-'( *
COI'II'IERCIAL
DEVELOPMENT
CLAI.I
AfiNUAL
REPORT
0stober1, 1979to September
30, 1980
by
Thomas
F. Gaurcr
GrcgoryP. Robart
0regonDepartnnnt
of Fish andllildlife
Natlonall4arineFisheriesServie
Administration
l{ational0ceanicandA0mspherlc
UnltedStates Oepartmntof Cormrce
Act
andOevelopmenl
CorrnerclalFisheriesResearch
Pnojectf{unterl-150-RSegrnntI
ContractNurnber
80-ABD-ORAB
Decenber,
1980
CONTENTS
PageNo.
ABSTRACT...
o....
r...
INTRODUCTI0N..........
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3...
..
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I
...
o...,,.......
I
A S S E S S M E N T O F H A R V E S T P Ot .T. E
. .N
. TIAL O I ' ' ' ' '......
1,,!ethods
. . . . . . . . . I
Iaquina B.ay. . . . r . . . . o . . . .
C
g
g
s
B
a
V
,
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o
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r
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R e s ul tsa n d D i scu ssi o n
Yaqui
Biomass
Esti
ation and.Biomasg
fslimates . . . . .. . . ..
COPA'IERCIALHARVEST0FC
e Li A
. .M
. . .S. . . . . . .
aaaa.ta
2
3
aalaoa
4
r l.,,
I'|ethods
_
I
?
aataaa
Plot E
Yaqqina Bay
CgosBay
1
. . . . . . . . r . . . . . . .. . . . . r . o . .
......
.....t.......r.1..r
ResultsandDiscussion
Y a q U i n aB a y . . . . . . . . , . . . . . . . . / .
COOSF€y ........
r.
......
r...
5
r.
5
5
i e . . . , . I
r...
r.,
6
6
ASSESSMENT
OF EFFECTS
OF COIVI4ERCIAL
CLA.FI
HARVEST
ONRECRUITMENT
. , t
7
7
7
L A B O R A T 0 R Y C L A F I S T U,D
. ,I.E S
lfgthods ..........
r..
r.
|,.,
9
9
9
. . . . . .
10
lvlethOdS . . . . . . . . . . . . , . . . r r . . | | . . , r t
! r
Rgsults andDiscussion....
o...
r...
o...
e, r...
ResultsandDiscussion
. . .
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o.........
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ACKNOI'ILEDGMENTS
. . . . r l . . . . . e . . . . . . . .,
L I T E M T U RCEI T E D . . . . . . . .
APPENDIX
1.
. . . o . .
.,
...
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r . . . . . . . . r . . . . . . . . . . . . . .',
r r o .
10
ll
TABLES
Table
I
2
3
4
5
6
7
PageNo.
PopulationandBiomass
Estimatesof subtidal clamsin Areaz,
Y a q u i nB
a a y , 1 9 7 5 - 8.0 . . . . . . . . . . . . . . . . , .
2
Computer
&neratedAbundance
of VariousCohortsof GaperCIams,
A r e a 2 , Y a q u i n a B a y. . . . . . . . . . . .
. o,
.. . . .
3
Estimates
of SubtidalClamsin Area2,
?gpulationandBiomass
P l o t E , Y a q u i nB
a a y ;O r e g o n1, 9 8 0 . . , . . . . . . . . . . . . , . i
4
PopulationandBiomass
Estimatesof Subtidal Clamsin Pigeon
P o i n t A r e a ,C o o s B a y r t g TaSn d 1 9 8 0 . . . . . . . . .
r..
....
4
Pounds
of ClamslhchanicallyHarvested
in Experimental
Fishery,
Yaquina BEy, 0regon, 1975-80 . . . . . . o o . r . . . . . . . r . .
6
Surmaryof Poundsof Clarm$ilechanically
Harvestedin Experinental
Fishery, CoosBay, 0regon,1.975-80
. . . . . . . . . . . . . . . . .
6
Poundsof Subtidal ClamsHarvestedin CoosBqy Conurercial
Fisheryr1980
8
.or.,r.......r
.r,......,
.
Surrnary
of Number
of l4arine0rganisms
0ccumingin Connprcially
Harvested
Plot C of Arca2r Yaquina
Bayr0regon . . . . . . . r .,
7
8
FIGURES
Fi gure
I
2
Mapof YaquinaBay, ShowingArea Approvedfor CornirercialClam
Harv9st....r..o........
