Sheepshead, continued 



Dissolved Oxygen: 



Minimum dissolved oxygen (DO) tolerances for this 

 species are not well known, but kills have been re- 

 ported in semi-open and closed canals in coastal 

 Louisiana where severe oxygen depletion occurred 

 (Adkins and Bowman 1976). 



Movements and Migrations : This is not considered a 

 true migratory species (Jennings 1985), but one tag- 

 ging study showed a maximum traveled distance of 

 109 km prior to the spawning season (Bryant et al. 

 1 989). Adults move to offshore waters in the spring and 

 return to bays after spawning. The sheepshead re- 

 mains in nearshore waters during warm seasons and 

 moves out of the estuaries during periods of low 

 temperatures (Gunter 1945, Dugas 1970, Jennings 

 1985, Bryant et al. 1989). 



Reproduction 



Mode : This species has separate male and female 

 sexes (gonochoristic). Fertilization is external, by 

 broadcast of milt and roe into the water column. 



Spawning : Spawning probably occurs offshore 

 (Springer and Woodburn 1960), from February through 

 April (Hildebrand and Cable 1938, Springer and 

 Woodburn 1960, Christmas and Waller 1973, Render 

 and Wilson 1993). The reported peak occurs during 

 the months of March and April (Beckman et al. 1991). 



Fecundity : Fecundity appears to vary between fish 

 from the inshore area, and older, larger fish that are 

 caught offshore (Render and Wilson 1993). Fish 

 caught offshore had an average fecundity of 87,000 

 eggs/batch and ranged from 14,000 to 250,000 eggs/ 

 batch. The average fecundity of fish from the inshore 

 area was 11,000 eggs/batch, and ranged 1,100 to 

 40,000 eggs/batch. Frequency of spawning was esti- 

 mated to be every 1 to 20 days. 



Growth and Development 



Egg Size and Embryonic Development : Eggs are ap- 

 proximately 0.8 mm diameter, and are buoyant. Hatch- 

 ing occurs in about 40 hours at 24-25°C (Johnson 

 1978, Tucker 1989). 



Age and Size of Larvae : Larvae are about 2.0 mm 

 when they hatch, and by 5 mm, they have absorbed the 

 yolk sac. Transition to the juvenile stage begins at 

 about 1 1 to 1 2 mm (Mook 1 977). 



Juvenile Size Range : Juveniles attain adult pigmenta- 

 tion patterns by approximately 25 to 30 mm (Johnson 

 1 978). Growth is rapid up to 6 to 8 years of age, after 

 which it levels off (Beckman et al. 1 991 ). 



Age and Size of Adults : Sexual maturity is reported to 

 occur in most individuals by age 2 (Beckman et al. 

 1 991 , Render and Wilson 1 993). All males are usually 

 mature by age 3, and all females by age 4. The 

 sheepshead is one of the largest members of its family 

 (Shipp 1988). It can grow up to 610 mm (Hoese and 

 Moore 1 977), and the record size in Louisiana is 9.6 kg. 

 Females exhibit a faster growth rate and achieve larger 

 maximum sizes than males. This is a long-lived spe- 

 cies with a life span of at least 20 years. Von Bertalanffy 

 growth equations have been developed for both sexes 

 (Beckman et al. 1991). 



Food and Feeding 



Trophic Mode : Little information is available regarding 

 the role of sheepshead in the trophic dynamics of 

 estuaries (Jennings 1985). Larvae are carnivorous. 

 Juveniles and adults are omnivores, but adults in 

 offshore environments function more as sessile animal 

 feeders, while juveniles feed primarily on plant material 

 in inshore habitats (Sedberry 1987). 



Food Items : Hildebrand and Cable (1938) found that 

 ostracods were the primary food for fishes less than 30 

 mm. Benson (1982) summarizes the diet of sheeps- 

 head as: larvae consuming primarily zooplankton, ju- 

 veniles consuming zooplankton as well as polychaetes 

 and chironomid larvae; large juveniles and adults eat 

 blue crab, young oysters, clams, crustaceans and 

 small fish. Juveniles and adults are basically omnivo- 

 rous feeding on plant material as well as crustaceans, 

 molluscs and small fishes (primarily young Atlantic 

 croaker) (Gunter 1945, Darnell 1961, Tabb and Man- 

 ning 1 961 , Kelly 1 965, Levine 1 980, Odum et al. 1 982, 

 Overstreet and Heard 1 982, Shipp 1 988). In one study, 

 smaller adults (<350 mm SL) were found to consume 

 mostly bryozoans, while larger fish (>350 mm SL), that 

 also fed heavily on bryozoans, included more bivalves, 

 echinoderms, and ascidians in their diet. Both size 

 groups consumed barnacles and decapods in lesser 

 amounts. Foraminiferans, cnidarians, polychaetes, 

 gastropods, and small arthropods were also eaten. 

 Algae may be important in the diet of sheepshead in 

 inshore habitats (Ogburn 1984), but plant material 

 becomes less important in the diet of adults as they 

 move offshore (Sedberry 1987). 



Biological Interactions 



Predation: Little information is available regarding pre- 

 dation of sheepshead, but it seems likely that larvae 

 and juveniles could be utilized as a food source by 

 predatory fishes. 



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