the use of measurement to determine the condition of

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1946

The Use of Measurement to Determine the Condition of Oysters in The Use of Measurement to Determine the Condition of Oysters in

Virginia Virginia

Alice Elizabeth Overcash College of William and Mary - Virginia Institute of Marine Science

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Recommended Citation Recommended Citation Overcash, Alice Elizabeth, "The Use of Measurement to Determine the Condition of Oysters in Virginia" (1946). Dissertations, Theses, and Masters Projects. Paper 1539617363. https://dx.doi.org/doi:10.25773/v5-vpgf-6w63

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THE USE OF MEASUREMENT

TO. DETERMINE THE CONDITION

OF OYSTERS IN VIRGINIA

ALICE ELIZABETH OVERCASH

SUBMITTED IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS OF

THE COLLEGE OF WILLIAM AND MARY

FOR THE DEGREE OF

.MASTER CF ARTS

1946

TABLE -OF CONTENTS

INDEX OF FIGURES

PAGE

i i

INDEX OF TABLES i v

INTRODUCTION 1

MATERIALS 2

METHODS 3

RESULTS AND DISCUSSION 6

SUMMARY AND CONCLUSIONS 39

BIBLIOGRAPHY 40

ACKNQNLEDGLIENTS 41

VITA 42

i i

INDEX OF FIGURES ' 4NO.

I . APPARATUS FOR DETERMINING- VOLUMETRIC MEASUREMENT

I I . LONGITUDINAL SECTION OF OYSTER SHELLS SHOWING SHAPE

I I I . RELATION OF TOTAL, SHELL, AND INNER VOLUMETO TOTAL WEIGHT FOR OYSTERS FROM PARROTT’ S ROCK, RAPPAHANNOCK RIVER

IV . MEAN SHELL,NET AND DRY MEAT WEIGHT FOR OYSTERS FROM PARROTT’S ROCK

V . MEAN CALCULATED VALUES FOR PERCENTAGE OF CAVITY,PERCENTAGE OF MOISTURE AND INDEX OF CONDITION FOR OYSTERS FROM PARROTT’ S ROCK

V I . RELATION OF TOTAL VOLUME TO TOTAL WEIGHT OF OYSTERS FROM YORK RIVER ROCK BETWEEN ICING AND INDIAN CREEKS

V I I . RELATION OF SHELL VOLUME TO TOTAL WEIGHT OF OYSTERS FROM YORK RIVER ROCK BETWEEN KING AND INDIAN CREEKS

V I I I . RELATION OF INNER VOLUME TO TOTAL WEIGHT OF OYSTERS FROM YORE RIVER ROCK BETWEEN KING AND INDIAN CREEKS

IX . MEAN SHELL WEIGHT FOR TWENTY-ONE GROUPS OF OYSTERS FROM'YORK RIVER: ROCK: BETWEEN KING AND INDIAN CREEKS

X. MEAN WET MEAT WEIGHT FOR TWENTY -ONE GROUPS OF OYSTERS FROM YORK RIVER ROCK BETWEEN KING AND INDIAN CREEKS

X I . MEAN DRY MEAT WEIGHT FOR T7/ENTY ONE GROUPS OF OYSTERS FROM YORK RIVER ROCK BET ADEN KING AND INDIAN CREEKS

X I I . MEAN CALCULATED VALUES OF PERCENTAGE OF CAVITY FOR TWENTY ONE GROUPS OF OYSTERS FROM YORK RIVER ROCK BETWEEN KING AND INDIAN CREEKS

PAGE

5

10

14

18

21

24

25

26

28

30

32

34

NO.

X l l l a .

X l l l b ;

INDEX OF FIGURES ( c o n * t )

MEAN CALCULATED VALUES OF INDEX OF CONDITION FOR OYSTERS FROM YORK RIVER ROCK BETWEEN KING AND INDIAN CREEKS

MEAN CALCULATED VALUES OF PERCENTAGE OF MOISTURE FOR OYSTERS FROM YORK RIVER ROCK BETWEEN KING AND INDIAN CREEKS

PAGE

35

35

i v

NO.

I .

I I .

I I I .

IV .

V .

V I .

V I I .

IX .

INDEX OF TABLES

PHYSICAL DATA FOR EIGHT AREAS WHERE SAMPLES WERE TAKEN. RANGE AND MEAN CONDITION VALUES ARE GIVEN

DRY WEIGHT, INNER VOLUME MEASUREMENTS AND RESULTING INDEX OF CONDITION FOR INDIVIDUALS FROM EIGHT ROCKS IN VIRGINIA

ACTUAL AND CALCULATED VLOUMSTRIC MEASUREMENTS IN TERMS OF TOTAL WEIGHT FOR EIGHT GROUPS OF OYSTERS FROM PARROTT!S ROCK IN THE RMPPAHAN* NOCK RIVER

MEAN AND RANGE IN WEIGHT OF SHELL VET AND DRY FEAT FOR EIGHT GROUPS OF OYSTERS FROM PARROTT!S ROCK,RAPPAHANNOCK RIVER

EIGHT LEANS OF CALCULATED VALUES FOR PERCENTAGE OF MOISTURE,PERCENTAGE OF CAVITY AND INDEX OF CONDITION FOR GROUTS OF OYSTERS FROM PARROTT’S ROCK, RAPPAHAKNOCIC RIVER

ACTUAL AND CALCULATED VOLUMETRIC MEASUREMENTS IN TERMS OF TOTAL WEIGHT FOR TWENTY ONE GROUPS OF OYSTERS FROM YORK RIVER ROCK BETWEEN KING AND INDIAN CREEKS

MEAN AND RANGE IN WEIGHT OF SHELL,VvET AND DRY MEAT WEIGHT IN GRAMS FOR TWENTY ONE GROUPS OF OYSTERS FROM YORK RIVER ROCK BETWEEN KING AND INDIAN CREEKS

TWENTY ONE MEANS OF CALCULATED VALUES FOR PERCENTAGE OF CAVITY, PERCENTAGE OF MOISTURE AND INDES OF CONDITION FOR GROUPS OF OYSTERS FROM YORK RIVER ROCK BETWEEN RING AND INDIAN CREEKS

PAGE

7

9

16

17

20

27

29

33

1 .

THE USE OE MEASUREMENT TO DETERMINE THE CONDITION

OE OYSTERS IN VIRGINIA

INTRODUCTION

I t i s o f i n t e r e s t t o p e r so n s en gaged i n th e o y s t e r in d u s

t r y th a t t h e y r e c e i v e a h ig h y i e l d o f o y s t e r m ea ts p e r volume

o f o y s t e r s . The y i e l d o f m eats i s known t o v a r y i n th e V i r

g i n i a a r e a . Some m eats produced are poor i n q u a l i t y and amount.

T h is a f f e c t s t h e m arket and n u t r i t i o n a l v a l u e . ( T u l l y 1936)

T h is stu d y w as begun i n an e f f o r t t o c h a r a c t e r i z e p rod u c

t i o n o f o y s t e r s in d i f f e r i n g l o c a l i t i e s in V i r g in ia by u s e o f

a c o n d i t io n fo r m u la . The fo rm u la w as d e r iv e d by H opkins (1937)

in s t u d y in g c o n d i t io n o f o y s t e r s in A p p a la c h ic o la Bay, and

m o d if ie d s l i g h t l y by Medcof and N e e d ie r (1941) when t h e y used

i t to compare the i n f l u e n c e o f tem p er a tu r e and s a l i n i t y on

o y s t e r s i n Canadian w a t e r s .

