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I U, 5, Fish on2 V/ildli+ Service National vJel!andi qesesrch Cen*i Biological Report 82(11.95) /bf: LQ,! lln i h m e Coulzvard TR EL-82-4 February 1989 Lafsyette, Louisiana 70506 Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and lnverte brates (Pacific Southwest) PlSMQ CLAM Fish and Wildlife Service Coastal Ecology Group Waterways Experiment Station U.S. Department of the Interior U.S. Army Corps of Engineers
Transcript

I

U, 5, Fish on2 V/ildli+ Service National vJel!andi qesesrch Cen*i

Biological Report 82(11.95) /bf: LQ,! lln i h m e Coulzvard TR EL-82-4

February 1989 Lafsyette, Louisiana 70506

Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and lnverte brates (Pacific Southwest)

PlSMQ CLAM

Fish and Wildlife Service Coastal Ecology Group

Waterways Experiment Station

U.S. Department of the Interior U.S. Army Corps of Engineers

B i o l o g i c a l R e p o r t 82(11.95) TR EL-82-4 F e b r u a r y 1989

Spec ies P r o f i l e s : L i f e H i s t o r i e s and Env i ronmen ta l Requi rements o f Coas ta l F i s h e s and I n v e r t e b r a t e s ( P a c i f i c Southwest )

PISMO CLAM

W i l l i a m N. Shaw Humboldt S t a t e U n i v e r s i t y

Fred T e l o n i c h e r Mar ine L a b o r a t o r y T r i n i d a d , CA 95570

and Thomas J. H a s s l e r

C a l i f o r n i a C o o p e r a t i v e F i s h e r y Research U n i t Humboldt S t a t e U n i v e r s i t y

A rca ta , CA 95521

P r o j e c t O f f i c e r Dav id Moran

U.S. F i s h and W i l d l i f e S e r v i c e N a t i o n a l Wet lands Research Cen te r

1010 Gause Bou leva rd S l i d e l l , LA 70458

Per formed f o r

Coas ta l Eco logy Group Waterways Exper iment S t a t i o n U.S. Army Corps o f Eng inee rs

V icksburg , MS 39180

and

U.S. Department o f t h e I n t e r i o r F i s h and W i l d l i f e S e r v i c e Research and Development

N a t i o n a l Wet1 ands Research Center Washington, DC 20240

Th i s s e r i e s should be re fe renced as f o l l o w s :

U.S. F i s h and W i l d l i f e Serv ice. 1983-19-. Species p r o f i l e s : l i f e h i s t o r i e s and env i ronmenta l requ i rements o f coas ta l f i s h e s and i n v e r t e b r a t e s . U.S. F i s h W i l d l . Serv. B i o l . Rep. 82(11). U.S. Army Corps o f Engineers, TR EL-82-4.

Th is p r o f i l e may be c i t e d as f o l l ows :

Shaw, W.N., and T.J. Hass ler . 1989. Species p r o f i l e s : l i f e h i s t o r i e s and env i ronmenta l requi rements o f coas ta l f i s h e s and i n v e r t e b r a t e s ( P a c i f i c Southwest 1--Pismo clam. U.S. F i s h W i l d l . Serv. B i o l . Rep. 82(11.95). U.S. Army Corps o f Engineers, TR EL-82-4. 12 pp.

PREFACE

This species p r o f i l e i s one o f a s e r i e s on coas ta l aqua t i c organisms, p r i n c i p a l l y f i s h , o f spo r t , commercial, o r eco log i ca l importance. The p r o f i l e s are designed t o p rov ide coas ta l managers, engineers, and b i o l o g i s t s w i t h a b r i e f comprehensive sketch o f t h e b i o l o g i c a l c h a r a c t e r i s t i c s and environmental requirements o f t h e species and t o descr ibe how popu la t ions o f t he species may be expected t o r e a c t t o environmental changes caused by coas ta l development. Each p r o f i l e has sec t ions on taxonomy, l i f e h i s t o r y , eco log i ca l r o l e , environmental requirements, and economic importance, i f app l i cab le . A t h r e e - r i n g b inde r i s used f o r t h i s se r i es so t h a t new p r o f i l e s can be added as they are prepared. Th is p r o j e c t i s j o i n t l y planned and f inanced by t he U.S. Army Corps o f Engineers and t h e U.S. F i s h and W i l d l i f e Serv ice.

Suggestions o r quest ions regard ing t h i s r e p o r t should be d i r e c t e d t o one of t h e f o l l o w i n g addresses.

