weakfish - usgs national wetlands research center
TRANSCRIPT
Biological Report 82(11.109) August 1989
Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Mid-Atlantic)
WEAKFISH
Fish and Wildlife Service Coastal Ecology Group
Waterways Ex~eriment Station
U.S. Department of the Interior U.S. Army Corps of Engineers
B i o l o g i c a l Repor t 82( 11.109) TR EL-82-4 August 1989
Species P r o f i l e s : L i f e H i s t o r i e s and Environmental Requirements o f Coasta l F ishes and I n v e r t e b r a t e s ( M i d - A t l a n t i c )
WEAKFISH
L inda P. Mercer Nor th C a r o l i n a D i v i s i o n
o f Mar ine F i s h e r i e s Morehead C i t y , NC 28557
P r o j e c t O f f i c e r David Moran
U.S. F i s h and W i l d l i f e Serv ice Na t i ona l Wetlands Research Center
1010 Gause Boulevard S l i d e l l , LA 70458
Performed f o r Coasta l Ecology Group
U.S. Army Corps o f Engineers Waterways Experiment S t a t i o n
Vicksburg, MS 39180
and
U.S. Department o f I n t e r i o r F i s h and W i l d l i f e Se rv i ce Research and Development
N a t i o n a l Wetlands Research Center Washington, DC 20240
Th is s e r i e s may be r e f e 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 : 1 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 o w s :
Mercer, L. P. 1989. Species p r o f i l e s : 1 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 (M id -A t l an t i c ) - -weak f i sh . U.S. F i s h W i l d l . Serv. B i o l . Rep. 82(11.109). U. S . Army Corps o f Engineers, TR EL-82-4. 17 pp.
PREFACE
'This species p r o f i l e i s one o f a se r i es on coasta l aquat ic organisms, p r i n c i p a l l y f i sh , o f sport , commercial, o r ecological importance. The p r o f i l es a re designed t o provide coasta 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 envi ronmental requirements o f the species and t o descr ibe how populat ions o f t h e species may be expected t o r e a c t t o environmental changes caused by coastal devel opnent. Each p r o f i l e has sect ions on taxonomy, l i f e h i s to ry , eco log ica l r o l e , environmental requirements, and econani c importance, i f appl i cab1 e. A t h r e e - r i n g b inder i s used f o r t h i s ser ies so t h a t new p r o f i l e s can be added as they a re prepared. Th i s p r o j e c t i s j o i n t l y planned and f inanced by t h e U.S. Army Corps o f Engineers and t h e U.S. F ish and W i l d l i f e Service.
M i l l i k i n and Wi1 l iams (1984) prev ious ly publ is t led a review o f t he nomenclature, taxononly, morphology, d i s t r i b u t i o n , l i f e h i s t o r y , popu la t ion s t r u c t u r e and dynamics, and t h e f i s h e r y o f t he b l u e crab.
Suggestions o r questions 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 o f t h e f o l 1 owing addresses.
In fo rmat ion Transfer S p e c i a l i s t Nat ional Wet1 ands Research Center U.S. F i sh and N i l d l i f e Serv ice NASA-S 1 i d e l l Computer Compl ex 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 At ten t ion : WESER-C Post O f f i c e Box 631 Vicksburg, MS 39180.
CONVERSION FACTORS
Metric to U.S. Customary
Multiply millimeters (mm) centimeters (cm) meters (m) meters (m) kilometers (km) kilometers (km)
To Obtain inches inches feet fathoms statute miles nautical miles
square meters (m2) square kilometers (km2) hectares (ha)
square feet square miles acres
liters (I) cubic meters (m3) cubic meters (m3)
gallons cubic feet acre-feet
milligrams (mg) grams (g) kilograms (kg) metric tons (t) metric tons (t)
ounces ounces pounds pounds short tons
kilocalories (kcal) Celsius degrees (OC)
British thermal units Fahrenheit degrees
U.S. Customary to Metric
inches inches feet (ft) fathoms statute miles (mi) nautical miles (nmi)
millimeters centimeters meters meters kilometers kilometers
square feet (ft2) square miles (mi2) acres
square meters square kilometers hectares
gallons (gal) cubic feet (ft3) acre-feet
liters cubic meters cubic meters
ounces (02) ounces (02) pounds (Ib) pounds (Ib) short tons (ton)
milligrams grams kilograms metric tons metric tons
British thermal units Ptu) Fahrenheit degrees ( F)
kilocalories Celsius degrees
CONTENTS
Page
PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i i i CONVERSIONTABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i v
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACKNOWLEDGMENTS v i
. . . . . . . . . . . . . . . . . . . . . . . . NOMENCLATURE/TAXONOMY/RANGE . . . . . . . . . . . . . . . . . . . . . . M O R P H O L O G Y / I D E N T I F I C A T I O N A I D S
. . . . . . . . . . . . . . . . . . . . REASON FOR INCLUSION I N THE SERIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L IFE HISTORY
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spawning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F e c u n d i t y
La rvae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J u v e n i l e s . . . . . . . . ..
A d u l t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GROWTH CHARACTERISTICS
. . . . . . . . . . . . . . . . . . . COMMERCIAL AND RECREATIONAL FISHERIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ECOLOGICAL ROLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Food H a b i t s
. . . . . . . . . . . . . . . . . . . . . . . . . . . Community Eco logy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D iseases
ENVIRONMENTAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tempera tu re
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S a l i n i t y . . . . . . . . . . . . . . . . . . . . . . . . . . . . D i s s o l v e d O x y g e n
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LITERATURE CITED
ACKNOWLEDGMENTS
I am g r a t e f u l t o Stuar t W i l k and Tony Pacheco o f the Nat ional Marine F isher ies Service, Sandy Hook, New Jersey, f o r t h e i r reviews o f the manuscript and h e l p f u l suggestions.
F igu re 1. Weakf ish (Cynoscion r e g a l i s ) ( f r o m Goode 1884).
