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.

Sex‐Specific Growth and Reproductive Dynamics of Red Drum in the Northern Gulf of Mexico

“…We found that although the relationship between GSI and GFBW in Red Drum was significant, it explained very little of the variance (10% for female‐specific values; 18% for male‐specific values), indicating that GSI is a good indicator of spawning preparedness (Corey et al. ). The significant relationship was likely attributable to the number of young (age < 5) individuals that were histologically identified as mature but had very low GSI values.…”

Changing climate associated with the range‐wide decline of an estuarine finfish

“…For the recent time series, the lack of correlation with neighboring estuaries and curious occurrence of correlation with furthest distance estuaries again indicates the lack of a regional pattern to this synchrony. The absence of a relationship with neighboring estuaries could be explained by the life history of southern flounder, a relatively short‐lived fish that matures by age‐1 or age‐2 (Corey, 2016; Midway & Scharf, 2012), as faster life history species (early reproduction, shorter generation time, short longevity) exhibit less spatial synchrony than slower life history species (Marquez et al, 2019). The lack of local scale spatial synchrony, combined with the evidence for a range‐wide decline, is concerning as increased synchrony among interacting spatial populations can reduce the resilience of declining stocks (Koenig & Liebhold, 2016).…”

Warmer waters masculinize wild populations of a fish with temperature-dependent sex determination

“…Southern flounder ( Paralichthys lethostigma ) are distributed in the southeastern United States, with populations in the Gulf of Mexico and along the Atlantic coast in North Carolina (NC), near the northern edge of the species range. Adult flounder are batch spawners that migrate out from estuaries to coastal waters to spawn during late fall to early winter 23 . The fertilized eggs are buoyant and will float for two to three days until hatching.…”