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Biological Report 82(11.100) March 1989

REFERENCECOPY

700 Cajun Dome Boulevard

Lafayette, Louisiana 70506

TR EL-82-4

Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates ( Mid-Atlantic)

BLUE CRAB

Fish and Wildlife Service U.S. Department of the Interior

Coastal Ecology Group Waterways ~xperiment Station U.S. Army Corps of Engineers

Bi 01 ogi cal Report 82( 11.100) TR EL-82-4 March 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 Coastal Fishes 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 ) BLUE CRAB

Jennifer H i l l , Dean L. Fowler, and Michael J. Van Den Avyle Georgia Cooperative F i s h and W i l d l i f e Research U n i t School o f Forest Resources U n i v e r s i t y o f Georgia Athens, GA 30602

Project Officer David Moran U.S. F i s h and W i l d l i f e Service National Wetlands Research Center 1010 Gause Boulevard S l i d e l 1 , LA 70458

U.S.

Performed f o r Army Corps o f Engineers Coastal Ecology Group Waterways Experiment S t a t i o n Vicksburg, M 39180 S and

U.S. Department o f the I n t e r i o r F i s h and W i l d l i f e Service Research and Development N a t i o n a l Wetlands Research Center Washington, D 20240 C

DISCLAIMER The mention o f t r a d e nmes i n t h i s r e p o r t does n o t c o n s t i t u t e endorsement n o r recommendation f o r use by t h e U.S. Fish and W i l d l i f e Service o r Federal Government.

T h i s s e r i e s may be referenced as f o l l o w s : Species p r o f i l e s : l i f e h i s t o r i e s U.S. F i s h and W i l d l i f e Service. 1983-19 and environmental requirements o f c o a s t a 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.

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T h i s p r o f i l e may be c i t e d as f o l l o w s : H i l l , J., D.L. Fowler, and M.J. Van Den Avyle. 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 coastal f i s h e s and i n v e r t e b r a t e s (Mid-Atlantic)--Blue crab. U.S. F i s h W i l d l Serv. B i o l Rep. 82(11.100). U.S. Army Corps o f Engineers, TR EL-82-4. 18 pp.

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PREFACE This species p r o f i l e i s one o f a s e r i e s on c o a s t a l aquatic organisms, p r i n c i p a l l y f i s h , o f sport, commercial, o r ecological importance. The p r o f i l e s a r e designed t o provide c o a s t a 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 ogi cal 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 describe how populations of 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 sections on taxonow, l i f e h i s t o r y , e c o l o g i c a l r o l e , environmental r e q u i rements, and econmi c importance, i f appl icab1 e. A t h r e e - r i ng b i n d e r is used f o r t h i s s e r i e s so t h a t new p r o f i l e s can be added as they a r e prepared. T h i s p r o j e c t i s j o i n t l y planned and financed by t h e U.S. Army Corps o f Engineers and t h e U.S. Fish and W i l d l i f e Service. M i l l i k i n and Williams (1984) previously published a review o f t h e nomenclature, taxononly, morphology, d i s t r i b u t i o n , l i f e history, population 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 h e b l u e crab. Suggestions o r questions r e g a r d i n g 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. I n f o r m a t i o n Transfer Special is t National Wetlands Research Center U.S. F i s h and W i l d l i f e Service NASA-Sl i d e l 1 Computer Complex 1010 Gause Boulevard S l id e l l , LA 70458

U .S. Army Engi neer Waterways Experiment S t a t i o n A t t e n t i o n : WESER-C Post O f f i c e Box 631 Vicksburg, M 39180. S

CONVERSION TABLE

M e t r i c t o U . S . Customary Multiply m i l l i m e t e r s (mm) c e n t i m e t e r s (cm) meters (m) meters (m) k i 1ometers (km) k i l o m e t e r s (km) square meters (m2) square k i l o m e t e r s (km2) h e c t a r e s (ha) l i t e r s (1) c u b i c 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) kilocalories (kcal) C e l s i u s degrees (OC)

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

To O b t a i n

inches inches feet fathoms statute miles nautical miles

10.76 0.3861 2.471 square f e e t square m i l e s acres g a l 1ons cubic f e e t acre- f e e t ounces ounces pounds pounds short tons B r i t i s h thermal u n i t s F a h r e n h e i t degrees

inches inches feet (ft) fathoms s t a t u t e m i l e s (mi) n a u t i c a l m i l e s (nmi ) square f e e t ( f t 2 ) square mi 1es ( m i 2, acres gallons (gal) cubic f e e t (ft3) acre-feet ounces (oz) ounces ( o z ) pounds ( l b ) pounds ( l b ) short tons (ton) B r i t i s h thermal u n i t s (Btu) F a h r e n h e i t degrees (OF)

25.40 2.54 0.3048 1.829 1.609 1.852

millimeters centimeters meters meters k i 1ometers k i 1ometers square meters square k i lometers hectares 1 it e r s c u b i c meters c u b i c meters mi 11 igrams grams k i 1ograms m e t r i c tons metric tons kilocalories Cel s i us degrees

CONTENTS

Page

............................................................ NOMENCLATURE. TAXONOMY. AND RANGE .......................................... MORPHOLOGY AND IDENTIFICATION AIDS ......................................... REASON FOR INCLUSION I N SERIES ............................................. LIFE HISTORY ............................................................... M a t i n g and Spawning ...................................................... Development .............................................................. Eggs ..................................................................... Larvae ................................................................... J u v e n i l e s ................................................................ A d u l t s ................................................................... M i g r a t i o n s ............................................................... GROWTH AND MOLTING CHARACTERISTICS......................................... THE FISHERY ................................................................ ECOLOGICAL ROLE ............................................................ ENVIRONMENTAL REQUIREMENTS................................................. Temperature .............................................................. S a l i n i t y ................................................................. T e m p e r a t u r e - S a l i n i t y I n t e r a c t i o n s ........................................ H a b i t a t .................................................................. Other Environmental F a c t o r s ..............................................

LITERATURE CITED

PREFACE CONVERSION TABLE ACKNOWLEDGMENTS

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iii iv vi

1 1 3 3 3

4

4 4 5 6 6 6 7 9 1 1 1 1 1 1 1 1 12 12

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ACKNOWLEDGMENTS W are g r a t e f u l t o Maurice K. Crawford, Douglas E. Facey, and Timothy J. e Welch f o r reviews and t o Sue Anthony f o r e d i t i n g and t y p i n g t h i s manuscript. Technical reviews were provided by Kenneth Tenore o f t h e U n i v e r s i t y o f Maryland and W. A. Van Engel o f t h e V i r g i n i a I n s t i t u t e o f Marine Science a t Gloucester Point. W wish t o thank the authors J. D. Costlow, Jr., and C. G. Bookhout f o r e use o f t h e i r drawing o f t h e Zoea f o r our Figure 4.