WEAKFISH
S c i e n t i f i c name . . . . . . Cynoscion r ega l i s
P r e f e r r e d common name . . . . Weakf ish ( F i g u r e 1 )
Other common names . . . . Gray t r o u t , squeteague, sea t r o u t , t r o u t , t i d e - runner
Class . . . . . . . . . . Oste ich thyes Order . . . . . . . . . . Perc i fo rmes Fami ly . . . . . . . . . . Sciaenidae
Geographical range ......... Weakf ish occur a long t h e A t l a n t i c coas t o f t h e U n i t e d S ta tes f rom sou thern F l o r i d a t o Massachusetts Bay, s t r a y i n g o c c a s i o n a l l y t o Nova Sco- t i a and i n t o t h e eas te rn G u l f o f Mexico (Goode 1884; H i 1 debrand and Schroeder 1928; B ige low and Schroe- der 1953; Guest and Gunter 1958;
Leim and S c o t t 1966; St ruhsaker 1969; We ins te in and Yerger 1976; Chao 1978) . They a r e most abundant f rom No r t h C a r o l i n a t o New York ( F i g u r e 2 ) .
MORPHOLOGY/IDENTIFICATION AIDS
The f o l l o w i n g d e s c r i p t i o n i s t h a t o f Johnson (1978), summarized from Jordan and Evermann (1896) , Eigenmann (1901), H i l deb rand and Schroeder (1928) , Ginsburg (1929) , P e r l m u t t e r (1939) , Massmann ( 1963), Tagatz ( 1967), Mi 11 e r and Jorgenson (1973) , and Chao (1978).
Dorsa l r ays 24-29, moda l l y 27. Anal r a y s 10-13, moda l l y 12. Ver tebrae 25. G i l l r a k e r s 4-5 upper,lO-12 lower , and t y p i c a l l y 5 + 12. A p a i r o f l a r g e canine-1 i ke t e e t h a t t h e t i p o f upper
jaw and a row o f d i s t i n c t l y en la rged t e e t h i n t h e lower jaw. Body e l on - gate, moderate1 y compressed. Head long, snout po i n t ed . Mouth l a r g e , ob l i que , lower jaw p r o j e c t i n g , m a x i l - l a r y reach ing t o p o s t e r i o r marg in o f p u p i l o r beyond. Dorsa l f i n w i t h a deep no t ch between t h e sp inous and s o f t p o r t i o n s . Caudal emarg inate i n i n d i v i d u a l s l e s s than 300 mm t o t a l l e n g t h (TL) . Co lo r dark o l i v e green above w i t h t h e back and s i des v a r i o u s l y burn ished w i t h pu rp l e , lavender , green, b l ue , g o l d o r copper, and marked w i t h a l a r g e number o f smal l dark spo ts which appear as o b l i q u e s t r eaks r unn ing a long s c a l e rows above l a t e r a l 1 i ne . Lower su r f ace fo rward t o t i p o f jaw w h i t e o r s i l v e r y , sometimes i r i d e s c e n t . Dorsa l f i n s dusky, t h e lower edge y e l l o w i s h a t base. P e l v i c and ana l f i n s ye l l ow ; p e c t o r a l f i n o l i v e on o u t e r s i de , u s u a l l y y e l l o w on i n n e r s i de .
REASON FOR INCLUSION I N THE SERIES
The weak f i sh i s one o f t h e most abundant f i s h e s i n t h e e s t u a r i n e and nearshore wa te rs o f t h e A t l a n t i c coas t (Wi 1 k 1979). I t i s a va l uab le r ec rea - t i o n a l spec ies and a major component o f t h e g i l l - n e t , pound-net, h a u l - se ine , and t r a w l f i s h e r i e s a long t h e coas t (H i l deb rand and Schroeder 1928; W i l k 1981). Per iods o f h i g h l and ings have g e n e r a l l y been f o l l o w e d by sudden and p r e c i p i t o u s d e c l i n e s i n ca tch , t h e causes o f which a r e n o t known. Over f i s h i ng and h a b i t a t a1 t e r a t i o n s have been suggested as p o s s i b l e causes.
LIFE HISTORY
Spawning
Weakf ish mature a t age I through- o u t t h e i r geographic range; however,
F i gu re 2. General d i s t r i b u t i o n o f t h e l e n g t h a t m a t u r i t y d i f f e r s between weak f i sh a long t h e A t l a n t i c coas t o f n o r t h e r n weak f i sh (Delaware Bay and t h e U n i t e d S ta tes ( f r om W i l k 1976). n o r t h ) and weak f i sh f rom No r t h Caro-
l i n a . I n n o r t h e r n f i s h , females matured a t 256 mm and males a t 251 mn TL (Shepherd and Grimes 1984) ; i n Nor th C a r o l i n a females spawned a t 230 rnm and ma1 es a t 180 mm TL (Me r r i ne r 19'76).
Weakf ish spawn i n t he nearshore and e s t u a r i n e areas o f t h e coas t a f t e r t h e s p r i n g i nsho re m i g r a t i o n (Welsh and Breder 1923; H i l deb rand and Schroeder 1928). The spawning season o f weak f i sh i s e a r l . i e r and somewhat longer i n Nor th C a r o l i n a than i n areas t o t h e n o r t h ; i t extends f rom March t o September, and peaks f rom A p r i l t o June (Me r r i ne r 1976). I n t h e New York B i g h t (Delaware Bay t o New York) , t h e season extends f rom May t o m id - Ju l y (Shepherd and Grimes 1984). Two spawning peaks a re r e p o r t e d f o r weak f i sh i n New York B i g h t e s t u a r i e s : t he e a r l i e r mid-May peak, a t t r i b u t e d t o t h e l a r g e s t i n d i v i d u a l s o r " t i d e - runners , " i s f o l l o w e d by a June peak developed by sma l l e r f.i sh (Shepherd and Grimes 1984).
