Brown shrimp, continued 



usually between depths of 46 to 91 m, but can range 

 from 18 to 137 m (Renfro and Brusher 1982). The 

 major spawning season is September through May; 

 however, spawning may occur throughout the year at 

 depths greater than 46 meters. In the northern Gulf of 

 Mexico, there are two spawning peaks: September - 

 November, and April - May. In waters off Texas, 

 spawning occurs in spring and fall at depths greater 

 than 14 m, and throughout the year at depths of 64 to 

 110 m. In shallower water, peaks of spawning are 

 during late spring and in the fall (Renfro and Brusher 

 1982). Brown shrimp may spawn more than once 

 during a season (Perez-Farfante 1969), and usually 

 spawn at night (Henley and Rauschuber 1981). 



Fecundity : Reitsema et al. (1 982) found brown shrimp 

 that averaged 192 mm TL released an average of 

 246,000 viable eggs, of which 15 % hatched. 



Growth and Development 



Egg Size and Embryonic Development : Eggsare round, 

 golden brown, and translucent measuring approxi- 

 mately 0.26 mm in diameter (Cook and Murphy 1 971 ). 

 They are demersal and hatch within 24 hours after 

 release into the water column (Kutkuhn 1966, Christ- 

 mas and Etzold 1977). 



Age and Size of Larvae : Larvae transform through 5 

 naupliar stages with average total lengths of 0.35, 

 0.39, 0.40, 0.44 and 0.50 mm respectively; 3 protozoeal 

 stages, average total lengths of 0.96, 1.71, and 2.59 

 mm; and 3 mysis stages, average total lengths of 3.3, 

 3.8 and 4.3 mm, to become postlarvae at an average 

 total length of 4.6 mm, in a period of 1 to 25 days (Cook 

 . and Murphy 1 969, Cook and Murphy 1 971 ). Postlarvae 

 enter the estuaries and transform into juveniles around 

 25 mm TL. Larval growth rate estimates are: nauplii, 

 0.1 -0.2 mm/day; protozoeae 0.3-0.35 mm/day; myses 

 0.4-0.5 mm/day (Ward et al. 1980). Postlarval growth 

 is at a maximum between 25 to 27° C, greater than 0.5 

 mm/day. 



Juvenile Size Range : Estuarine juveniles range from 

 25 to 90 mm. The shrimp spend about 3 months on the 

 nursery grounds, and then move back offshore at sizes 

 ranging from 80 to 1 00 mm TL (Copeland 1 965, Cook 

 and Lindner 1970, Parker 1970). Growth rates are 

 temperature dependent and tend to decrease after 

 maturity. Juveniles have grown 3.3 mm/day at tem- 

 peratures above 25°C; growth decreases from 29 to 

 33°C (Zein-Eldin and Renaud 1986). 



Age and Size of Adults : Growth of offshore adults has 

 not been studied in detail. Females usually reach 

 sexual maturity at about 140 mm TL (Henley and 

 Rauschuber 1981). Brown shrimp have lived over two 

 years in captivity (Zein-Eldin pers. comm.). 



Food and Feeding 



Trophic Mode : Larvae are omnivorous, and feeding 

 begins with the first protozoeal stage (Cookand Murphy 

 1969). Juveniles and adults forage nocturnally on 

 available food, and are more carnivorous, progressing 

 from "encounter-feeders" to selective omnivore-preda- 

 tors (GMFMC 1981, Zein-Eldin and Renaud 1986, 

 Minello and Zimmerman 1991). 



Food Items : Larval stages feed on phytoplankton and 

 zooplankton. Postlarvae feed on epiphytes, phytoplank- 

 ton and detritus, but faster growth is attained on animal 

 food (e.g. Artemia, fish meal, shrimp meal, and squid 

 meal) (Gleason and Zimmerman 1 984, Zein-Eldin and 

 Renaud 1 986, Zein-Eldin pers. comm.). Juveniles and 

 adults prey on polychaetes, amphipods, and chirono- 

 mid larvae, but also detritus and algae (GMFMC 1 981 , 

 Zein-Eldin and Renaud 1986). Optimal growth of 

 juveniles in a laboratory feeding study was obtained 

 using a diet that consisted of a mixture of animal and 

 plant material (McTigue and Zimmerman 1 991 ). Brown 

 shrimp were found to rely more heavily on animal 

 material in their diet than white shrimp, and this may be 

 the result of interspecific competition. 



Biological Interactions 



Predation : Predation is probably the most usual direct 

 cause of brown shrimp mortality in estuarine nurseries 

 in the northern Gulf of Mexico (Minello et al. 1989b). 

 Habitat location may affect the degree of predation with 

 such factors as differences in vegetation, substrate, 

 and waterturbidity altering mortality rates (Minello et al. 

 1 989a). A wide variety of predators, including carnivo- 

 rous fishes and crustaceans feed on this species. In 

 estuarine waters, the southern flounder is considered 

 the major predator of juvenile brown shrimp especially 

 during the spring, but spotted seatrout, sand seatrout, 

 and inshore lizard fish also prey heavily on penaeid 

 shrimp (Stokes 1 977, Minello et al. 1 989a, Minello et al. 

 1989b). Other piscine predators include: sand tiger 

 shark, bull shark, dusky shark, ladyfish, gafftopsail 

 catfish, hardhead catfish, sheepshead, rock sea bass, 

 bluefish, comon snook, silver seatrout, pinfish, pigfish, 

 gulf killifish, red snapper, lane snapper, southern king- 

 fish, spot, silver perch, black drum, red drum, Atlantic 

 croaker, crevalle jack, cobia, code goby, Spanish mack- 

 erel, gulf flounder (Gunter 1945, Kemp 1949, Miles 

 1 949, Springer and Woodburn 1 960, Harris and Rose 

 1 968, Boothby and Avault 1 971 , Odum 1 971 , Carr and 

 Adams 1 973, Diener et al. 1 974, Bass and Avault 1 975, 

 Stokes 1 977, Overstreet and Heard 1 978a, Overstreet 

 and Heard 1 978b, Danker 1 979, Overstreet and Heard 

 1 982, Divita et al. 1 983, Saloman and Naughton 1 984, 

 Sheridan et al. 1 984, Minello et al. 1 989a, Minello et al. 

 1989b). Penaeid shrimp are an important link in the 

 energy flow of food webs by feeding on benthic organ- 

 isms, detritus, and other organic material found in 



58 



