Red drum, continued 



Substrate : Newly hatched larvae are found in the Gulf 

 surf over pure sand bottoms. After entering bays and 

 estuaries, they occur over substrates of mud, sand, or 

 sandy mud bottoms as well as in and among patchy 

 sea grass meadows, but prefer muddy bottoms. Small 

 juveniles seem to prefer medium soft mud to firm sandy 

 substrates (Peterson 1986). Small fish are probably 

 more successful at capturing prey in the less dense 

 vegetation areas, while living in areas of greater sea 

 grass density probably helps them to avoid predation 

 (Pearson 1928, Simmons and Breuer 1962, Yokel 

 1966, Perret et al. 1980, Ward and Armstrong 1980, 

 Benson 1 982, Holt et al. 1 983, Overstreet 1 983). They 

 are normally associated with such sea grasses as 

 Halodule beaudettes, Ruppia maritima, and Thalassia 

 testudinum (Zimmerman 1969, Perret et al. 1980). 

 Large juveniles and adults are common over muddy, 

 sandy, or oyster reef bottoms with little or no sea grass 

 (Yokel 1966, Lee et al. 1980, Perret et al. 1980). 



Physical/Chemical Characteristics : 

 Temperature: Tolerance of environmental conditions 

 changes with age, life history stage, season, and 

 geography (Crocker etal. 1981). No major difference 

 between thermal tolerances appears to exist between 

 populations of red drum from the Gulf of Mexico and 

 mid-Atlantic coast (Ward et al. 1993). 



Temperature - Eggs and Larvae: Eggs and newly 

 hatched larvae tend to be stenothermal while 10 day 

 and older larvae are more eurythermal (Crocker et al. 

 1981). Eggs and larvae from captive spawns have 

 developed over a temperature range of 20° to 30°C 

 with optimal survival at 25°C. Highertemperatures (30 

 and 35°C) are associated with poor survival of yolk sac 

 larvae (Holt et al. 1981a, Overstreet 1983, Lee et al. 

 1984). Larvae and post-larvae have been collected in 

 the wild from 1 8.3° to 31 .0°C (Yokel 1 966, Perret et al. 

 1 980, Peters and McMichael 1 987, Van Hoose 1 987). 



Temperature - Juveniles: Juveniles are eurythermal, 

 and are found in waters ranging in temperature from 

 2.0° to 34.9°C (Gunter 1945, Simmons and Breuer 

 1962, Yokel 1966, Franks 1970, Perret et al. 1971, 

 Wang and Raney 1971, Christmas and Waller 1973, 

 Pineda 1975, Tarver and Savoie 1976, Bonin 1977, 

 Barret et al. 1 978, Adkins et al. 1 979, Perret et al. 1 980, 

 Holt et al. 1981a, Daniels and Robinson 1986, Peters 

 and McMichael 1987). They appear to prefer tempera- 

 tures ranging from 10° to 30° (Ward and Armstrong 

 1980). Juveniles in heated discharge waters have 

 survived up to 35°C, but at 39°C some died, apparently 

 from handling stress (Overstreet 1983). Large num- 

 bers have been killed in sudden severe cold spells, but 

 normally fish will move into deeper waters during 

 periods of extreme temperatures (Simmons and Breuer 

 1962, Adkins et al. 1979). In a laboratory study, fish 



ceased feeding between 7° to 9°C and death generally 

 occurred when temperatures fell to 4°C or lower for 

 several days (Miranda and Sonski 1985). 



Temperature - Adults: Adults are also eurythermal, and 

 have been collected over a temperature range from 

 2.0° to 33°C (Simmons and Breuer 1 962, Yokel 1 966, 

 Juneau 1 975, Perret et al. 1 980, Ward and Armstrong 

 1 980, Daniels and Robinson 1 986). Adults are consid- 

 ered more susceptible to the effects of winter cold 

 waves than smaller fish (Yokel 1966), and they nor- 

 mally move into deeper waters for refuge (Simmons 

 and Breuer 1962). 



Salinity: All life stages are sensitive to high salinities 

 when combined with high temperatures, but suscepti- 

 bility is influenced by the size of the fish (Simmons 

 1957). 



Salinity - Eggs and Larvae: Eggs and larvae in particu- 

 lar are sensitive to environmental conditions (Overstreet 

 1 983). Eggs from hatchery spawns develop success- 

 fully into feeding larvae at salinities of 10 to 40%o in a 

 temperature of 25°C. Below 10%° the hatch rate is 

 poor, and below 25% eggs sink resulting in losses from 

 fungal infection, crowding, and low oxygen (Vetter et 

 al. 1983). High salinities coupled with high tempera- 

 tures were associated with poor yolk sac larvae sur- 

 vival (Holt et al. 1 981 a). The best salinities reported for 

 24 hour survival and hatch are 30%o at 25°C and 34 to 

 36.5%« at 23° to 26°C (Neff et al. 1982, Overstreet 

 1 983, Lee et al. 1 984). Eggs have been collected in the 

 field from 21 °C to 23°C in a salinity range of 29 to 32% 

 (Johnson and Funicelli 1991). Larvae from hatchery 

 spawns were more stenohaline than older life stages, 

 particularly during the first two weeks after hatching 

 with best survival at about 30%o (Crocker et al. 1 981 , 

 Holt et al. 1 981 a, Overstreet 1 983). One article reports 

 tolerance from <1 to 50%o and a preference of 20 to 

 40% o salinity (Ward and Armstrong 1 980). Larvae and 

 post-larvae collected in the wild were found over a 

 salinity range of 8 to 36.4%o (Yokel 1966, Peters and 

 McMichael 1 987, Van Hoose 1 987). One study reports 

 spawning occurring during a salinity range of 14.7 to 

 18.5%o (Hein and Shepard 1986a). 



Salinity - Juveniles and Adults: Both juveniles and 

 adults are euryhaline (Gunter 1942, Gunter 1956, 

 Simmons and Breuer 1962, Yokel 1966, Perret et al. 

 1980, Crocker et al. 1981, Holt et al. 1981a, Benson 

 1982, Daniels and Robinson 1986). They are very 

 efficient osmoregulators with the ability to tolerate 

 abrupt changes in salinity which is especially important 

 to juveniles in the estuarine environment. Juveniles 

 appear more tolerant to low salinity, whereas adults 

 which are less dependent on estuarine areas and 

 spend more time at sea are more tolerant of high 



294 