Figure 1. Rlue Crab. BLUE CRAB NOMENCLATURE ,TAXONOMY, AND RANGE Scientific name.. .Callinectes sapidus (Rathbun) Preferred common name. .......Bl ue crab .Edible crab, Other common names.. crab; young females are called sally crabs; adult females are called sooks; and males are called j i m i e s , jirnmydicks , or channelers (Van Engel 1958) Crustacea Class Order Decapoda Family.. .Portunidae Subfamily Portuninae South America, including the Gulf of Mexico. It has been collected occasionally in Maine and northward to Nova Scotia (Piers 1923; Scattergood 1960). It occurs throughout the Mid-Atlantic Region (Figure 2) (Sullivan 1909; Churchill 1919; Van Engel 1958). MORPHOLOGY AND IDENTIFICATION AIDS The blue crab is grayish or bluish green, with red on carapace spines (Will iams 1965). Pincers on the chelipeds are blue in males and red in mature females. Underparts are off-white with tints of yellow and pink (Williams 1965). Young crabs often are brownish with conspicuous white markings (Newcombe 1945).

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Geographic range: The blue crab (Figure 1) occurs in coastal waters--primarily bays and brackish estuaries--from Massachusetts Bay southward to the eastern coast of

NEW YORK

PHILADELPHIA

ATLANTIC OCEAN

Coastal distribution Area of high abundance

KILOMETERS

F i q u r e 2. D i s t r i b u t i o n o f t h e b l u e c r a b i n t h e M i d - A t l a n t i c Region,eastern U n i t e d States. Chesapeake Bay supports t h e m a j o r commerical f i s h e r y i n t h i s r e g i o n .

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Although t h e s e a r e t y p i c a l c o l o r patt e r n s , r a r e forms have been c a p t u r e d t h a t were e n t i r e l y blue (Maryland Tidewater News 1950 ; Haefner 1961). The c a r a p a c e , i n c l u d i n g l a t e r a l s p i n e s , i s u s u a l l y 2.5 times a s wide a s l o n g , moderately convex, and n e a r l y smooth, e x c e p t f o r small t u b e r c l e s on i n n e r b r a n c h i a l and c a r d i a c r e g i o n s . The a n t e r i o r margin o f t h e carapace has a median o r f r o n t a l region t h a t extends between t h e compound e y e s , and two 1a t e r a l r e g i o n s . Members of the subfamily Portuninae have n i n e a n t e r o l a t e r a l t e e t h on t h e c a r a p a c e , with t h e l a t e r a l tooth similar t o others in s i z e . The genus Call i n e c t e s has an antenna t h a t i s n o t excluded from t h e o r b i t ; male C a l l i n e c t e s a l s o have a T-shaped abdomen. The abdomen i s t r i a n g u l a r i n immature females and i s broadly rounded and f o l d e d 1o o s e l y a g a i n s t t h e v e n t r a l s i d e of t h e t h o r a c i c s t e r n a i n mature females ( F i g u r e 3 ) . The medial r e g i o n of C . s a p i d u s has two f r o n t a l t e e t h between t h e i n n e r o r b i t a l t e e t h (Williams 1984). REASON F R INCLUSION IN SERIES O The b l u e c r a b s u p p o r t s a v a l u a b l e commercial fishery throughout t h e

!!id-Atlantic S t a t e s and along most of t h e e a s t e r n and g u l f c o a s t s of t h e United S t a t e s . E s t u a r i e s a r e e s s e n t i a l in i t s l i f e history; the species' high abundance i n e s t u a r i e s and i t s omnivorous f e e d i n g h a b i t s s u g g e s t t h a t i t p l a y s an important r o l e i n t h e s t r u c t u r e and f u n c t i o n of e s t u a r i n e communities. I t i s a p r e d a t o r of commercially valuable clams and o y s t e r s (Newcombe 1945), and young a r e preyed upon by a l a r g e number of e s t u a r i n e and marine animals , i n c l u d comercially important ing other species such a s t h e s t r i p e d b a s s , Morone s a x a t i l i s (Manooch 1973). LIFE HISTORY Mating and Spawning Blue c r a b s mate i n Chesapeake Bay from May through October (Van Engel 1958; Williams 1984). The spawning season was significantly shorter d u r i n g y e a r s i n which temperatures were low for extended periods (Daugherty 1952). Mating occurs primarily in relatively low-salinity w a t e r s i n t h e upper a r e a s of e s t u a r i e s and lower p o r t i o n s of r i v e r s ( P y l e and Cronin 1950; Darnel 1 1959; Williams 1965; Tagatz 1968). Will iams (1965) d e s c r i b e d the b l u e c r a b ' s mating behavior. The male may mate d u r i n g i t s t h i r d o r f o u r t h i n t e r m o l t phase a f t e r i t matures. Females mate o n l y once i n t h e i r l i v e s , b u t t h e sperm from t h i s mating i s s t o r e d i n seminal recept a c l e s and may be used a s o f t e n a s t h e female spawns, g e n e r a l l y two o r more times d u r i n g a 1- o r 2-year period (Van Engel 1958; Will iams 1965). When t h e female i s ready t o molt i n t o t h e mature s t a g e , i t i s c a r r i e d under t h e m a l e ' s body; t h e s e p a i r s arc? c a l l e d doublers. The female i s r e l e a s e d d u r i n g m o l t i n g and i s then r e c l a s p e d w i t h t h e abdomens f a c i n g each o t h e r . Spermatophores produced by t h e ma1 e a r e t h e n passed v i a c c p u l a t o r y s t y l e t s i n t o t h e spermathecae. Pleopods of

Figure 3 . Ventral view of t h e blue c r a b male (A), immature female (B), and mature female (C) ( T r u i t t 1939).

t h e male and swimmerets o f t h e female a r e i n t r o m i t t e n t organs which a i d i n copulation. A f t e r copulation, the female i s t u r n e d around and c a r r i e d u n t i l h e r s h e l l hardens ( W i l l i a m s 1984). A f t e r mating, females m i g r a t e t o high-sal i n i t y waters in lower estuaries, sounds, and nearshore (Churchill 1919; spawning areas Darnel 1 1959; F i s c h l e r and Wal b u r g 1962). These overwinter before spawning by burrowing i n t h e mud a t t h e mouths o f bays (Cook 1981; Schmidt 1985). Most females spawn f o r t h e f i r s t time 2 t o 9 months a f t e r m a t i n g W i l liams 1965). (Churchill 1919; 1965).

