,000.00 a yea r still applied, this would bring the

total cost to about $20,000.00 annually, or about $2.00 2. dozen.

If the seed cost was found to be about. 05 ~ each, the final direct

cost of production plus ovcrhead would rise to about $2.30 per

dozen.

Although the cost of the one-year cycle is some .20¢ a dozen more

than the two-year cycle, there are certain advantages. The total

space, floatation and number of trays needed is somewhat less,

but, perhaps of more importance is the element of risk. In the

two-year cycle the potential crop is exposed to. the risk of storm

damage, and possibly other sources of loss, for two gro'\ving

seasons and through one winter, whereas by this method the

exposure to such risk is limited to one growing season, a difference

of about 12 months. It is difficult to assess the economic impor­

tance of this reduction in exposure, but in some areas it may be

eA-irernely important.

c) Sequential Analysis of Total Costs and Yield

Another approach to the economic analysis of tray culture is to

look at the accumulation of costs and profits over a series of

years, in p a.rt to determine the point at which the operation should

be expected to make a profit, and in peut to include the purchase

,

- 37 -

and depreciation of capital equipment. In this analysis some of

the data presented previously will be used again, but to be added

are the capital equipment costs and allowances for depreciation,

at rates dependent upon the type of equipment. It will be assumed

that the grower will not be successful in bringing all his crop to

Il1.arketable size even after two seasons, and that there will be a

partial carryover of stock from one year to another. The infor-

Il1.ation required for this analysis is presented in Tables V and VI.

- 38 -

TABIE V

SEQUENTIAL ANALYSIS OF COSTS FOR TIIE PRODUCTION OF 10,000 DOZE~J OYSTERS,

USHJG A TWO-YEAR PRODUCTION CYCIE

ITEM YEAR ONE

A.. rrPnPTa1 Ruc;;inec:;s $ 3,000 (Legal, leases, permits, office, travel, etc.)

Miscellaneous 1,000 Operating (gas, oil,

expendib1e items,

TCTAL

Bo Direct Costs: Seed Trays Flo.2.ts Labour Harvesting Packaging Materials

TOTAL

C. Capital Equipment Bont/Motor Pumps Winch/Boom Packing Plant Depreciation

(@ 15%)

TaJ'AL --

GRAND 'l'OTALS A+B

A+B+C

etc. )

$ 4,000

S 750 360 300

1,000

50

S 2,460

S 2,600 300 400

400 ---$ 3,700

:$ 6,460

$10,160

YEAR TWO

$ ",000

1,000

$ 5,000

S 750 1,800 1,500 7,125 1,000

670 250

S13,095

12,000

2,200

$14,200

$18,095

$32,295

YEAR THREE

S 1,000

1,000

$ 5,000

S 750 1,800 1,500 7,125 1,000

670 250

$13,095

2,200

,'" .) 2,200

$18,095

$20,295

YEAR FOuR

$ '1,000

1,000

$ 5,000

$ 750 1,Roo 1,500 7,125 1,000

670 250

813,095

2,200

S 2,200

$18,095

520,295

YEAR FIVE

S 1,000

1,000

S 5,000

$ 750 1,800 1,500 7,125 1,000

670 250

S13,095

2,200

S 2,200

818,095

520,295

f ~ , f j

f J I

t

j i

.j j

. i I

1

1 !

- 39 -

TABLE VI

SEQUENTIAL A..~ALYSIS OF THE COST/PROFIT RELATIONSHIPS FOR THE

PRODUCTION OF 10,000 DOZEN OYSTERS, USING A TWO-YEAR CYCLE

YEAR ONE YEAR TWO YEAR THREE YEAR FOUR

Sales Volume (dozens) 8,000 10,000 11,UOO

Sales €! $3/dozen 24,000 30,000 33,000

Annual Profit/Loss Gross (Less Direct Costs and General Business) -$ 6,460 $ 5,905 $11,095 $14,095

Net (Less all Costs) -$10,160 -$ 8,295 $ 9,705 $12,705

Accumulated Profit/Loss Gross(Less Direct Costs and General Business) -$ 6,460 -$ 505 $10,590 $24,685

NET (Less all Costs) -$10,160 -$18,455 -$ 8,750 $ 3,955

YEAR FIVE

11,000

33,000

$14,095

$12,705

$38,780

$16,660

Using the estimates provided in Tables V and VI, it would appear

that the break-even point would be reached in the fourth year of

operations, if all costs are included. At the end of the fifth year

of operations a total of $103,340 will have been spent on general

business expenses, operations and capital equipment, including a

15% per annum allowance for depreciation. The operation should

have produced a total of 40,000 dozen oysters with a predicted

market value of about $120,000.00. The owner would also have

on hand an inventory of oysters for the following year worth approxi-

mately $7,000.00, and capital equipment worth $6,800.00 at

SALES

GROSS PROFIT (Direct Costs

- 40 -

depreciated value. If the profits, inventory and depreciated value

of equipment are considered, the total value of the operation at

the end of five years will be about $30,000.00 and the predicted

net earnings should remain at about $13,000.00 per annum.