I n fo rma t i on Trans fer S p e c i a l i s t Nat iona l Wetlands Research Center U.S. F i s h and W i l d l i f e Serv ice NASA-Slidell Computer Complex 1010 Gause Boulevard S l i d e l l , LA 70458

U. S. Army Engineer Waterways Experiment S t a t i o n A t ten t i on : WESER-C Post O f f i c e Box 631 Vicksburg, MS 39180

CONVERSION TABLE

M e t r i c t o U.S. Customary

M u l t i p l y

m i l l i m e t e r s (mm) cent imeters (cm) meters (m) meters (m) k i l omete rs (km) k i l omete rs (km)

square meters (m2) 10.76 square k i lomete rs (km2) 0.3861 hectares (ha) 2.471

1 i t e r s (1) cub ic meters (m3) c u b i c meters (m3)

m i l l i g r a m s (mg) grams (g) k i lograms (kg) m e t r i c tons (t) m e t r i c tons (t)

k i l o c a l o r i e s ( k c a l ) Ce ls ius degrees (OC)

U.S. Customary t o M e t r i c

inches 25.40 inches 2.54 f e e t ( f t ) 0.3048 f a t homs 1.829 s t a t u t e m i l e s (mi) 1.609 n a u t i c a l m i l e s (nmi) 1.852

square f e e t ( f t2 ) square m i l e s ( m i 2 ) acres

ga l 1 ons (ga l ) cub ic f e e t ( f t 3 ) a c r e - f e e t

ounces (02) ounces (02) pounds ( l b ) pounds ( l b ) s h o r t tons ( ton )

B r i t i s h thermal u n i t s (Btu) 0.2520 Fahrenhei t degrees (OF) 0.5556 (OF - 32)

To Obta in

inches inches f e e t fathoms s t a t u t e m i l e s n a u t i c a l m i l e s

square f e e t square m i l e s acres

g a l l o n s cub ic f e e t a c r e - f e e t

ounces ounces pounds pounds s h o r t tons

B r i t i s h thermal u n i t s Fahrenhei t degrees

m i l l i m e t e r s cen t imete rs meters meters k i l o m e t e r s k i l o m e t e r s

square meters square k i l o m e t e r s hectares

l i t e r s c u b i c meters c u b i c meters

m i l l i g r a m s grams k i 1 ograms m e t r i c tons m e t r i c tons

k i l o c a l o r i e s Ce ls ius degrees

CONTENTS

Page

PREFACE .................................................................. iii CONVERSION T A B L E ......................................................... i v ACKNOWLEDGMEIVTS .......................................................... v i

NOMENCLATURE/TAXONOMY/RANGE .............................................. 1 MORPHOLOGY/IDENTIFICATION A I D S ........................................... 1 REASON FOR INCLUSIOIV I N S E R I E S ........................................... 1 L I F E H I S T O R Y ............................................................. 3

S p a w n i n g ................................................................. 3 ....................................................... F e c u n d i t y a n d E g g s 3 L a r v a e ................................................................... 3 ............................................... P o s t l a r v a e a n d R e c r u i t m e n t 3 M a t u r i t y a n d L i f e S p a n ................................................... 5 ................................................... GROWTH C H A R A C T E R I S T I C S 5 ........................................... COMMERCIAL AND SPORT F I S H E R I E S 6

ECOLOGICAL ROLE .......................................................... 7 ENVIRONMENTAL REQUIREMENTS ............................................... 8

L I T E R A T U R E C I T E D ......................................................... 11

ACKNOWLEDGMENTS

We acknowledge t h e r e v i e w s by F red Wendel l , C a l i f o r n i a Department o f F i s h and Game, Mor ro Bay, and A r t h u r H a s e l t i n e , C a l i f o r n i a Department o f F i s h and Game, Monterey.

F i g u r e 1. Pismo clam.

PISMO CLAM

S c i e n t i f i c name . . . . . . . T i v e l a s t u l t o r u m (Mawe 1823)

P r e f e r r e d common name . . . Pismo c lam ( F i g u r e 1 )

Other common name . . . . G i a n t t i v e l a C lass . . . . . . . . . . . . B i v a l v i a Order . . . . . . . . . . . V e n e r o i d a F a m i l y . . . . . . . . . . Vener idae

Geograph ic range: The Pismo c lam i s r a r e t o common ( i n t h e low i n t e r t i d a l zone and o f f s h o r e t o a d e p t h o f 10-25 m) a l o n g t h e P a c i f i c c o a s t f r o m Mon te rey Bay ( F i g u r e 2 ) t o Bah ia Magdalena, Ba ja , C a l i f o r n i a ( F i t c h 1953) .

MORPHOLOGY/IDENTIFICATION AIDS

g rowth l i n e s ; beak n e a r l y c e n t r a l ; l i g a m e n t obv ious , e l o n g a t e , s e t i n deep groove; p e r i o s t r a c u m sh iny , g r e e n i s h t o brownish; s h e l l p a l e b u f f t o d a r k c h o c o l a t e , o c c a s i o n a l l y marked w i t h brown o r pu rp le -b rown bands ( M o r r i s e t a l . 1980).

REASON FOR INCLUSION I N SERIES

The Pismo c lam s u p p o r t s an i m p o r t a n t s p o r t s h e l l f i s h e r y . An e s t i m a t e d 150,000 p e o p l e once sought t h e c lams on Pismo Beach, C a l i f o r n i a , d u r i n g a s i n g l e weekend ( F r e y 1971); however, sea o t t e r s have d e p l e t e d t h e s u p p l y t h e r e s i n c e 1981, and as of 1986 t h e r e i s no f i s h e r y (A.M. H a s e l t i n e , C a l i f . F i s h and Game; pe rs . comm. 1.