Development Growth and development o f t h e b l u e crab, as i n o t h e r crustaceans, consist o f a series o f larval, juvenile, and a d u l t stages d u r i n g which a v a r i e t y o f morphological, b e h a v i o r a l , and p h y s i o l o g i c a l changes occur. These changes are most dramatic when t h e animal m o l t s (sheds i t s r i g i d exoskeleton) permitting growth and changes i n body shape. Before m o l t i n g , a new s h e l l i s formed beneath t h e o l d exoskeleton, which then loosens and i s c a s t o f f . The new shell i s i n i t i a l l y soft, but it expands and hardens i n a few hours. The stage between m o l t s i s termed intermolt. Much o f t h e i n f o r m a t i o n summarized here was o b t a i n e d from comprehensive s t u d i e s o f t h e b l u e c r a b i n the Chesapeake Bay area by C h u r c h i l l (1919), Newcombe (1945), and Van Engel (1958).

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From May through August, the female extrudes f e r t i l i z e d eggs i n t o a cohesive mass o r "sponge" t h a t remains attached t o s e t a e on t h e appendages o f t h e abdomen u n t i l t h e l a r v a e emerge ( C h u r c h i l l 1919; Newcombe 1945; P y l e and Cronin 1950). The sponge, which may c o n t a i n 700,000 t o 2 m i l l i o n eggs, i s formed i n about 2 hours ( C h u r c h i l l 1919; T r u i t t 1939; W i l l iams 1965). I n c u b a t i o n general l y r e q u i r e s 1-2 weeks. I n Chesapeake Bay, larval r e l e a s e appears t o be concentrated between t h e V i r g i n i a capes (McConaugha e t a l . 1986). The presence o f empty egg cases on swimmerets o r t h e occurrence o f 1arqe.. b r i u h t - r e d a d u l t nemertean worms (cai-cinonemertes c a r c i n o h i l a ) on t h e g i l l s o f a mature fema e i n i c a t e s t h a t t h e c r a b has spawned a t l e a s t once ( C h u r c h i l l 1919; Hopkins 1947). After reaching sexual m a t u r i t y , these worms f e e d on t h e egg masses c a r r i e d b y female crabs and l i v e i n t h e g i l l s o f t h e c r a b a f t e r t h e eggs h a t c h (Hopkins 1947). I n l o w e r Chesapeake Bav. mature r e d Carcinonemertes ' o c c u r r e i j n t h e g i l l s o f more t h a n 95% o f t h e female crabs t h a t had spawned; immature crabs supported o n l y immature, 1 i g h t - c o l ored worms (Hopkins 1947).

The eggs a r e b r i g h t orange when f i r s t d e p o s i t e d , b u t become ye1 1ow, brown, and t h e n dark brown b e f o r e h a t c h i n g (Van Engel 1958). The c o l o r change i s caused by a b s o r p t i o n o f t h e ye1 l o w yo1 k and development o f dark pigment i n t h e eyes and on t h e body. m Eggs a r e about 0.25 m i n diameter Sandoz and Rogers (Churchi 11 1919). (1944) r e p o r t e d t h a t h a t c h i n g o f b l u e c r a b eggs o n l y occurs a t s a l i n i t i e s o f 23-33 p p t and temperatures o f 19-29 OC. M o r t a l i t y o f eggs has been attributed to fungal infection, predation, s u f f o c a t i o n i n stagnant water, and exposure to extreme temperatures (Couch 1942 ; Humes 1942 ; Rogers-Tal b e r t 1948) On t h e average, o n l y one o u t o f e v e r y m i l l i o n eggs s u r v i v e s t o become a mature a d u l t (Van Engel 1958).

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Larvae F i r s t s t a g e l a r v a e , c a l l e d zoeae, measure approximately 0.25 m wide a t m hatching (Figure 4). Churchill

width; development t o t h i s stage r e q u i r e s 31-49 days (Costlow and Bookhout 1959). The megalopa l a r v a , i l l u s t r a t e d by Churchill (1919) and Newcombe (1945), is more crab1 i k e i n appearance than t h e zoea; i t s carapace i s broader i n r e l a t i o n t o i t s l e n g t h , and i t has pinching claws and pointed j o i n t s a t t h e ends o f t h e l e g s . I t swims f r e e l y , b u t g e n e r a l l y s t a y s near bottom i n nearshore o r lowere s t u a r i n e , high-sal i n i t y a r e a s (Tagatz 1968). The megalopal s t a g e l a s t s 6 t o 20 days, a f t e r which t h e l a r v a molts i n t o t h e "first crab" s t a g e , charact e r i z e d by a d u l t p r o p o r t i o n s and appearance. Figure 4. Zoea (from Costlow, J r . and Bookhout 1959). Juveni 1es (1942), Hopkins (1943), and Costlow and Bookhout (1959) provided i l l u s t r a t e d d e s c r i p t i o n s o f t h e morphology of zoeae. The l a r v a e bear l i t t l e morphological resemblance t o a d u l t s (Hopkins 1943), a r e f i 1t e r f e e d e r s , and a r e planktonic (Darnel 1 1959). Evidence s u g g e s t s t h a t b l u e c r a b zoeae hatch i n Chesapeake Bay, Chincoteague Bay, Delaware Bay, and o t h e r e s t u a r i e s and d r i f t o u t t o s e a , where t h e y f e e d and grow (Cook 1981; Finchham 1981; S u l k i n e t a1. 1982). These l a r v a e may m i g r a t e v e r t i c a l l y i n t h e water column t o reach f l o o d and ebb t i d e s , which t r a n s p o r t them back i n t o t h e bay a r e a . The zoeae and a l l subsequent 1 ife s t a g e s can i n c r e a s e body size o n l y by molting (Hay 1905). Zoeal development depends on s a l i n i t y and temperature, b u t development time has been shown t o be v a r i a b l e even i n a s i n g l e s a l i n i t y temperature regime (Costlow and Bookhout 1959). Larvae molt seven t o e i g h t times b e f o r e e n t e r i n g t h e n e x t s t a g e of development (Costlow and Bookhout 1959). The f i n a l molt o f t h e zoea i s c h a r a c t e r i z e d by a conspicuous change t o t h e second l a r v a l s t a g e (megalops) a t about 2.5 mm carapace The j u v e n i l e "first crab" is t y p i c a l l y 2.5 mm wide (from t i p t o t i p of t h e l a t e r a l spines of t h e carapace). J u v e n i l e s gradual 1 y m i g r a t e i n t o s h a l l o w e r , l e s s - s a l i n e waters i n upper e s t u a r i e s and r i v e r s , where t h e y grow and mature ( F i s c h l e r and Walburg 1962). Van Engel (1958) r e p o r t e d t h a t many j u v e n i l e s had completed t h i s m i g r a t i o n by fa1 1. Nw evidencel, e however, suggests t h a t t h e bulk may n o t reach t h e upper p a r t s o f t r i b u t a r i e s and Chesapeake Bay u n t i l t h e following summer (W.A. Van Engel', V i r g i n i a I n s t i t u t e o f b r i n e Science, cmm.) Gloucester Point; pers. Males, which p r e f e r 1 o w - s a l i n i t y w a t e r s , general l y m i g r a t e f a r t h e r upstream than do f e m a l e s , which tend t o s t a y i n t h e lower r i v e r s and e s t u a r i e s (Dudley and Judy 1971; Music 1979)