Fecund i t y
Ls t ima tes o f f e c u n d i t y f o r southern weak f i sh d i f f e r f rom those f o r f i s h f rom t h e New York B i g h t . A weak f i sh 500 mm TL f rom No r t h C a r o l i n a produced 2,051,080 ova, whereas a n o r t h e r n f i s h o f t h e same l e n g t h produced o n l y 306,159 ova (Me r r i ne r 1976; Shepherd and Grimes 1984) . The f o 1 lowing r e l a t i o n s h i p s between f e c u n d i t y ( F ) and s tandard l e n g t h (SL) i n m i l l i - meters , t o t a l l e n g t h (TL) i n m i l l i - mete rs , we igh t (W) i n grams, and gu t - t e d we igh t (GW) i n grams, where I n i s t h e n a t u r a l l o g a r i t h m and r i s t h e c o e f f i c i e n t o f de te rm ina t i on , were p resen ted f o r weak f i sh i n No r t h C a r o l i n a (Me r r i ne r 1976):
I n F = -2.154 + 2.776 I n SL;
I n F = -1.884 + 2.642 I n TL;
and t h e New York B i g h t (Shepherd and Grimes 1984) :
I n F = -16.322 + 4.659 I n TL;
I n F = 1.975 + 1.542 I n GW;
Larvae
The embryology and l a r v a l deve l - opment o f weak f i sh were descr ibed by Welsh and Breder (1923) , Pearson (1941) , Harmic (1958) , Sco t ton e t a l . (1973), Lippson and Moran (1974) , Johnson (1978), and Powles and Stender (1978) . Hd tch ing occurs i n 36-40 hours a t 20-21 O C (Welsh and Breder 1923). Weakf ish l a r v a e range f rom 1.5 t o 1.75 mm TL a t ha t ch i ng and become demersal by 8 mm TL (Welsh and Breder 1923; Pearson 1941). Weakfish l a r v a e have been c o l l e c t e d i n nearshore waters t o 70 km o f f s h o r e i n coas ta l i ch thyop lank ton surveys ( B e r r i e n e t a l . 1978).
Juveni 1 es
The use o f e s t u a r i n e areas as nu r se r y grounds by weak f i sh i s w e l l documented. J u v e n i l e s a re c o l l e c t e d most f r e q u e n t l y i n t r a w l sampl ing o f t he deeper waters o f r i v e r s , bays, and sounds, r a t h e r than i n beach se i ne c o l l e c t i o n s f rom shoal areas (Greel ey 1939; Massmann e t a l . 1958; Schwartz 1961, 1964a; R ichards and Castagna 1970; Thomas 1971; Chao and Musick 1977).
Ex tens ive sampl ing o f Nor th Caro- l i n a sounds r evea led t h a t j u v e n i l e weak f i sh were most abundant i n a reas des igna ted by t h e Nor th C a r o l i n a D i v i s i o n o f Mar ine F i s h e r i e s as secon- dary nu r se r y areas (usua l 1 y s h a l l ow bays o r n a v i g a t i o n channels cha rac te r -
i z e d by moderate depths, s l i g h t l y h i g h e r s a l i n i t i e s , and presence o f sand and/or sand-grass bot toms) r a t h e r t h a n i n p r i m a r y n u r s e r y areas ( s h a l l o w t r i b u t a r i e s o f l o w s a l i n i t y and mud and/or mud-grass bo t tom) ( S p i t s b e r g e n and W o l f f 1974; P u r v i s 1976) . I n Chesapeake Bay and Delaware Bay j u v e n i l e w e a k f i s h m i g r a t e f rom h i g h t o low s a l i n i t y a reas th roughou t t h e summer, r e t u r n t o h i g h s a l i n i t y w a t e r s i n f a l l , and l e a v e t h e e s t u a r i e s by December ( H i l d e b r a n d and Schroeder 1928; Massmann e t a l . 1958; Thomas 1971; Chao and Musick 1977).
J u v e n i l e w e a k f i s h a r e d i s t r i b u t e d a long t h e c o a s t f r o m Long I s l a n d t o N o r t h C a r o l i n a a t dep ths o f 9-26 m i n l a t e summer and f a 1 1 ( C l a r k e t a l . 1969) . Young-of - the-year w e a k f i s h were caugh t i n ocean t r a w l su rveys a l o n g t h e c o a s t o f N o r t h C a r o l i n a i n 1968-1981 a t dep ths o f 9-18 m d u r i n g f a l l and w i n t e r , and f rom N o r t h C a r o l i n a t o F l o r i d a a t depths o f 9-11 m i n w i n t e r and e a r l y s p r i n g ( W i l k and S i l ve rman 1976) .
A d u l t s
A d u l t w e a k f i s h m i g r a t e seasonal 1 y between i n s h o r e and o f f s h o r e w a t e r s (Welsh and Breder 1923; M e r r i n e r 1973; W i 1 k 1976, 1979, 1980) . Warming o f c o a s t a l wa te rs i n s p r i n g prompts an i n s h o r e and n o r t h e r l y m i g r a t i o n o f a d u l t s f r o m t h e i r w i n t e r i n g grounds t o sounds, bays, and e s t u a r i e s ( F i g u r e 3 ) . The l a r g e r f i s h move i n s h o r e f i r s t and t e n d t o congregate i n t h e n o r t h e r n p a r t o f t h e range ( W i l k and S i l ve rman 1976; W i l k e t a l . 1977) . Catch r e c o r d s f r o m t h e pound-net and h a u l - s e i n e f i s h e r i e s i n Delaware Bay, Chesapeake Bay, and Paml ico Sound i n d i c a t e t h a t t h e l a r g e f i s h a r e f o l - lowed by a second group o f smal l e r w e a k f i s h i n summer ( H i g g i n s and Pedrson 1928; Massmann 1963; Da ibe r and Smi th 1971; S h o l a r 1979; DeUr ies 1980, 1981) . S h o r t l y a f t e r t h e i r F i g u r e 3. Movements o f t h e w e a k f i s h i n i t i a l appearance, w e a k f i s h r e t u r n t o a l o n g t h e A t l a n t i c c o a s t o f t h e U n i t e d t h e l a r g e r bays and p o s s i b l y t o t h e S t a t e s d u r i n g s p r i n g and summer ( f r o m ocean t o spawn. I n n o r t h e r n a reas a W i l k 1976) .
