Updating Size and Age at Maturity Schedules for Southern Flounder,

Southern flounder Paralichthys lethostigma are consistently among the most valuable finfish resources in North Carolina.  However, elevated harvest rates during the past two decades have contributed to a ‘depleted’ status for the stock.  Current estimates of size- and age-at-maturity for southern flounder have recently been questioned, necessitating validation of maturation schedules to ensure accurate estimates of mature stock biomass.  We collected 501 southern flounder throughout the 2009 spawning season from multiple North Carolina locations to generate independent estimates of size- and age-at-maturity.  All fish were assigned a maturity stage based on macroscopic guides, 239 individuals were analyzed histologically, and several additional morphological characteristics were recorded to improve descriptions of maturity stages.  Our estimate of total length at 50% maturity (L50) developed from histologically-staged fish was approximately 410mm—between 20–60mm greater than previous estimates.  We found strong agreement between macroscopic and histological staging for immature and fully mature individuals; however, there was substantial variation in histologically-based maturation for fish classified macroscopically as ‘developing’.  Examination of morphological characteristics showed that ovary dimensions change during maturation; the center of the lobe becoming thicker when oocytes reach the cortical alveoli stage.  No regional differences within the state were detected in patterns of maturity.  Otolith microchemistry will be analyzed to help describe patterns of habitat use as they relate to reproductive events.