Mapof Lower CoosBay, ShowingArea Approvedfor Connercial Clam
Harvgst
3
4
5
6
7
tz
. r..
e.
r......................
c
Year-Class
Composition
of Subtidal GaperClarmCollectedfrom
13
Area 2n YaquinaBqy, Oyegon,1980
t4
Length-Class
Composition
of SubtidalGaperClamsCollected
frontArga2, YaquinaBay, Oregon,1980. . . . . . . . . . . . . . .
t4
CalculatedEstimatesof l,laturalf'4ortalityfor GaperClamsby
Year-Class,
Area2o Yaquina
Bay,0regon . . . . . . . . . . . . . .
15
Year-Class
of Subtidal GaperClamsCollectedfrom
Conposition
Plot E of Area2, Yaquina
Bay,Oregon,L980 . . . . . . . .
. .
16
Length-Class
Composition
of Subtidal GaperClamsfrom Plot E
of Area2, YaquinaBay, 0tcgon, 1980 . . . . . . . . . . . . . . .
16
(Continued)
FIGURES
Fi gune
I
9
10
11
12
PageNo.
Year-CIass
Composition
of Subtidal GaperClamsCollectedfrom
PigeonPoint Areaof CoosBay, Oregon,Lgg0. . . . . . . . .
17
Length-classcomposition
of subtidal Gaperclamscollected
from PigeonPoint Areaof CoosBayr 0regon,1980 . . . . . .
17
Year-Class
Composition
of Subtidal GaperClamsConnrercially
Harvestedfrom PigeonPoint Area of coosBay, 0nagon,r.9g0-.
18
Length-Clas_s
Composition.of
Subtidal GaperClamsCornrnercially
Harvestedfrom PigeonPoint Areaof CoosBqy, Oregon,1990 :
1B
Survivalof GaperClamSet, lglg year Class,Area2, plot C,
YaquinaBay. . . o . . . c . . . . . . .
13
14
. . . . . .
19
Number
of raxonomic
Groupsof Macrofaunal
Benthosin Areazn
Plot C, Yaquina
BEy. r . . . . . . . . . . .
. . . . . .
20
Total Number
of BenthicInvertebrates,Area2, plot C,
YaquinaBqy . r......
15
16
L7
. r..
r..
2t
r..
TemporalDistribution of Macoma
inqwinata in Area 2, Plot C,
YaquinaBay....
., r . . . .. . ....
. . . .. . ..
Gnrwthcurve of Manila Littleneck clamsspawnedand planted
from Normal and Fast GrowingBrood stock in Netarts Bay, 1990
Growthcurve of Manila Littleneck clams Planted in Fenced,
Unfencedand Eelgrass CovercdAreas of Netarts Bay, !.980 . .
22
a
23
24
COMMERCIAL
CLA}4
PRODUCTION
ABSTRACT
P o pu l a ti o na n d b i o ma sse stimatesand age and size of clamswer e calc ul ated
for an area in YaquinaBqy having cormercial harvest potential. The data revealed
that the 1.975year class remainedstrong for gaper clams. Approximately4.3
m i l l i o n p o u n d s(1 ,9 3 4 " 5mt) o f gaper su,er eestimatedfor the ar ea and a h ar v es t
q u o t a o f 2 0 0 ,0 0 0p o u n d s(9 0 ,7 mt) wasestablished.
Estimatesof natural mortality was calculated for six year classes of gaper
c l a m si n Y a q u i n aB a y a n d ra n g edfr om 0.12 to 0.89,
D u eto d i ffi cu l ti e s cl a mhar vester shad in getting U.S. Ar m yCor pof Engi neer s
and Division of State Landspermits for YaquinaBay, no clamswere harvestedin
1980. This comparesto a harvest of 74,565pounds(33.8 mt) in 1979.
In CoosBay 60,741 pounds(27.5 mt) of clamsb,ereharvested. Production
figures showedthat 273 pounds(0.1 mt) were taken/hour.
Post harvest surveys showedno significant difference, at the 95%confidence
level, in numbersof clam set settling out in the treatment areas and contrrl
sites. The samewas true for 1.7other taxa of benthic invertebrates sampled.
An a l y s i s o f va ri a n cea l so sh o lved
no significant differ ence in taxonomicdi v er s i ty
in the treatrnnt and control plots.