The form u la f o r th e in d e x o f c o n d i t io n o f an o y s t e r used

in t h i s s tu d y i s 1 000 m u l t i p l i e d by th e d r ie d w e ig h t o f th e

meat i n grams d iv id e d by t h e volum e of t h e s h e l l c a v i t y in

m i l l i l i t e r s . The volume o f th e s h e l l c a v i t y b e i n g th e r e l a

t i v e l y f i x e d v a l u e and regard ed a s the l i m i t o f sp a ce w hich

th e meat may occu p y , t h i s in d e x o f c o n d i t io n th e n i s e s s e n t i

a l l y th e r a t i o o f the amount o f s o l i d s i n the m eat w ith r e

s p e c t to th e s p a c e e n c lo s e d by th e s h e l l s .

By d e te r m in in g i n d i v i d u a l c o n d i t i o n v a l u e s f o r sm all

sam ples from v a r i o u s r o c k s i t was e x p e c te d t h a t a mean c o n

d i t i o n v a lu e would s e r v e f o r com paring th e p ro d u c in g a r e a s .

L o c a t in g th e b e t t e r producing a r e a s would l e a d t o a s tu d y o f

2

e n v iro n m en ta l f a c t o r s p r e v a i l i n g on them c o n d u c iv e t o th e p r o

d u c t io n o f good o y s t e r m e a ts .

P r e l im in a r y d e t e r m in a t io n s showed t h a t i n d i v i d u a l c o n d i t i o n

v a l u e s fo r o y s t e r s from one l o c a l i t y v a r i e d w i d e l y . In o r d e r to

e v a lu a t e th e use o f th e mean in d e x o f c o n d i t i o n f o r comparing

r o c k s in V i r g i n i a , i t was n e c e s s a r y to make a d e t a i l e d s t u d y o f

l a r g e r sam ples to s tu d y i n d i v i d u a l v a r i a t i o n and d e term in e t h e

number t o t e s t f o r a r e p r e s e n t a t i v e sa m p le ,

A la r g e number o f o y s t e r s w ere sam pled from two r o c k s .

I n d i v i d u a l c o n d i t io n v a l u e s w ere d e ter m in e d f o r t h e s e o y s t e r s

and a d d i t i o n a l m easurem ents w ere made to f i n d a s u i t a b l e i n d i

c a t i o n o f s i z e so t h a t c o n d i t i o n m igh t be compared w i t h s i z e .

MATERIALS

Sam pling o y s t e r s from t h e r o c k s . O y s te r s w ere ta k e n f o r

the most p a r t from p u b l ic r o c k s in th e York and Rappahannock

R i v e r s . Sam ples u s u a l l y c o l l e c t e d by d r e d g in g w ere assumed

to be t y p i c a l o f the bed a s a w h o le ; th u s t h e i n d i v i d u a l s

r e p r e s e n te d grow th i n f lu e n c e d by th e v a r i e t y o f e n v ir o n m e n ta l

f a c t o r s p r e v a i l i n g on the r o c k .

The sam p les were ta k e n w h i l e o y s t e r s w ere h i b e r n a t i n g and

presum ably l i t t l e v a r i a t i o n in c o n d i t i o n was t a k in g p l a c e .

P r y th e r c h (1923) found t h a t t h e h ib e r n a t in g p e r io d i s d e ter m in e d

m a in ly by t h e te m p e r a tu r e o f th e w a te r . When wra t e r tem p era tu re

i s a s h ig h a s 19 o r 2 0 °C ., f e e d i n g and spaw ning ta k e p l a c e . At

lo w e r te m p e r a tu r e s l i t t l e p h y s i o l o g i c a l change o c c u r s . T h e r e -

3

f o r e th e c o n d i t i o n o f th e o y s t e r i s assum ed t o be f a i r l y s t a b l e .

Sam ples ta k en on d i f f e r e n t d a t e s when th e tem p era tu re o f the

w a te r wras b e low 19° C. co u ld be compared.

S e l e c t i o n o f 07/ s t e r s f o r t e s t i n g . I t was o b v i o u s l y a d v i s

a b le t o s e l e c t f o r th e t e s t s o n l y o y s t e r s w h ic h could be opened

w ith o u t undue breakage o f the s h e l l s . I t was found th a t shape

was a f a c t o r i n d e te r m in in g p o s s i b l e s h e l l b r e a k a g e . H owever,

v e r y few o f th e o y s t e r s were r e j e c t e d f o r t h i s r e a s o n .

In th e f i r s t sam p les no s e l e c t i o n was made f o r s i z e , but

l a t e r o y s t e r s w ere s e l e c t e d on th e b a s i s o f l e n g t h or t o t a l

w e ig h t so t i n t c o n d i t i o n m ight be compared to s i z e .

S t o r a g e . Due t o t h e l e n g t h o f t im e ta k e n to make th e

d e t e r m in a t io n s , i t w as n e c e s s a r y in th e c a s e o f l a r g e sa m p les

t o s t o r e them f o r s h o r t p e r io d s e i t h e r i n runn ing s e a w a te r

com parable i n s a l i n i t y t o t h e w a t e r s from w h ich t h e y were ta k en ,

or in a r e f r i g e r a t o r a t 13° C. In th e l a t t e r c a se t h e y were

p la c e d w i t h the b i l l s up t o p r e v e n t t h e l o s s o f s h e l l l i q u o r .

METHODS

O y ste r s s e l e c t e d f o r th e t e s t s w e re t h o r o u g h ly c le a n e d

o f mud by b r u s h in g . A l l f o u l i n g organ ism s w ere rem oved . The

o y s t e r s -with a d h er in g s h e l l w h ich could not be broken o f f w ere

d i s c a r d e d .

The w e ig h t s o f th e t o t a l o y s t e r , i t s s h e l l and th e wet

and dry meat were m easured and v o lu m e t r i c m easurem ents w ere

determ ined- f o r th e t o t a l o y s t e r and f o r th e s h e l l s . The l e n g t h

from umbo to b i l l and th e maximum w id th o f the s h e l l were m easured .

4

The t o t a l w e ig h t and th e t o t a l vo lum e w ere m easured a f t e r

the w e tn e ss o f th e o u t s i d e s h e l l s had been s t a n d a r d iz e d by im

m ersin g t h e o y s t e r in w a t e r and a l lo w in g i t to d r a in f o r two to

fo u r m in u te s . T o t a l w e ig h t o f th e l i v e o y s t e r in c lu d in g th e

w e ig h t o f t h e w et s h e l l s , s h e l l l i q u o r and w et meat was m easured

t o th e n e a r e s t t e n t h gram on a t o r s i o n b a l a n c e .

Volume was d e term in ed by t h e o v e r f lo w m eth od . ( F i g . I )

F re sh w a te r from t h e b eaker was drawn in t o th e tube and a l lo w e d

t o s ip h o n o f f u n t i l e q u i l ib r iu m was r e a c h e d . The o y s t e r w as

p la c e d in t h e b ea k er and th e d i s p l a c e d w a t e r w a s caught in a

b u r e t t e and measured d i r e c t l y . The f o l l o w in g s c a l e was adop ted

f o r m easuring th e v a r io u s s i z e d o y s t e r s :

1 .0 0 0 m i l l i l i t e r b e a k e r , 102 m i l l i m e te r s i n d ia m e te r , c o n t a in in g 625 m i l l i l i t e r s o f w a te r ; o v e r f lo w measu re d i n a 50 m i l l i l i t e r b u r e t t e , g r a d u a te d in 0 .1 m i l l i l i t e r s . A ccur a c y + 0 .2 m i l l i l i t e r s .

