The Validity of Otolith Age Deterrninations for Haddock(Melanograntrtlus aegl,efinus L.) frorn the

Locheport, N.S., Areat''

Bv A. C. Konr-snFisheries Research Board of CanadaBi,ological Station, St. Andrews, N.B.

ABSTRACTAn analysis of otolith edge types, age compositions, length distributions, and an examina-

tion of growth from age*length data as cornpared to growth from tagging data are presented

as evidence for the validity of the otolith method ,rf age determination for Lockepott haildock.

INTRODUCTIONIN nrs srr-mv of haddock in Norwegian r,vaters Saetarsdal (1953) has pointedout that haddock scale and otolith data have been used in many investigations

without testing the validity of the method for the fish involved. He then demon-

strated the validity of methods of aging haddock in Norr,vegian waters. This

paper presents evidence for the validity c,f the otolith age reading method forhaddock found ofi Lockeport, Nova Scotia. Ntethods of sampling comrrelcial

landings for sizes and ages are described.

SOURCE OF MATERIAL

The inshore Lockeport area (Fig.1) was selected for study because ofcontinuoqs quarterly sampling of landings carried out during the years 1946 to1954. Here, the fishery for haddocl< is prosecuted almost entirely by hook andline methods. Small longliners (40-45 ft. ) and handliners catch most of thefish taken from the inshore grounds from May to October, while medium

longliners (45-55 ft. ) fish this inshore are,a during the bad weather months of

November to April.The stocks of haddock exploited in the area are thought to be fairly local.

McCracken (1956) tagged haddock in southwestern Nova Scotia waters in

1953. Returns indicated little mixing of tLaddock from the area with those in

other regions.

METHODSSenrpr-rxc

Sampling of commercial landings has been carried out as a routine atLockeport since September of 1946. The rJata dealt with here include materialcollected by Mr. D. N. Fitzgerald, from that time until December, 1954. Thiscornprises a series of 53 samples, totalling 11,590 ffsh.

tn"";'r,"a for publication June 16, 1958.2B,ased on part of a thesis accepted by the Faculty of Graduate Studies and Research,

trIcGill University, in partial fulfflment of the requiremr:nts for the degree of Master of Sciencein ZooTogy.

1229

J. Frsu. Rrs. Bo. Car.+an,r., 15(6), pp. 1229-1238, 1958.Printed in Canada.

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'ou$w\\t'ir'-

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l-'

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' . (: a'"

/ *...*"'!T,lf"\ "^^- ,

" - l - 1 :

1230

Frc. l Principal groundffshing areas ofi Nova Scotia.

When commercial catches of haddock were landed at Lockeport, the two

commercial size categories, scrod (ca.40-45 cm. in length) and large (over ca.

46 cm,), were sampled separately for length and age. Otoliths were usually

taken from one-fffth of the fish measured. In order to weight these sample grouPs

to correspond to amounts of large and scrod landed, weights of each category

landed at the ffsh plant from the area for the sampling day were used. Average

weights of individuals in the two categories were obtained by counting the

numbers of haddock in boxes of standard weight.The equation used to obtain the weighting factor for each of the groups

was as follows:

t " nW ' :

f X n .

where T - total number of fish in catchto - total number of one size category in catchn : total number of ffsh sampledna : total number of the size category in the sample

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/, was estimated by taking the average weight of an individual of the sizecategory in question and dividing the total weight of that category landed bythis average. T was found as the total f, f t, from each size. This procedure forweighting samples of commercial landings of haddock was initiated by Dr.W. R. Martin in 1946.

ExelarlrerroN or Oror-rrrrs

Routine examinations of Lockeport haddock otoliths for age determinationshave been carried out successively since 1946 by Miss R. I. Peterson, Miss A. R.MacMorran, Mrs. J. M. Stuart and the author. All of these people have had aperiod of overlap with their successor in order that the interpretation of marksfound in the otolith would be consistent.