4
g r e a t e r p r o p o r t i o n o f t he a d u l t s spend t h e summer i n ocean wate rs r a t h e r than i n e s t u a r i e s .
As wate r temperatures d e c l i n e i n f a 1 1, weak f i sh form aggrega t ions and move o f f s h o r e and g e n e r a l l y southward a long t h e coas t ( N e s b i t 1954; Massmann e t a ) . 1958; . W i l k 1976; W i 1 k and S i l- verman 1976) ( F i g u r e 4 ) . The Con t i - n e n t a l She l f f rom Chesapeake Bay t o Cape Lookout, NC, appears t o be t h e major w i n t e r i n g ground f o r weakf ish. A s tudy o f t h e w i n t e r t r a w l f i s h e r y o f f t he V i r g i n i a and N o r t h C a r o l i n a coas ts i n d i c a t e d t h a t most weak f i sh were caught i n t h e sou thern f i s h i n g a rea between Ocracoke I n l e t and Bodie I s l a n d , NC, a t depths o f 18-55 m (Pearson 1932). Some weak f i sh may remain i n inshore wa te rs th roughou t t h e w i n t e r f rom Nor th Caro l i n a southward (Goode 1884; H igg i ns and Pearson 1928; H i l deb rand and Cable 1934).
GROWTH CHARACTERISTICS
Weakf ish growth i s p a r t i c u l a r l y r a p i d d u r i n g t h e f i r s t year . I n Dela- ware Bay, j u v e n i l e s may grow f rom 20 t o 35 mm/month d u r i n g June-September ( I c h t h y o l o g i c a l Assoc ia tes 1980) and may a t t a i n l e n g t h s r ang ing f rom 100 t o 175 mm TL th roughou t t h e range. The v a r i a b i l i t y o f s i z e s w i t h i n yea r c lasses r e s u l t s f rom t h e extended spawning season. Massmann e t a1 . (1958) and Thomas (1971) found two d i s t i n c t s i z e groups o f young-of- the- year weak f i sh i n f a 1 1 i n Chesapeake Bay (45 and 85 mm) and Delaware Bay (30-40 and 110-130 mm). T h i s appar- e n t l y r e f l e c t s two separate spawning peaks. Thomas (1971) d i d n o t f i n d a bimodal l e n g t h d i s t r i b u t i o n f o r a d u l t weak f i sh which may be due t o d i f f e r e n - t i a l m o r t a l i t y o f late-spawned weak- f i s h o r t o compensatory growth.
Weakf ish age and growth s t u d i e s F i gu re 4. Movements o f t he weak f i sh i n d i c a t e d geographic v a r i a t i o n s i n a long t h e A t l a n t i c coas t o f t h e U n i t e d growth, w i t h a p a t t e r n of i n c r e a s i n g S ta tes d u r i n g f a l l and w i n t e r ( f r o m s i z e toward t h e n o r t h e r n end o f t h e W i l k 1976).
range ( T a b l e 1 ) . Shepherd and Grimes (1.983) found t h a t n o r t h e r n w e a k f i s h c o l l e c t e d between Cape Cod, MA, and Ocean C i t y , MD, were l a r g e s t a t each age and a t t a i n e d a g r e a t e r maximum s i z e and l o n g e v i t y (810 mm TL a t age X I ) . S i z e a t age o f w e a k f i s h c o l l e c - t e d between V i r g i n i a Beach, VA, and Cape Fear , NC, was l o w e s t (370 mm TL a t age 111) and s i m i l a r t o t h a t r e p o r t e d b y T a y l o r (1916) and M e r r i n e r (1973) . I n w e a k f i s h f rom Chesapeake Bay (Ocean C i t y , MD, t o V i r g i n i a Beach, VA) s i z e a t age and maximum s i z e were i n t e r m e d i a t e and were comparable t o what Seagraves (1981) r e p o r t e d f o r Delaware Bay i n 1979. Shepherd and Grimes (1983) suggested t h a t t h e s e g rowth v a r i a t i o n s may r e s u l t f rom d i f f e r i n g a1 l o c a t i o n s o f energy t o somat i c g rowth a c c o r d i n g t o env i ronmenta l and m i g r a t o r y requ i remen ts . Growth o f w e a k f i s h o f s o u t h e r n o r i g i n may a l s o be l i m i t e d by p r e y a v a i l a b i 1 i t y o r by g e n e t i c d i f f e r e n c e s .
Records o f w e a k f i s h s i z e a t v a r i o u s ages show d i f f e r e n c e s ove r t i m e ( T a b l e 2 ) . A comparison o f female w e a k f i s h f rom t h e New York B i g h t showed t h a t age-IV females i n 1929 averaged 340 mm
TL compared t o 480 mm TL i n 1952 and 580 mm TL i n 1980 ( P e r l t n u t t e r e t a l . 1956; Shepherd and Grimes 1983) . Known l o n g e v i t y was 8 y r i n 1929, 6 y r i n 1952, and 11 y r i n 1980. S i m i l a r changes i n g rowth and l o n g e v i t y were r e p o r t e d f o r w e a k f i s h i n Delaware Bay (Seagraves 1981).
Growth o f w e a k f i s h was d e s c r i b e d by t h e von B e r t a l a n f f y g rowth curve:
where It i s l e n g t h a t age t, Lm i s t h e a s y m p t o t i c l e n g t h , K i s t h e Brody g rowth c o e f f i c i e n t , t i s age, and t i s t h e h y p o t h e t i c a l age a t wh ich t h ? f i s h wou ld have been z e r o l e n g t h . Von B e r t a l a n f f y g rowth parameters showed a t r e n d o f dec reas ing v a l u e s o f Lm f rom n o r t h t o sou th , w i t h t h e e x c e p t i o n o f Delaware Bay w e a k f i s h i n 1979 (Seagraves 1981; Shepherd and Grimes 1983) ( T a b l e 3 ) . A l a r g e r a s y m p t o t i c . l eng th was o b t a i n e d f o r Delaware Bay w e a k f i s h i n 1979 t h a n i n 1956.