Il'lTR0DUCTI0l,l
l d e co n ti n u e do u r stu d i e s on the clam r esour cesin 0r egon' sestuar ies . Our
objectives were: (1) to monitor the cormercial harvest of subtidal clams in
Yaquinaand Coosbays and evaluate the effects of mechanicalharvest on subtidal
c l a mp o p u l a ti o n sa n d h a b i ta t; ( 2) to calculate natur al npr tality of gape r c l am s
in YaquinaBay and; (3) to npnitor grrowthof laboratory reared tt{anilalittleneck
clam released in Netarts Bay.
ASSESS}4INT
OF HARVEST
POTENTIAL
Twoareas were resurveyedin 1980 to determine the commercialharvest
potential for gaper clams. Area 2 in YaquinaBay (Figure 1) has been surveyed
every year since 1975and the PigeonPoint area of CoosBay was previously
surveyedin 1975{Figure 2).
Methods
Y a q u i n aB a y
Departnentof Fisheries
Using techniquesdevelopedby the l,'lashington
(Goodwin,1973) and the OregonDepartnentof Fish and t{ildlife (Gaumer
and
H a l s t e a d, L 9 7 6 )w e co ]l e cte d data on the' subtidal clampopulationsin Yaqui na
Bay. Twenty-foursampleswere taken from the 18.4 acre (7.4 ha) site. Data
-2collectedprovidedestimateson numbers
andbiomass,s i z e , w e i g h t , a g e a n d s p e c i e s
composition,
recruitnrent
andnatural mortality"
Followingour assessment
of clamstocksin Area2, we selected a 0.9 ac r e
(0.4 ha) portion of the area for the 1980corrnercialc l a mf i s h e r y ( P l o t E ,
Figure1). Datasimilar to that collectedfor Area2 was obtainedfr om P l ot E.
9ogsBay
Thesanp4B acre (19.4 ha) site, that h,asapproved
in L975for the connprcial
harvestof clamsin CoosBaywasresurveyed
in 19'80using the sanetechniques
developed
for YaquinaBqy. sixty two samples
wer€coileited.
ResultsandDiscussion
Bay
-Y a q u i n a
Fromour sanplesweestimatedthat
lgUqn anc Bioma@
21.6
e 1) which is nearly tjre sanp number
estimatedin L979. Gaperc1am,the target species in the comnprcialfishery,
represented
over 11 million of this total with a biomassestim atedat 4.3 m i l l i on
pounds( 1.,934.5
mt),
T a b le 1 ,. P o p u l a ti o na n d Biom assEstim atesof Subtidal Clamsin Ar ea 2,
Y a q u i n aB a y, 1 9 75- 80.
t"
Sp e c i e s
Gaper
36,300,00025,566,40029,316,00010"560,00011,116,700 11,050,000
Cockle
183,200
16,800
0
32,000
16,700
0
Li ttleneck
366,400 216,800 116,000
48,000
133,300
66,700
Butter
416,000 333,600 200,000 240,000 200,000 366,700
I rus
13,532
,800 20,566,400 12,049,600 11,200,000 10r I00,000 10,100,000
Pi ddock
1,700,000
0
0
0
0
0
Tota]
Gaper
52,499,40046,700
,0a0 41,681,60022,080,A}a21,566,7002I,583,400
5 ,C84,200 5 ,217,2AA 4 , 9 6 8 , 9 9 1 4 , 1 3 6 , 8 0 0 3,461,100 4 ,265,600
F i g u r e 3 sh o w sth e ye a r cl a s s compositionof gaper clam sin Ar ea 2. Th e 1975
y e a r c l a s s co n ti n u e sto re p re se nta m ajor ity of the cJam s( 85.2A) fn the popul ati on.
$ h a n _ a go
e f th e cl a msw a s 5 .3 ye ar s, an incr easeof 0.9 year s since 1979, ill us tr ati ng
t h e l a c k o f re cru i tme n t. Ou r g a perset sam plinghas shownno significant su r v i v al
-3of set since 1976. Samples
in 1980weretaken too early to expectthat year class
to showin the sampies.Agecomposition
data for butter, cockieandlittleneck
clamsis not presenteddue to the fer^rclamscollected.
in Figurre4. f'lean
. Thelgngth distribution of gaperclamsfromArea2 is shcnvn
size wasBB.7mman increaseof 5.5 mmsince Lg7g.
4ppticationof an iterative nunnricalfitting routine involvingleast squares
techniques(SteeleandToryey,1960)to gaperclampopulationestimatesprovided
regressionlines with variablerates of natural mortatity (Figure5). t'aUteZ
generatedcohort abundance
showscomputer
over time with corrdsponding
valuesof m.