The s h e l l o f t h e Pismo c lam The Pismo c lam l i v e s i n t h e sandy reaches l e n g t h s o f 150 m o r more, i s beaches a l o n g t h e C e n t r a l and Sou the rn s t rong , heavy, and genera l l y smooth C a l i f o r n i a c o a s t -- a h a b i t a t t h a t i s though s c u l p t u r e d w i t h f i n e c o n c e n t r i c h i g h l y v u l n e r a b l e t o d e g r a d a t i o n f r o m

CAPE MENDOCINO

\ \

SAN FRANCISCO BA k' \

\ \

\

CALIFORNIA \ \

\\

PACIFIC OCEAN

B * LOS ANGELES

gF@$$$ Coastal distribution $i&*>.~

M I L E S 0 5 0 100

0 50 100

K ILOMETERS

---_ -\ Figure 2 . D i s t r i b u t i o n o f t h e Pismo clam along t h e C a l i f o r n i a coast . The clam o n l y occurs on broad sandy beaches exposed t o strong s u r f w i t h i n t h e range i n d i - cated on t h e map. A lso , t h e clam sometimes occurs i n entrances t o bays, sloughs, and e s t u a r i e s .

dredg ing and o i l p o l l u t i o n ( o i l s p i l l s ) . S u b s t a n t i a l losses o f c lam popu la t i ons r e s u l t i n g f rom man's man ipu l a t i on o f t h e coas ta l zone cou ld be expected t o cause an economic l oss t o t h e s p o r t f i s h e r y .

I n many areas, r e c r u i t m e n t o f Pismo clams has been very low and t h e popu la t i on has dec l i ned almost s t e a d i l y over years. Exact causes f o r l a c k o f r e c r u i t m e n t a r e no t f u l l y known. Fu r t he r losses o f pa ren t s tocks f rom degrada t ion and/or o v e r f i s h i n g cou ld be expected t o f u r t h e r reduce t h i s impo r t an t r e c r e a t i o n a l she1 l f i she ry .

LIFE HISTORY

Spawning

The sexes o f t h e Pismo clam are separa te ( F i t c h 1961) a l though e a r l y i n v e s t i g a t o r s be l i e ved t h e clam t o be hermaphrod i t i c (Weymouth 1923). Most clams become sexual l y mature a f t e r t h e i r f i r s t w i n t e r , a t s h e l l l e n g t h as s h o r t as 17-20 mm (Coe 1947). Gametogenesis begins i n March o r A p r i l and r i p e gametes f i r s t appear i n A p r i l and May. Gonadal development proceeds r a p i d l y i n June and Ju l y ; spawning begins i n l a t e J u l y o r e a r l y August and con t inues t o t h e end o f November (Coe 1947 1. Nybakken and Stephenson (1975) found t h a t t h e main spawning o f clams a t Pismo Beach and Monterey occurred d u r i n g September and October w i t h some occurrence f rom June t o August. Coe (1947) found a s i m i l a r spawning c y c l e f o r clams f rom San Diego.

Discharge o f gametes appears t o t ake p l a c e when t h e r e i s a f a i r r i s e i n water temperature ( F i t c h 1961). As i n most b i va l ves , males u s u a l l y spawn f i r s t and t h e i r r e l e a s e o f gametes s t imu la tes t h e females t o spawn. Spawning may occur severa l t imes d u r i n g t h e season s i nce o n l y a p o r t i o n o f t h e gametes r i p e n a t one t ime. Hermaphrodites a re r a r e . Out o f 289

c l ams examined, on 1 y t h r e e hermaphrodites were found (Nybakken and Stephenson 1975).

Fecund i t y and Eggs

The eggs o f Pismo clams a re ve r y smal l , 0.074-0.081 mm i n d iameter (Coe and F i t c h 1950). The number o f eggs per female inc reases w i t h s h e l l s i ze , r ang ing f rom 10 t o 20 m i l l i o n and averaging 15 m i l l i o n (Coe 1953; F i t c h 1957; F i t c h 1961). E a r l i e r , Weymouth (1923) es t imated t h e number o f eggs per female t o be 47 t o 98 m i l l i o n .

Larvae

L i t t l e i s known about t h e Pismo clam f rom t h e t ime eggs a re spawned u n t i l t h e clams appear on t h e beach. The f r e e swimming l a r v a l l i f e i s es t imated t o l a s t f o r 3 weeks (Coe 1947) d u r i n g which t h e l a r v a e can be swept a longshore f o r 40 t o 100 m i l es . Larvae and p o s t l a r v a e l e s s than 2.3 mm have never been found d r i f t i n g i n t h e sea. Recent f i n d i n g s a t t h e C a l i f o r n i a F i s h and Game, Mar ine Resources Labora to ry , G r a n i t e Canyon, C a l i f o r n i a , i n d i c a t e t h a t t h e l a r v a e have a h i g h weight/volume r a t i o and may remain on o r near t h e bot tom most o f t h e t ime and move ve r y l i t t l e .