After the break-even point, our estimates based on Table VI

would sug~est that the ratio of net prof; t to totA 1 v~ llif' of C;A J f'S

would average 38.5 annually. By way of comparison with

similar ratios, which do not include the costs of plant overhead,

financing costs, etc. for the process of fresh, canned and IQF

oysters produced by conventional means refer to Table VII.

TABLE VII

COMPARISON OF PROFIT/SALES RATIOS FOR TRAY CULTURED OYSTERS. AND

SEVERAL VARIETIES OF PROCESSED OYSTERS PRODUCED BY CONVENTIONAL ME~NS

TRAY CULTURE CONVENTIONAL CULTURE* Fresh Canned IQF

$33,000 $1,802,819 $764,100 $587,100

$14,100 $ 98,016 $183,830 $214,530 Only)

PROFIT/SALES RATIOS 38.5 5.4 24.1 36.5

*From: Hardy, 1975

- 41 -

At the end of the fifth year of operations, the ratio of gross profit

to total sales is estimated to be 32.3%, while the similar ratio for

total net profit is expected to be about 13.8%. In terms of the ·re-

turn on total investment, after five years of operations the pre-

dicted return is about 16.1%. Once the break-even point has been

reached, however, the return on annually invested capital should

be at the rate of 62.5% per annUlU.

It should be pointed out that the previously presented figures are

based on the assumption that the grower starts with small seed

only, as outlined in Table IV. Another approach, as suggested

earlier, would be to use a one-year cycle during the first year,

in combination with the two-year cycle. Thus, by purchasing

enough large seed (40 rnrn) as well as the small in the first year,

the grower should be able to advance the breakeven point by one

year and ensure some cash-flow during the first year of opera-

tions. It would probably require about $40,000.00 during the first

year to employ this strategy, but the expected return would make

it worthwhile.

d) Effect of Increasing Froduction on Total Costs and Net Profit

Of some concern m.ay be the effect of increasing production on the

expected total annual costs and on net profit. If one can assume

that the assessment for capital equipment and depreciation, and

general business expenses, would not change significantly, but

- 42 -

that the direct or variable operating costs would remain pro-

portional to production volume, then the data presented in

Table VIII would be relevant.

TABIE VIII

THE EFFECT ON TOTAL COSTS At'ID NET PROFIT OF VARIOUS INCREASES IN

PRODUCTION VOLUME, AFTER THE BREAK-EVEN POINT HAS BEEN REACHED

PRODUCTION VOLUME ~DOZENS} 10,000 20,000 30,000 40,000

Fixed Costs $ 7,200 $ 8,200 $ 9,200 $10,200

Variable Costs 13,100 26,200 39,300 52,400

TOTAL COSTS $20,300 $34,400 $48,500 $62,600

NET PR·OFIT $ 9,700 $25,600 $41,500 $57,400

PROFIT/SALES RATIO 32.3% 42 07% 46.1% 47.8%

L

!

- 43 -

XI. GROWTH STUDIES

During the two year period of the project a series of studies were con-

ducted to provide some base line data on the growth of oysters in trays as

a function of initial size, density and seed type. Other studies compared

growth on trays at Tucker Bay with growth at Ten-Mile Point, near

Victoria. The present report will summarize the findings of four of these

studies.

1. Growth in Nestier Trays as a Function of Initial Size:

Although there seemed a considerable quantity of data on the growth

of oysters by conventional means in B.C. waters, we could find no data

on the growth rate in Nestier trays. We heard rumours to the effect

that the Nestier tray was not an effective means of raft culture; we

had heard that of various trays used on the East OJast of Canada, the

Nestier was considered the worst. But we could find no comparable

data for the Pacific oyster. Being new to oyster culture, we very much

felt the need for some information upon which we could base predictions

and select strategies.

