Age structure and age at maturity of southern flounder (Paralichthys lethostigma) in the New River: Implications for size-based management

ABSTRACT

The lack of demographic data for southern flounder in North Carolina has presented an important need to obtain accurate information on population size and age structure for further management.  Age and size structure of 206 fish returned by commercial fishermen from a larger tagging study were examined. Southern flounder ranged from 320 to 507 mm TL and all fish were estimated at 0, 1, or 2 years of age. Of 174 individuals that could be aged, 29 were age-0 (17%), 129 were age-1 (74%), and 16 were age-2 (9%). The mean TL of all fish was 386mm. Macroscopic staging of gonads indicated that 0% of age-0 fish were mature, 48% of age-1 fish were mature, and 67% of age-2 fish has reached sexual maturity. Using January 1st as an assumed birth date, monthly ages were calculated and ranged from 8 to 35 months. Using monthly ages and macroscopic gonad stages, it was estimated that the age at which 50% of the females (T_mat) were mature was 22 months when fish with developing gonads were assumed to be immature. The length at which 50% of individuals had reached maturity (L_mat) for this scenario was estimated to be 402 mm TL. If, however, fish with developing gonads were considered to be mature, the L_mat was decreased to 329 mm TL. T_mat could not be calculated for this scenario because of insufficient numbers of immature fish. If southern flounder with developing gonads do not mature in time to spawn in the following winter, the estimated L_mat (402 mm TL) is considerably higher than the L_mat currently assumed for the species (345 mm TL). Histological examination of gonads is likely required to clarify this difference. Results from this study may help to highlight regional variation in population dynamics for this species and should encourage the acquisition of coast wide demographic data for southern flounder.