Pos t l a r vae and Recru i tment

A t metamorphosis t h e clam develops a f o o t and a t taches t o sand g r a i n s w i t h a byssus. Th i s at tachment he lps t h e clam t o m a i n t a i n i t s e l f i n t h e c o n s t a n t l y moving sand o f a wave- beaten coas t (Weymouth 1923). The l e n g t h o f a byssus can range f rom 45 t o 92 mm o r as much as f i v e t imes t h e l e n g t h o f t h e clam. As t h e clam inc reases i n s i z e t h e byssus d isappears. The c l am ' s i n c r e a s i n g we igh t and bur row ing power then he l ps t o m a i n t a i n i t on t h e beach.

Recru i tment was examined i n t h e Pismo Beach area beg inn ing i n 1919, and a su rvey was conducted annua l l y f rom 1925 t o 1965 except f o r d u r i n g

1942-45 (Weymouth 1923; He r r i ng ton Pismo clams were sampled a t t h r e e 1929; A l p i n 1947a; Bureau o f Mar ine l o c a t i o n s : 100 yd n o r t h o f t h e p i e r F i s h e r i e s 1948; C o l l y e r 1951; F i t c h a t Pismo Beach; 1.1 mi south o f t h e 1952, 1954, 1955; Baxter 1961, 1962; p i e r (Oceano s e c t i o n ) ; and 0.5 mi Car l i s l e 1966). Young-of- the-year and south o f t h e n o r t h boundary o f t h e a d u l t s o f a l l ages were sampled d u r i n g clam re fuge (Le Grande s e c t i o n ) . The t h e surveys (Tab le 1 ) . sampl i n g sec t i ons o r t r a n s e c t s were

Table 1. Number o f clams, by age groups, taken i n t h r e e sec t i ons on Pismo Beach surveyed each year, 1925-65.

Year Age ( yea rs ) of

survey 0 1 2 3 4 5 6 7 - > 8 T o t a l

16 cm wide and 20 cm deep, and extended across the beach from high t i d e l i n e t o as low as i t i s possible t o dig during one of the lowest t i d e s of the year.

Sets of clams a t Pismo Beach, as indicated by the number of young-of- the-year col lected (Table 11, were good in 1929-31, 1935, 1937, 1946, 1957, 1959, 1964, and 1965, and poor in 1928, 1934, 1938, 1949, 1951, 1953, 1955, 1956, and 1961. I n l a t e r years ( a f t e r 1965), s e t t i n g in the Pismo Beach area was extremely poor (James Hardwick, Cal i f . Fish and Game; Pers. comm. 1. Causes fo r these e r r a t i c s e t t i n g pat terns are not known. Coe (1953) speculated tha t the var iable recruitment was due t o the vagaries of the ocean currents t h a t bring larvae t o the beach a t the end of the pelagic stage.

Maturity and Life Span

Pismo clams mature during the f i r s t f u l l summer of l i f e a t La J o l l a , Cal i fornia . and durina the second summer of i i f e in the northern edge of t h e i r range. They a re 17 mm t o 31 mm long a t f i r s t maturity (Coe and Fitch 1950). Morris e t a l . (1980) wrote t h a t females spawn fo r the f i r s t time in the second or th i rd summer a f t e r hatching.

The age of the Pismo clam can be determined by r ings on the shel l (Figure 1). The rings used in age determination are usually formed in f a l l or winter , or when the clam i s subjected t o the most prolonged period of disturbances. The longest clam on record a t Pismo Beach was seven and three-eighths inches long and was about 26 years o ld , but the ages of a number of clams from Baja Cal i fornia have exceeded 35 years. G i l l i l a n (1964) recorded a 53-year-old clam a t Zuma Beach, Cal i fo rn i a , tha t measured only f i v e and one-quarter inches long.

GROWTH CHARACTERISTICS

The Pismo clam grows continuously throughout i t s l i f e (Fi tch 1950). Increase in shel l growth i s g rea tes t in spring, summer, and ea r ly f a l l . The average year ly increase in length during the f i r s t 4 years of l i f e i s s l i g h t l y more than 20 mn. A t age 10 the annual increase i s usually not more than 5 mm. Minimum legal length on most beaches (4.5 inches) i s f i r s t reached in 5 years but may not be reached unti 1 8 or 9 years. A t Pismo Beach, clams reach legal minimum length between ages 7 and 8 (Figure 3 ) .

Growth r a t e s apparently vary among beaches. Herrington (19291, who constructed growth curves fo r cl ams from four beaches between Morro and Monterey Bays (Figure 41, reported t h a t clams from Turt le Bay grew f a s t e s t and those from Morro Bay slowest.

Figure 3. Growth of Pismo clams a t Pismo Beach. These averages have been determined from the r e s u l t s of the annual census f o r the years 1923 through 1949, excluding 1942 through 1945 (Fi tch 1950).