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Growth and maturation proceed during a series o f molts and intermol t phases; each o f t h e s e c r a b s t a g e s is i d e n t i f i e d by t h e number o f molts t h a t have occurred s i n c e t h e megalopal stage. Churchill (1919) e s t i m a t e d t h a t j u v e n i l e s reached t h e 9 t h o r 10th c r a b s t a g e by October i n Chesapeake Bay. Molting and growth s t o p d u r i n g winter (Churchill 1919; Darnel 1 1959), b u t resume a s waters warm. The c r a b s

generally reach maturity during the spring or summer of the year following the year of hatching. Adults In the Chesapeake Bay, sexual maturity i s reached a f t e r 18-20 postlarval molts, a t the age of 1-1.5 years (Van Engel 1958; W i 11iams 1965). Males continue t o molt and grow a f t e r they reach sexual maturity, b u t females cease to molt and grow when they mature and mate. After the females mate and migrate t o spawning areas, they e i t h e r remain there f o r the r e s t of t h e i r l i v e s o r move only short distances out t o sea (Williams 1965). In warmer months, males generally s t a y in 1ow-sal i n i t y waters such as creeks, r i v e r s , and upper e s t u a r i e s (Churchill 1919; Van Engel 1958; Dudley and Judy 1971; Music 1979). Early work by Fiedler (1930), Trui tt (1937), and Cronin (1949) on blue crabs i n the Chesapeake Bay indicated t h a t females overwintered a t the mouth of the bay and spawned there in spring, whereas the migration of males was nondirect i o n a l . Crabs bury themselves i n mud i n winter and emerge when temperatures r i s e i n spring (Cook 1981; Schmidt 1985). The maximum age f o r most blue crabs in the Mid-Atlantic Region i s 3 years (Churchill 1919; Mil 1iams 1965) ; adults thus l i v e an average of l e s s than 1 year a f t e r reaching maturity (Hay 1905; Truitt 1939). Migrations Adult blue crabs a r e excellent swimmers and a l s o can move quickly on land. They r a r e l y move from one estuarine system t o another (Porter 1956; Cargo 1958; Fischler and Walburg 1962; Judy and Dudley 1970). When they do leave an estuary, they usually remain i n adjacent coastal areas, though a few tagged female crabs have been recovered 100-540 bn from t h e i r release s i t e s .

Migrations of blue crabs w i t h i n estuarine systems a r e related t o phases of t h e i r l i f e cycle, t o the season, and ( t o a l e s s e r extent) t o searches f o r favorable environmental conditions (Churchill 1919; Fiedler 1930; Truitt 1939; Fischler and Wal burg 1962). Most blue crabs move t o r e l a t i v e l y deeper, warmer waters i n winter and return t o r i v e r s , t i d a l creeks, s a l t marshes, and sounds when conditions become more favorable in the spring (Livingston 1976; Subrahmanyam and Coul t a s 1980).

G O T AND MOLTING CHARACTERISTICS R WH From the f i r s t crab stage t o the adult , successive i n term01 t stages of the crab a r e morphological l y s i m i l a r except f o r s i z e . The number of molts during c e r t a i n l i f e stages (e.g., larval and juvenile) i s r e l a t i v e l y uniform among crabs, b u t the r a t e of molting (and hence growth) varies considerably and is affected by many environmental factors, including temperature and sal i n i t y Consequentl y , i t i s generally not possible t o determine the developmental stage of a p a r t i c u l a r crab from i t s s i z e or external c h a r a c t e r i s t i c s (Churchill 1919). Migrations and movements within e s t u a r i e s f u r t h e r complicate estimation of growth r a t e s , and repeated sampling a t one location can lead t o erroneous conclusions (Darnel 1 1959; Adkins 1972; Palmer 1974). Thus, the growth and molting patterns described here were derived in p a r t from laboratory studies.

.

Crabs mol t often when small , b u t l e s s frequently as they grow l a r g e r (Van Engel 1958). Each molt t y p i c a l l y r e s u l t s in a 25%-40% increase i n carapace width (Churchi 11 1919; Gray and Newcombe 1939; Van Engel 1958). Resul t s of Churchi 11 ' s (1919) 1aboratory studies on growth of Chesapeake Bay blue crabs serve as a general guide1 ine f o r growth patterns of blue crabs i n Virginia and adjacent States

(Table 1 ) . Rates o f growth v a r y w i t h age and sex (Newcombe 1948). The increase i n s i z e associated w i t h spec i f i c m o l t s may be g e n e t i c a l l y cont r o l l e d , b u t environmental c o n d i t i o n s are b e l i e v e d t o have a g r e a t e r influence. Unfavorable water condi t i o n s , inadequate food, o r i n j u r i e s such as t h e l o s s o f one o r more legs can cause s m a l l e r increases i n s i z e o r no growth f o l l o w i n g a m o l t (Van Engel 1958). I n j u v e n i l e s , t h e increment o f growth i n successive m o l t s appears t o be g r e a t e s t i n h i g h s a l i n i t y waters (Tagatz 1968).