Estimatesof natural mortality for individuai cohortsrangefrpm 0.tZ to 0.89.
This rangein estimatesreflects possibledifferencesin envircnnrental
influences
andsurvival of individualyear classesof gaperclams. Anothersourceof variation
c o u l db e d i f f i c u l t i e s i n _ a s s i g n i nagc c u r a t ea g e se s p e c i a l l yt o o t d e ry e a r c l a s s e s .
ItlealBourne(Pgry. Qoq'm.)
has suggested
that clamsin exceisof five years of age
frequentlyexhibit false checksmakfngaccurateage determinationformost species
of bay clamsextremelydifficult.
Table 2.
ComputerGeneratedAbundance
of Various Cohortsof GaperClams,
A re a 2 , Y a q u i n aBay.
t977
1967
196 8
1969
1970
1972
1975
t97B
r
3,95B,000 1 , 5 1 2 , 0 0 0 893,790
4 5B , 1 5 0
t75,020
0"gg
Ll ,932,000 2,957,500 1,380,400 530,800
129,880
0.t2
16,277
185,280
742,490
0. Bg
,AA0 6 , 1 7 1,5 0 0 3,666,100
10,894,000 4 , 6 6 6 , 9 0 0 2 , 9 3 6 , 9 0 0 1 , 6 3 0 1, 0 0
698,300 3 1 8 , 5 2 00 . 7 9
21,371,000 1 2 , 0 3 6 , 0 0 0 8 , 7 9 5 , 3 0 0 5 , 9 0 3 , 2 0 0 3,324,500 1 1 9 5 3 1 6 0 00 . 5 3
34,757
,AAo 27,806,000 24,611.
,000 2 l . , 0 7 4 , 0 0 0L6,850,5001 3 , 7 0 5 , 0 0 0 . 2 0
P o p u l a ti o na n d B i o ma ssE stimates,Ar ea 2" Plot E. lG estim atedthat 3.8
milli
f A r e a2 ( T a b l e3 ) . 0 f t h i s
t 0 t a 1 , 5 7 6 ,7 0 0 w e re g a p e r cl a msweighingan estim ated?26r 90Apounds( 102.9 m t) .
F i g u r e 6 sh o vrsth e ye a r cl a ss ccm positionof gaper clam sin Plot E. Sanp l i ngi n
P l o t E r e ve a l e dth e fi rst e vi d enceof 1980year class gaperset. Plot E was
inventoried in April two monthsafter Area 2. The strrongshowingof the 1970"7L
a n d 7 2 y e ar cl a sse s i n P l o t E also suggestsan ir uegular sur vival of gape r c l am
set. This test plot was one of the few sampledwherethe 1975year class was not"
dominant, Meanage of the gaperswas 3.1.years.
Length frrequencyof gaper clams in Plot E is shownin Figure 7, l.'lean
size
o f t h e c l amsi n th e p re h a rve stsam plewas 51.6 nr nwhich is 37.1 nr asmaller than
f o r c l a m sfo u n d i n th e o ve ra l l Ar ea 2.sam p1e.This again r eflects the ir npac tof
t h e s t r o n g sh o w i n go f th e i n co m ing1980year class.
-4Table3. Populationandtsiomass
Estimatesof Subtidal
C l a m isn A r e a2 , P l o t E , Y a q u i n aB a y , 0 r e g o n ,
1980.
Number
IP€CI€S
Gaper
Cockle
L i ttl e n e ck
Butter
I rus
ilentnose
Total
576,740
30,000
30,000
103,300
3,096,700
3,300
'3,940
,000
D r c m a s (sl b s
?26,9AA
tlot cal culated
Not calculated
tlot cal culated
49,900
Not cal cul ated
276,800
CoosBay
Po p u l a ti o na n d B i o ma ssE stim ates. lr leestimatedthat 3.7 million clam si nhabit
ntal c' !amhanvestingar ea in CoosBay
( T a b l e 4 ) . 0 f th i s to ta l , 6 0 6 ,400wer e gaper clam sweighing464,4A0pounds
( 2 1 0 . 6 m t). T h e 3 .7 mi l l i o n toial clamsin this ar ea r epr eients a r educt i onof
2 2 . 7 n i l l i on cl a mssi n ce o u r 1 975sur veyof the samear ea. Eachspeciesex per i e n c e da s i ro i l a r re d u cti o n i n n umber with
sever el speciesnot even appear i ngi n
s
tfie 1980sanple (Table 4). Although there has been a commercialfishery in the
s a r p a r e a si n ce L 9 7 5 ,l e ss th a n 200,000clam shave been r epor tedtaken. It s houl d
a l s o b e e r n p h a si zeth
d a t th e fi sher y has occur r edin a sm al1por tion of the enti r e
u n i t a n d ou r sa mp l i n gsh cw e da unifor m ' lack of clam sover the entir e ar ea . One
p o s s i b l e e xp l a n a ti o nfo r th e reduction in nunber sof clam sis the r ecent d eepeni ng
a n d w i d e n i n go f th e ma i n sh i p c hannelwhich is adjacentto the connpr cialpl ot.