14

12

10

- E S 8

E Y Y 6

4

2

0

0 2 4 6 0 10 12 14 ACE IN Y H R S

L

Table 2. Yea r l y land ings o f Pismo clam i n thousands o f pounds ( round we igh t ) .

T o t a l Year C a l i f . shipmentsa pounds

1930 108 9 F i g u r e 4. Growth curves f o r Pismo 1931 104:7 clams f rom Pismo-Oceano Beach, Morro 1932 110.3 Beach, Monterey Bay, and T u r t l e Bay 1933 106.2 ( H e r r i ng ton 1929).

1934 140.7

COMMERCIAL AND SPORT FISHERIES

P i smo clams have been gathered and used over t h e pas t 2,000 years, as judged by t h e occurrence o f t h e i r s h e l l s i n I n d i a n k i t c h e n middens (heaps o f s h e l l s and o t h e r r e f u s e ) a long t h e C a l i f o r n i a coast . I n i t i a l l y these clams were eaten and she1 1s were used as ornaments o r as household a i d s f o r d i g g i n g o r s c rap i ng (F rey 1971).

I n t h e e a r l y 19001s, teams o f horses p u l l i n g plows were used t o c o l l e c t clams commercial l y f rom Pismo Beach t o Impe r i a l Beach. The clams were loaded i n wagons and l a t e r f ed t o hogs and ch ickens (F rey 1971).

' ~ r o m south o f t h e i n t e r n a t i o n a l boundary. Cleaned we igh ts r epo r t ed on f i s h r e c e i p t s have been m u l t i p l i e d by 8 t o supp ly round we igh ts g i ven here (Bureau o f Mar ine F i s h e r i e s 1949 1.

On t h e b a s i s of t h e records ma in ta ined f rom 1916 t o 1947 (Table 21, i t was es t imated t h a t 6.25 m i l l i o n l b o f clams were harves ted by commercial d i gge rs d u r i n g t h i s p e r i o d c a t c h was n e a r l y 100,000 I b , and t h e ( F i t c h 1954). The average annual h i ghes t was 665,684 l b i n 1918.

Commercial d i g g i n g has n o t been a l lowed i n C a l i f o r n i a s i nce 1948.

Clam meats were impor ted f rom Mexico beg inn ing i n 1935. One of t h e main sources was San Qu in t i n , 220 m i l e s south o f T i j u a n a ( A l p i n 1947b). Clams were c o l l e c t e d by fo rks , p laced i n b u r l a p bags, loaded i n wheel- barrows, moved t o shore, and shucked; t h e meats were then washed and p laced i n 5 -ga l l on cans. From 86.7 thousand pounds t o 53.4 m i l l i o n pounds were shipped annua l l y t o C a l i f o r n i a f rom 1941 t o 1947 (Table 2) . Impor ts then ended because i t became t o o c o s t l y t o t r a n s p o r t them t o t h e cannery (Bureau o f Mar ine F i s h e r i e s 1949).

Clams are c o l l e c t e d by a v a r i e t y o f methods. The most common d i g g i n g t o o l i s a s i x - t i n e d p o t a t o fo rk . Clams a re p laced i n a sack a t tached t o t h e wa i s t . Some f ishermen use a r a k e made of a p i t c h f o r k w i t h an extended handle. A rope a t taches t h e r a k e t o t h e wa i s t . I n deeper water, f i s h i n g i s done by tow ing a long-handled rake f rom a s k i f f . When a clam i s s t r uck , a d i v e r recovers it. Using another method, s k i n d i v e r s wear ing face masks and l y i n g on paddle boards c o l l e c t clams by l o c a t i n g them i n d i v i d u a l l y . When a s iphon h o l e i s seen, t h e clam i s dug ou t o f t h e sand w i t h a s h o r t d i g g i n g bar. Clams a re sometimes l oca ted when t h e s iphon ho les a re encountered by t h e bare f e e t of a wading f isherman. Fishermen a l s o l o c a t e clams by l o o k i n g f o r hyd ro i d co l on i es , which o c c a s i o n a l l y grow on t he edge o f t h e she1 1 o f some clams.

The d a i l y bag l i m i t o f clams has been reduced over t h e years from 200 i n 1911 t o 10 i n 1985. As o f 1986, t hey must be 4.5 inches o r g rea te r i n l eng th i n San L u i s Obispo County and south, and 5.0 inches o r g r e a t e r i n Monterey County and nor th . A1 1 unders ize clams must be r e t u r n e d t o a ho l e (dug w h i l e l o o k i n g f o r c lams). The number o f c lam d i gge rs i n C a l i f o r n i a i s n o t known. An es t imated 150,000 d i gge rs were seen and over

75,000 l b o f clams were caught on Pismo Beach on one weekend. I n a 10- week per iod , 4 m i l l i o n pounds were taken f rom a 4 -mi le s t r e t c h o f Pismo Beach (F rey 1971). As o f 1986, sea o t t e r p r e d a t i o n has p u t an end t o t h e f i s h e r y the re .

