Evaluation of an Accurate and Non-Lethal Tool to Assess Maturity of North Carolina Southern Flounder

Southern flounder (Paralichthys lethostigma) in North Carolina are a highly valued commercial and recreational fishery resource. Presently, southern flounder stocks are classified as overfished and overfishing is still occurring. Fishery managers place emphasis on the importance of having updated maturity schedules and knowledge of a species life history when developing stock assessments and setting harvest limits. Macroscopic classification of maturity has proven unreliable in some cases, and alternatives, such as histology, can be expensive. In this study, we explore a non-lethal method of determining maturity by examining levels of reproductive hormones. Non-lethal blood samples (n=107) were taken throughout the fall of 2011 from inshore female southern flounder. We assayed two hormones, estradiol and testosterone, and compared their levels to other measures of maturity, including gonodosomatic and hepatosomatic indices and histologically-validated maturity. Both testosterone and estradiol were significantly different (P < 0.001) in mature and immature fish and both hormones showed significant temporal variation with peaks in October and November. Although hormone levels decreased in December, this can be attributed to a decrease in proportion of mature individuals sampled; mature fish migrate offshore in the fall and few remain late in the season. Overall, hormone assays provide promise toward an easy and cost-effective way to determine maturity for future southern flounder management and stock recovery.