Until early in 1954 haddock otoliths were kept in vials containing a 50%solution of glycerin with a few crystals of thymol added. However, tests showedthat annuli in otoliths from commercial sizes of haddock were iust as easily seenafter they had been stored dry in envelopes. Since the labour of sampling wasreduced by this method, it was adopted.

Otolith age reading was carried out as follows: On the convex side of thesacculus of the otolith

-there is a longitudinal groove, the sulcus acusticus. The

otolith was broken across the interruption in this groove, the fracture surfacebeing perpendicular to the longitudinal axisr, An experienced otolith reader couldusually make a clean break here by exerting pressure widr the thumbs and fore-fingers. The few poor fractures resulting from this method could be remediedby grinding down the piece that was ioo long.

The resulting pieces of otolith were imbedded in a cube of modelling clay,the surfaces of the fractures being set flush with the horizontal upper surfaceof the cube. They were covered with a few drops of 50% glycerin solution. Thehyaline and opaque rings found in the cross-section of the otolith were thencounted with the aid of a stereoscopic microscope (9X) and refected bluelight. These rings were most easily obsen'ed at the pointed end of the cross-section.

Ring counts were translated to ages by a method based on the knowledge ofthe time of formation of opaque and hyaline zones and the approximate timeof the fish's "birthday''. For Nova Scotian waters the haddock birthday wasarbitrarily established as the ffrst day of Fe,bruary. Although this date may havebeen about a month early according to data summarized for 1953 spawning, itwas convenient for growth studies and ring count translation. February, Marchand April were theri combined as one qrrit". of the year in which tir"r" *u,little growth in length, and in which hyaline zones were found at the edge ofthe otoliths of most of these fish,

Table I has been prepared to show the notation used to record readings ofotoliths for any month of the year and the standartl translation of these readingsto age groups. The date of capture was essential to correct translation fromzone numbers to ages.

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T,q.nll i. E,ramples of observed ring courtts and edge types on haddock

_ . t " t t ah . , . " t d t h " t .

T ime of capture

Quarterof year N1[onths

Number ofh1'aline

'fype and width

zones oI eclgc zonei\ge groupassignation

Feb.Mar.A n r

tii ;

narrou' h)'alittewide hyalinenarrow opaquelvide opaque

1\'Ia_vJuneJ., ly ii

narrow hyalinervide hyalincnarroN opaque*'ide opaqLle

Aug.SeptOct. ii

narrow h1'a l i r tegide h1'nlinenarro\v opaque*-irle opaque

(zl" in Oct . )44555

No ' lP n : t r r o l v h1 ' a l i ne 4a

I \i r,i"l ] I I ide, h)'-alill: !.

ti ' I r llarrow opaque 9

. lan l 5 ot i4" up"qu" b

oln these cases it is assumed that a uew hyaline z-onc h.us formed at the

edgc of the otolith before the birthday of the.{rsh in the lollowlng^r eDruary'

Th"erefore, it is not counted as a year-zone for age-group asslgnatlon'

VALIDITY OI- THE OTOLITH N{ETHOD OF AGE DETE}iMINATION

Snasonar- CnaNcBs rN OroLrrH Etcas

The types of marginal deposit founcl on Lockeport haddock otoliths at

difierent tiies of the yEar are siown in Fig. 2. Almosi all the-otoliths sampled

from January to May tf en"h year had hyaline zones at the edges' In the 1954

Jone su-ple opuqo" edges appeared' The peak opaqu e -zo71e formation at the

Lage of tli" otolittir occuired f^r^om August to October, and a great predominance

of "hyaline

zones was again observeJ by December. The failure of any one

sample to show 100% opaque zones was usually due to the formation of "false

che&s" or "subsidiary zones" (Hickling, 1933, p. 30).The presence of these zones of hyilinr maierial forming within some of the

opaque iorr", ,t"""rsitated the recording of a hyaline "*g: "":"

though these

*o"ia have been recognized and ignoreJin age ieading if the otolith had grown

further.This yearly rhythm of 2 types of. zone in otoliths and scales of fish has been

discussed by daetarsdal (195Si. The general opinion oj the authors he quotes

is that seasonal changes Lt th" type recorded in Fig. 2 are good evidence for

the validity of the method.