Visual observationsat each samplestation revealedwhat appearedto be mcre
f l u i d s a n do ve r mu cho f th e a rea. Althcughthese obser vationswer € subjec ti v e,
previous observationsin the area showedless sand and more gravel and rock.
Table4.
Species
P o p u l a ti onand BiomassEstimatesof Subtidal Clam sin
P i g e o nP cint Ar ea, CoosBay, 1975and 1980.
1975
Number
Biomass
1980
Biomass
t'{umber
Gaper
Cockle
Li ttl eneck
Butter
I rus
Piddock
Petricola
Bentnose
Cryptomya
Bodega
5,648,700 1,530,800
606,400 464,400
202,200
23,000
16,900 Not Calculated
843,000
71,600
151,B0o
248,200
236,100
809,200
1 6 , 0 1 8 , 6 0 0 Not CalculateC2,fi?B,LAA
ntt
0
25?,940
0
101,000
||rt
0
2,647,304
It
tl
67,300
0
0
101,ooo
Total
25,438,300
ll|l
iltl
lt
tl
iltt
illl
lltl
illi
illl
ltll
iltl
1,873,5oo
3,692,204
464
"1gg
- 5T h eye a r cl a ss co mp o si ti onof gaper clam ssam piecl
in CoosBay is showni n
l j g u r e _ 9 . _ A s i n P l o t E o f Y a quinaBay, the 1980incom ingyear cliss l,lasdom i nant.
T h e 1 9 6 9 - 7 4ye a r cl a sse sw e re also wel1 r epr esented. 0f- par t' icular inter es t w as
t h e t o t a l l a ck o f th e 1 9 7 5ye a r class, which, since 1975,"hasbeen the dom i nant
y e a r c l a s s i n a l l g a p e rp o p u l ationssanpledin Yaquina,Tillannok and Netar ts bay s .
The near absenceof L976-79year classes of gapers in CoosBay was similar to that
f o u n d i n Y a q u i n aB a y. Ga p e rcl am age aver aged5.7 year s.
F i g u r e 9 sh o rssth e l e n g th -class com positicncf gaper
clamsin CoosBq y .
i
l'leansize of the gaperswas 102"8mm.
CO|-{f4ERCIAL
HARVEST
OF CLAMS
In 1980we issued six permits to comnercialclam fishermento mechanically
h a r v e s t s u b ti d a l ci a ms/i n e xp e r im entaitest p1ots. Per mitswenr r equir cd si nc e
t h e u s e o f me ch a n i came
l a n sto har vest clamsis uniawful. Ihe per mits spe c i fi ed
t h e p o u n d so f cl a msth a t co u l d be har vested,season,har vest ar ea ancihar ves t
e q u i p n e n t. In a d d i ti o n , mtn th ly r epor ts giving poundsand number sof clam s
harvestedand hours clf effort t,ilererequired of each operator. The seasonstarted
July 1, 1980sdnd endedDecernber
31, 1980.
l4ethods
Ya q u i n aB a y
Twocomnercialclam harvesting pennits were issued for the 1.980season,
P l o t E o f A re a 2 i n Y a q u i n aB a ywas designatedthe har vest ar ea ( Figur e 1) . A
q u o t a o f 2 00 ,0 0 0p o u n d s{9 0 .7 m t) was set for the ar ea.
D u et o d i ffi cu 'l ti e s th e tw o clam har vestor shad in obtaining appr opr iate
permits from the U.S. ArmyCorp of Engineersand the OregonDivision of State
L a n d s ,n 0 co n fi € rci a lh a rve st o f clam soccur r edin 1980" Althoughthe fill and
removallaws have been "on the books" during previous harvest years, the USACE
and DSLonly begairenforcing these laws as they apply to subtidal clam harvesting
in 1980.