2 .0 0 0 m i l l i l i t e r b e a k e r , 128 m i l l i m e te r s i n d ia m e te r c o n t a in in g 1330 m i l l i l i t e r s o f w a t e r , o v e r f lo w measu red i n 100 m i l l i l i t e r b u r e t t e , g r a d u a te d i n 0 .2 m i l l i l i t e r s . A ccu - r a c y + 0 .2 m i l l i l i t e r s .

T o t a l volum e r e f e r s to the amount o f w a te r d i s p l a c e d by

th e l i v e o y s t e r w i th the v a l v e s c l o s e d . The s m a l l amount o f

carm ine which had b e e n added t o the w a te r in the b e a k er was

d e t e c t e d in t h e g i l l s i f th e v a l v e s opened w h i l e t h i s d e t e r

m in a t io n wra s b e in g made. S e v e r a l su ch o y s t e r s w ere d i s c a r d e d .

The o y s t e r s w ere opened w i t h a r e g u l a r o y s t e r k n i f e by

i n s e r t i n g t h e b la d e a t th e umbo and r e l e a s i n g t h e h in g e

l i g a m e n t . C a r e fu l i n s e r t i o n o f th e b la d e n e c e s s a r y to cut th e

Sm all - Medium

Medium - Large

5

F ig u r e I

A pparatus f o r D eterm in in g V o lu m e tr ic M easurem ents

6

the a d d u c to r m u scle In su re d minimum m u t i l a t i o n o f th e m ea t .

T his method o f o p en in g cau sed no breakage o f the s h e l l s

in th e m a j o r i t y o f c a s e s .

The w hole f r e s h meat was a l lo w e d to d r a in on c o a r s e f i l t e r

p ap er f o r t h r e e or fo u r m in u te s . I t w a s then p la c e d on a w atch

g l a s s o f known w e ig h t and w eigh ed to th e n e a r e s t t e n t h gram on

a t o r s i o n b a la n c e .

The w a tch g l a s s c o n t a in in g t h e w e t meat was th e n p la c e d in

an oven r e g u la t e d a t a u n iform tem p eratu re o f 35° C. and d r ie d

t o c o n s ta n t w e i g h t . U s u a l ly t h e m eats r ea ch ed c o n s t a n t w e ig h t

w it h in t w e n t y - f o u r to t h i r t y - s i x h o u r s , depend ing on th e s i z e

o f t h e m eat .

The g l a s s c o n t a in in g t h e d r ie d meat was t r a n s f e r r e d i n t o a

d e s s i c a t o r and a l lo w e d t o c o o l b e fo r e w e ig h in g on a c h a in o m a tic

b a la n c e to th e n e a r e s t th o u sa n d th gram.

E x a c t ly th e same m ethods were used i n d e te r m in in g th e s h e l l

w e t n e s s , s h e l l w e ig h t and s h e l l volume a s w ere employed f o r th e

t o t a l o y s t e r . The in n e r volum e i s t h e c a l c u l a t e d d i f f e r e n c e b e

tween t o t a l and s h e l l v o lu m e .

RESULTS AND DISCUSSION

C e r ta in a r e a s w ere s e l e c t e d f o r sam pling f o r th e c o n d i t io n

t e s t s . The p h y s i c a l o b s e r v a t i o n s made when t h e s e sam p les w ere

ta k en and th e mean c o n d i t i o n v a l u e s a s w e l l a s th e range w i t h i n

a sample a r e g i v e n i n T ab le I .

The mean in d e x o f c o n d i t i o n r a n g e s from 6 2 .3 5 f o r Aberdeen

Rock t o 9 3 .7 3 f o r P a r r o t t 1s . The s i g n i f i c a n c e o f t h e s e v a lu e s f o r

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com paring t h e r o c k s i s q u e s t io n a b le i n v ie w o f th e s m a l l number

o f i n d i v i d u a l s i n t h e sam p les and th e w id e ran g e i n c o n d i t i o n

v a lu e w i t h i n th e sam p le .

I n d i v i d u a l v a r i a t i o n s . W hile d e t e r m in a t io n s w ere b e in g

made i t was a p p a r e n t t h a t t h e r e w as a d i f f e r e n c e in th e p r o p o r

t i o n o f th e s h e l l c a v i t y f i l l e d w i t h m ea t . The l a r g e s t m eats

by c u r s o r y o b s e r v a t io n do not a lw ays come from t h e o y s t e r s w i t h

t h e l a r g e s t s i z e d c a v i t y .

The q u a l i t y o f t h e m eat a s w e l l a s t h e amount i s v a r i a b l e

in specim ens from th e same sa m p le . M eats th a t were f l a c c i d and

r e l a t i v e l y d a rk er i n c o lo r b le d more a f t e r b e i n g r e l e a s e d from

t h e s h e l l th a n t h o s e o f a f i r m e r t e x t u r e and creamy c o l o r , and

when d r ie d t h e form er had a lo w e r d r ie d w e ig h t i n d i c a t i n g th a t

t h e r e were l e s s s o l i d s i n t h e l i v e b o d y .

A sm a ll d i f f e r e n c e i n d ry m eat w e ig h t a c c o u n ts f o r a w id e

range in c o n d i t i o n v a l u e . (T a b le I I ) For example, two o y s t e r s

( i n Sample VI) h a v in g an in n e r volume o f 33*5 m i l l i l i t e r s and a

d i f f e r e n c e in d r ie d meat w e ig h t o f 1 .0 7 grams showed a c o n t r a s t -

o f 3 1 .9 4 i n in d e x o f c o n d i t i o n .

F a c t o r s p o s s i b l y i n f l u e n c i n g i n d i v i d u a l v a r i a t i o n . The

shape o f o y s t e r s in th e sample v a r ie d from t h o s e o f f a i r l y u n i

form c o n to u r w i t h a deep cupped v a l v e , t o th o s e o f a more un

even o u t s id e ap p eara n ce v / i t h s h a l lo w e r c a v i t i e s . ( F ig . I I )

Shape i s an im p orta n t f a c t o r in two r e s p e c t s ; i t i n f l u e n c e s the

volume o f the s h e l l c a v i t y and In many i n d i v i d u a l s i t was o b

se r v e d t h a t b e t t e r q u a l i t y m eats were found i n th e more r e g u la r

s h e l l s w i t h cupped c a v i t i e s . I t may be t h a t t h e same e n v ir o n

m e n ta l f a c t o r s co n d u c iv e to un iform s h e l l shape fa v o r p r o d u c t io n

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10

f i g u r e I I

L o n g i t u d in a l S e c t i o n o f O y ster S h e l l s Showing Shape

A. Thin I r r e g u l a r S h e l l s , S h a l lo w C a v ity

B. T h ick R eg u la r S h e l l s , Cupped C a v ity

I I

o f good q u a l i t y m e a ts . P r o b a b ly t h e s e d i f f e r e n c e s i n meat p r o

d u c t io n and s h e l l sh ape r e f l e c t v a r y in g p h y s i c a l c o n d i t i o n s to

w h ich t h e i n d i v i d u a l s on a r o c k a r e s u b j e c t e d .