(Churchill 1919). Mature females range i n s i z e from 55-204 rnm; males m may reach 209 m ( W i 11iams 1984).

-

THE FISHERY T h e ' b l u e crab supports the l a r g e s t crab f i s h e r y i n t h e U n i t e d States, r e p r e s e n t i n g about 50% o f t h e t o t a l weight o f a l l species o f crabs harvested (Thompson 1984, NMFS 1986). Annual commercial landings i n t h e United States averaged 86,000 t (190 the harvest m i l 1i o n 1bs) i n 1980-85; i n 1985 was valued a t $53 m i l l i o n (NMFS 1986). I n 1982, t h e average wholesale p r i c e f o r l i v e b l u e crabs was $24 p e r bushel (NMFS 1982). Sholar (1982) summarized most aspects o f t h e A t l a n t i c b l u e crab f i s h e r y and r e p o r t e d landings, by State, for 1950-77. An annotated b i b l i o g r a p h y on t h e b l u e cr'ab f i s h e r y and b i o l o g y was published by Tagatz and H a l l (1971). A r e p o r t on t h e b l u e crab

Van Engel (1958) r e p o r t e d t h a t crabs hatched i n l a t e May i n Chesam peake Bay were 64 m wide by November and 127 m wide (harvestable s i z e ) by m t h e f o l l o w i n g August. The age o f sexual m a t u r i t y v a r i e s from 12-18 months j n Chesapeake Bay (Newcombe Average s i z e 1945; Van Engel 1958). a t m a t u r i t y i s a l s o v a r i a b l e ; i t has been estimated t o be about 178 m m carapace width i n Chesapeake Bay

Table 1. Growth o f d i f f e r e n t l i f e stages o f b l u e crabs i n t h e l a b o r a t o r y a t temperatures and s a l i n i t i e s t y p i c a l o f Chesapeake Bay ( C h u r c h i l l 1919). L i f e stage Carapace w i d t h (mm) Increase i n w i d t h (mm) Mol t i n t e r v a l (days) Age (days)

Mega1 ops 1 s t crab 2nd crab 3 r d crab 4 t h crab 5 t h crab 6 t h crab 7 t h crab 8 t h crab 9 t h crab 10th crab 1 1 t h crab 12th crab 1 3 t h crab 14th crab 15th crab

dynamics i n Chesapeake Bay was publ i s h e d by t h e Chesapeake B i o l o g i c a l Laboratory (Jones e t a1 1983).

.

business because these crabs must be tended continuously (Adkins 1972). Management o f the commercial b l u e crab f i s h e r y i s u s u a l l y l o c a l , and has included measures such as carapace w i d t h l i m i t s , n e t mesh-size t i m i t s , c o n s t r a i n t s on gear type, closed seasons and areas, p r o h i b i t i o n o f the harvest o f sponge crabs o r o t h e r females, quotas, and 1i c e n s i n g (Bearden 1978). Even so, an assessment o f the blue crab f i s h e r y i n Chesapeake Bay suggested t h a t b l u e crabs are curr e n t l y being overfished (Tang 1983). The b l u e crab a l s o supports a r e c r e a t i o n a l f i s h e r y and a v a r i e t y o f small-scale commercial harvests and sales by "weekend operators Gears used i n c l u d e handlines, pots, and collapsible traps. Recreational fishermen g e n e r a l l y are l i m i t e d t o a maximum o f f i v e pots (Sholar 1982). Landings from these a c t i v i t i e s have r a r e l y been q u a n t i f i e d .

Harvests from the M i d - A t l a n t i c Region d u r i n g 1977-85 composed about h a l f o f t h e t o t a l U.S. commercial blue crab harvest; commercial landings were about 40,000 t o r 90 m i l l i o n I b s (NMFS 1982). Almost 90% o f commercial b l u e crab landings i n the M i d - A t l a n t i c are from the Chesapeake Bay r e g i o n i n Maryland and V i r g i n i a ; landings are much smaller i n Delaware and New Jersey (NMFS 1981, 1986). Much o f the harvest i s processed f o r commercial packaging s i n g u l a r l y o r mixed w i t h o t h e r food products and represents a $60 m i l 1 i o n i n d u s t r y (NMFS 1985). Blue crabs are caught throughout the year, b u t most are taken d u r i n g the summer and e a r l y f a l l (Music 1979). Hard crabs (having hardened exoskeletons) are taken p r i m a r i l y i n shallow water i n the warmer months w i t h crab pots o r t r o t l i n e s . The use of t r o t l i n e s f o r b l u e crabs has g e n e r a l l y diminished i n the New England s t a t e s (Sholar 1982) , whereas the use o f crab pots has increased (Tang 1983). Dredges (and l e s s frequently, scrapes) are used i n deeper o f f s h o r e waters i n w i n t e r t o take crabs burrowed i n t o the mud (Adkins 1972; Tang 1983; Schmidt 1985). Fishing pressure has been s t e a d i l y increasing i n t h e Chesapeake Bay area; numbers o f fishermen, boats, and pots increased t h r e e f o l d between 1950 and 1975 (Table 2). Cronin (1983) reported a 7.6-fol d increase between 1948 and 1981 i n the number o t licenses f o r crabbing issued i n Mary1and. Recently molted "soft-she1 1" crabs represent a smaller p o r t i o n o f t h e t o t a l i n d u s t r y , a1 though they have a higher value per crab (Haefner and Garten 1974). Methods o f processing used i n t h e s o f t - s h e l l i n d u s t r y were reviewed by Haefner and Garten (1974). Few fishermen engage i n t h e s o f t s h e l l

."

Commercial harvests o f b l u e crabs f l u c t u a t e widely. For example, the annual harvest i n Chesapeake Bay f l u c t u a t e d between 45 and 94 m i l l i o n I b s from 1966 t o 1980, t y p i c a l o f harvests over the l a s t 50 years (Finchham 1981). Rees (1963) and More (1969) found no d i r e c t r e l a t i o n s h i p between commercial catches and r e c r u i t m e n t o f harvestabl e crabs i n subsequent years. Pearson (1948) found t h a t the s i z e o f the spawning stock a l s o f a i l e d t o determine the s i z e o f the population t h a t survived t o l e g a l s i z e f o r commercial f i s h i n g . He noted that fluctuations in abundance were r e l a t e d p r i m a r i l y t o r a t e s o f s u r v i v a l d u r i n g the f i r s t year o f l i f e . Apparently, there are no r e l i a b l e methods f o r p r e d i c t i n g harvests. Popu l a t i o n f l u c t u a t i o n s have apparently been caused by extreme c o l d weather, reduced s a l i n i t i e s from heavy r a i n s (Pearson 1948), p a r a s i t i s m by t h e leech Myzobdella l u u b r i s (Hutton and S o g a n d a r e s - B e r n a l k t o x i c wastes

Table 2. the blue 1982).