CoosBay
Four commercialclam harvesting permits were issued for CoosBay, Three of
the permits allowed the use cf a hand held water jet and the fourth permit
a l l o w e c !t h e u se o f a su b su rfa cesuction pum p. As with YaquinaBay, difficul ti es
i n o b t a i n i ng fi l l a n d re mo va lp er m its delayedthe har vest of clamsuntil 0c tober .
l d es a mp l e dth e co mme rci a ilyhar vestedclamsfor sfze, age and species
i ti on.
compos
- 6R e s u i t sa n d D i s c u s s i o n
Yaqulra Bay
A s n e n ti o n e de a rl i e r, n o clam swer e comm er ciallyhar vesiedin the ex per i nr ental
f i s h e r y in .Y a q u i n a .B a y. T h i s was the fir st year sinle tgZS thJt clamsr e r e nol
h a r v e s t ed(T a b l e .5 ). 0 f th e ciamshanvestecJ
in the fisher y since lg7l, SS,B6,
p o u n d s( tfg .7 mt) o r 9 9 .5 %w e r e gaper clar ns.
Table 5.
Poundsof ClamsI'lechaliqqt
ly Harvesteclin ExperimentalFishery,
Y a q u i n aB a y, Or egon,1975- 80.
Gaper
1,478
Cockl
e
24
Li ttl eneck
0
Butter
0
I rus
0
0
0
0
0
0
68,074
10
Total
0
69,057
1,502
lrg
s90
334
162,351
0
1
22
44
73,959
0
0
606
0
fl
305,862
34
50
1,219
378
162
"419
74,565
0
347,542
0
0
U
0
CoosBay
T h e co mn e rci ahl a rve st i n CoosBay pr oducecl
50,741pounds( 27.5 m t) ofw hi c h
6 0 ' 6 1 6p ou n d s(2 7 ,5 mt) o r 9 9 ,8%wer e gaper clans ( iable 6) . The r er nainAer
w .r -e
butter clams. The fishery extendedfronr'septcrnber
(Table 7):
through l\,lovember
E a c h . t r i p a ve ra g e d4 .3 h o u rs o f dive tir e. Har vestfiguies r cvealecl' tha t273
p o u n d s / h o u(1
r 2 4 kg l h r) o r 1 ,1 68 pounds/tr ip ( 5:1 kg/tr ip) wer e i.aken.
T a b l e 6 " S u mma ry
o f P cu ndsof Clamsiviechanically
Har vestedin
ExperinrentalFishery, CoosBay, 0regon, 197b-80.
Total
Gaper
Butter
Li ttleneck
14,467
735
0
r02,442 1 1 , 9 3 1 36,744 1 3 , 3 5 1 . 6 0 , 6 1 6
n
Total
t5,2A2
1 0 3 ,5 8 4 11, 9 3 1
L ,1 4 2
0
0
0
U
36,74rt
39
511
1 3, 9 01
r25
0
60,741
239,551
2,041
511
242,lA3
G a p ercl a msa ve ra g e d8 .9 years of age with the 1972year class being pr ev a ' l e n t i n t he h a rve st (F i g u re 1 0) . The clans aver aged133.7nr m( Figur e 11) . In
1979the clamsharvestedfrom the samear ea aver aged126.4mmin shell len gth.
- 7T a b 'l e7 . P o u ndsof Subtidal ClarnsHarvestedin CoosBay
C o n mer cial
Fisher y, 1980.
VE
September
0ctober
l{ovember
9 ,9 26
28"577
22,113
Totai
6 0,6 16
0
725
9,926
28"577
22,?38
37.0
103.0
82.5
125
6A,74L
222.5
U
TiSSESSMENT
0F EFFTCTS
0F C0I4I4ERCIAL
CLAI4
HTT,RVEST
0l{ RECRUITMENT
itlethods
In 1980we continuecl-toevaluate the effects of comrnercial
harvest on recruitnpnt of clamsin YaquinaBay. Samplingprccedureswere sorrrcwhat
modified from
'i i m ptes
p r e v i o u ssa n p l i n g (Ga u meert. a1., i979i.' l.ler educe,J
the iir . or inJiviJJu i
t c l I ' f t 2 (0 .0 9 'n z)-b u t i n cre a secl' sim plins
intunsity to 12.samples
each per tr eatm e n t a n d co n tro l p l o ts"
Benthic sampleswere retunneCto the laboratory and all invertebrates were
sorted into taxonomicgroups. Invertebrates eas.il;r"icfentified"reruseparated
to
s p e c i e s . A l l o th e t.w q re g ro u pedby far nity, or Oer o.- pr ,viu.- - n two way
an
al
y
s
s
o f v a r i a n cew a s a p p l i e clti l te st fcr possibie var iaiion clueto tem por alsepar atii on
q f ^ s - a m n l i n g .p e ri o d s.