In June 1974, ten oysters of each of three size-clas ses (5.2, 3.4,

and 1.9 mm) were placed in a Nestier tray and suspended from one of

our rafts. Measures of weight and length were taken in June, and

length was again measured in December 1974. Starting in April 1975,

and continuing throughout the gromng season, both length and ".,-eight

measurements were taken each :month (except Septem.ber), until

- 44 -

November. In 1975, the trays and the oysters were spray-cleaned

each month, after the nature of the fouling had been determined.

The basic growth data can be found in Tables IX and X. From

these Tables and Figures 1 and 2, it can be determined that the rate of

growth is very nearly the same for the three size-classes used in this

sh.ldy; <111 thrp.p. ~d7.p.l'l eai.ned about 40 mIn per year; or 80 rn.m over

the two-year period of the study. Thus 7 under these somewhat ideal

conditions (low density and frequent cleaning), the grower could pro­

bably expect to produce a marketable oyster fro:m 40 :mIn seed in one

growing season, even using Nestier trays. It would take two seasons

to produce :marketable oysters from seed that was initially much less

than 40 :m:m in length. Of interest.to the grower might be the obser­

vation that in 1975 there was practically no change in length during the

last t-w·o :months of the season, but there was a considerable increase

in weight during this period, q.t least for the two larger sizes (l25 mm

and 115 :m:m); the s:mallest size (95 :mm) showed no weight gain in

October in this study.

Of the original 10 oysters in each size-class there were 9 Large,

7 Medium., and 8 S:mall rem.aining in December 1974. From the size

of the empty shells in the tray, it was apparent that this :mortality

took place soon after they were put in the water, as little or no growth

had taken place. There was no loss in 1975.

A record of fouling was kept during the 1975 season. The first

sign of fouling was noted in May, consisting of brown algae and some

- 45 -

small mus sels. In June, a fairly heavy barnacle set was found t pre­

sumably having taken place earlier in May. Most of the barnacles had

set on the outside of the tray, although some of the larger oysters had

as many as 10 barnacles on their shells. At this stage the barnacles

were easily removed with water from a medium pressur~ pumping

system. In August, a second mussel set was noted, while in No­

vember, many very small seastars were found, both outside and

inside the tray.

It should be pointed out that the growth rate found in tills study may

not apply in other areas, where the water is colder, or much warmer.

However, assuming a pattern of water temperature similar to the

one found here (Table XVI), and provided a comparable food supply is

available, the present data should indicate the probable optimum grow-th

rate for oysters of these size classes, grown in trays similar to the

Nestier design. Also worthy of note, the pattern of fouling, in 1975,

may not be typical, as we experienced a relatively late spring on

Lasqueti; one month late according to local information. Other data

(Quayle, 1969) would suggest that it is more usual for the barnacles

to have a major set early in April rather than in May.

One conclusion to be reached from the results of this study is that

the Nestier tray can be used efficiently to produce oysters by raft cul­

ture, at least as far as growth rate is concerned. The growth in the

trays compares favourably with some data provided by Quayle (FRB.

Bulletin 169, 1969) for seed grov.rn on cultch shells and suspended from

- 46 -

rafts. The only other data we have located pertaining to growth in

Nestier trays was pro'vided by Woo on the East Coast. He obtained

less than one mm. growth in length and 6.7 gram gain in weight for

oysters in the 91.8 mm size-class during one season. We obtained

34.0 mm growth in length, and a gain in weight in excess of 100 grams

for oysters of the same initial size. To what extent this marked dif-

ference is due to the species of oysters, local conditions, cleaning

rate, or fouling can not be determined. At least for conditions

similar to those around Lasqueti Island, and provided the trays are

cleaned regularly, it is apparent that the growth in trays is not ' ';

.~

markedly dissimilar to the growth that occurs for other types of raft-

culture. 1 J

2. Growth as a Function of Type of Seed:

Fairly ea.rly in our production program we recognized that part of

the success of tray-culture depends upon locating a reliable source of

appropriate seed. In 1975, there were essentially three types of seed

available, Panel, Diamond Chip. and Wilson Chip (hatchery). We had

no data on the relative survival and growth rates for these different

types of seed, so a study was designed to provide data of a compara-

tive nature.

Both Fanel and DialTIond Chip seed are collected by suspending the

collection m.edium in Fendrell Sound prior to the annual natural oyster

spat. When delivered~ Panel Seed is still attached to plywood panels

- 47 -

covered with a thin veneer of cement, supposedly 300 seed per panel.