Rnr-errvn AeuNreNcr op Ypen-Cr-essBs

The age compositions of sarnples of Lockeport haddock landings for the

Vears 1946 to 1952 are shorvn in Fig. 3. The most abundant single yeal-classianded by the fishery during this period was the one spa\\''ned in 1943. In the

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J l;i"'::i il t-l n il [-j- ['] '"'":t U tJ -t--l; il "'

::"F ["j il __ ; ;IH"

':tffi_ il

Frc. 2. Type of deposition found in the edge of the cross-section of haddock otolitlrs

fromtheinshoreLockeportgrounds.Blacksectionsindicatethepercentage-ofopaque

"dg", "rrd white section^s thJpercenta'e of h1'aline edges in the otoliths of the sample'

The number of ffsh in each sample is shown'

Figure it is seen to enter the landings in relatively _larg_e numbers in the fourth

q"?r,", of 1g46. The l94B year;glaycontinued to be dominant in ths,landings

Jp ao ,h" fourth quarter of tg+g. Furthermore, it is greater than neighbouring

ySur-"turr", in the second and fourth quarters of 1950, first quarter of 1951'

hrst quarter of 1958, and first and fouith quarters. of 1954. Dgl"g the same

periods a contrast is provided by the relatively small numbers of the 1942 yeat-

ilass. Continued abundance and scarcity of certain year-classes in continuous

sampling of fish populations have been used as evidence of validity of the age

detJrmiiation method by such investigators as Graham (1929), Dannevig

(1933), and Hi le (1941).' Sin"e the 1943 year-class has passed through the fishery, there has been

no single year-class ihat has been dominant in the landings ovel a number of

y"urr. ?o*-, five-, six- and seven-year-old fish have made up the bulk of the

iandings for each quarter, rvith a number of year-classes contributing' The

commJrcial cull at about 40 cm. fork length eliminates many of the two- and

three-year-old haddock from the landings'

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A d € Y 6 o r s

Frc. r3. dgs composition of the landed hook,and-iineLockeport grounds, Numbers of otoliths examined are

1943 year-class is shown in

- O c I N o Y - J o n

4 Q( 2 0 ) t*.

( 4 0

8 0

4 0

o

o20

o

il 6.) ( s 5 )

i.,_,__._-.,_{ 4 0

{ r 2 0 ) ( 8 0 )

r.*( 4 0 )

lA"-fi-

(90 )

J*^l,

f l 2 0 )

2

( 8 4

i,,( 2 0 0 )

JTI.. f lor )

Jl-i (48)

#tIT t . 5 ( 4 o )

- r l i l n-| | E i

( 4 0 ) 0 )

l- l-t r

( 4 0 ) J Lrr"' (60) | | i ( r 2 0 )

{ 4 o ) I

t l _ I- f I I i ! r i| | F-=_& _t

( 9 0 )

-rfl Il r i l -

_ i I | | I t u + :

( 7 9 1 0 2 0 )

L

-l-l lf-.'. ,"( 7 9 )

i t lril l-rl1-g: -

( 4 0 1 ( 8 0 )

F e b

| 9 5 0

1 9 5 3

I 9 5 2

haddock catch from the inshorerecorded for each sample. The

black.

Lewcrrr DrsrnrsurroNs oF THE 1946-1949 Sauer-esGraham (1929) and Menon (1950) have shown that if zone formation in

scales and otoliths can be correlated with the Petersen method of assigning agesto peaks in length-frequency graphs, the method of aging must produce- amajority of correct determinations. Both investigators have indicated

-that these

modgs can only be recognized in the first 3 or 4 age groups. Length distributionsof older age groups tend to overlap, flattening the curve when the total sampleis portrayed.