The sam ples w ere r e p r e s e n t a t i v e o f the bed a s a w hole s i n c e

t h e y w e re removed by d red g in g a l a r g e a r e a o f th e r o c k . In g e n

e r a l i t i s t r u e t h a t t h e b o tto m o f a r o c k may v a r y from s o f t mud

b u i l t up w i t h s h e l l t o h ard er b o ttom w hich i s u s u a l l y h ig h e r .

I t has been n oted by o t h e r w o rk ers th a t t h e more u n ifo r m ly shaped

s h e l l s come from h a rd er b o t to m s .

The p r e se n c e o f c u r r e n t s and e d d ie s over p a r t s o f th e rock

g i n f l u e n c e the amount o f foo d a v a i l a b l e f o r th e o y s t e r . Crowd-

e in g and c l u s t e r i n g a s w e l l a s th e p o s i t i o n o f t h e i n d i v i d u a l i t -3B s e l f a l s o h a s d i r e c t b e a r in g on t h e amount o f f o o d t h a t th e©

o y s t e r h a s to com pete f o r , th u s i n f l u e n c i n g grow th and c o n d i t i o n .s

As f o r o t h e r f a c t o r s p o s s i b l y a f f e c t i n g c o n d i t i o n , t h e p a r a

s i t i c a n n e l id P o ly d o ra c i l i a t a may be m e n t io n e d . A number o f

o y s t e r s i n t h e s e sam p les were i n f e s t e d to v a r y in g d e g r e e s by

t h e worm. By i n s p e c t i o n i t w a s n o ted t h a t s h e l l s i n f e s t e d to

a m oderate o r heavy d e g r e e p o s s e s s e d dark and w a te r y m e a t s .

Luntz ( 1 9 4 1 ) a p p l ie d th e c o n d i t i o n form u la i n a s tu d y o f

th e e f f e c t o f P o ly d o ra c i l i a t a on Sou th C a r o lin a o y s t e r s . H is

a n a ly s e s in d ic a t e d th at t h i s worm c a u s e s a l o s s i n meat w e i g h t .

L u n tz 1 s e x p la n a t io n i s t h a t th e worm " u p se ts t h e norm al l i f e

o f the o y s t e r by r e s t r i c t i n g i t s l i v i n g space and f o r c i n g the

o y s t e r t o d e v o te c o n s id e r a b le o f i t s e n e rg y i n s h e l l b u i ld in g

w h ich would o t h e r w is e be u n n e c e s s a r y .”

T h is assu m p tion i s p ro b a b ly tr u e a l s o o f o y s t e r s i n f e s t e d

w i t h th e b o r in g sp onge C lio n a s p . M eats o f i n d i v i d u a l s whose

12

s h e l l s w ere i n f e s t e d w i t h t h i s sponge w ere n o t i c e a b l y o f p oor

q u a l i t y . C o n d it io n v a lu e s cou ld not be o b ta in e d f o r many o f

t h e s e i n f e s t e d o y s t e r s b e c a u se b rea k a ge o f th e s h e l l and i t s

p o r o c i t y i n t e r f e r e d w i t h a c c u r a t e v o lu m e t r ic m easu rem en ts .

The o y s t e r s from P a r r o t t ' s rock c o n ta in e d a number o f

o y s t e r c r a b s , P in n o th e r e s o s tr e u m . The l a r g e r c r a b s occu py

c o n s id e r a b le sp a ce i n th e s h e l l c a v i t y . In l a t e r sam p les th e

c o n d i t io n v a lu e s f o r i n d i v i d u a l s c o n t a i n i n g c ra b s w e re com

pared w i t h th e mean c o n d i t i o n o f t h e sa m p le .

A more d e t a i l e d s t u d y o f o y s t e r s from P a r r o t t ’ s r o c k . To

e v a lu a t e the mean in d e x o f c o n d i t i o n a s a method o f com paring

p ro d u cin g a r e a s a l a r g e r sam ple was t e s t e d . T h is was done in

o r d e r t o s t u d y th e e x t e n t o f v a r i a t i o n and t o d e te r m in e th e

number o f i n d i v i d u a l s t o t e s t f o r a r e p r e s e n t a t iv e sa m p le .

The P a r r o t t 1 s Hock sample taken on March 2 9 , 1 9 4 5 , had a

mean in d e x o f c o n d i t io n o f 93*73 , the h ig h e s t v a l u e f o r t h e

r o c k s sam pled. T h e r e fo r e , i t was assumed th a t t h e y r e p r e s e n te d

a good s t o c k o f o y s t e r s . The l a r g e r sample was ta k e n from t h i s

r o ck on A p r i l 19, 1945* 4 t th a t tim e th e w a te r tem p er a tu r e was

18° C. and th e s a l i n i t y was 1 6 . 8 o / o o . At t h i s te m p e r a tu r e , as

h as been s t a t e d , any p h y s i o l o g i c a l changes s i n c e the March

sam p lin g w ere p ro b a b ly n e g l i g i b l e . Th in sample in c lu d e d some

f o r t y o y s t e r s and r e p r e s e n te d a s i n e range of 52 to 94 m i l l i

m ete rs i n l e n g t h and 20 to 99 grams in t o t a l w e ig h t .

For t h i s group o f o y s t e r s the l i n e a r measurements o f

l e n g t h from umbo to b i l l and maximum w id th o f the s h e l l , and the

t o t a l w e ig h t , t o t a l vo lu m e, v.et «.::C 1 :7 a t w e i g h t , s h e l l

w e ig h t and s h e l l voIulsj n - s i c c >-lv <; iy we re r .easu red . The in n e r

13

volum e and in d e x o f c o n d i t i o n were c a l c u l a t e d f o r each i n d i v i

d u a l on t h e b a s i s o f t h e s e m easu rem en ts .

In o r d e r to d e term in e w h eth er or not c o n d i t i o n v a l u e s

v a r ie d v / i th s i z e , s e v e r a l m ethods o f g r o u p in g w ere t r i e d : f i r s t ,

in 5 m i l l i m e t e r i n t e r v a l s a c c o r d in g to l e n g t h , and s e c o n d ly , i n

t e n gram c l a s s i n t e r v a l s a c c o r d in g t o t o t a l w e i g h t .

When th e r e l a t e d m easurem ents were p l o t t e d g r a p h i c a l l y

a g a i n s t t h e l e n g t h and then a g a i n s t t h e t o t a l w e ig h t , b e t t e r

c o r r e l a t i o n was shown i n t h e l a t t e r . I t i s e v i d e n t from th e

d a ta and from o b s e r v a t io n t h a t w id th and depth v a r y l a r g e l y

in d e p e n d e n t ly o f l e n g t h , and t h a t t o t a l w e ig h t was an i n c l u

s i v e and p r a c t i c a l m easure of s i z e .