In the case of Diamond Chip, when this seed is delivered it comes on

sma1l diaInond shaped cement chips roughly one inch in size, with an .

average of about 1.5 oysters per chip.

Wilson Chip seed is produced in a hatchery at Ray \.f'nter,

Washington. When it is delivered, it COInes on chips of shell about

3 InIn square. Usually the count is about 1.0 oyster per chip.

The cost of the three types of seed is different, and the handling

probleIns are dissiInilar. Although experience right suggest that there

should be no essential difference in the survival and growth rates for

these three types of seed, we felt the need for some eInpirical data.

For exaInple, to our knowledge, because it is new on the Inarket, no

one had gro'wn Diamond Chip to maturity, and we could locate no ' one

who had grown the three types in Nestier trays • .. In April of 1975, 40 samples of each type of seed were placed in

Nestier trays, 20 of each type in separate trays. The six trays "vere

then banded together into a single experimental set, and suspended

from one of the rafts. At regular monthly intervals the set \vas re-

moved from the water and spray cleaned. Measures of length for each

individual oyster V\rere obtained each month during the gro\ving season

from. April to November (except Septem.ber). Sim.ilarly, '..veight mea-

Slues were obtained each month. Tables XI and XII and Figures 3 and

4 sUInrnarize the ITlean length and weight Ineasurcs for the three types

of seed.

- 48 -

As can be seen, the Wilson and Panel seed started at roughly the

same length (45.6 and 51.4 mm respectively) and over the season grew

es sentially the same in length (49.6 and 44.8 rom respectively). The

Diam.ond Chip began at 18.7 mm and increased by 58.2 mm to rea ,::h a

length of 76.9 mm by October.

As measured by weight gain, the Wilson Chip increased the most

(60.0 grams), with the Fanel next (51.5 grams) and the Diamond Chip

last (43. 8 grams).

It was found that one Diamond Chip and two Panel seed died during

July. There was no other mortality.

Observations on fouling suggested that, as in the first study, the

first Inajor s.Qurce came in April from a brown algae, the second in

May from a heavy barnacle set, and minor set of mussels; the third

was a small quantity of encrusting sponge (bright yellow) and a minor

barnacle set in August.

Once again, it was confirmed that seed oysters in the range of

45 to 50 rom, weighing an average about 13 grams could become of

marketable proportions in one growing season in Nestier trays. It is

also interesting to note that whereas all three types of seed added

weight in October, there was no increment in length, confirming the

observations of the fir st study.

Concerning the Diamond Chip, one observation may be relevant

for others who may wish to use thi.s seed. When grown in trays, the

v~ry rapid growth seems to encou rage the shell initially to "flow" and

I'fold" Clronnd the Chip to \vhich it is attache d. This does not occur

, .,

• 1 .;

,

~t 1 .,

• f

" ~·t r '

- 49 -

with Wilson Chip, probably because of the difference in the size of the

chip. Also, by about June there was a markeJ tendency for the edge of

the shell of one oyster to fuse with the cement of an adjacent one, pro-

ducing a clustering effect. If these are separated at this stage, there

would appear to be little or no mortality, whereas if left until August

or September when the fusing effect is more pronounced, the risk of

damago is groatly incroased. Once again, this tf.'nrlpnry for Rdjacent

oysters to fuse was far greater in the case of the Diamond Chip seed

than it was for the other types, presumably because of the size and the

nature of the chips .

On the basis of these data, it would appear that all three seed types

grow in Nestier trays at essentially the same rate. It is also apparent

that a grower could expect to produce a marketable oyster in one season,

only if he started with seed that was at least 45-50 mm in length; seed

any smaller than this would probably require part of a second season to

complete its growth.

,3. Growth in Weight as a Function of Size and Density *

One of the essential questions in tray culture has to do with the efficient

use of trays. Part of the problem arises from the initial cost of the trays

themselves, and part has to do with the effect of tray design on \vater cir-

culation and food supply. The problem of.circulation is one that COIl-

tinually arises in any discussion of the Nestier tray. Initially, we

were advised to limit the density to about 32 oysters per tray, pre-

sumably due to the effects of crowding on the competition for the

limited supply of food. Quite obviQusly the cost of producing an

oyster will depend on the number one can crowd into a tray,

... This study was designed and carried out by Amelia Humphries.