- Ih" Lockeport haddock inv-estigation has indicated that if one extremelyabundant year-class appears in the landings, preceded and followed by one ormore_ poor year-classe-s, the peak produced by the abundant year-class in thelength dishibutions of the samples may be followed for a number of years. Inthe length djstributions of Lockeport haddock landings (Fig. a)

" p""k enters

the sample distribution in the fourth quarter of 1946. From then until the thirdquarter of 1949 it is possible to follow this peak through the samples as it moves

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E 1 9 4 6

r, Itr 1948

5 4 8 . 5 5 6 5 6 4 5 7 2 . 5

L o n g l h - C n

Frc. 4. Length distributions of the haildock landed at Lockeport, N-S., drrring varrous quarters

of the years"Ig46 to lg4g. Broken lines indicate the length-distribution of the total age sample.

S o l i d l i n e s s h o w t h e l e n q t h d i s t r i b u t i o n o f t h e l g 4 S y e a r - c l a s s '

,"f8 f

u|.q i

E

t 2

6

2

o

t o

I

6

2

0t

l;t

:i

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along the length scale. Independent age readings for these samples show that theffsh sizes in the 1943 year-class correspond with this mode in the overall lengthcomposition. In 1946 age determinations showed that the mode was made upof S-year-old fish, In 1947 they were 4-year-olds, in 1948, 5-year-olds, and in1949, 6-year-olds. Thus, the evidence demonstrates that this particular groupof haddock has added one year mark per year to their otoliths. This is furtherevidence that the otolith method of aging these fish is valid.

ColrpenrsoN or Gnowrrr rnolr AcB-LENGTH aNrr TaccrNc Dare

Lengths of Lockeport haddock at tagging and recapture are available forfish tagged in 1953 (McCracken, 1956 ). In order to demonstrate that growth dataobtained from otolith readings were equivalent to those found for tagged fish,individuals recaptured after approximateiv one year's freedom were selected.Twenty-three fish met this criterion, of which all but 3 were of ages 5 to 8(Table II). Comparable growth data from commercial samples of otoliths andlengths are recorded in Table III.

tiiitJJ. 1954 recaptures of haddoch tassed near Lockeport, N. S.,

Length at Length at N{onth oftagglng recapture tagging

( l ) ( t ,+,) ( r95: l )

N{onth ofrecapture Age in years

( 1954) at recapture

M.yM,.yNIayMuyMoyNIayX,IayN{ayuneu1y, , l r r

ul1'

r r l r -r l r zr l w. . 1 - ,u r v

r r l v

uly

AugustALrgust

In order to plot both age-length and tagging data on the same basis, astraight line transformation was used. This transformation has been employedby Ford (1933 ) and walford ( 1946 ) for age-length data, and by lvlanzer andTaylor (1947) and Lindner (1953) for tagging data. Lengths at tagging andage-length means for rg53 ( ft ) g'ere plotted against length at recapiure ancl

c1n.

534854504954585450564r)60O I

a t

64665550525+505650

cm.5147

494853565 1

C J

47564ti4764o o

O J

48,194q

5 145

March 6April I.1pnr cM,.y 6N{ay 7\'{a1' 6JLrlyJ., ly 6M,ryMay 7J U n e D

June 11June 6J une t)Ar:gust 11AugustAugust 8August 6September 6September 5NIay 6Junc 6August 6

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' l l.teLn III. Ages and mean lengths of haddock sampled at Lockeport in 1953 and 1954.

6

1953Nlean length in cm. (1,)Number in sample

4 t r . D

2 I5 1 . 930

ll|J . tl

72D D . D' K

195.{X{ean length in cm. (1y. .1)Number in sample

4 9 . 5 5 6 . 026 27

5 8 . 77

59.710

age-length means for 1954 (lr+t).Least squares fits for the two sets of pointsgave the follorving straight line equations (in centimetres):

and

These two lines are plotted in Fig. 5, together with the Points to which they arefftted.

I t + t : 9 . 8 + 0 . 8 6 l t

I t + r : 1 0 . 3 + 0 . 8 6 1 ,

for tagging data

for age-length data.