The l i n e a r e q u a t io n e x p r e s s in g th e r e l a t i o n o f t o t a l

w e ig h t t o t h e th r e e v o lu m e tr ic m easurem ents , t o t a l volum e,

s h e l l volum e and in n e r volume have b een o b ta in e d by the method

o f th e l e a s t s q u a r e s . The i n d iv i d u a l v a lu e s and th e l i n e o f*

b e s t f i t f o r t h e s e r e l a t i o n s h i p s a r e r e p r e s e n te d f o r th e P a r

r o t t ' s rock sample in F ig u re I I I . I t i s n o ted th a t in th e

t o t a l w e ig h t range o f 2 0 -1 0 0 grams th e t o t a l volum e ra n g es

fr o m -12*0 to 6 0 . 0 m i l l i l i t e r s , w h i l e the in n er volume range

i s o n ly 4 * 5 to 2 2 . 2 m i l l i l i t e r s .

The e q u a t io n s f o r t h e s e w e ig h t volume r e l a t i o n s h i p s when

x r e f e r s t o t o t a l w e ig h t and y to t h e v o lu m e tr ic measurement

a r e :

T o ta l volume y = e .5 1 2 x * 4.0U7Sh e l 1 v o l urne y * o . 3 ■■*‘8 x - 2 . * 11In n e r volum e y -0 .1 7 8 x ♦

Jl com parison o f the a c t u a l v. 1 th c a lc u l a t e d mean v a lu e s

f o r t o t a l , s h e l l and in n e r volume f o r the P a r r o t t ' s hook sample

1/

f i g u r e . kiliti| R e la t io n of T o ta l ^ h e l l and I n n e r ; Volume t o Total; “ e i g h t Tor O y s te rs iRroiii" p a r r o t t * s RocL, vRahpahannockI 1 ' : River -#£ n t , . frtt

1......;.-,: 1_ 6 G _ 1 i-------TOTAL WEIGHT IN GRAMS

15

a r e g i v e n in T ab le I I I . The s ta n d a rd e r r o r o f t h e e s t im a t e

was computed f o r the mean v o lu m e tr ic m easurem ents by th e

•va lu es o f y from th e t h e o r e t i c a l and N r e p r e s e n t s th e number

i n t h e g r o u p .

The s ta n d a r d e rro r o f the e s t i m a t e f o r th e t o t a l w e ig h t -

t o t a l volum e r e l a t i o n s h i p i s _+ 1 .9 2 m i l l i l i t e r s ; fo r th e

t o t a l w e i g h t - s h e l l volume r e l a t i o n s h i p +_ 1 .1 4 m i l l i l i t e r s ;

and f o r t o t a l w e ig h t - in n e r volume r e l a t i o n s h i p +_ 1 .6 4 m i l l i

l i t e r s .

S in c e t h e t o t a l w e ig h t seemed to be th e b e t t e r measure

o f s i z e , th e i n d i v i d u a l m easurem ents f o r ea ch o y s t e r were

arran ged in term s o f t o t a l w eight in t e n gram c l a s s i n t e r

v a l s . The mean v a l u e s fo r the s h e l l , w e t and d r y m eat w e ig h t s

and th e range of the i n d i v i d u a l v a l u e s f o r the same a r e g iv e n

i n T ab le 1 7 , and the mean v a l u e s r e p r e se n te d i n F ig u r e 1 7 .

The r e l a t i o n o f s h e l l w e ig h t to t o t a l w e ig h t ( i n the

2 0 -9 9 gram range) i s f a i r l y c o n s t a n t . T h is m ight be e x

p e c te d s i n c e th e a v e r a g e per cent age of the t o t a l w e ig h t th a t

i s s h e l l i s 7 6 .5 p e r c e n t fo r t h i s sample from P a r r o t t * s Rock.

The range i n mean s h e l l v.ei grit i s from 17 t o 73 grams.

The w e ig h t o f the w e t v a r i e s c o n s id e r a b ly among the

i n d i v i d u a l s . The p rob ab le e x p la n a t io n f o r the v a r i a t i o n s i s

t h a t th e w e ig h t o f o y s te r meat i s o n ly s l i g h t l y h e a v ie r than

when d e q u a ls t h e d e v i a t i o n o f th e a c tu a l

w a te r a s i s i n d i c a t e d by the com p u ta tion s fo r th e p e r c e n ta g e

o f m o is tu r e or w a t e r c o n t e n t , sr.d the amount o f b l e e d in g t h a t

t a k e s p la c e on th e w atch g l a s s v a r i e s evm a f t e r stan d ard

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18

F ig u re IV .Mean S h e l l , Wet and Dry Meat Weight f o r O y s te rs from P a r r o t t ’ s

2 ,0-

m Rook.

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TOTAL WEIGHT IN GRAMS

19

d r a in a g e o f th e meat* The mean v a l u e s f o r w e t meat w e ig h t

range from 2 .9 to 9 .2 grams i n t h i s s a m p le . (T ab le IV , F i g . IV)

When the w e t meat w e ig h t w as used i n a fo rm u la f o r an in d e x

o f c o n d i t i o n , i t was l e s s c o n s i s t a n t th a n th e in d e x o f c o n d i t i o n

based on d r ie d meat w e i g h t , even th ou gh t h i s v a l u e a l s o v a r i e s

c o n s id e r a b ly . The ran ge in mean w e ig h t o f d r i e d m eats w as from

0 . ^ 1 4 t o 2 . 1 7 & grams; but t h e r e i s a c o n s i s t a n t i n c r e a s e in t h i s

v a lu e in o y s t e r s up to a t o t a l w e ig h t o f 85 gram s. (T ab le IV,

F i g . XV)

The p e r c e n ta g e o f m o is tu r e w as d e r iv e d b y th e fo rm u la

w et meat w e ig h t — d r ie d meat w e ig h t f o r t h i r t y - t h r e e in & i-wet meat w e ig h t

v i d u a l s in t h e sa m p le . The p e r c e n ta g e ranged from 6 O. 3 t o 9 0 .2

(T ab le V ) . However, s e v e n t y - n i n e p e r c e n t o f th e i n d i v i d u a l

v a lu e s f e l l w i t h i n the 8 0 .2 to 8 7 . 5 r a n g e . The means f o r th e

c l a s s i n t e r n a l s e x h i b i t a s m a l l ran g e from 77*3 p e r c e n t t o

3 3 .5 p e r c e n t . ( F ig . V) The mean p e r c e n ta g e o f m o is tu r e f o r

t h i s e n t i r e sample from P a r r o t t ' s was 8 1 .4 p e r c e n t .

H o p k in s’ (19 37 ) form ula 100 x in n e r vo lum e was c a l c u l a t e dt o t a l volume

f o r each i n d i v i d u a l i n t h e sample in o r d e r t o d e te r m in e th e

p e r c e n ta g e o f c a v i t y . C o n c e iv a b ly t h i s v a l u e m ight v a r y

from one ro ck to a n o t h e r and th e p o t e n t i a l p r o d u c t io n o f m eats

on th e r o c k s w here t h i s p e r c e n ta g e i s h ig h e r cou ld be g r e a t e r .

The mean p e r c e n ta g e o f c a v i t y f o r t h i r t y - n i n e i n d i v i d u a l s in

P a r r o t t ' s Rock sam ple was 4 0 . 5 . The means f o r e ig h t groups

ranged from 3 6 . 5 to 47*3 (T ab le V, F i g . V) T h is w a s e x p e c te d

i n v iew o f the s m a l l r a n g e in in n e r volum e compared w i t h th e

t o t a l volume r a n g e .

The mean in d e x o f c o n d i t io n f o r t h e sam ple w as 9 1 .0 1 .