ECOLOGICAL ROLE

The Pismo clam i s a f i l t e r feeder on d e t r i t u s , a1 though l i v i n g , one- c e l l e d organisms fo rm a cons iderab le p o r t i o n o f t h e d i e t (F rey 1971). Water taken i n through t h e i n c u r r e n t s iphon passes over t h e g i l l s where food p a r t i c l e s a re removed. The types o f food u t i 1 i zed i n c l u d e phy top lank ton (such as diatoms 1, bac te r i a , zooplankton, eggs and sperm, and d e t r i t u s f rom d i s i n t e g r a t i o n o f p l a n t s and animals. H a l f o f t h e stomach con ten ts i s sand ( F i t c h 1950). I n f eed ing a clam 3 inches long f i l t e r s as much as 60 1 o f water per day. I n t r a c e l l u l a r d i g e s t i o n i s done by phagocy t i c c e l l s of t h e d i g e s t i v e d i v e r t i c u l u m , a i ded by m i g r a t o r y phagocytes i n t h e lumen o f t h e a l i - mentary canal (Coe 1947).

Since Pismo clams l i v e b u r i e d i n t h e sand, e p i z o i c growth on t h e s h e l l i s r a r e - - t u f t s o f t h e hyd ro i d C l y t i a bake r i o c c a s i o n a l l y l i v e on t h e t i p of t h e c l am ' s exposed s h e l l .

The Pismo clam has many p reda to r s i n c l u d i n g g u l l s , sharks, rays, and some s u r f f i s h e s such as t h e C a l i f o r n i a co rb i na ( M e n t i c i r r h u s undu la tus ) . Rays use t h e i r wings t o c r e a t e a s u c t i o n t h a t p u l l s t h e clams f rom t h e sand. The rays then mouth t h e exposed clams and c rush and sha l low them (Frey 1971).

The moon s n a i l , P o l i n i c e s sp., ea t s clams up t o 2 years o l d . It d r i l l s a h o l e i n t h e s h e l l w i t h i t s r a s p i n g tongue and then i n s e r t s t h e tongue through t h e h o l e and ea ts t h e s o f t body o f t h e clam. Cancer crabs, Cancer, have been observed t o

7

crack t he s h e l l o f clams up t o 2.5 cm long w i t h t h e i r f r o n t p incers.

ENVIRONMENTAL REQUIREMENTS

A t Sunset Beach, Santa Cruz County, Hawbecker (1939) watched g u l l s p i ck up sublegal s i z e clams discarded by d iggers, c l imb t o an a l t i t u d e o f 9 t o 12 m, and then drop the clams on the hard packed sand. The f a l l broke the s h e l l s and enabled t h e g u l l s t o ea t t h e clam.

I n areas where sea o t t e r s (Enhydra l u t r i s ) forage, clam ~ o ~ u l a t i o n s decreased s i q n i f i c a n t l v . A 'sea o t t e r has been observed t o eat 24 Pismo clams i n 2.5 h (Stephenson 1977 1. Wendel 1 e t a1 . (1986) repor ted t h a t a sea o t t e r can consume 80 clams pe r day. Clams decreased f rom 6.5 t o 0.5/m2 a t Moss Landing and from 0.55- 0.80 clams/m2 t o 0.15 clams/m2 a t Zmudowski Beach from 1972 t o 1974 (Stephenson 1977). M i l l e r e t a l . (1975) est imated t h a t o t t e r s a te 520,000 t o 700,000 Pismo clams i n one year a t Monterey Bay.

Sea o t t e r s are d i r e c t l y respons ib le f o r t h e l oss o f t h e clam spo r t f i s h e r y i n t h e Pismo Beach area (Wendell e t a l . 1986). The spo r t ca tch dec l ined from 343,000 clams i n 1978 t o 0 i n 1983.

Larva l cestodes have been found i n Pismo clams (Warner and Katkansky 1969 1. They occur as ye1 1 owish-whi t e cysts, 3.2-3.8 mn i n diameter. The cestodes have been i d e n t i f i e d as t he l a r v a l stage of tapeworms i n s t i ng rays and skates. The pa ras i t es can stop the c lam's sexual development bu t are no t harmful t o man i f eaten (Frey 1971). Commensal pea crabs, occasion- a l l y found i n t h e mant le cav i t y , feed on food p a r t i c l e s c o l l e c t e d by t h e clam's g i l l s (Frey 1971).

L i t t l e i s known about t he env i - ronmental requirements of t h e l a r v a l stage of Pismo clams. F i t c h (1950) repor ted t h a t o n l y a small f r a c t i o n o f 1% of spawned eggs become mature clams. Causes f o r t he m o r t a l i t y are unknown, bu t may inc lude sudden changes i n temperature and sa l i n i t y .

Post l a r vae are known t o d i e du r i ng heavy r u n o f f s from r i v e r s ( F i t c h 1950). O i l and o ther po l l u t a n t s a f f e c t mor ta l i t y . Red t i d e caused by a d i n o f l a g e l l a t e bloom, as w e l l as extremely c o l d weather, can k i l l young clams ( F i t c h 1950). M o r t a l i t y r a t e s f o r Pismo clams a t Pismo Beach (Frey 19711, i n d i c a t e t h a t of 1,000 clams 0.5 year o ld, o n l y 5 were s t i l l a l i v e a t age 7.5 (Table 3).