- 50 -

without reducing the beneficial effects of raft culture l because the

higher the density the lower the costs associated with traysl suspension

systems and cleaning and handling.

To test the effects of variations in density a preliminary study was

designed to compare variations in density for oysters of different ini-

tial sizes, as measured by the average weight per oyster. Three 'size-

classes were selected in terms of initial weight, 28-29, 16-18, and 9

graIns. These three groups were then split into two sub-groups each

and placed in Nestier trays in varying densities: 4, 71 10, and 12

dozen per tray. The trays were then separately placed as the top trays

in six separate bundles of trays, and were suspended from one of the ::;

rafts early in April. Measures of the total weight of the spray-cleaned -'

oysters were obtained each month from April to August.

The general results can be seen in Table XIII and Figure 5. It will

be noted that one of the experimental sets was lost in July, so there are

no measures for that condition in July or August. It is quite apparent

that on average the less dense (4 dozen per tray) put on slightly more

weight than did the less dense (34 grams vs. 30.5), but that the dif-

ference is very small.

It is of significance to note that there was little or no difference in

weight gain between the 7 and lO dozen per tray groups. In fact, all the

oysters in both the se groups achieved marketable size by the end of

October. The average weight gain for these two groups considered

together is only 5 grams less than comparable sizes at a density of

4 dozen per tray.

- 51

Before suggesting that the carrying capacity of the Nestier tray

should be increas ed from 4 to 8 or more dozen, however, a major

limitation of this study should be pointed out. All the experimental

trays were placed at the top of a separate set of trays. Observations

suggest that growth is always best in the upper and lower trays in a

set, presumably because of water circulation and food supply, A study

has been deslgned to determine to what extent density can be increased

in the other trays in a set and still obtain the needed rate of growth.

It may turn out that there is an optimum density for each position in

the set. The net effect may be to significantly increase the overall

carrying capacity of a given quantity of trays. For example, if the

upper and lower trays can each carry 8 dozen, the second and fourth

5 dozen, and the middle tray only 4 dozen, the total yield for such a

set would be 30 dozen, in contrast with our current practice of reducing

the density before growth is completed to 4 dozen per tray, or to a

total of 20 dozen per set. A 30% increase in carrying capacity would

entail a considerable reduction in the overall costs of production, and

greatly increase the yield from a given quantity of trays and suspension.

4. Comparison of the Growth Rates for Three Seed Types at Tucker Bay and Ten-Mile PO_l_·n_t_: __

One of the questions of importance to growers has to do with the

relative advantage of raft culture with variations in growing conditions.

As a first step in gathering such data for tray culture, the second ex-

periment, comparing the growth of three types of seed, was repeated

- 52 -

at Ten-Mile Point, near Victoria.

Arrangements had been made with Al Meadows of Pacific Oyster

tvlariculture Ltd. to suspend an experimental set at Ten-Mile Point,

in Sooke Harbour (Gooderich Island) and in Roche Cove. Unfortunately,

only the set at Ten-Mile Point survived the ravages of water borne

vandals. To provide a possible explanation for any differences th~t

might be observed, records were kept of surface water temperature

at the various sites. Those for Tucker Bay and Ten-Mile Point are

presented in Table XVI.

The comparative data for Tucker Bay and Ten-Mile Point are

presented in Tables XIV and XV for length and weight gains respectively.

It should be noted that there are no data available from Ten-Mile Point

on the weight gain for the Diamond Chip Seed.

It is quite clear that the growth as measured by length and weight

was just over half as much at Ten-Mile Point as at Tucker Bay. From

the data on surface water temperature, it would seem likely that the

reduced rate of the growth at Ten-Mile Point could be accounted for by

the colder water; Ten-Mile Point, on the average, was 10.30 F. colder

than Tucker Bay. At Tucker Bay the average temperature exceeded

60° F. during four months of the growing season, whereas at Ten-t-lile

Point the average monthly temperature never did exceed 54° F.

A~though this study adds little to knowledge, it does underline the

importance of selecting potential mariculture sites in terms of factors

such as temperature and food supply. It seems quite unlikely that an

economically sound oyster mariculture operation could be conducted

, '.

::-.~; -.. -.-

-1 ~

"

1

1 I 1

I '; j

- 53 -

in areas such as Ten-Mile Point, at least not in competition with areas

¥<-:i.th better growing conditions, as it would probably require three years

there to produce marketable oysters, even using raft culture. Subse-

quent bacteriological tests on oysters produced at Ten-Mile Point also

suggested that the area is tot') dangerously polluted, for the production

of oysters.