20

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21F ig u r e V

Mean C a lc u la ted . V a lu e s f o r P e r c e n ta g e o f M o is tu r e , P e r c e n ta g e o f C a v i ty ,a n d I n d e x o f C o n d it io n f o r O y s te r s ■ from

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1-GOTOTAL WMIGHT IN GRAMS

22

A ga in c o n s id e r a b le i n d i v i d u a l v a r i a t i o n i s n o t e d , f o r th e

v a l u e s o f d i f f e r e n t s i z e c l a s s e s r a n g e from 5 2 . 5 3 to 2 1 0 . 0 1 .

(T a b le V) The mean c o n d i t i o n v a l u e s f o r th e e i g h t g ro u p s

range from 7 3 .8 9 to 1 1 2 .5 9 . (F ig u re V) N ine p e r c e n t o f th e

i n d i v i d u a l s c o n ta in e d o y s t e r cra b s P in n o t h e r e s o s tr eu m . The

mean in d e x o f c o n d i t i o n f o r t h e s e i n d i v i d u a l s w as 7 1 . 7 4 com

pared t o 9 0 . 0 1 f o r th e e n t i r e sa m p le . The com p arison i s

g iv e n a s an i n d i c a t i o n o f e f f e c t o f t h e c r a b , but a more thorough

a n a l y s i s i s made i n th e d i s c u s s i o n o f a l a t e r sa m p le .

The mean in d e x o f c o n d i t i o n f o r th e sam p le o f 9 0 . 0 1 d i f f e r s

o n ly 3*73 i n c o n d i t io n v a l u e from th e mean f o r 16 s p e c im e n ts

ta k e n from th e same ro ck on March 29 , 1 9 4 5 .

A Large York E lv e r S a m p le . Large sa m p le s w e re ta k e n from

a l a r g e rock betw een K ing and I n d ia n F i e l d Creeks i n York R iv e r .

C o l l e c t i o n s were made on November 2 0 , 1945 , and F ebruary 2 2 ,

1 9 4 6 . The tem p er a tu r e o f the w a te r was 1 2 .5 ° C. and 5 .3 ° C .,

and th e s a l i n i t y w as 1 8 .5 0 / 0 0 and 1 2 . 8 0 / 0 0 , r e s p e c t i v e l y .

The d e p th where th e sa m p le s w ere ta k e n v a r ie d b e tw een f o u r

and s i x f e e t , and th e hot tom w as composed o f sand and mud b u i l t

up w i t h s h e l l . The i n d i v i d u a l m easurem ents were grouped t o

g e t h e r when th e d a ta were a n a ly z e d , s i n c e i t w a s assum ed th a t

l i t t l e v a r i a t i o n in c o n d i t i o n w ould be t a k in g p la c e a t t h e s e

w a te r te m p e r a tu r e s .

The d a ta f o r t h i s r o c k i n c lu d i n g m easurem ents and c a l c u

l a t i o n s f o r 145 i n d i v i d u a l s r e p r e s e n t in g a s i z e ra n g e o f 71 t o 133

m i l l i m e t e r s i n l e n g t h and 60 t o 2 6 0 grams i n t o t a l w e ig h t w ere

a n a ly z e d a s f o r th e P a r r o t t ’ s Rock sa m p le .

23

The r e l a t i o n s o f t h e v o lu m e t r i c measurem ent t o t o t a l

w e ig h t are e x p r e s s e d in a l i n e a r e q u a t io n a s d e term in ed by

t h e method o f t h e l e a s t s q u a r e s . The t h r e e e q u a t io n s a re

g iv e n as f o l l o w s : when x r e f e r s to t o t a l w e ig h t and j [ t o

t h e v o lu m e t r ic m easurem ent:

^ o t a l volume y = 0 .*>56K+ 1 * 5 7 4S h e l l volume y = O. 3 6 4 - 2 .6 2 9I n n e r volume y = 0 . 1 9 6 -+ 1 . 6 7 1

The i n d i v i d u a l m easurem ents o f t o t a l vo lum e, s h e l l vo lum e,

and in n e r volume arranged i n term s o f t o t a l w e ig h t and th e l i n e

o f b e s t f i t a r e g iv e n i n F ig u r e s V I , V II and V I I I , r e s p e c t i v e l y .

The com parison o f th e a c t u a l and c a l c u l a t e d mean v a l u e s f o r

th e tw e n ty -o n e c l a s s i n t e r v a l s a r e p r e s e n te d in Table V I .. . The

sta n d a rd e r r o r o f th e e s t im a t e f o r th e t h r e e r e l a t i o n s h i p s i s

_+ 3*94 m i l l i l i t e r s f o r th e t o t a l w e i g h t - t o t a l volum e r e l a t i o n

s h ip ; _+ 3*33 m i l l i l i t e r s f o r th e t o t a l w e i g h t - s h e l l volume

r e l a t i o n s h i p ; and + 3*33 m i l l i l i t e r s f o r th e t o t a l w e i g h t -

in n e r volume r e l a t i o n s h i p .

The r e l a t i o n o f th e mean s h e l l w e ig h t i n grams t o th e

t o t a l w e ig h t i s r e p r e s e n t e d by a d i r e c t p lo t o f th e tw e n ty -

one mean v a l u e s . ( F ig . IX) The r e l a t i o n i s f a i r l y c o n s t a n t .

For t h e e n t i r e sample 7 9 . 8 p e r c e n t o f the t o t a l w e ig h t i s

s h e l l . O y s te r s in t h i s sample ranged from 60 to 260 grams

in t o t a l w e i g h t , and s h e l l w e ig h t ranged from 43 t o 235 grams.

The mean w et w e ig h t o f th e m eats f o r th e tw e n ty -o n e groups

a c c o r d in g to t o t a l w e ig h t a r e r e c o r d e d in Table VII..... ( F i g . X)

The range i n w e ig h t f o r t h i s v a lu e i s from 4*6 to 31*0 gram s.

T hese d a ta i n d ic a t e d t h a t th e r e i s a d e c r e a s e in w et meat w e ig h t

in t h e c l a s s e s of o y s t e r s above 245 grams i n t o t a l w e i g h t .

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29

31

The minimum dry w e ig h t f o r an o y s t e r in t h i s sam p le was

0 .6 7 0 gram, the maximum 6 .1 4 2 . (T a b le VII ) The mean v a l u e s

f o r t h e tw e n ty -o n e g rou p s show a d i f f e r e n c e o f 3*924 gram s.

As i n w et m eat w e ig h t th e r e i s a d e c r e a s e i n t h i s v a lu e fo r

t h e two groups h a v in g a mean t o t a l w e ig h t a b ove 245 gram s.

( P ig . XI)

The mean p e r c e n ta g e o f m o is tu r e f o r th e sam ple c a l c u l a t e d

a f t e r d e te r m in in g t h e v a lu e f o r one hundred f o r t y - f i v e i n d i

v i d u a l s i s 8 2 . 2 . The mean p e r c e n ta g e o f t h e tw e n ty -o n e groups

v a r i e s from 8 0 .4 to 87 .5 * This would i n d i c a t e th a t t h e r e i s a

sm a l l v a r i a t i o n i n th e s o l i d c o n t e n t o f t h e o y s t e r s . However,

c o n s id e r in g t h e la v v a lu e s f o r d r ie d m eat w e i g h t , a s e v e n p e r

c e n t d i f f e r e n c e i n s o l i d c o n t e n t i s s i g n i f i c a n t .