Pismo clams u s u a l l y l i v e i n t he i n t e r t i d a l zone on f l a t beaches o f t h e open coast, bu t are sometimes found i n entrance channels t o bays, sloughs, and es tuar ies . The i r normal depth i n t he sand i s 5.2 t o 15.6 cm (Armstrong 1965). They l i v e i n an environment o f rap id , severe and f o r c e f u l i n t e r a c t i o n of water and sand. They are slow diggers and are found i n a c h a r a c t e r i s t i c p o s i t i o n on the open coasts r e l a t e d t o t h e waves: t h e f r o n t h inge and excur ren t siphon face t h e ocean and t h e mant le edge and i n c u r r e n t siphon face land. Clams i n bays are o r i en ted a t random. They bury themselves by j e t t i n g water from the a n t e r i o r o f t he s h e l l w h i l e they bury t he f o o t . The weight o f t h e s h e l l he lps t o c a r r y t h e clam downward (Mor r is e t a l . 1980). The most p roduc t ive areas fo r Pismo clams have extensive upwell i n g o f cool oceanic water t h a t b r ings w i t h i t inorgan ic n u t r i e n t s essen t i a l f o r phytoplankton blooms (Coe and F i t c h 1950).

Tab le 3. Pismo clam m o r t a l i t y r a t e s (percentage o f losses a t Pismo Beach; F r e y 1971 1.

Number Age o f c l ams Number o f Percent Number c l arns

( y e a r s ) c l ams l o s s clams l o s t remaining

LITERATURE CITED

A l p i n , J.A. 1947a. Pismo c lam i n c r e a s e . C a l i f . F i s h Game 33(3):129-131.

A l p i n , J.A. 1947b. Pismo clams o f San Q u i n t i n , Lower C a l i f o r n i a . C a l i f . F i s h Game 23(1):31-33.

Armstrong, L. R. 1965. Burrowing 1 i m i t a t i o n s i n Pelecypoda. Vel i g e r 7(3):195-200.

Bax te r , J.L. 1961. R e s u l t s o f t h e 1955 t o 1959 pismo c lam censuses. C a l i f . F i s h Game 47(2):153-162.

Bax te r , J.L. 1962. The pismo clam i n 1960. C a l i f . F i s h Game 48(1):35-37.

Bureau o f M a r i n e F i s h e r i e s . 1948. 1947 pismo c lam census. C a l i f . F i s h Game 34(2) :82.

Bureau o f M a r i n e F i s h e r i e s . 1949. The commercial f i s h c a t c h o f C a l i f o r n i a f o r t h e year 1947 w i t h an h i s t o r i c a l r e v i e w 1916-1947. C a l i f . F i s h B u l l . 74:267 pp.

C a r l i s l e , J.G., J r . 1966. R e s u l t s o f t h e 1961 t o 1965 pismo c lam censuses. C a l i f . F i s h Game 52(3):157-160.

Coe, W.R. 1947. N u t r i t i o n , g rowth and s e x u a l i t y o f t h e pismo c lam ( T i v e l a s t u l t o r u m ) . J. Exp. Zool . l O K I X 1 - 2 4 .

Coe, W.R. 1953. Resurgent p o p u l a t i o n s o f l i t t o r a l mar ine i n v e r t e b r a t e s and t h e i r dependence on ocean c u r r e n t s and t i d a l c u r r e n t s . Eco logy 34(1):225-229.

Coe, W.R., and J.E. F i t c h . 1950. P o p u l a t i o n s t u d i e s , l o c a l g rowth r a t e s and r e p r o d u c t i o n o f t h e pismo clam ( T i v e l a s t u l t o r u m ) . J. Mar. Res . 9 (3):188-210.

C o l l y e r , R.D. 1951. R e s u l t s of t h e pismo c lam censuses, 1948, 1949 and 1950. C a l i f . F i s h Game 37(3) :331- 334.

F i t c h , J.E. 1950. The pismo clam. C a l i f . F i s h Game 36(3):285-312.

F i t c h , J.E. 1952. The pismo c lam i n 1951. C a l i f . F i s h Game 38(4):541- 547.

F i t c h , J.E. 1953. Common mar ine b i v a l v e s o f C a l i f o r n i a . C a l i f . F i s h Game F i s h B u l l . 90. 102 pp.

F i t c h , J.E. 1954. The pismo c lam i n 1952 and 1953. C a l i f . F i s h Game 40( 2 ) : 199-201.

F i t c h , J.E. 1955. R e s u l t s o f t h e 1954 pismo c lam census. C a l i f . F i s h Game 4 1 ( 3 ) :209-211.

F i t c h , J.E. 1957. The p l i g h t of t h e pismo clam. Outdoor C a l i f . 18 (1 ) :3 - 4.

F i t c h , J.E. 1961. The pismo clam. S t a t e o f C a l i f o r n i a , Dep. F i s h and Game, Mar. Res. Leaf. 1. 23 pp.

