Gulf menhaden, continued 



from Calcasieu Lake, Louisiana to between Mobile Bay 

 and Perdido Bay, Alabama (Table 5.17) (Reintjes and 

 Pacheco 1966, Dugas 1970, Lewis and Roithmayr 

 1 981 , Powell and Phonlor 1 986, Christmas et al. 1 988, 

 Nelson et al. 1992). 



Life Mode 



This is an estuary dependent, marine migratory spe- 

 cies (Ahrenholz 1991). Eggs and larvae spend 3-5 

 weeks in offshore waters as currents carry them into 

 estuaries. Juveniles are nektonic and adults are pe- 

 lagic (Tagatz and Wilkens 1973, Wagner 1973, Perry 

 and Boyes 1978, Deegan 1985). Schooling behavior 

 first appears during late larval development, and con- 

 tinues throughout the gulf menhaden's life span (Christ- 

 mas et al. 1983). 



Habitat 



Type : Food availability is probably the most important 

 requirement for determining habitat suitability (Christ- 

 mas et al. 1 982, Deegan 1 990). The gulf menhaden is 

 estuarine dependent, spending most of its life in estu- 

 aries and nearshore waters of the Gulf of Mexico 

 (Lewis and Roithmayr 1 981 , Christmas et al. 1 982). It 

 spawns in coastal and offshore waters in the winter. 

 Larvae are found in greatest densities nearthe surface 

 (Govoni et al. 1989), and over the inner to middle 

 continental shelf. Larvae are known to occur from 

 September through April (Ditty et al. 1 988), with peak 

 densities in January and February (Ditty 1 986, Shaw et 

 al. 1985b). They spend 3-5 weeks in offshore waters 

 before moving into the quiet, low salinity shallows of 

 marshes and estuaries and their tributaries, where 

 they transform intojuveniles. Juveniles move to deeper, 

 open estuarine waters, and individuals greater than 50 

 mm SL are found primarily in this area. They remain in 

 open water habitats until the following fall. Adults live 

 in estuaries and nearshore waters during the spring 

 and summer, and occur in depths of 1 .8 to 1 4.6 m (Fore 

 and Baxter 1972, Christmas and Waller 1975, Lewis 

 and Roithmayr 1978, Simoneaux 1979, Christmas et 

 al. 1982, Deegan 1985, Nelson and Ahrenholz 1986, 

 Deegan 1990, Ahrenholz 1991). During the fall and 

 winter months they are found offshore at depths of 7.3 

 to 87.8 m. 



Substrate : This fish inhabits the water column, and no 

 direct use of the substrate is apparent. It is generally 

 caught over soft mud bottoms, and it is assumed soft 

 mud substrates are preferred because of the abun- 

 dance of benthic organisms and the richer organic 

 content (Christmas et al. 1982, Lassuy 1983). 



Physical/Chemical Characteristics : 

 Temperature: Eggs have been collected in the wild 

 from 17 to 20°C (Christmas et al. 1988). Water 

 temperature preference for juveniles and adults is 



between 12° and 30°, but they have been taken in 

 waters over a range extending from 2.5 to 35.5°C. 

 Temperature tolerances have also been observed to 

 be quite wide at lower salinities. Active avoidance of 

 temperatures above 30°C has been reported, as well 

 as a kill occurring at 39°C (Miller 1 965, Holcomb 1 970, 

 Copeland and Bechtel 1971, Wagner 1973, Gallaway 

 and Strawn 1 974, Christmas and Waller 1 975, Pineda 

 1975). Gunter and Christmas (1960) reported that 

 fishery activities in Mississippi Sound begin in the 

 spring as water temperatures reached 23°C, and slow 

 in the fall at approximately the same temperature. 



Salinity: This species has been collected in salinities 

 ranging from fresh to hypersaline. Gravid adults, 

 fertilized eggs, and early larvae are typically associ- 

 ated with the higher salinities of the open Gulf of 

 Mexico, generally 29%o and higher. Post-larvae and 

 juveniles occupy a wider range of tolerance, generally 

 occurring from 5 to about 30% o . However, they may 

 also enter freshwater tributaries (Mettee et al. 1996). 

 Non-gravid and developing adults occupy mid-range 

 salinities in the deeper part of estuaries, with high 

 abundances at 20-25%o reported (Wagner 1 973, Pineda 

 1975, Perry and Boyes 1978, Marotz et al. 1990), but 

 are capable of tolerating ranges from to 67%o (Etzold 

 and Christmas 1979). Mass mortalities have been 

 reported under hypersaline conditions of 80%oorgreater 

 (Springer and Woodburn 1 960, Holcomb 1 970, Tagatz 

 and Wilkens 1 973, Wagner 1 973, Gallaway and Strawn 

 1 974, Shaw et al. 1 985a, Christmas et al. 1 988). 



Dissolved Oxygen: Christmas (1 981 ) suggests a mini- 

 mum dissolved oxygen (DO) concentration of 3 parts 

 per million (ppm); however, the empirical basis for this 

 minimum was not given. Marotz et al. (1 990) found that 

 in estuarine waters with DO concentrations below 2 

 ppm, seaward movements of gulf menhaden increased. 



Movements and Migrations : Gulf menhaden migration 

 patterns coincide with productivity peaks occurring in 

 different areas of an estuarine system (Deegan 1985, 

 Deegan 1 990). Larvae are carried shoreward from the 

 central breeding grounds offshore for 3 to 5 weeks by 

 currents, and then are distributed along nearshore 

 areas throughout the range, predominantly by longshore 

 current (Shaw et al. 1 985b). Larvae can begin migrat- 

 ing into estuaries in October, and continue through late 

 May. Peak influxes of larvae moving into Texas and 

 Louisiana tidal passes occur during November-De- 

 cember and February-April. During flood tides, larval 

 gulf menhaden may be dense in the the mid-stream of 

 tidal passes, to maximize transport into estuarine ar- 

 eas (Raynie and Shaw 1994). They are then carried 

 through open bays and into shallow estuarine areas 

 (tidal creeks and ponds) by tidal flow when about 1 5-25 

 mm. They may then enter brackish and/or freshwater 



136 