S i n ce o u r r .latashowe,J
no var iaticn,:r e tJ sam plinqin
d l t t e r e n t t i m e p e r i o d s , a o n e s , a { a n a l y s i so f v a r i a n c ew a su t i l i z e d ' a s ' i h e ' n p s t
p o w e r f u l t e st fo r_ e va l u a ti n g<l iffer encesin num beroi- tu*onJ*i. g..ups
bet w eentreatment and control.
R e s u i t sa n d D i s c u s s i o n
The macrobenthicdata collectec! from treatment and control plots
of Area 2,
P l o t . ! . o f Y a q u i l aB a yi s s h o w n
i n T a b t e8 . n n'level
atvits-;i G;i;nie'taiieri to i[ow
signlficant differencesat the 95%confidence
in any oi i1.,.five-speciei
of clamsor in any of 1,7other taxa of benthic inverteoiaiessampleci.A;;.;ing1!,
there is no evitlencethat the conrnerciai
harvestcf suUtiOitgapb.iiu*r-nlr-ani
innBdiatedetrinental effect on benthic fauna. Yet to be unclerstcod
is the near
total mortalilV i;f new'lyrecruitecigapenclamsin both the treatmentand control
areasof Yaquina
Bay (Figure12),
Analysisof variancealso showe,J
that in the treatmentandcontrrl plots,
taxonomic
cjiversitydid not differ significantly eittrer in nu*Oers
of taka
represented
ncr in numbers
of individuals(Figures13 an.J14). Theopporiunistic
t&eonalfeutryqta,(f,iacorna.
claqr)_increased
fdliJwing narveit tn- tgiB-fFibri..i-1s)
andby f{ay1979haCreachecl
102.5/0"09
mzin the lontrot. Similar reciuitnenl
g! uaotla inqutnata was reportedby Swartz,€t. 0l , ig80: ay i{ovemuer
of 1g79
Enenumbers
of MaamainqaLnatahad decreased
to levejs similar to that of the
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-9c o n t r o l . A s i m i ' l a r p a t t e r n i n r ecr uitmentfor this spec' ieswas obser vedfor
t h e i n c o m i n g1 9 8 0y e a r - c 1 a s sf o l l o w e db y a n o t h e rd e c l i n e t o c o n t r o l l e v e ' l sb y
the fal I of 1980.
F i g u re 1 4 sh o w sth e to ta l numberof benthic inver tebr atesin the tr eatm ent
a n d c o n t r o l p l o t s . R e c r u i t m e nat n d m o r t a l i t y t h r o u g h o u t h e s a m p l i n gp e r i o d w a s
s ' i m i l a r f o r b o th tre a tme n ta n d c o n t r o l . T h e f l u c t u a t i o n s i n t o t a l n u m b e ros f
b e n t h i c i nve rte b ra te sre fl e cts the recruitment and mortality of the Macoma
clam.
LABORATORY
CLAM
STUDIIS
O u r l ab o ra to ry cl a m stu d i es wer e ter minatedin 1975. Since then we h av e
a n n u a l l ym o n i t o r e dt h e g r o w t ho f c l a m sp l a n t e d i n N e t a r t s B a y .
Methods
,
T w ostu d i e s w e re co n ti n u e din Netar ts Bay. Onecom par ed
the gr owth
c h a r a c t e r i s t i c so f M a n i l ai i t t l e n e c k c l a m st h a t w e r e ' s e l b c t e df o r i h e i r f a s t
g r o w i n ga b i l i t y v s . n o r m a lg r o w i n gc l a m s( G a u m earn d L u k a s , 1 9 7 5 ) ;t h e o t h e r
c o m p a r egro
d w tho f cl a msi n a scr eenedenclosur evs. unscr eened
ar eas.