/'"

E

5 2 5 4 t j ,

" " .

t u 6 0 6 2 6 4 6 6

Frc. 5. Straight line transformations for growth in length of Lockeport

haddock from tagging and ageJength data. Fish lengths (lt) are plotted

against lengths one year later (lr*1). Dots indicate tagging points. Opencircles indicate ageJength points.

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The Figure and the equations show that both lines have the same slope, andthey are separated on the 1111 axis by only 0.5 cm. It is evident that the growthparameter arrived at by the otolith age reading method is essentially the sameas that calculated by measurements of tagged haddock. This adds a further pieceof evidence justifying the use of haddock otoliths as an aging tool.

DISCUSSIONFour types of evidence for the validity of the otolith method of aging

Lockeport haddock have been presented in the preceding sections. The dataused were taken from samples of commercial landings which consist mainly offish 3 to 9 years old. Since only 67o of the landings by number are made up offish over these ages, the otolith method of age determination is considered to beapplicable for commercial samples of haddock at Lockeport. Otolith readershave noted in their experience with samples from this and other Nova Scotianareas that annuli are readily distinguished in otoliths from the majority of olderhaddock, and it is assumed that otolith readings are also valid for haddock over9 years of age. As noted by Kohler and Clark (1958), this is not true of scaleage reading.

Less detailed examinations of data on year-class strengths and otolith edgechanges for haddock from other Nova Scotian fishing grounds provide a similardegree of confidence in age readings from their otoliths.

ACKNOWLEDGMENTSThe author wishes to thank Dr. W. R. Martin for guidance during the course

of the study, Dr. F. D. N'IcCracken for the use of tagging data, and D. N. Fitz-gerald for the eficient sampling of landings at Lockeport.

REFERENCESDaxnuvrc, A, 1933. On the age and growth of the cod (Gadus callarias L.) from the

Norwegian Skagerrak coast. Rept. Noruoegian Fish,. and Mar. Inaest,,4(1), 145 pp.Fono, E. 1933. An account of the herring investigations conducted at Plymouth during thc

years from 1924 to 1933. J. Mar. Biol. Ass. U. K., t9: 305-384.Gnarlarr, M. 1929. Studies of age determination in fish. Part II. A survey of the literature.

U.K. Mi,n. Agr. and, Fish., Fish. lruaest., Ser. 2, lI(3), 50 pp.I{rr-n, Rar-eH. 1936. Age and growth of the cisco (Leuci,chthys artedi (Les:ueur)) in the

lakes of the northeastern highlands, Wisconsin. BuIl. U.S. Bur. Fish.,43(19): 2IL-3L7.Konr-nn, A. C., and J. R. Cr-am. 1958. Haddock scale-otolith comparisons. J. Fish, Res.

Bd. Canada, t5(6) : I%9-1246.LrNnNnn, M. J. 1953. Estimation of growth rate in animals by marking experiments. U.S.

Fish and Wildli.fe Sens., Fish. BuIl.,78(54): 65-69.MaNzrn, J. I., and F. H. C. T,q.yr,on, L947, The rate of growth in lemon sole in the Strait

of Georgia. Fish. Res. Bd. Canada,Pac. Prog. Reprs., No. 72, pp.24-27.McCnacrnN, F. D. 1956. Cod and haddock tagging off Lockeport, N.S. Fisft.. Res. Bd.

Canada, Atlantic Prog. Repts., No. 64, pp, 10-15.NIrNoN, M. D. 1950. Bionomics of the poor-cod (Cadus lninutus L.) in the Plymouth area.

l . Mar. BioI. Assn.,29(I): 185-299.Sanransoar,, G. S. 1953. The haddock in Norwegian waters. Nortpegian Fish. and Mari,ne

Inaest., l0(9), a6 pp.Wer-rono, L. A. 1946. A new graphic method of describing the growth of animals. Brol.

BuII. ,90(2): L4I-L47.

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