Frey, H.W. 1971. C a l i f o r n i a ' s l i v i n g mar i ne r e s o u r c e s and t h e i r u t i l i z a t i o n . C a l i f . Dep. F i s h Game, The Resources Agency. 148 pp.

G i l l i l a n , W. 1964. Pismo c lam survey. Outdoor C a l i f . 25(2):10-11.

Hawbecker, A.C. 1939. Feeding o f g u l l s on pismo clams. Condor 41(3):120.

H e r r i n g t o n , W.C. 1929. The Pismo clam: f u r t h e r s t u d i e s o f t h e l i f e h i s t o r y and d e p l e t i o n . C a l i f . F i s h Game, F i s h B u l l . 18. 58 pp.

M i l l e r , D.J., J.E. Hardwick, and W.A. Dahlstrom. 1975. Pismo clams and sea o t t e r s . C a l i f . F i s h Game, Mar. Resour. Tech. Rep., 31 :49 pp.

M o r r i s , R.H., D.P. Abbot, and E.C. Haderl i e . 1980. I n t e r t i d a l i n v e r t e b r a t e s of C a l i f o r n i a . S t a n f o r d U n i v e r s i t y Press, S tan fo rd , C a l i f . 690 pp.

Nybakken, J., and M. Stephenson. 1975. E f f e c t s o f e n g i n e e r i n g a c t i v i t i e s on t h e eco logy o f Pismo

clams. Corps o f Eng. Misc. Paper NO. 8-75. 65 pp.

Stephenson, M.D. 1977. Sea o t t e r p r e d a t i o n on pismo clams i n Monterey Bay. C a l i f . F i s h Game 63(2):117- 120.

Warner, R.W., and S.C. Katkansky. 1969. A l a r v a l cestode f rom t h e pismo clam, T i v e l a s t u l t o r u m . Cal i f . F i s h Game -8-251.

Wendell, F., R. Hardy, J. Ames, and R. Burge. 1986. Temporal and s p a c i a l p a t t e r n s i n sea o t t e r (Enhydra l u t r i s ) range expansion and i n t h e l o s s o f Pismo clam f i s h e r i e s . C a l i f . F i s h Game 72(4):197-212.

Weymouth, F.W. 1923. The l i f e - h i s t o r y and growth o f t h e pismo clam ( T i v e l a s t u l t o r u m Mawe). C a l i f . F i s h m e , F i s h B u l l . 7. 103 pp.

REPORT DOCUMENTATlON 1. Rc'Om no- r M E B i o l o a i c a l Report 82(11.95)* I I

Humbol d t S t a t e U n i v e r s i t y C a l i f . Coop. F ishery Res. U n i t ,

Fred Te lon i che r Mar ine Laboratory Humbol d t S t a t e U n i v e r s i t y T r i n i d a d , CA 95570 Arcata, C A 95521 (c)

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Species P r o f i l e s : L i f e Hi s t o r i e s and Environmental Requirements of Coastal Fishes and I n v e r t e b r a t e s ( P a c i f i c Southwest) -- Pismo Clam

7. Mhor(s)

W i l l i a m N. Shaw and Thomas J . Hass ler b. hdonnlns Or#mnlxmtlon Mmmm and M d m s

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U.S. Department o f t h e I n t e r i o r P.O. BO-x 631. Washingtonb D.C. 20240 V i cksburg, MS 39180

Nat iona l Wetlands Research Center U.S. Army Corps o f Engineers F ish and W i l d l i f e Serv ice Waterways Experiment S t a t i o n

1% Supplmmmntmvy Notms

U.S. Army Corps o f Engineers Repor t No. TR EL-82-4

1% TW 01 Rmpor( & hriod Connd I

16. Abstncl (Llmlt: 200 words)

Species p r o f i l e s a r e l i t e r a t u r e summaries o f t h e taxonomy, morphology, d i s t r i b u t i o n , l i f e h i s t o r y , and environmental r e q u i r m e n t s o f coas ta l aqua t i c species. They a r e prepared t o a s s i s t i n environmental i n p a c t assessment. The Pismo clam ( T i v e l a s t u l torum) suppor ts an impor tan t s p o r t f i s h e r y i n t h e P a c i f i c Southwest reg ion , b u t has no p resen t commercial inportance. Th is rev iew desc r ibes t h e l i f e h i s t o r y (spawning, eggs and l a r v a l stages, p o s t l a r v a e and j u v e n i l e s , m t u r i ty , and l i f e - s p a n ) 1, g rowth c h a r a c t e r i s t i c s , fo rmer commercial and s p o r t f i s h e r i e s , eco log i ca l ro le1 , and environmental requirements.

She1 l f i s h L i f e cyc les F i s h e r i e s Growth Feeding h a b i t s

Pismo clam Aauacu l ture 8 - - -

T i v e l a s t u l t o r u m Environmental requirements E c o l o g i c a l r o l e

ID. Avmllmblllty Stmimmmnt

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12 P. Pr iu

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