Leng th -we igh t r e l a t i o n s h i p s have been deve loped f o r w e a k f i s h f r o m t h r o u g h o u t t h e M i d - A t l a n t i c Region
Tab le 1. Mean t o t a l l e n g t h s (mm) a t age o f w e a k f i s h f rom t h r e e r e g i o n s ( f r o m Shepherd and Grimes 1983) .
Ocean C i t y , MD V i r g i n i a Beach, VA Cape Fear , NC t o t o t o
Cape Cod, MA Ocean C i t y , MD V i r g i n i a Beach, VA Age 1979-81 1979-81 1979-81
qroup Ma1 e Female Ma1 e Femal e Male Fema 1 e
Table 2 . Mean t o t a l l e n g t h s (mm) a t age o f weak f i sh .
Chesa- peake
a P e r l m u t t e r e t a l . (1956) . c T a y l o r (1916) . b Seagraves (1981) . d M e r r i n e r (1973) * TL approx imated by: TL = 1.21 SL.
Table 3. Von B e r t a l a n f f y growth parameters f o r w e a k f i s h (sexes combined) where L i s t h e a s y m p t o t i c l e n g t h i n m i l l i m e t e r s (SL) (S tandard l e n g t h approx imated by: s E = T L / ~ . z ~ ) , to i s t h e h y p o t h e t i c a l age a t which t h e f i s h would have been z e r o l e n g t h , K i s t h e Brody growth c o e f f i c i e n t , and W i s w e i g h t i n grams.
Area
Cape Cod, MA - Ocean C i t y , M D ~
Ocean C i t y , MD - V i r g i n i a Beach, V A ~ 567 0.051 0.350 3026.0
V i r g i n i a Beach, XA - Cape Fear, N.C. 331 -1.270 0.550 608.3
Delawgre Bay 1956 315 -
Delawgre Bay 1979 735 0.084 0.236 -
a Shepherd and Grimes (1983) . b Seagraves (1981) .
( T a b l e 4 ) . M e r r i n e r (1973) found M e r r i n e r 1973; W i l k 1981) . D u r i n g s i g n i f i c a n t l e n g t h - w e i g h t d i f f e r e n c e s t h e p e r i o d 1940-49, pound n e t s , h a u l between males and fema les wh ich he se ines , g i l l n e t s , and t r a w l s t o o k a t t r i b u t e d t o p r o p o r t i o n a t e l y g r e a t e r a p p r o x i m a t e l y 63%, 11%, 3%, and 23% o f development o f o v a r i a n t i s s u e r e l a t i v e t h e t o t a l c a t c h , r e s p e c t i v e 1 y . Dur - t o t e s t i c u l a r t i s s u e . i n g 1970-79, t h e c o n t r i b u t i o n o f t h e s e
same f o u r gear t y p e s was 20X, 11%, 9%, and 60%, r e s p e c t i v e l y ( W i l k 1981) .
COMMERCIAL AN11 RECREATIONAL FISHERIES
The p r i n c i p a l commerci a1 methods used t o h a r v e s t w e a k f i s h i n c l u d e t r a w l s , pound n e t s , hau l se ines , and g i l l n e t s . I n a d d i t i o n , w e a k f i s h a r e caugh t i n p u r s e s e i n e s , f l o a t i n g t r a p s , trammel n e t s , f y k e n e t s , hoop n e t s , and hand l i n e s . G e n e r a l l y t h e s e f i s h e r i e s can be c l a s s i f i e d as m ixed o p p o r t u n i s t i c f i s h e r i e s t h a t concen- t r a t e d i r e c t 1 y on w e a k f i s h f o r b r i e f p e r i o d s ( W i l k and Brown 1982) . D u r i n g t h e m id -19701s , h igh -speed p e l a g i c t r a w l s i n t h e f o r m o f p a i r e d t r a w l s and m id -wa te r t r a w l s were i n t r o d u c e d i n t h e New Jersey-Delaware area.
A l t h o u g h t h e methods used t o h a r v e s t w e a k f i s h f o r f o o d have e s s e n t i a l l y remained t h e same, t h e r e have been s i g n i f i c a n t s h i f t s i n t h e c o n t r i b u - t i o n s o f t r a w l s and pound n e t s d u r i n g t h e p a s t 40 y r ( P e r l m u t t e r 1959;
Commerci a1 1 a n d i ngs o f w e a k f i s h have f l u c t u a t e d w i d e l y s i n c e t h e l a t e 1 8 0 0 ' s . Two peaks i n l a n d i n g s have o c c u r r e d s i n c e 1940, an a l l - t i m e h i g h o f 18,800 t i n 1945 and 16,300 t i n 1980. The d i s t r i b u t i o n o f w e a k f i s h l a n d i n g s has s h i f t e d h i s t o r i c a l l y f r o m one g e o g r a p h i c a r e a t o a n o t h e r ( W i l k 1980) ( F i g u r e 5 ) . The Chesapeake Bay r e g i o n (Mary land and V i r g i n i a ) c o n t r i - b u t e d most t o t h e t o t a l w e a k f i s h l a n d - i n g s i n t h e 1 9 4 0 1 s , f o l l o w e d by t h e M i d - A t l a n t i c Reg ion (New York , New Je rsey , and De laware ) , and t h e South A t l a n t i c Region ( p r i m a r i l y N o r t h Caro- l i n a ) . Weakf ish l a n d i n g s remained l o w i n a l l r e g i o n s t h r o u g h o u t t h e 1 9 5 0 ' s and 1 9 6 0 ' s . S i n c e 1971, South A t l a n t i c Reg ion l a n d i n g s have exceeded t h o s e i n one o r b o t h o f t h e n o r t h e r l y r e g i o n s . The s h i f t i n c a t c h t o t h e South A t l a n t i c Reg ion i s p r o b a b l y more
Tab le 4 . Leng th -we igh t r e l a t i o n s h i p s f o r w e a k f i s h u s i n g t h e e q u a t i o n : l o g W ( g ) = l o g a + b l o g L (mm), where W i s w e i g h t i n grams, L i s l e n g t h i n m i l l i m e t e r s (*TL, +SL), and a and b a r e c o n s t a n t .
