Common snook, continued 



advantage of two-layered circulation as the mecha- 

 nism for transport into the upper reaches of estuaries 

 (Tolleyetal. 1987). 



Juvenile snook inhabit neritic and estuarine areas. 

 They prefer protected bodies of water, usually of small 

 surface area and shallow water depth, when small 

 (Springer and Woodburn 1960), and seagrass beds 

 when larger (Gilmore et al. 1983). Shoreline vegeta- 

 tion is also considered a possible important element as 

 juveniles also occur in areas with vegetation otherthan 

 seagrass (McMichael et al. 1989). They have been 

 collected in ditches, tidal pools, headwaters of creeks, 

 ponds, bays, and shorelines in freshwater to euhaline 

 salinities in water depths from 0.3 to 1 .2 m (Lunz 1 953, 

 Marshall 1958, Springer and Woodburn 1960, Tabb 

 and Manning 1 961 , Gunter and Hall 1 965, Linton and 

 Rickards 1 965, Merriner et al. 1 970, Martin and Shipp 

 1 971 , Breuer 1 972, Dahlberg 1 972, Fore and Schmidt 

 1973, Ager et al. 1976, Hoese and Moore 1977, 

 McMichael et al. 1 989). In southwest Florida, Fore and 

 Schmidt (1973) reported that primary nursery areas 

 were brackish, shallow, warm tidal streams and dredged 

 canals with slow currents, soft bottoms, and little sub- 

 merged vegetation, but often with shoreline stands of 

 red or white mangrove. McMichael et al. (1989) 

 described a similar habitat for juvenile snook in the 

 Tampa Bay area. On the Florida east coast, Gilmore 

 et al. (1983) reported that juveniles with standard 

 lengths (SL) that average 27.5 mm are typically found 

 in freshwater tributaries. They begin to move from 

 stream banks and bank vegetation to deeper water or 

 salt marshes at 60 mm SL, 40 to 70 days old. Juveniles 

 move from this habitat at an average size of 67 mm SL, 

 showing up in seagrass beds after reaching lengths of 

 1 00 to 1 50 mm SL. Their residence here is from 1 to 6 

 months with most fish leaving at 300 mm SL. 



Adults are found in estuarine and neritic waters. They 

 inhabit Gulf passes, channels, beaches, river mouths, 

 mangrove or salt marshes, brackish estuarine waters, 

 and tidal ponds, lakes, and streams (Higgins and Lord 

 1 926, Marshall 1 958, Tabb and Manning 1 961 , Gunter 

 and Hall 1 963, Odum 1 971 , Kushlan and Lodge 1 974, 

 Ager et al. 1 976, Hoese and Moore 1 977). They have 

 been reported in waters from 0.3 to 3.66 m in depth and 

 in salinities ranging from fresh to euhaline (Baughman 

 1943, Gunter and Hall 1963, Cooley 1974, Kushlan 

 and Lodge 1974, Loftus and Kushlan 1987). In sum- 

 mer, they have been reported in offshore areas such as 

 coral reefs as far as 70 miles west of Key West, Florida, 

 in the Dry Tortugas National Park (Schmidt pers. 

 comm.). 



Substrate : Juveniles and adults have been found over 

 bottoms of clay, mud, mud-sand, sand, sand with 

 rocks, detritus with mud and sand, and sand with shell 



(Breuer 1957, Marshall 1958, Gunter and Hall 1963, 

 Gunter and Hall 1 965, Bruger 1 981 , McMichael et al. 

 1989). 



Physical/Chemical Characteristics : 

 Temperature: The common snook is very sensitive to 

 temperature, with detrimental effects occurring at ap- 

 proximately 15°C or lower (Marshall 1958, Gilmore et 

 al. 1983). 



Temperature - Eggs: Eggs have not been observed in 

 the wild, but they have been successfully spawned and 

 developed at 28° ± 1 ° C (Shaf land and Koehl 1 979, Lau 

 and Shafland 1982, Tucker 1986). 



Temperature - Larvae: Larvae propagated in laborato- 

 ries have been successfully reared at 24.6 to 32.4°C 

 (Shafland and Koehl 1979, Lau and Shafland 1982, 

 Tucker 1 986). Snook larvae have been collected from 

 Naples Bay, Florida, in temperatures ranging from 

 28.7° to 31 .4°C (Tolley et al. 1 987). In a hatchery study, 

 snook larvae reared at 24°C did not survive, and 

 development rates increased with incubation tempera- 

 ture. Optimum yolk utilization efficiency and larval 

 growth occurred at 26°C (Limouzy 1993). 



Temperature - Juveniles and Adults: Juveniles and 

 adults have been collected in waters with a tempera- 

 ture range of 1 4.2° to 35.6°C (Marshall 1 958, Springer 

 and Woodburn 1 960, Tabb and Manning 1 961 , Gunter 

 and Hall 1963, Linton and Rickards 1965, Merriner et 

 al. 1970, Martin and Shipp 1971, Dahlberg 1972, 

 Cooley 1974, Shafland and Foote 1983, McMichael et 

 al. 1989). Temperature tolerance may differ through- 

 out the common snook's range due to such parameters 

 as genetic stock, salinity, size, and diet (Howells et al. 

 1 990). In laboratory experiments on the effect of falling 

 temperature, juveniles ceased feeding at 14.2°C, lost 

 equilibrium at 12.7°C, and died at 12.5°C (Shafland 

 and Foote 1 983). Other studies suggest a lower lethal 

 temperature for juvenile snook of 9°C in salt water 

 (19% ) and 10°C in freshwater (Howells et al. 1990). 

 Abnormal behavior has been reported below 14.2°C, 

 with death occurring from 9 to 17°C. The lower lethal 

 limit for small juveniles has been reported as 9 to 14°C, 

 while that of sub-adults and adults probably approaches 

 the lower end of a 6 to 13°C range, making them 

 somewhat more tolerant of colder temperatures than 

 fingerlings (Marshall 1958, Springer and Woodburn 

 1 960, Gunter and Hall 1 963, Shafland and Foote 1 983, 

 Howells et al. 1 990). Many field studies have reported 

 snook as lethargic, stunned, or killed as a result of 

 winter freezes (Marshall 1958, Cooley 1974). Gunter 

 (1 941 ) reported a severe winter kill of snook along the 

 Texas coast due to cold weather in 1940. 



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