The mean p e r c e n ta g e o f c a v i t y f o r th e 145 i n d i v i d u a l s

i s 3 6 . 6 . The means f o r th e groups ranged from 4 2 . 8 p e r c e n t f o r

t h e c l a s s a v e r a g in g 65 grams i n t o t a l w e ig h t t o 31*2 p e r c e n t

f o r t h e c l a s s whose mean t o t a l w e ig h t i s 263 gram s. (T a b le V I I I )

A lth o u gh th e r e i s v a r i a t i o n in th e mean p e r c e n ta g e o f c a v i t y ,

t h e r e i s an i n d i c a t i o n o f a d e c r e a s e i n th e t o t a l w e ig h t range

r e p r e s e n te d in t h i s sam p le . ( F ig . X II)

The mean in d ex o f c o n d i t io n f o r t h e sam ple i s 8 6 .6 8 . The

mean in d ex of c o n d i t io n v a r i e s from 6 7 .80 to 1 0 7 .7 4 . I t i s

n o te d th a t f o r the c l a s s e s from 174 to 263 grams i n t o t a l

w e ig h t the v a lu e s are more c o n s ta n t th an in t h e p r e c e d in g c l a s s e s ,

r a n g in g o n ly from 8 1 .4 9 to 9 0 .7 9 . (T ab le V I I I , F ig . X I I I ) As

an a id in a n a ly s in g in d iv id u a l v a r i a t i o n c a r e f u l p h y s i c a l o b s e r

v a t i o n s on th e amount and q u a l i t y o f m eats w ere n o te d w h i l e

32

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36

d e t e r m in a t io n s w ere made. I t was n o t i c e a b l e t h a t th e amount

o f m eat v a r ie d and th o s e w hich lo o k ed v e r y w a te r y had an in d e x

o f c o n d i t i o n a s low as f o r t y . F o r ty -o n e p e r c e n t o f th e i n d i v i

d u a ls c o n ta in e d o y s t e r crabs, P in n o t h e r e s o s tr e u m . The crabs

w eighed from 0 .4 5 gram t o 1 . 1 gram s. The mean in d e x o f c o n d i

t i o n f o r th e o y s t e r s c o n t a in in g cra b s i s 8 2 .3 0 c o n t r a s t e d w ith

a mean o f 9 0 .3 9 f o r th e rem ain in g 86 i n d i v i d u a l s in the sam ple .

These low c o n d i t i o n v a l u e s f o r o y s t e r s c o n t a in in g P . ostreu m

co n f irm s th e o b s e r v a t io n t h a t t h e y had l e s s meat o f p o o r e r q u a l i t y .

The crab was found i n th e g i l l chamber, o f t e n a g a in s t the l a b i a l

p a l p s . C o m p etit io n f o r fo o d , in j u r y t o th e g i l l o f i t s h o s t

and th e amount o f sp a c e th e crab o c c u p ie s may be p o s s i b l e e x

p l a n a t io n s f o r t h e low c o n d i t i o n v a l u e s . These a ssu m p tio n s

ar e confirm ed by S tau b er (1945 ) who s t a t e s t h a t th e o y s t e r

crab f e e d s on fo o d m a t e r i a l s t r a in e d by t h e o y s t e r and i n d o

in g so i n j u r e s th e g i l l s o f i t s h o s t .

As a means of com paring th e measurem ent f o r th e o y s t e r s

from P a r r o t t ’ s Rock w i t h t h o s e from th e York R iv e r rock betw een

King and In d ia n F i e l d C reek s , means were c a l c u l a t e d f o r i n d i

v id u a l m easurem ents f a l l i n g w i t h i n th e r a n g e o f 60 to 99 grams

i n t o t a l w e i g h t . The r e s u l t s are based on tw en ty -tw o m easu re

m ents fo r P a r r o t t ’ s and t w e n t y - s i x fo r th e Rock betw een King

and I n d ia n F i e l d C reek s .

37

Measurement P a r r o t t * s RockM iddle York

R iv e r Rock

T o t a l w e ig h t S h e l l w e ig h t T o ta l Volume S h e l l volume In n e r volume

7 8 . 9 gins. 6 0 .4 gms. 4 4 * 5 m is . 27*4 m is . 1 7 . 2 m is .

7 . 9 gms. I . 6 3 6 gms.

8 2 .8 gms. 6 4 • 0 gm s•4 7 . 7 m i s .2 8 . 7 m is . 1 9 . 0 m is .

8 . 7 gms. 1 .4 9 6 gms.

Wet meat w e ig h t Dry m eat w e ig h t

C a l c u l a t io n s

P e r c e n t c a v i t y P e r c e n t m o is tu r e In d e x o f c o n d i t io n

4 1 .58 2 . 49 5 .3 1

3 9 .68 3 . 88 5 .9 9

T hese c a l c u l a t i o n s i n d i c a t e th a t th e o y s t e r s removed from

P a r r o t t 1 s Rock a r e b e t t e r in term s o f s o l i d c o n t e n t , p e r c e n ta g e

o f a v a i l a b l e sp ace by v o lu m e, and a c t u a l p r o d u c t io n o f m eat a s

r e f l e c t e d in a h ig h e r c o n d i t i o n v a lu e than th e o y s t e r s from

the York R iver Rock.

T h is s tu d y h a s been l i m i t e d i n s e v e r a l w a y s . The random

n e s s o f th e sam p lin g te c h n iq u e l i m i t e d any s p e c i f i c in fo r m a t io n

on th e e f f e c t o f the v a r i e t y o f e n v ir o n m e n ta l f a c t o r s on co n

d i t i o n . Should t h i s t y p e s tu d y be c a r r ie d f u r t h e r , i t i s r e c -

commended t h a t sm a ll a r e a s of a r o c k b e sam p led and marked f o r

ta k in g s u c c e s s i v e s a m p le s . A s t r i c t e r s e l e c t i o n o f o y s t e r s on

th e b a s i s o f shape could be made t o s e e how d e f i n i t e l y shape

a f f e c t s c o n d i t i o n .

In t h i s ty p e o f s t u d y i t w ould be p r a c t i c a l t o t e s t

o y s t e r s o f known a g e s t o s e e i f t h e m eats c o n t in u e to keep

pace w i t h t h e s h e l l g row th o r i f a t some p e r io d i n th e l i f e

o f the o y s t e r th e p r o d u c t io n o f m eats c o n t in u e and l i t t l e

grow th o f the s h e l l s t a k e s p l a c e . C o n d it io n v a l u e s w ould be

h ig h i f th e m eats c o n t in u e to growT a s s h e l l g ro w th d e c r e a s e s .

38

Knowing i f c o n d i t i o n v a r i e s w i t h a g e would i n d i c a t e th e

l e n g t h o f t im e o y s t e r s sh o u ld be a l lo w e d t o grow i n o r d e r t o a

o b t a in th e maximum amount o f meat p er volume o f o y s t e r s .