Length L o c a t i o n Sex Log a b r n range (mm)
New York B i g h t a * Combined -4.877 2.948 0.99 666 59-768
Cape Cod, MA b, Ocean C i t y , MD Combined -5.030 2.976 0.99 418
Delaware BayC+ Combined -4.423 2 .861 0.99 182 195-725
N o r t h C a r o l i n a d+ Male -4 .558 2 .851 0.99 482 Femal e -4.343 2.946 0.99 610 Combined -4.374 2.934 0.99 1,650
a From W i l k (1979)l. b From Shepherd and Grimes (1983) . c From Seagraves (1981) . d From M e r r i n e r (1973) .
8
4- MIDDLE ATLANTIC
10- CHESAPEAKE
z 8- SOUTH ATLANTIC (North Carolina)
6-
4-
YEARS
F i gu re 5. U . S . commercial l and ings o f weak f i sh by geographic r eg i on .
a r e f l e c t i o n o f t h e inc reased mob i l i t y o f t h e Nor th C a r o l i n a f . i sh i t i g f l e e t , and a concomi tant s h i f t i n t h e cen te r o f l and ings t o No r t h Ca ro l i na , r a t h e r than an ac tua l s h i f t i n d i s t r i b u t i o n o f weak f i sh ( W i l k 1981) .
Weakf ish have a l s o been impo r t an t t o t h e r e c r e a t i o n a l f i s h e r y s i nce a t l e a s t t h e 1800 's (Goode 1884). Ang le rs take weak f i sh f rom boa ts w h i l e t r o l l - i n g and d r i f t f i s h i n g , and f rom boa ts and shore w h i l e c a s t i n g , l i v e b a i t f i s h i n g , j i g g i n g , s t i l l f i s h i n g , and chumming, p r i m a r i l y d u r i n g t h e warmer months o f t h e year (Freeman and Wal- f o r d 1974a, b, c , 1976a, b ) . Data from t h e Na t i ona l Mar ine F i s h e r i e s Serv ice Mar ine Recrea t iona l F i she ry S t a t i s t i c s Survey a l s o i n d i c a t e a peak i n t w c r e a t i o n a l 1 andings i n 1980 (20,544 t ) f o l l o w e d by a sharp d e c l i n e by 1982 (Tab le 5 ) .
Table 5. Es t imated number and we igh t o f weak f i sh caught by r e c r e a t i o n a l f ishermen i n t h e M i d - A t l a n t i c Region (New Y o r k - V i r g i n i a ) 1979-87. (Na t i ona l Mar ine F i s h e r i e s Se rv i ce Mar ine Rec- r e a t i o n a l F i she ry S t a t i s t i c s Survey, A t l a n t i c and G u l f Coasts 1979-87).
Year Number Weight ( thousands) ( t )
* P r e l i m i n a r y da ta
ECOLOGICAL ROLE
Food H a b i t s
Weakf ish feed p redominan t l y on penaeid and mysid shr imps, anchovies, and c l u p e i d f i s h e s (Welsh and Breder 1923; Thomas 1971; M e r r i n e r 1975; S t i c kney e t a l . 1975; M ichae ls 1984). A s h i f t o f food h a b i t s w i t h growth was r e p o r t e d by Thomas (1971) , M e r r i n e r (1975) , and S t i c kney e t a l . (1975) . Young weak f i sh feed mos t l y on mys id shr imp and anchovies; o l d e r weak f i sh feed on whatever c l u p e i d spec ies a r e abundant i n an area. M ichae ls (1984) r e p o r t e d t h a t anchovies ( r a t h e r than c l u p e i d s ) were t h e s i n g l e most impor- t a n t p rey f i s h o f weak f i sh c o l l e c t e d o f f s h o r e (dep ths > 6 m). Canniba l ism was r e p o r t e d t o be s i g n i f - i c a n t i n weak f i sh (Thomas 1971; Me r r i ne r 1975). Weakf ish feed p r i - m a r i l y between dusk and dawn (Lascara 1981; M ichae ls 1984). Chao and Musick (1977) c o r r e l a t e d f eed ing s t r u c t u r e s w i t h t h e food h a b i t s o f j u v e n i l e sc i aen ids . The weak f i sh has an o b l i q u e mouth t h a t enables i t t o cap-
t u r e p e l a g i c p rey f rom above and i n f r o n t of i t . Other adap ta t i ons f o r success fu l p r e d a t i o n i n c l u d e a p a i r o f l a r g e canine t e e t h a t t h e t i p of t h e upper jaw f o r g rasp ing l a r g e r swimming p rey and a f u s i f o r m body shape f o r f a s t p u r s u i t .
A s t udy o f f i s h p reda to r -p rey i n t e r a c t i o n s i n areas o f ee l g rass (Zos te ra mar ina) i n Chesapeake Bay i n d i c a t e d t h a t weak f i sh a re impo r t an t t o p ca rn i vo res i n t h i s h a b i t a t (Lascara 1981). F i e l d da ta and l a b - o r a t o r y observa t ions have suggested t h a t weak f i sh f o rage a long t h e p e r i - phery o f e e l g rass beds d u r i n g p e r i o d s o f low l i g h t (dusk t o dawn). The h i g h percentage o f b l u e crabs ( C a l l i- nec tes sap idus) ( 40 ) and spo t ( L e i o - stomus xan thurus ) (18) i n weak f i sh stomachs i n d i c a t e d t h a t some f eed ing occu r red i n ee l g rass beds, s i n c e these an imals were cons i de rab l y more abun- dan t t h e r e than a t ad j acen t non-vege- t a t e d sampl ing s i t e s . The l a c k o f ee l g rass i n stomachs and t h e o b l i q u e mouth p o s i t i o n o f t h e spec ies sugges- ted , however, t h a t weak f i sh f eed pe l a - g i c a l l y and n o t deep w i t h i n t h e vege- t a t i o n . I n l a b o r a t o r y exper iments , weak f i sh cap tu red fewer p rey as t h e percentage o f v e g e t a t i v e cover i n - creased (Lascara 1981) .
