Growth and Spawning Dynamics of Southern Flounder in the North-Central Gulf of Mexico

Abstract

Southern Flounder Paralichthys lethostigma is the most commonly harvested flatfish in the north-central Gulf of Mexico (GOM), yet knowledge of this species’ growth and reproduction is limited for the Mississippi region. Given the offshore spawning migrations and likely mixing between state-managed units of the GOM Southern Flounder stock, small-scale environmental influences may constitute a major driver of life history dynamics during early life residency in nearshore estuaries. Therefore, estimates of local demographic characteristics are needed for effective fishery management. Here, we describe critical life history traits of Southern Flounder, including estimation of growth rates and maturity. The three-parameter von Bertalanffy growth function best described female-specific growth: mean asymptotic length L_∞ was 514 mm TL, mean growth coefficient k was 0.67 year^–1, and mean theoretical age at zero length t₀ was –0.50 years. The estimated female-specific mean length at 50% maturity (L₅₀) was 303 mm TL, and the female-specific mean age at maturity was 0.96 years. Although we observed significant differences between L₅₀ estimates in the GOM, length-at-age parameter estimates were similar to those reported for other areas of the GOM. Both individual growth and length-at-maturity estimates were significantly different from those reported for the Atlantic, suggesting basin-level differences in population characteristics, with faster growth and earlier maturation in the GOM. Histological indicators and gonadosomatic index data indicated that the spawning season in the north-central GOM occurs from November to January and that Southern Flounder are batch spawners with asynchronous oocyte development. Our study provides a description of growth and spawning dynamics that will contribute to future stock assessment efforts focused on the Southern Flounder fishery in Mississippi and the GOM.

Received July 25, 2016; accepted January 24, 2017

ACKNOWLEDGMENTS

Funding for this research was provided by the Mississippi Tidelands Trust Fund Program, administered by the Mississippi Department of Marine Resources, and awarded to S.D.C. and R.T.L. We thank the many individuals who assisted in collecting fish for the project, as well as staff of the Marine Education Center and the Center for Fisheries Research and Development, University of Southern Mississippi, for their constant support with field sampling. We are grateful to Gary Gray for providing technical expertise in otolith-based aging methods and to the Project INSPIRE student interns for assistance with laboratory sample processing.