Common snook, continued 



Spawning : In Florida, spawning occurs from May to 

 mid-November with peak spawning periods from June 

 to July along the southeast and southwest coasts, and 

 in August along the east central coast. These peaks 

 may vary among locations. In a study of snook in 

 Tampa Bay, a diel and lunar sampling protocol was 

 used to determine peak periods of various reproduc- 

 tive activities (Roberts etal. 1988). Thegonadosomatic 

 index of adult snook and the catch per unit effort 

 (CPUE) of larvae were highest during the new moon 

 period in June and July. Eggs were most abundant 

 during late evening and early morning hours. Some 

 spawning may occur year round in the warmer parts of 

 the range (Marshall 1 958, Volpe 1 959, Ager et al. 1 976, 

 Moe 1 972, Tucker 1 986). In south Texas, the primary 

 spawning period is June to August (MatlockandOsburn 

 1987). One female with roe was reported from Corpus 

 Christi, Texas in July (Baughman 1943). Snook can 

 spawn repeatedly during a single season (Fore and 

 Schmidt 1973, Seaman and Collins 1983). Fish ready 

 to spawn congregate in schools in shallow, saline, 

 open waters just offshore in such areas as river mouths, 

 estuarine passes, and along open beaches in the 

 vicinity of inlets. Actual spawning is most likely to occur 

 in shallow nearshore waters (Marshall 1958, Volpe 

 1 959, Linton and Rickards 1 965, Moe 1 972, Ager et al. 

 1 976, Bruger 1 981 , Gilmore et al. 1 983). Salinities of 

 >20% o are necessary to activate sperm for successful 

 spawning (Ager et al. 1 976, Shafland and Koehl 1 979). 



Fecundity : Spawning females produce large numbers 

 of eggs; a female with a fork length (FL) of 584 mm 

 contained about 1 ,440,000 eggs (Volpe 1 959). Fecun- 

 dity has been tentatively estimated at 20,412 eggs/kg 

 body weight, with some fractional spawning being 

 reported (Marshall 1958, Ager et al. 1976). Common 

 snookcan be considered batch-synchronous, i.e., they 

 can spawn once every 3 to 4 days for about 152 days 

 from mid-April to mid-September in Florida waters. 

 Batch fecundity is approximately 850,000 eggs, and if 

 there are 38 spawning events per season, total fecun- 

 dity for a 800 mm FL female could be 32,000,000 eggs 

 per year (Taylor pers. comm.). 



Growth and Development 



Egg Size and Embryonic Development : Development 

 is oviparous. Eggs are 0.68 to 0.73 mm in diameter, 

 spherical, yellowish-white in color with transparent yolk 

 material containing a single well defined oil globule that 

 ranges from 0.17 to 0.30 mm in diameter. Hatching 

 rates reported in laboratory experiments are 16-18 

 hours at 28°C and 24 to 30 hours at 27.8° to 30.6°C. 

 Fertilized eggs float in salt water with a salinity of >20%o 

 (Ager et al. 1976, Lau and Shafland 1982, Tucker 

 1986). 



Age and Size of Larvae : Larvae are 1 .4 to 1 .5 mm SL 

 at hatching and have a large yolk sac that contains a 

 large oil globule in the anterior portion, and a transpar- 

 ent finfold present around most of the body (Lau and 

 Shafland 1 982, Tucker 1 986). Their length increases 

 to about 2.1 mm SL by 36 hours after hatching (AH) 

 (Lau and Shafland 1982). At this time eyes are 

 becoming pigmented, the mouth begins to develop, the 

 yolk sac is absorbed, and the gut increases in diameter 

 and is partitioned (Lau and Shafland 1982). Eyes and 

 jaws are complete 32 to 48 hours AH and the digestive 

 system is functional by 72 hours AH (Shafland and 

 Koehl 1 979, Tucker 1 986). At approximately 96 hours 

 AH, larvae are 2.2 to 2.3 mm SL, the oil globule is 

 completely absorbed, and the swimbladder is visible 

 above the gut. Notochord flexion begins from 3.6 to 3.8 

 mm SL, and is usually complete by 4.5 mm. Caudal fin 

 is visible by 3.2 mm SL; pelvic fin buds visible between 

 5.0 to 5.5 mm SL, pelvic girdle completely ossified by 

 8.6 mm SL and heavily lined with teeth (Lau and 

 Shafland 1982). The larval stage ends with scale 

 development at 1 3.8 to 1 6.4 mm SL, 34 days AH (Lau 

 and Shafland 1982). Growth rate for larvae varies. 

 Newly hatched larvae at 28°C±1 °C grow 1 .02 mm/day 

 for a few hours, slowing rapidly to about 0.15 mm/day 

 when about 2.4 mm SL. Growth rate then increases 

 gradually with increasing size from 0.15 to 0.50 mm/ 

 day in snook between 3.5 to 22.0 mm SL (Lau and 

 Shafland 1 982). The osteological develpment of larval 

 snook is described in detail by Potthoff and Tellock 

 (1993). 



Juvenile Size Range : The minimum size described for 

 juveniles is 1 3.8 mm SL (Lau and Shafland 1 982). The 

 caudal skeleton is ossified by 21 .9 mm SL, and by 26.4 

 mm SL melanophores begin to form along lateral line, 

 darkening it and the fins. Juveniles have appearance 

 of small adults at this point (Lau and Shafland 1982). 

 The reported growth rate for juveniles in the wild is 0.5- 

 1.2 mm/day (Fore and Schmidt 1973, Gilmore et al. 

 1 983, McMichael et al. 1 989) with a reported average 

 of 0.6-0.7 mm/day for the first eight months of life 

 (McMichael et al. 1989). Juveniles are 163 mm FL at 

 the end of their first winter, and 342 mm FL by the end 

 of their second (Volpe 1959). Some juveniles mature 

 by the end of their second year, but most are not mature 

 until their third year when they reach a FL of 500 mm 

 (Marshall 1958, Volpe 1959). 



Age and Size of Adults : Marshall (1958) reported 

 minimum sizes for adults of 337 mm FL for females, 

 and 338 mm FL for males. Predicted size and age for 

 Florida gulf coast snook at 50% maturity are 401 mm 

 FL at 1.93 years for males, and 499 mm FL at 2.64 

 years for females (Taylor pers. comm.). Estimates for 

 Florida east coast snook at 50% maturity are 379 mm 

 FL at 2.26 years for males, and 644 mm FL at 3.68 



197 