Community Ecology
Surveys a long t h e A t l a n t i c coas t i n d i c a t e d t h a t e s t u a r i e s p r o v i d e feed- i n g a reas and spawning grounds f o r a d u l t weak f i sh and a re impo r t an t nu r se r y areas f o r t h e young. S tud i es i n Delaware Bay (Thomas 1971) and Chesapeake Bay (Chao and Musi ck 1977) showed t h a t seve ra l spec ies o f sc iaen. ids, i n c l u d i n g weak f i sh , s i l v e r perch ( B i i r d i e l l a -chrysoura)-, spo t , c roaker (Micropogonias undu la tus ) , and b l a c k drum (Pogoni as c romis ) were ab l e t o c o e x i s t i n t h e e s t u a r i e s : p robab le reasons i n c l u d e d i f f e r e n c e s i n s p a t i a l and tempora l d i s t r i b u t i o n , re1 a t i v e abundance (abundances o f dominant compe t i t o r s may be reduced by p h y s i c a l d i s t u rbance o r p r e d a t i o n ) ,
and f ood h a b i t s . Juven i l es o f these spec ies e n t e r t h e e s t u a r i e s a t d i f f e r e n t t imes o f t h e year , and w i t h - i n a g i ven pe r i od , t h e h i g h e s t ca tches o f each spec ies a re i n d i f f e r e n t areas and depths. A l though weak f i sh and c roaker bo th p r e f e r t h e deeper water i n o r near channels, c roaker do n o t e n t e r e s t u a r i n e areas u n t i l f a l l a f t e r most weak f i sh have l e f t . D i f f e r e n c e s i n t h e morphology o f t h e f eed ing apparatus enable each spec ies t o f eed a t d i f f e r e n t l e v e l s o f t h e water column.
Diseases
Mahoney e t a l . (1973) r e p o r t e d t h a t weakf ish, espec i a l 1 y j u v e n i l e s , a re one o f t h e most s u s c e p t i b l e spec ies t o t he " f i n r o t " d i sease of mar ine and euryha l i n e f i s h e s i n t h e New York B i g h t . The c o n s i s t e n t and most s t r i k i n g f e a t u r e o f t h e d isease i n weak f i sh i s nec ros i s o f t h e caudal f i n f o l l o w e d by invo lvement on t h e o t h e r f i n s . P o l l u t i o n i s suspected t o have a r o l e i n t h e d isease. T h i s d isease has a l s o been observed i n weak f i sh f rom Delaware Bay and Georgia.
ENVIRONMENTAL REQUIREMENTS
Temperature
Weakf ish eggs i n a1 1 s tages o f development were c o l l e c t e d i n Peconic Bay, NY, and Nar raganse t t Bay, R I , a t temperatures o f 12-24 "C ( P e r l m u t t e r 1939; Herman 1963) . Labora to ry t e s t s i n d i c a t e d t h a t ha t ch i ng o f weak f i sh eggs was op t ima l between 18 and 24 "C ( t iarmic 1958).
Weakf ish have been c o l l e c t e d over a temperature range o f 9.5 t o 30.8 "C (Massmann e t a l . 1958; R ichards and Castagna 1970; M e r r i n e r 1976). I n areas o f h i g h e s t abundance o f j u v e n i l e weak f i sh i n Delaware Bay, water temperatures ranged f rom 28.0 "C i n J u l y t o 17.2 "C i n October ('Thomas
1971) . Decreas ing wa te r tempera tu res i n f a l l appear t o i n i t i a t e movement o f most w e a k f i s h o u t o f t h e e s t u a r i e s t o deeper wa te r . O lde r w e a k f i s h appear t o precede t h e young o f t h e y e a r i n moving o u t o f t h e e s t u a r i e s ( H i l d e b r a n d and Cable 1934; Massmann e t a l . 1958; Thomas 1971) .
Only a few w e a k f i s h have been c o l l e c t e d a t tempera tu res below 10 OC i n Delaware Bay o r Chesapeake Bay (Massmann e t a l . 1958; Abbe 1967; Thomas 1971) . H i l d e b r a n d and Cable (1934) r e p o r t e d t h a t some sma l l w e a k f i s h (122-182 mm TL) remained i n N o r t h C a r o l i n a e s t u a r i e s and nearshore c o a s t a l wa te rs y e a r - r o u n d e x c e p t d u r - i n g b r i e f c o l d snaps. Dead and numb w e a k f i s h were seen i n s h a l l o w w a t e r s when w a t e r tempera tu res sudden1 y dropped t o 5 OC ( S m i t h 1907; H i l d e - b rand and Cab1 e 1934 ) .
Schwar tz (1964b) s u b j e c t e d f i v e w e a k f i s h c o l l e c t e d a t 20.7 O C t o normal w i n t e r w a t e r tempera tu res . Swimming speed s lowed d r a s t i c a l l y as t h e w a t e r tempera tu re approached 10 oC, f e e d i n g ceased a t 7.9 oC, and a l l f i s h d i e d a t 3 .3 OC. W i l k (1979) r e p o r t e d t h a t as tempera tu re was g rad - u a l l y i n c r e a s e d (0 .05 o C / ~ ) f r o m t h e a c c l ima ted tempera tu re range o f 19-20 O C t o a l m o s t 29 oC, w e a k f i s h showed a 35% i n c r e a s e i n swimming speed accom- p a n i e d by t i g h t e r and more f r e q u e n t school i ng; however, as t h e f i s h became a c c l i m a t e d t o 29 O C t h e i r a c t i v i t y decreased t o a p o i n t s i m i l a r t o t h a t b e f o r e t h e tempera tu re was inc reased . T h i s i n c r e a s e d a c t i v i t y may h e l p t o move t h e an ima ls f r o m r e g i o n s o f ad- v e r s e h i g h tempera tu re .