Numbers of gear u n i t s , crab pounds, fishermen, and boats crab f i s h e r i e s of the Chesapeake Bay s t a t e s , 1950-1975

operating i n (from Sholar

Year

Pots

Trot1 i nes

Dredges

Scrapes

Crab Pounds

Fishermen

Boats

(Cottam and Hig ins 1946; Mills 1952), and predation qAcHugh 1967). Larval movements may a f f e c t recruitment back i n t o bays (McConnaugha 1983). If larvae a r e scattered by winds and storms while they a r e offshore, o r i f water currents i n f a l l do not allow larvae t o return t o the bay, harvests a r e l i k e l y t o be low the next f a l l and following spring. Conversely, calm conditions o r mild storms w i t h onshore winds t h a t d i r e c t currents i n t o the bay may 1ead t o exceptional harvests (Finchham 1981). In accord w i t h t h i s hypothesis, Van Engel (1958) determined t h a t a large p a r t of blue crab

f l uctuations can be explained by variations in oceanographic and atmospheric conditions (VIMS 1981).

ECOLOGICAL ROLE Blue crabs perform a v a r i e t y of ecosystem functions and can play a major r o l e i n energy t r a n s f e r w i t h i n e s t u a r i e s . A t various stages i n t h e l i f e cycle, blue crabs serve as both prey and as consumers of plankton, small invertebrates, f i s h , and other

crabs. They are important d e t r i tivores and scavengers throughout t h e i r range. Zoeae are phytopl anktivorous (Darnel1 1959), and r e a d i l y consume i d i n o f l age1 1ates and copepod naupl i (Tagatz 1968). The omnivorous megalopa eats f i s h larvae, small shellfish, and aquatic p l a n t s (Van Engel 1958; Darnel1 1959; Tagatz 1968). Cannibalism i s common among a l l l i f e stages o f b l u e crabs (Hay 1905; C h u r c h i l l 1919; Darnel1 1959; Tagatz 1968)

.

,

P o s t - l a r v a l crabs are considered general scavengers, bottom carnivores, d e t r i t i v o r e s , and omnivores (Hay 1905; Darnel1 1959; Adkins 1972). Food h a b i t s t u d i e s have shown t h a t t h e predominant foods consumed vary t g r e a t l y among 1ocal i i e s . Some comon items are dead and l i v e f i s h , crabs, organic debris, shrimp, mollusks ( i n c l u d i n g mussels, clams, oysters, and s n a i l s ) , and aquatic plants (Newcombe 1945; Darnel 1 1959; W i l l iams 1965; Tagatz 1968; Seed 1980; Arnold 1984; Warren 1985). T r u i t t (1939) found t h a t r o o t s , shoots, and leaves o f eel grass (Zos t e r a ) , d i t c h grass and (Ruppia), sea l e t t u c e (K), s a l t marsh grass (S a r t i n a ) were c o m o n l y eaten by crabs i n sa t marshes, t i d a l creeks, and o t h e r shallow e s t u a r i n e areas. Darnel 1 (1958) concluded t h a t mollusks were t h e dominant food of crabs l a r g e r than 120 m m wide. A1 though predator-prey interactions a r e complex (West and W i l l i a m s 1986), these r e l a t i o n s h i p s may be s t a b i l i z e d by predator avoidance mechanisms. For example, the periwinkle ( L i t t o r i n a i r r o r a t a ) reduces i nj u r y and m o r t a l it y r a t e s caused by b l u e crab by c l i m b i n g t a l l grass d u r i n g h i g h t i d e s (Warren 1985). Some b i v a l v e s a l s o escape predation as they develop t h i c k e r s h e l l s . Blue crab feeding on i n f a u n a l b i v a l v e s was found t o be a f u n c t i o n o f t prey avai 1a b i 1i y and she1 1 s t r e n g t h r e 1a t i v e t o predator of t h e s t r e n g t h r z n d o n and Kennedy 1982).

Blue crabs a r e t h e prey o f a v a r i e t y o f animals. Egg masses, carried by females, are often s p e c i f i c a l l y attacked by some f i s h e s (Adkins 1972). L a r v a l stages are eaten by f i s h , s h e l l f i s h , j e l l y f i s h , combjell ies, and various o t h e r plankt i v o r e s (Van Engel 1958) Juveni 1es a r e i d p o r t a n t prey o f many f i s h such as spotted sea t r o u t (C noscion nebulosus), red drum ( * ocel l a t u s ) , b l a c k drum cromis),and sheepshead (Archosar us r o b a t o c e halus), as we *wading b i r d s (Fontenot Adkins 1972; and R o g i l l i o 1970; Barrass and K i t t i n g 1986). Barrass and K i t t i n g (1986) showed t h a t crabs l e s s than 10 m l o n g respond t o recorded vocal i z a t i o n s o f 1aughing g u l l s (Larus a t r i c i l l a ) by f l e e i n g o r hiding; thus, t h e absence o f v i s u a l cues i n t u r b i d waters apparently does n o t h i n d e r t h e d e t e c t i o n o f avian predators by b l u e crabs. J u v e n i l e and a d u l t b l u e crabs are consumed by mammals, a v a r i e t y o f b i r d s , and several f i s h e s , i n c l u d i n g s t r i p e d bass (Manooch 1973), American eel, An ui11a r o s t r a t a (Wenner and Musick 1 9 h sandbar shark, Carcharhinus p l umbeus (Medved and Marshal 1 1981).