T h is s tu d y was l i m i t e d by t h e amount o f t im e i t to o k

t o o b ta in i n d i v i d u a l m easu rem en ts . The t im e amounted t o

about t h r e e and one h a l f hou rs t o s e l e c t , c le a n ,a n d make

th e m easurem ents and c a l c u l a t i o n s f o r a s i n g l e o y s t e r . I n

l i g h t o f t h i s s t u d y , i t i s s u g g e s t e d t h a t sam p les ta k e n f o r

com p arative p u rp o se s c o n s i s t o f a t l e a s t f o r t y i n d i v i d u a l s

and t h e d e te r m in a t io n s o f th e m easurem ents f o r volume o f

th e s h e l l c a v i t y and d r ie d meat w e ig h t be made f o r f i v e

o y s t e r s s im u l t a n e o u s ly . I f c a r e f u l sam p lin g t e c h n iq u e be

u se d , t h i s would make i t p o s s i b l e t o d e ter m in e mean c o n d i t io n

v a l u e s f o r more a r e a s .

39

SUMMARY AND CONCLUSIONS

1 . The in d e x o f c o n d i t i o n o f a n o y s t e r i s t h e r a t i o o f t h e amount o f s o l i d s i n th e meat t o t h e s p a c e e n c lo s e d by the s h e l l s ,

2 . There i s w id e range i n th e in d ex o f c o n d i t i o n f o r o y s t e r s grow ing on t h e same o y s t e r rock b e c a u s e the amount and q u a l i t y o f meat produced by t h e i n d i v i d u a l s v a r i e s ,

3 . O y s te r s w ith l a r g e c a v i t i e s do not a lw a y s produce meat i n p r o p o r t io n t o t h e volum e o f c a v i t y p r e s e n t .

4 . The h i g h e s t mean c o n d i t i o n v a l u e f o r a r o c k sam pled in t h i s studjr was fo r P a r r o t t *s Rock i n t h e Rappahannock R iv e r .

A mean c o n d i t i o n v a lu e of 9 0 -1 0 0 f o r a r o c k i s c o n s id e r e d good f o r th e V ir g in ia a r e a .

6 . T o t a l w e ig h t o f an o y s t e r i s b e t t e r th a n le n g t h and w id th a s a u s e a b le and p r a c t i c a l m easure o f s i z e .

7 . O y s te r s c o n t a in in g P in n o th e r e s ostreu m had a lo w e r in d e x o f c o n d i t i o n th a n o t h e r o y s t e r s in th e same sam p le .

8 . The p e r c e n ta g e of m o is tu r e o f the o y s t e r s s t u d i e d v a r i e s between 7? and S7 p ercen t(m ean v a l u e s ) .

9 . I t i s recommended t h a t i n a com p arative s t u d y of c o n d i t i o n o f o y s t e r s i n V i r g i n i a , sam ples o f a t l e a s t f o r t y o y s t e r s be t e s t e d and d e te r m in a t io n s b e made f o r f i v e o y s t e r s s i m u l t a n e o u s l y .

40

BIBLIOGRAPHY

H op k in s, A* E . (1937) " I n v e s t i g a t i o n s i n F lo r id a "P r o g r e s s i n B i o l o g i c a l I n q u i r i e s Report 3 0 , pp . 4 9 - 5 0 .

L u n tz , G. R . , J r . (1941) " P o lyd ora , a P e s t in South C a r o lin aO y s t e r s ." J ou rn a l of th e E l i s h a M it c h e l l S c i e n t i f i c S o c i e t v . V o l ume LV II, No. 2 , pp . 2 7 3 -2 8 3 .

M ed cof, J . C. and / 1 Q/ 1 N e e d ie r , A. W. H.

N e e d ie r , A. W. H. (1934)

P r y th e r c h , H. F . (1928)

" I n f lu e n c e o f Temperature and S a l i n i t y on t h e C o n d it io n o f O y s t e r s . ( Q strea v i r g i n i c a ) Jo u rn a l o f tn s f i s h e r i e s Rese a r c h Board o f Canada. V o l . Y, N o. 3, PP. 273-253^

"The S to r a g e o f O y s te r ^ in th e S h e l l . " B i o l o g i c a l Board o f Canada B u l l e t i n XLIV.

" I n v e s t i g a t i o n o f t h e P h y s i c a l C o n d it io n s C o n tr o l l in g Spawning o f O y ste r s and O ccurance, D i s t r i b u t io n and S e t t i n g o f O y ster Larvae in M ilfo r d Harbor, C on n ecti c u t . B u l l e t i n o f Bureau o f F i s h e r i e s Y o l . JCLIV, No. 10 54> pp . 4 2 9 - 3 0 3 .

S ta u b e r , L e s l i e A. (1945) "P in n o th e r e s o s tr e u m , P a r a s i t i con th e American O y s te r , Q str ea (gryp haea) v i r g i n i c a , B i o l o g i c a l B u l l e t i n Y o l . LXMXVTII, No. 3 , pp . 2 6 9 -2 9 1 .

T u l l y , John P . (1936) "The N u t r i t i v e V a lu e of M arine.P ro d u c ts P rox im ate A n a ly s e s o f F resh B r i t i s h Columbia O y s t e r s ." J o u r n a l o f t h e B i o l o g i c a l Beard o f CanadaV o l . I I ,' El"oV 5 7 PP-

41

ACKH 0 WLEDGMENTS

The f a c i l i t i e s f o r t h i s s tu d y w ere p r o v id e d by

t h e V i r g i n i a F i s h e r i e s L ab ora tory o f t h e C o i le g e o f

W ill ia m and Mary and Commission o f F i s h e r i e s . Thanks

a r e e x ten d ed to a l l p e r so n s who have a id e d d i r e c t l y

o r i n d i r e c t l y i n t h i s w ork.

S p e c i a l acknow ledgm ents a r e made t o D r. J .G .M ack in ,

£>r. 'S.H . H opk in s, D r. H.Malcolm Owen, and Mr. R. W inston

M enzel f o r making c o l l e c t i o n s and o f f e r i n g v a lu a b le su g

g e s t i o n s . ^ in d than k s a r e e x p r e s s e d t o Dr. Makin f o r a

drawing o f t h e a p p a r a tu s; to Dr. Donald W. D a v is and

Dr. Owen f o r a d v i s e on t h e form o f t h e m a n u sc r ip t; and

M rs. L o u is e M. G la s s f o r t y p in g t h e m a n u sc r ip t . S p e c i a l

a p p r e c ia t i o n i s ex ten d ed t o ^ r . C u r t i s L. ^ewcombe under

whose d i r e c t i o n t h i s s tu d y was made p o s s i b l e .

BQLL

ESE

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LUAIA

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MARY

42

Kame:

Born:

T r a in in g :

P o s i t i o n s

VITA

A l i c e E l i z a b e t h O vercash

May 1 , 1 9 2 4 .

S t a t e T ea ch ers C o l le g e P a r m v i l l e , V i r g i n i a . Septem ber 1940-Tune 1944* B .S . D egree i n E d u ca tio n Major f i e l d B io lo g y

C o l le g e o f ^ i l l i a m and ^ary Course work f o r M.A. D egree Septem ber 1 9 4 4 -Tune 1 9 4 6 .

h e ld : L ab o ra to ry a s s i s t a n t 1943S t $ t e T each ers C o l l e g e .

B io lo g y D ep artm en t.

L a b o ra to ry a s s i s t a n t V i r g i n i a f i s h e r i e s L a b o ra to ry Septem ber 1 9 4 4 - Tune 1 9 4 6 .

the use of measurement to determine the condition of

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