S a l i n i t y
Weakf ish a r e e u r y h a l i n e and have been c o l l e c t e d a t s a l i n i t i e s r a n g i n g o f 0 .1 t o 32.3 p p t (Massmann e t a l . 1958; R i c h a r d s and Castagna 1970; W i l k and S i l ve rman 1976; W i l k e t a l . 1977) . Harmic (1958) c o l l e c t e d eggs and l a r v a e i n Delaware Bay a t s a l i n i t i e s o f 1 2 . 1 t o 31.3 p p t . J u v e n i l e s have been t a k e n i n s a l i n i t i e s f rom 0 .1 t o 31.7 p p t , b u t a reas o f most abun- d a n t ca tches had s a l i n i t i e s o f 2.0 p p t i n June t o 10.8 p p t i n August (Mass- mann e t a l . 1958; R i c h a r d s and Casta- gna 1970; Thomas 1971) . A d u l t s were c o l l e c t e d over a s a l i n i t y range o f 6.6 t o 32.3 p p t ( R i c h a r d s and Castagna 1970; W i l k and S i l ve rman 1976; W i l k e t a l . 1977) .
D i s s o l v e d Oxygen
I n f o r m a t i o n on r e l a t i o n s h i p s be- tween d i s s o l v e d oxygen and weakf i sh t o 1 erance o r p r e f e r e n c e s i s scarce. Thomas (1971) r e p o r t e d t h a t u p r i v e r movement o f j u v e n i l e w e a k f i s h i n t h e Delaware R i v e r was b l o c k e d by l o w oxygen c o n c e n t r a t i o n s (1.0-2.3 ppm). I n a reas o f t h e most abundant c a t c h e s o f j u v e n i l e w e a k f i s h i n Delaware Bay, mean d i s s o l v e d oxygen ranged f r o m 4.2 ppm i n J u l y t o 7.4 ppm i n October.
P o l l u t i o n
I n a model o f t h e e f f e c t s o f p o l l u t i o n on a mult ispecies group o f coastal f ishes , weakfish showed r e 1 a ' t i v e l y 1 arge depressions i n abundance i n response t o chronic o r acute pol 1 u t i o n , but then recovered r e l a t i v e l y q u i c k l y ( i n 6-10 years) (Schaaf e t a l . 1987).
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Species P r o f i l e s : L i f e H i s t o r i e s and Environmental Requirements o f Coasta l F ishes and I n v e r t e b r a t e s ( M i d - A t l a n t i c ) - - W e a k f i s h
10272 -101
7. Au(hor(s) I L Petformin# Orlanlzatlon Re@. No.
REPORT DOCUMENTATION 1. RE'Om 2. PAGE I B ~ 01 O g i c d l Repor t 82( 11.109)d
N o r t h C a r o l i n a D i v i s i o n o f Mar ine F i s h e r i e s P.O. Box 769
S. Raclpl*nt's Accasslon No.
I Morehead City, NC 28557 I -- -- 12. Spon.orln8 O~anlzatlon Name and Addmsn
(I2)
U.S. Department o f t h e I n t e r i o r U. S. Army Corps of Engineers Washington, DC 20240 Waterways Exper iment S t a t i o n F i s h and W i l d l i f e S e r v i c e P.O. Box 631 N a t i o n a l Wetlands Research Center Vicksburp, MS 39180
I
13. Supplementafy Note* I U.S. Army Corps o f Engineers Report No. TR EL-82-4
16. Ahtract (Limit: 200 word.) I 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, morpholog.~, range, l i f e h i s t o r y , and env i ronmenta l requ i rements o f c o a s t a l a q u a t i c spec ies . They a r e designed t o a s s i s t i n env i ronmenta l impact assessment. Weakfish a r e one o f t h e most abundant f i s h e s i n t h e e s t u a r i n e and nearshore waters o f t h e A t l a n t i c coast . Weakf ish mature a t age I t h rouqhou t t h e i r range and spawning takes p l a c e i n c o a s t a l and e s t u a r i n e waters from March t o September. J u v e n i l e s u t i l i z e t h e deeper areas w i t h i n e s t u a r i e s as n u r s e r y grounds, m i g r a t e f rom h i g h t o low s a l i n i t y areas th rouqhou t t h e summer, r e t u r n t o h i g h s a l i n i t y areas i n f a l l , and most l eave t h e e s t u a r i e s by l a t e f a l l . Some may remain i n e s t u a r i n e and nearshore c o a s t a l waters i n w i n t e r , p a r t i c u l a r l y i n sou the rn areas. A d u l t weak f i sh m i g r a t e seasona l l y , n o r t h i n s p r i n g and sou th i n f a l l and between i n s h o r e and o f f s h o r e waters . Growth r a t e s , maximum s i z e , and l o n g e v i t y o f weak f i sh a r e h i g h e r a t t h e n o r t h e r n end o f t h e range. Weakfish a r e an i m p o r t a n t r e c r e a t i o n a l and commercial spec ies i n t h e M i d - A t l a n t i c . Weakfish feed predominant ly on mys id shr imp and anchovies as j u v e n i l e s , and on c l u p e i d s and anchovies as a d u l t s . Weakfish have been found ove r a tempera ture range o f 9.5 t o 30.8 "C. J u v e n i l e weak f i sh have been found ove r a w i d e r s a l i n i t y range (0.1-31.7 p p t ) than a d u l t s (6.6-32.3 p p t ) .
E s t u a r i e s Temperature Fishes Growth S a l i n i t y H a b i t a t requ i rements L i f e c y c l e s D isso l ved oxygen Food h a b i t s F i s h e r i e s
b. IdentlRen/OD.n.Ended Terms
Weakfish Cynoscion r e q a l i s Spawning
I 1 U n c l a s s i f i e d (5.- ANSI-239.IO OPTIONAL FORM 272 (4-71
(Formerly NTIE35) hpastment of Commwu
C. COSATl fl*ld/Group
21. NO. of Pal*.
17 -- a m c e
1 L Avallablllty Statement
Unl i m i t e d
19. Scurity Class (This R*mrO
U n c l a s s i f i e d 20. kcurity Class (This Paw)
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