R e s u l t sa n d D i s c u s s i o n
M a n i l a l ' i t t l e n e c k c l a m ss p a w n eidn A u g u s t1 9 7 4f r o m f a s t g r o w ' i n g
parent
s t o c k g r e w2 . 3 r y s i n c e J u n e 1 9 7 9a n d a v e r i g e d3 9 , 2 m mi n . l e n g l h , w h 6 r e a sp r o g e n y
f r o m t h e " n o r m a l , " . c l a mg sr e w3 . 2 m ma n d a v e i a g e d3 7 . 3 m m( f i g i r e ' i 6 ) .
wehavdb e e nu n a b l et o d e t e r m i n es u r v i v a l o f t h e M a n i i ac l a m sd u e t o t h e i r m o v e m e n t
outsideof the study p1ot.
E v i d e n ceo f n a tu ra l sp a w ningwas found with the r ecover yof one 1977y ear c l a s s c l a mt h a t a v e r a g e d
23.8mm.
M a n i l ac l a m sp l a n t e d i n t h e s c r e e n e dt e s t p l o t a v e r a g e d
3 g . 6 m m ,a n
i n c r e a s eo f 2 . 6 m ms i n c e 1 9 7 9 ,w h e r e a sc l a m sp l i n t e d i n a i a d j a c e n tu n s c r e e n e d
t e s t p l o t a v e r a g e d4 0 . 0 m m ,a n i n c r e a s eo f ? . 5 m ms i n c e 1 9 7 9 . M a n i l a sp l a n t e d
a d j a c e n tt o a n e e l g r a s sb e d a n d a t a s l i g h t l y l o w e r e l e v a t i o nw e r e4 4 . 9 m m ,a n
i n c r e a s eo f 2 . 0 m ms i n c e 1 9 7 9( F f g u r e1 7 ) . C l a m si n a i l t h r e e t e s t p l o t s
a v e r a g e di 3 . 1 n r n rw h e nr e l e a s e d .
- 10ACKi{OI,ILEDG}{ENTS
l ' J ew i sh to th a n k L a i rn o ns
0sis, Jean llcCr ae,and Br ucelr ji' !liam sof th e
0 r e g o nDe p a rtrn e notf F i sh a n d t' lilcliife, DaveBer nar dof 0r egcnState Univer s i ty
and i'larian Aschefor their assistance in the study.
LITERATURE
CITED
'CIam
Gauner,Thor,ras
F. anCBruceC. Halstead. L976. t4ethodsof Supplenenting
a n d A b a l o n eP ro d u cti o n , Conxn.
Fish. Res. and Devel. Act. July 1, 1975to
J u n e 3 0 , 1 9 7 6 . On e . D e pt. of Ffsh and itfi' ldlife Pr c,c.Rept. 65 pp,
Gaurner,
ThomasF. and Gerald Lukas. L975. l4ethrrcls
of Supp'lementing
Clamand
Ab al o n eP ro d u cti o n . C o m mFish.
.
Res. anciDevel. Act. Juty 1, 1974tc r
June 30, L975. Fish Conna,
of 0re. Proc. Reiit. 34 pp
Gaurer, ThomasF., GregoryP. Robart and AnneGeiger. 1979. CregonBay clam
D i s tri b u ti o n , A b u n d a n ce,
Plantfng Sites anclEffects of Har vest, ConmF
. i s h.
Res. and Devel. Act. October Lu 1978to September
30, L979. 0re. Dept.
of Fi sh and ['liI dl i fe. Proi" Rept. 47 pp.
G o o d v l i n"
C ,L . 1 9 7 3 . D i si ri b u tion and Abundance
of SubticlalHar d- shellC l am si n
Pu ge tS o u n d ,l ,rl a sh i n g to n.
hiash.Dept. of Fish. Tech. Rept. f{ o. L4. 81 pp.
S t e e l , R ob e rtG.D . a n d Ja me sH. Tcr r ie. 1950. Pr inciples and Pr ocedunes
of
St a ti sti cs. McGra w -H i llBookCompany,
Inc. 481.pp"
Sw a r t z , R .C ., H .A . D e B e n F
, ,A . Cole and L.C. Bentsen. 1980. Recover yof the
l 4 a cro b e n th oast a D re d g eSite in Yaqu' ina
Bay,0r
- 20,egon. Jn Rober tA. B ak er ,
( e d ) C o n ta mi n a n ts
a n tl& d im ents, Voi' . 2, Ch:
6 391- m 8. AnnAr bor
sci. FilETffi
nnn'A6'oF;Tf"
Appendix1
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