Habitat Use by Juvenile Gag, Mycteroperca microlepis (Pisces: Serranidae), in Subtropical Charlotte Harbor, Florida (USA)

Estuaries playa key role in the juvenlle stage of gag (Myeteroperca microlepis). The use of estuarine habitats by juvenlle gag has been examined in temperate estuaries, which are at the northern limits of the range of this species, but the importance of subtropical estuaries during fue early life history of this species has not heen studied extensively. Gag were collected in subtropical Charlotte Harbor, Florida, during routine monthiy sampling from January 1996 to Decemher 2002. Juvenlle gag were collected using a 21.3-m seine, a 183-m haul seine, and a 183-m purse seine. A total of 738 individuals ranging from 30 to 489 rom standard length (SL) were collected in 4,480 samples. Most gag (96%) were probably young-of-the-year « 288 rom SL). The majority of juveniles were collected in polyhatine Gasparilla and Pine Island sounds from April to December, with a few larger individuals captured year-round. The observed period of gag settlement was similar to thet reported in other subtropical and temperate estuaries, but gag in Charlotte Harbor remained in fue estuary longer and egressed at a larger size 1han did gag in other estuaries. Relative abundance of juvenile gag within Charlotte Harbor was greatest on shallow seagrass shoals but was also high along flinging mangrove shorelines, which is a habitat not previously reported for gag. INTRODUCTION Estuaries play a key role in the juvenile stage of gag (Mycteroperca micro/epis) (Keener et aI. 1988). The species ranges from New York to Bra.zi\, including the entire Gulf of Mexico (GOM), and juveniles have been reported to occur in temperate and subtropical esmaries from Vrrginia 10 fue northeastern GOM (Haese el al. 1961, Hood and Schlieder 1992, Koenig and Coleman 1998). This economically important serranid spawns in large aggregations, such as those found at traditional West Florida Shelf sites in the GOM, primarily during February and March (Hood and Schlieder 1992, Collins et aI. 1998). The planktonic larvae move into estuaries and settle out at about 15 rom standard length (SL) in the first available habitat, such as polyhaline seagrass beds and oyster shell habitats near inlets and mouths of tidal creeks (Ross and Moser 1995, Mullaney and Gale 1996). As juvenile gag grow rapidly during their estuarine residence, they may also use manmade habitats like seawalls and jetties (Hastings 1979, Bullock and Smith 1991). Latitudinal differences in climate appear to affect the duration of estuarine residence and size attained by juvenile gag before they dlsperse to non-estuarine habitats (Ross and Moser 1995). Juveniles are usually found in North Carolina estuaries from April to September and in estuaries along the northeastern GOM from April to October (Ross and Moser 1995, Koenig aod Coleman 1998). The first cold front of fall is thought to trigger their egress to deeper ocean water (e.g., Ross and Moser 1995). In temperate estuaries such as Bogue Sound, North Carolina, maximum reported size does not exceed 200 nun SL (Ross and Moser 1995), but in subtropical estuaries such as Tampa Bay, Florida, gag can reach 360 nun SL (Hood and Schlieder 1992). Ifubitat use by juvenile gag has been examined in temperate estuaries, which are at the northern limits of the range of this species; however, the importance of subtropical estuaries daring the early life history of this species has not been studled extensively. Despite the effects of increasing urbanization aod the resultant demll.llds for freshwater resources, Charlotte Harbor, a large subtropical estuary in southwestern Florida, supports mll.lly suitable habitats for juvenile gag (e.g., seagrass beds, oyster shell habitats). Although joveniles have been collected from seagrass beds within the estuary (Wang and Raney 1971, Hanson et aI. 2004, Fitzhogh et al. 2005), questions regarding aspects of habitat use, especially use of tropical climate habitats like mangroves, have not been examined. Thus, the objective of this study was to use an estuary-wide dataset from a long-term fisheries-independent monitoring program in Charlotte Harbor to examine distribution, seasonality, habitat use, and relative abwuill.llce of juvenile gag in a subtropical estuary. MATERIALS AND METHODS Stndy location Charlotte Harbor, located on the southwestern coast of Florida, is one of the largest estuaries in Florida and