- 54 -

XII. CONCLUSIONS

The most significant conclusion to be drawn from the present study is

that an economically successful production of specialty oysters for the half-

shell market can be based on the use of trays. Compared with the Profit /

Sales ratios of other types of oyster production and processing, tray cul-

tured half-shell oysters would appear to be the most successful, even when

a reasonably heavy investment in capital equipment is included in the cost ! ..

estimates.

It is also clear that a superior, marketable product can be produced on

a two-year cycle. A one-year cycle could be used if a reliable supply of

35-45 mIn seed could be found.

It is also clear, that whatever the limitations of Nestier trays may be,

they are capable of being used economically. The earlier apprehensions,

-primarily originating from the East Coast where the growing conditions and

the species used are different, seem to be unwarranted. This is not to say

that a better, more economical tray could not be designed, but more on this

later.

The most costly component in the use of trays for raft-culture is labour.

Of the various direct costs of production it accounts for at least 33%.

Another major factor in the success of this method is a reliable supply of

appropriate seed. The most inexpensive form at the moment is Fanel Seed,

but there is, or could be, a demand for seed in the 40 mm size-class. At

the present time, it is not available on a sufficiently reliable basis. If it

c-ould be s-_'pp1.ied in reasonably accurate quantities, at $30.00, or even at

I , , . J

\ t l

l f ( I .

'1'15**' H AI

- 5S -

S50.00 per 1000, it would increase the flexibility of a tray culture operation,

and still permit it to be economically feasible.

Although very little has yet been done to test it, a market of some con-

siderable si.ze does exist for the speci alty oysters produced by tray culture.

It does not seem unreasonable to expect that this market will remain, even

during periods of depression, as it seems to be hased on a poplllRtion of

people who have developed an expensive taste and are likely to retain the

means to satisfy it.

It does seem quite unlikely that tray-culture will do anything imme-

diately for the general problem of meeting the world's food shortage, or

help solve the problem of protein deficiency - the costs of production by

present methods is far too high, at least in this country. What the future

holds in te1~S of increased need or technological improvements is hard to

say. As a potentially valuable source of food, it should not be overlooked,

however.

One factor that most urgently requires attention is the design and pro-

duction of an inexpensive yet suitable tray. The Nestier is not ideal: it is

expensive, and its design provides less than optimum water circulation.

h~at is needed is a tray with essentially the same carrying capacity, with

holes at least twice as large, for half the price. It would also seem to make

sense to design separate trays for the production of seed and mature oysters,

or to design one that could easily be converted from one function to another.

.. 56 -

XIV. REFERENCES

1. McNichol, D. Personal Cooonunication. Bluenose Oyster Farm, Valley Mills, Malagewatch, Cape Breton Island, N.S.

2. Quayle, D.B., Pacific Oyster Raft Culture in British Columbia. Fisheries Research Board of Canada, Bulletin 178, 1971.

3. Quayle, D.B., Pacific Oyster Culture in British Columbia.

4.

5.

6.

7.

Fisheries Research Board of Canada. Bulletin 169, 1969.

Parsons, J., Advantages of Tray Cultivation of Pacific Oysters in Strangford Lough, N. Ireland. Aquaculture, 3,221-229, 1974.

Hurlburt, C.G. and Hurlburt, S.W. Blue Gold: Mariculture of the Edible Blue Mussel. Marine Fish~ri~~eview, 37; October, 1975.

Curtin, L., Oyster Farming in New Zealand, New Zealand Marine Department, Technical Report No, 72, 1971.

Hardy, S.L., Preliminary Economic Study: New Shellfish Processing Plant, Edwin, Reid and Associates Ltd., Vancouver, B.C. May, 1975.

1974 Size June Class ----

Large 5.2

Medium . 3.4

Small 1.9

1974 Size June Class

Large 9.5

~!cdium .2

Sm311 .1

''''~'"''''''''''''P\ .. __ ~~ .. ~.~. ~~~~_'-~"~_~~Mq~~~ __ ~" v TABLE IX

AVERAGE LENGTH (CM) FOR THREE SIZE-CLASSES

GROWN IN NESTlER TRAYS DURING 1974 and 1975

Dec.

9.1

7.3

5.4

Dec.

