Gray snapper, continued 



juveniles (15-35 mm) are present in shallow basins 

 with Thalassia present adjacent to mud banks, and 

 postlarval juveniles have been found over dense (1000- 

 4000 shoots/m 2 ) seagrass beds of Halodule wrightii 

 and Syringodium filiforme. Juveniles are recorded 

 from Thalassia grass flats; soft marl bottoms, marl 

 sands, fine marl mud with shell and rock outcrops, and 

 detritus; seagrass meadows and mangrove roots; 

 seagrass meadows near jetties and pilings (Tabb and 

 Manning 1 961 , Rutherford et al. 1 983, Rutherford et al. 

 1989a). Adults typically occur around hard bottoms, 

 natural and artificial, but also soft bottoms; wharves, 

 pilings, rocky areas; sand, rubble, rock with supporting 

 alcyonarians, sponges and Thalassia; coral reefs, rock 

 outcrops, shipwrecks; sandy grass beds, coral reefs, 

 sandy, muddy and rocky bottoms (Springer and 

 Woodburn 1960, Starck and Davis 1966, Starck and 

 Schroeder 1 971 , Manooch and Matheson 1 984). It is 

 also suggested that the preferred substrate is mud. 

 They are occasionally found in areas of alcyonarian or 

 algal growths. In one study, specimens between 110 

 and 275 mm were recorded in areas of mud to shelly- 

 sand bottoms (Lindall et al. 1973). 



are considered to be generally non-migratory, and tend 

 to remain in areas in which they have become estab- 

 lished. A mark-recapture study in Florida, however, 

 found movement to the southwest as the individuals 

 grew, with a mean travel distance of 1 8.3 km (Bryant et 

 al. 1989). Some movements are noted in connection 

 with feeding, environmental conditions, and seasonal 

 spawning. Mature fish migrate to offshore reefs during 

 the summer to spawn. Most return to the inshore and 

 estuarine habitats, however, some remain near the 

 reefs (Starck and Schroeder 1 971 ). Adults that inhabit 

 reefs move off into surrounding waters to feed at night 

 (Starck and Davis 1966, Moe 1972). 



Reproduction 



Mode : The gray snapper has separate male and fe- 

 male sexes (gonochoristic), but exhibits no apparent 

 external dimorphism. Sex ratio is reported as equal 

 (Croker 1 962, Starck and Schroeder 1 971 , Rutherford 

 et al. 1 983). Eggs and milt are broadcast into the water 

 column, and fertilization is external, with no indication 

 of nest building or egg guarding (Starck and Schroeder 

 1971, Grimes 1987). 



Physical/Chemical Characteristics : 

 Temperature: Eggs are found in the marine seawater 

 zone in the vicinity of offshore reefs (Starck and 

 Schroeder 1971). Larvae have been recorded occur- 

 ring in ranges of 1 5.6 to 27.2°C (Hardy 1 978) and 26 to 

 28°C in vitro (Richards and Saksena 1980). Juveniles 

 are found in temperature ranges of 17.2° to 36.0°C 

 (Hardy 1978); 16 to 31 °C (Tabb and Manning 1961); 

 and 12.8° to 31.7°C (Rutherford et al. 1989a). Adults 

 occur in water temperatures from 13.4° to 32.5°C 

 (Springer and Woodburn 1960, Wang and Raney 

 1 971 ), and their lower lethal limit is 1 1 °-1 4°C (Starck 

 and Schroeder 1971). Increased mortalities accom- 

 pany sudden temperature drops (Starck 1971). 



Salinity: Eggs have been hatched in vitro in a salinity 

 range from 32 to 36%o (Richards and Saksena 1980). 

 Larvae and juveniles are euryhaline. Juveniles have 

 been observed in salinities ranging from to 66.6%o 

 (Tabb and Manning 1 961 , Bortone and Williams 1 986, 

 Rutherford et al. 1 983, Rutherford et al. 1 989a). Adults 

 are euryhaline and have been found in salinities rang- 

 ing from to 47.7%o (Hardy 1978, Wang and Raney 

 1971). 



Migrations and Movements : Newly hatched larvae are 

 planktonic, but develop rapidly and make their way to 

 the inshore nursery areas at about 1 mm (Starck and 

 Schroeder 1 971 , Chester and Thayer 1 990). By about 

 80 mm, early juveniles move to deeper estuarine 

 habitats, but have been observed moving out of an 

 area in response to extreme temperatures (Starck and 

 Schroeder 1971, Chester and Thayer 1990). Adults 



Spawning : The gray snapper is a summer spawner, 

 typically from June through August, but is also reported 

 to spawn in September in the Florida Keys (Starck and 

 Schroeder 1971, Grimes 1987). Spawning occurs 

 offshore in the Gulf of Mexico around reefs or shoals. 

 Evidence indicates batch spawning occurs at night 

 near full moons throughout the reproductive cycle 

 (Starck and Schroeder 1971, Grimes 1987). The 

 spawning season may be protracted over a long period 

 (Druzhinin 1970). 



Fecundity : Since gray snapper are multiple spawners, 

 batch fecundity and spawning frequency must be esti- 

 mated in order to describe overall fecundity. Collins 

 (pers. comm.) has estimated batch fecundity of 20 gray 

 snapper from northwest Florida. These fish were 

 captured in the summer months of 1993-1995, and 

 ranged from 333 to 641 mm TL. Batch fecundity 

 estimates ranged from 29,000 to 1 ,256,000 hydrated 

 oocytes. Estimates of spawning frequency for gray 

 snapper have not yet been completed (Collins pers. 

 comm.). In other studies, a 315 mm female produced 

 590,000 eggs (Starck 1 971 , Hardy 1 978), while a 354 

 mm standard length (SL) fish produced 548,000,000 

 (Grimes 1987). One gram of ovarian tissue has been 

 reported to contain 1 25,000 eggs (Starck and Schroeder 

 1971). 



Growth and Development 



Egg Size and Embryonic Development : Eggs are ovipa- 

 rous, non-adhesive, ranging 0.04-0.06 mm in diam- 

 eter, and contain a single central oil globule (Starck and 

 Schroeder 1 971 , Grimes 1 987). These demersal eggs 



230 