.

d

+

The b l u e crab i s h o s t t o sevd era1 p a r a s i t e s and diseases, b u t many i n f e c t i o n s a r e temporari 1y e l i m i nated during molting. After their l a s t m o l t , a d u l t b l u e crabs may serve as a 1odgi ng place f o r barnacles , bryozoans, and o t h e r s e s s i l e organisms , (Darnel 1 1959; W i l l iams 1965). The ~ a l a n u s amphi tri t e and barnacles Chelonibia a t u f a t t a c h t o t h e carapace b u t genera y have 1 i t t l e physioi o g i c a l e f f e c t on t h e crab (Darnel1 1959; W i 11iams 1965)'. a1 thoush t h e s t a l ked barnacle octalasmi s 1o i e i may c l o a a c r a b ' s s i l t s and s i l l c h a m b e r s ( c a k e y 1961) and saccul i n i d barnacles may prevent m o l t i n g (Steele 1982). I n f e c t i o n s by the protozoan Paramoeba p e r n i c i o s a have been responsible f o r numerous crab mortal it i e s along t h e eastern seaboard (Mahood e t a1. 1970).

h

Blue c r a b s have been implicated a s c a r r i e r s of s t r a i n s of t h e bacterium Vibrio c h o l e r a e which a r e io outbreaks of human respons br c h o l e r a (Moody 1982; Welsh and Sizemore 1985; Huq e t a1 1986). This Vibrio i s apparently a n a t u r a l p a r t of t h e e s t u a r i n e ecosystem and i n h a b i t s Chesapeake Bay and o t h e r major f i s h i n g a r e a s (Greer 1981) ; however, t h e s e and o t h e r p a r a s i t e s pose no t h r e a t t o humans i f t h e blue c r a b s a r e properly s t o r e d , cleaned , and cooked.

.

within a range of 15-34 O C ( L e f f l e r 1972). Experiments by Holland e t a1 (1971) indicated that mortal i t y increased a t temperatures above 30 O C . L e f f l e r (1972) noted t h a t c r a b s a l s o acclimated t o 34 O C were hyperactive. A c t i v i t y and aggression of c r a b s a l s o decreased with temperature u n t i l a t 1 3 O C almost no movement occurred. Sal i n i t y Blue c r a b s occupy water ranging from a near-ocean s a l i n i t y of 34 ppt t o freshwater i n r i v e r s a s f a r a s 195 k upstream from t h e c o a s t (Tagatz m 1968; Palmer 1974). Newcombe (1945) wrote t h a t s a l i n i t i e s of 22-28 ppt a r e needed f o r normal hatching of eggs and f o r normal development of zoeae, b u t s u r v i v a l and growth of megalopae and small j u v e n i l e c r a b s may be normal a t s a l i n i t i e s a s low a s 5 ppt. When s a l i n i t y i s very low, l a r v a e may hatch prematurely and d i e i n t h e prezoeal s t a g e (Van Engel 1958). Gunter (1938) noted t h a t post-larval blue c r a b s move i n t o freshwater and may do s o througho u t t h e s p e c i e s ' range. Specific s a l i n i t y l e v e l s a r e not c r i t i c a l f o r p o s t l a r v a l c r a b s (Odum 1953; Costlow 1967; Adkins 1972; Palmer 1974), although t h e occurrence of mature ma1 e s general l y decreases with i n c r e a s i n g s a l i n i t y above 10 ppt (1971) (Music 1979). Holland e t a1 found t h a t s a l i n i t i e s w i t h i n t h e range of 2-21 ppt had l i t t l e e f f e c t on growth and s u r v i v a l of j u v e n i l e s .

.

ENVIRONMENTAL REQUIREMENTS Temperature Water temperature i n f 1uences growth and s u r v i v a l o f blue crabs. Williams (1965) found t h a t l a r v a l c r a b s , r e a r e d a t temperatures 1e s s than 21 "C, d i d n o t develop beyond t h e f i r s t zoeal s t a g e and d i d not progress p a s t t h e t h i r d zoeal s t a g e when reared a t 30 O C o r higher. Blue c r a b s a r e more t o l e r a n t of low temperatures than a r e many s p e c i e s of f i s h e s and shrimp (Music 1979). Their a b i l i t y t o burrow i n t o t h e s u b s t r a t e apparently enables them t o be i n s u l a t e d from cold water (Music 1979; Weinstein 1979). The upper i n c i p i e n t l e t h a l temperature f o r j u v e n i l e blue c r a b s i s 33 O C (Holland e t a l . 1971). L e f f l e r (1972) measured growth of crabs a t f o u r temperatures, s t a r t i n g with 22-nnn c r a b s , and found t h e following mean carapace widths a f t e r 70 days: 56 mn a t 34 O C , 48 mn a t 27 "C, 40 m a t 20 O C , and 38 mm a t 1 5 "C. The r e l a t i o n s h i p between growth r a t e and water temperature was reported by Churchi 11 (1919), Winget e t a l . (1976), and L e f f l e r (1972). Growth r a t e was proportional t o water temperature; growth and molting ceased below 15.5 "C (Churchill 1919) and below 1 3 O C ( L e f f l e r 1972). Mortal i t y was determined t o be d i r e c t l y proportional t o temperature

.

Temperature

- Salinity

Interactions

Optimal temperatures may vary with o t h e r environmental v a r i a b l e s including s a l i n i t y (Winget e t a l . 1976). Costlow (1967) found t h a t s u r v i v a l of megalopae exceeded 70% a t 20-30 "C when s a l i n i t y was g r e a t e r than 10 ppt, but never exceeded 50% a t 15 O C . Larval development progressed normally a t 25 O C when s a l i n i t y was between 20.1 and 31.1 p p t , but d i d n o t progress normally beyond t h i s s a l ini t y range (Nil l iams 1965).

Habitat The b l u e crab i n h a b i t s a l l areas o f e s t u a r i e s t o some e x t e n t ( C h u r c h i l l 1919; Newcombe 1945; Palmer 1974; Music 1979). Weinstein (1979) found t h a t shallow s a l t marsh h a b i t a t s were important nurseries f o r juveniles. Mature ma1es p r e f e r creeks, r i v e r s , and upper e s t u a r i e s , b u t t h i s may be a response t o s a l i n i t y r a t h e r than t o other physical o r b i o l o g i c a l features of the habitat such as refuge ( C h u r c h i l l 1919; W i l 1 iams 1965; Music 1979). When n o t mating, mature females t e n d t o remain i n h i g h s a l i n i t y areas o f lower e s t u a r i e s and surrounding waters ( C h u r c h i l l 1919; Van Engel 1958; Palmer 1974; Music 1979). The optimal h a b i t a t f o r small crabs i s shallow e s t u a r i n e water w i t h bottoms o f s o f t d e t r i t u s , mud, o r mud-she1 1 (Adkins 1972). Larger crabs p r e f e r r e d deeper e s t u a r i n e waters having harder bottom substrates. Other Environmental Factors Among t h e many stresses t h a t a f f e c t b l u e crabs w h i l e t h e y occupy