1975 April May June July Aug.

9.2 9.4 10.0 10.9 11.7

7.6 7.6 8.1 9.0 9.7

5.8 5.7 6.5 7.2 8.3

TABLE X

AVERAGE WEIGHT (GRAMS) FOR THREE SIZE-CLASSES

GROWN IN NESTlER TRAYS DURING 1974 and 1975

1975 April May June July Aug.

63.3 66.7 80.0 108.9 123.3

41.4 38.6 45.7 68.6 82.9

21.3 18,7 27.5 43.8 58.8

,

Sept. Oct. Nov.

12.5 12.6

10.4 10.4

9.5 9.4

S=pt. Oct. Noc.

154.4 164.4

100.0 108.6

76.3 76.9

Wi 1 I'; on ChiJ:l

Panel

Dia..llond Chip

Wilson Chip

Panel

Diamond Chip

- 58 -

TABlE XI

AVERAGE LENGTH .AS A FlTl';""CTION OF SEED TYPE (MM)

April May June July Aug. Sept.. Oct. Nov.

)2.4 71.() 9h.O

51.4 64.9 75.1 87.8 96.2 94.6

18.7 43.8 63.8 76.9

TABLE XII

A'VERAGE "'EIm-IT .AS A FUNCTION OF SEED TYPE (GRAMS)

April May June July Aug. Sept. Oct. Nay.

ll.O 12.5 17.8 33.5 53.0

14.5 16.1 19.4 33.9 47.1 66.0 72.2

3.0 3.6 4.9 14.8 46 0 8 55.1

===.-----.---- ·:~.===_=o_=:_-====---------·-·------==__=

1 •

.~ . .'

· '.

~ 1

1

- 59 -

T ...... t.l3I.E XIII

MEA.!.\f WEIGHT AS A FLTNCTIO~ OF SIZE k'\l) DE~SJTY (GR .. A1!s)

Dozen April May June July Aug.

Large 7 28 32 35 44 ;9

Medium 10 16 19 22 32 46

Small 12 9 11 13

Large 4 30 34 39 49 67

Medium 4 18 22 25 36 55

Small 4 9 11 14 21 36

TABLE XIV

CO~fPARISON OF AVERAGE GAIN IN LEKGTH (MM) AT TUCKER BAY k'ill TEN-MILE POINT,

FOR THREE T1TES OF SEED

Tucker Bay Ten~lile Pciint Difference

WILSO\, 49.6 29.1 20.5

DIA\iOND 53.2 33.3 24.9

PAXEL 44.~ ~4 • .2 20~6

.. ---

WIISON

PAt'lEL

LASQuL'fr ISLAND

TEN-MILE POli\'T

- 60 -

TABLE XY

COlvrFARISON OF WEIGl-IT GAIN AT TUCKER BAY M'D TEN-MILE POIl-.'T,

FOR TWO SEED TYPES

Tucker Bay Ten-Mile Point Difference

60.00 25.9

51.5 22.4

TABLE XYI

COMPARISON OF AVERAGE MONTHLY SURFACE WATER TE1lPERATURES

AT LASQUETI ISLAND .A..loffi TEN-MILE POINT.

April May June July Aug. Oct. Nov.

60.3 69.7 68.8 61.3 56.0

50.9 52.7 53.0 54.0 52.6 48 0 0

1

1 I

I 1 ) I

1. Cedar Log Floats

20 Cedar Log Floats

? . 3. Tray Suspended FroIn Cable

4. Steel Drum. Floats

i , ~

~ .. ~ I ~

~ ~ i f f

I I i f , t

1 i i I J I '!

f f r f ,

! i

i J , r

~ I

! i

5. Nestier Grow-Out Trays

6~ Nestier Grow-Out Trays

7. Seed On Plywood Panels 1

·f

8. Seed On Cern.ent Chip

,...,... _._--------------------_ ... _--_._---------------_ .. __ .....-.

I 1 t f

[ t

I r l I

9. Hatchery Seed

10. Packing Plant

-' . - ,~~--.

- .... ...... ..... -.- •.... ~ :'

: -;-.~;:::; . ~ - :;::;.:;...:, =~ -- ..... - ,. ...... ~ .. ........ :;:: ~:::t · _ . """'~~ - ,. ~-~ ~-.. ~

• 'r'~,...,, ' .. .. .-r __ .... :::P_...-r-t'I'-

:.'OJr_~"'"

11. Packing Plant

12. Encrusting Sponge

F

oS j .

.-

; I

I . ~ -1 1 j

,,§ ~ '.'

