Seasonal Migration in the Southern Hogchoker, Trinectes maculatus fasciatus (Achiridae)

Life history patterns often respond to local environmental conditions. The seasonal migration pattern of the northern hogchoker has been described, but the southern subspecies rarely has been studied. Todocument the migratory movements and the habitat characteristics of the southern hogchoker, long-term survey data and specimens collected during 1993 were examined. Moderate depth (5.8-6.4 m), low water clarity (0-1.2 m), moderate oxygen concentration (4-9 ppm), and sand-mud substrata generally defied hogchoker habitats. Hogchoker habitats only showed seasonal shifts in temperature and salinity characteristics. Hogchokers were only collected in low salinity (0-2 ppt) waters during the winter. but exhibited three abundance peaks in relation to bottom salinity during the summer samples at 0 , 5 , and 18 ppt. The survey data and the data from the 1993 specimens support the hypothesis that southern hogchokers are following a migration pattern similar to that described for the northern subspecies. The distributionof Trinectes maculatus fasciatus, the southern hogchoker, extends south from approximately SouthCarolina to the Yucathpeninsula. The range of the northern subspecies (T. m. maculatus) extends from the South Carolina coast north to Massachusetts (Hildebrand and Cable 1938, Gilbert andKelso 1971). Hogchokers are small estuarine fish with a complicated migration pattern. Newly-hatched individuals begin moving into freshwater areas following summer estuarine spawning and begin migrating into low salinity areas the next spring. This downstream distance is extended progressively each year until maturity, when spawning occurs in the outer areas of the estuary. A return migration into freshwater occurs each fall for the winter period (Dove1 et al. 1969). Life history patterns may vary in response to local ecological conditions and the timing of environmental factors can often dictate differences in the evolution of these traits (Steams 1976, Boyce 1979). The migratory movements and many life history factors of the northern hogchoker have been widely studied. However, the southern subspecies has only been the subject of a few studies along the Atlantic coast (Castagna 1955, Smith 1986). The purpose of this study was to determine if the movement pattern documented in the northern subspecies is also present ina Gulf population of southern hogchokers. While individual collections have documented hogchokers in both freshwater streams and estuaries along the Mississippi coast, I also examined continuous survey data to clarify seasonal movement patterns. These survey data were also used to describe habitat characteristics of * Current address: University of South Florida, Departbaent of Biology, Tampa, Florida 33620, USA T. m. fasciatus. Finer details of the migration pattern were investigated by examining the reproductive condition and age of hogchokers along the salinity gradient during 1993. Hogchoker distribution and habitat data were obtained from a fishery survey conducted since 1980 along the salinity gradient from the Back Bay of Biloxi offshore to Horn Island by personnel of the Gulf Coast Research Laboratory (GCRL), Ocean Springs, Mississippi. The survey samples consisted of standardized 10 minute tows with a 4.9 m flat otter trawl. Deeper trawls, at stations 83 and 84, required 30 minute tows with a 12.2 m flat otter trawl. Both trawls cozlsisted of a 19.1 mrn stretchmesh body with a 6.4 nun mesh cod end liner. Monthly collections were made at six sites along the salinity gradient and hogchokers were commonly caught at four of these sites: Bayou Bernard (36). Keesler Marina (34), Biloxi East Channel (37), and Bellefountain Buoy 8 (32) (Figure 1).