nursery areas a r e p e s t i c i d e s , domestic and i n d u s t r i a l wastes, a1 t e r a t i o n o f c u r r e n t s , and d e s t r u c t i o n o f marshlands (Adkins 1972). Blue crabs a r e adversely a f f e c t e d by a wide range o f toxicants, including naphthalene (Pearson 1979; Sabourin 1982), dimethyl naphthalene (Mantel e t a1 1985), methoxychlor (Bookhout and Costlow 1976) , DOT (Commercial F i s h e r i e s Review 1946; Mahood e t a l . 1970), benzene ( S a i f f and C r i s t i n i 1982; Mantel e t a l . 1985), Kepone ( F i s h e r e t a l . 1983), t h e organophosphate fenitrothion (Johnston and C o r b e t t 1985), cadmium (Brouwer e t a l . 1984), and a c i d r u n o f f ( L i v i n ston e t a,. 1976; L a u g h l i n e t a1 19787.

.

.

E f f e c t s from these t o x i c a n t s range from sub1 e t h a l responses, such as decreases i n i o n exchange e f f i c i e n cy a t t h e g i l l s (Sabourin 1982) and decreased growth (Mantel e t al. 1985), t o d i r e c t m o r t a l i y (Commercial t F i s h e r i e s Review 1946). Severity o f t h e e f f e c t s depends on t h e t o x i c a n t , concentration, t i m e exposed, s a l i n i t y , t i d a l c y c l e , age and m o l t phase o f crab, and o t h e r v a r i a b l e s . Many o f t h e t o x i c a n t s a r e bioaccumulated i n b l u e crabs and passed t o humans and o t h e r n a t u r a l predators.

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Van Engel, W .A. 1958. The b l u e c r a b and i t s f i s h e r y i n Chesapeake Bay. P a r t 1. Reproduction, e a r l y development, growth, and migration. Commer. F i s h . Rev. 20(6) :6-17. VA. I n s t . Mar. S c i . Sea Grant Program. (vIMS). 1981. P r e d i c t i n g V i r g i n i a ' s

W i l l iams, A.B. 1984. Shrimps, l o b s t e r s , and crabs o f t h e A t l a n t i c c o a s t o f t h e e a s t e r n U n i t e d States, Maine to Florida. S m i thsonian -. I n s t i t u t i o n Press, Washington, D.C. 550 pp.

Winget, R.R., C.E. E p i f a n i o , T. Runn e l s , and P. A u s t i n . 1976. E f f e c t s o f d i e t and temperature on growth and m o r t a l i t y o f t h e b l u e crab, C a l l i n e c t e s sa idus, maintained i n a r e c i r c u l a t i n g cu t u r e system. Proc. N a t l She1 1f i s h . Assoc. 66:29-33.

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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 Coastal Fishes 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 ) - - B l ue Crab.

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G e o r g i a Cooperative F i s h and W i l d l i f e Research U n i t School o f F o r e s t Resources U n i v e r s i t y o f Georgia GA 30602

12 Spon.orlnl O~..nlmlon

Name and Addms

WO.

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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 Service N a t i o n a l Wetlands Research Center Washington, DC 20240

U.S. Army Corps o f Engineers Waterways Experiment S t a t i o n P.O. Box 631 Vicksburg, M 39180 S

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Species p r o f i l e s are sumnaries o f t h e l i t e r a t u r e on taxonomy, l i f e h i s t o r y , and environmental requirements o f coastal f i s h e s and a q u a t i c i n v e r t e b r a t e s . They are prepared t o a s s i s t w i t h impact assessment. The b l u e crab, C a l l i n e c t e s sapidus, occurs i n lower reaches o f freshwater r i v e r s , e s t u a r i e s , and coastal waters along t h e A t l a n t i c seaboard and G u l f o f Mexico, and t h e species supports t h e l a r g e s t crab f i s h e r y i n t h e U n i t e d States Chesapeake Bay provides t h e g r e a t e s t p r o d u c t i o n o f b l u e crabs on t h e e a s t coast. The b l u e c r a b ' s h i g h abundance i n e s t u a r i e s , d i v e r s e f e e d i n g h a b i t s , and importance as prey f o r o t h e r marine animals i n d i c a t e i t s i m p o r t a n t r o l e i n t h e s t r u c t u r e and f u n c t i o n of e s t u a r i n e communities. Female b l u e crabs spawn i n high-sal i n i t y lower e s t u a r i e s of c o a s t a l areas; t h e r e s u l t i n g l a r v a e are p l a n k t o n i c and develop i n t o j u v e n i l e s a t 5 t o 10 weeks o f age. J u v e n i l e s g r a d u a l l y m i g r a t e i n t o shallower, l e s s - s a l i n e upper e s t u a r i e s and r i v e r s where they grow and mature a t 1-2 y r o f age. Mating occurs i n t h e upper e s t u a r i e s a f t e r which females m i g r a t e t o areas having h i g h e r s a l i n i t i e s . Growth and s u r v i v a l of b l u e crabs are s t r o n g l y a f f e c t e d b y water temperature and s a l i n i t y , b u t tolerances vary w i t h l i f e stage. Larvae r e q u i r e temperatures o f 20-30 OC and s a l i n i t i e s o f 10-30 p p t f o r p r o p e r development, b u t s a l i n i t y and t e m p e ~ a t u r etolerances a r e broad f o r advanced j u v e n i l e s and a d u l t s . Blue crabs use n e a r l y a l l areas w i t h i n e s t u a r i e s as nursery h a b i t a t and crab populations are s e n s i t i v e t o changes i n p h y s i c a l f e a t u r e s o f contamination of these areas.

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As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water resources, protecting our fish and wildlife, preserving the environmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration.

U.S. DEPARTMENT OF THE INTERIOR

FlSH AND WILDLIFE SERVICE

TAKE PRIDE in America

UNITED STATES DEPARTMENT O THE INTERIOR F

FlSH AND WILDLIFE SERVICE

National Wetlands Research Center NASA-Slidell Computer Complex 1010 Gause Boulevard Slidell. LA 70458 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE, $300

POSTAOE AND FEE8 PAID

U 8 DEPARTMENT OF THE INTERIOR lNl423

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