. , .... ~ ... ~ . . i -~ ;:'::1 #:;: ~

I

i

I ! i

~ f."

~~ ~!. :r '

j .. ; i

i ... ~ ... .... .:.1

~J l: I

" 1 I j

I

- -" I:!';~.~ -- 7'''-r''..j ,

M:~i

" 13. Encrusting Sponge

14. Typical Tray-Cultured Oysters

. ...

- .~

,£;~~~~~r~~l~~ .. ~~~~~ w _.::V:~0\. -_.._. ".~~.j.f:.;..':;'~ . ... . .;~- _ ......

15. Typical Tray-Cultured Oysters

~

~ --/: k--

-_.-PANEL ---- // -- ------- ... " ,,"

/ // ,-...... ,.,.. ... ~ILSO~

,

/1 -- '" !"-_.- '" ~'"

II ...... ,." -

.Q!A~~E V/ ,..

// 'I i

I I

I I

, .. ./.

-" ,,,

JUNE DEC. APRIL MAY JUNE JULY AUG. SEPT. OCT. NOV . .

1974 1975

GROWTH AS A FUNCTION OF ORIGINAL SIZE (LENGTH) FIGURE I

170

160

150

140

130

120

110

100

(I)

:!E 90 « 0: C) 80

Z 7 0

6 0

5 ... z « 40 1--· lsJ ~

30

20

10

o

L V

/ [7

/ [7

/

17 --

/ //

/ L,.-//

V /" v' , ;7 1------~~~ ,,~ .,,' " ~ /1

," " ,

) "

/ /' o~Q ",' ~~ ,.

~, ,,"

/ '?o~ If ","

~,...;/ " "

// -...- '/" " / ~ , ,

/ / i

" ",,"

",'-

V,/ "," -, ",,,"

v:~ 1" /. '/

JUNE DEC. APRIL MAY JUNE JULY AUG. SEPT. OCT. NOV.

1974 1975

GROWTH AS A FUNCTION OF ORIGINAL SIZE (WEIGHT) FIGURE 2

t , t ti r~ <

t , !

I 10.0

r ! r

I V) 8.0 f.IJ 0::

I ~ LrJ :!: I- S,P Z f.IJ 0

Z I· f.

J: 4jJ l-

.

~

/ V

-? I .... ;,,,' t--__

~/ --

V "," SO~

/~ !-''' -N'':,.. .......... /'" V ,,' ." "

~ ,,-"

" " ","

,~ V

-~ .. , " e>

Z lJJ

'" .-'" .-

-1 .... , ,"

Z <t -. 20

• f.IJ

,. DIAMOND I .... " ....

:

~

o APRIL MAY JUNE JULY AUG. SEPT. OCT. NOV.

1975

LENGTH AS A FUNCTION OF SEED TYPE FIGURE 3

80

70

60

(/)

~ <t 50 0::: C)

Z 40

l-X 30 C)

LoU ~

20 Z <t W ~ 10

v ;; 1--"'/

./ V;I ,./ ,.

~~ v ,/

~,.

~ / V/· " , //

, , ~

vi "," ~,;

;,,"

WILSON ~~ ",'

"'~ /'" ~ANEL- ,,/ "',

,," O\AM~!:,~-1-------1.-" ---

0 I

APRIL MAY JUNE JULY AUG. SEPT. OCT .. NOV.

1975

MEAN WEIGHT AS A FUNCTION OF SEED TYPE FIGURE 4

·1 80

i 70 qt.l ~.

8 ~ ~~ t" ~ 60 m (I) ~ ~ ;or ...

¥-f « 50

;;J 0:: ~1 (!)

&~ z ~;!{ 40 ~ .. :1 ...

:t: (!)

~ 30

"~ ~ ".

;. ~ Z ~ i.

1 « 20 .. ~

lIJ :E

10

/ /

jj / / ,

,,,.I I' '" ~// ",'

'" ",,'" ./ ",,' V, V -... ~ ~ ,

" 4 DOZ _ ... ::...-'" -,'

7 DOZ. ~ V / --~

, , ~ ....... " ... -- .... ~ 1/'

4 DOZ. t::=---j...--' ... ....... 10 DOZ. -... -1--" ....

- ........ ~ 4 DOZ. ~ 12 DOZ.

0

APRIL MAY JUNE JULY AUG.

1975

GROWTH IN WEIGHT AS A FUNCTION OF SIZE A.ND DENSITY fIGURE 5