Southern flounder (Paralichthys lethostigma) stock structure inferred from otolith shape analysis

Abstract

Abstract-Examination of otolith morphometric variation has been shown to provide improved descriptions of stock structure for several marine fish species. We examined spatial variation in otolith shape of southern flounder (Paralichthys lethostigma) to understand population structure at the following geographic levels: ocean basin (Atlantic and Gulf of Mexico); regional coastal waters (Texas, Florida) and (Georgia, South Carolina); and local coastal waters (North Carolina). To reduce variability, we considered only age-1 female fish. From digitized otolith images, we extracted descriptions for common shape indices and elliptical Fourier coefficients and found strong evidence for differences at the ocean basin scale, but only weak evidence for structure at either within-basin (i.e., among states) or within-state (local) spatial scales. Our finding of inferred stock structure differences between the ocean basins aligns with the geographic break in the distribution of this species-the absence of this species from the southern portion of Florida-as well as with recent genetic findings. Currently, state-level management of southern flounder in both areas does not account for any basin-wide population mixing and, therefore, by default, assumes a separate unit stock for each state, although our findings indicate that mixing could be extensive. Additional sources of information (e.g., genetics, life history traits) collected at appropriate spatial scales should be examined to confirm suspected levels of mixing and to determine suitable management strategies for the conservation of southern flounder stocks throughout their ranges.

Spatial and temporal variability in growth of southern flounder (Paralichthys lethostigma)

“…Males, on the other hand, provided less precise estimates of growth rates due to smaller sample sizes; however, we did detect a weak geographic signal in which growth rates tended to increase with populations south and west. Our analysis did not detect any between basin differences in growth rates for either males or females, which we hypothesized to exist (at least for females) based on previously-established stock differences (genetic [Anderson et al, 2012] and otolith shape [Midway et al, 2014]) at the basin scale.…”

“…Genetic work has established two distinct basin populations-the Gulf of Mexico and southeastern US Atlantic Ocean (Anderson et al, 2012). However, genetic work and otolith morphometrics (Midway et al, 2014) have failed to identify any structuring within basins. Despite lack of genetic structuring within basins, phenotypic differences may exist.…”

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

“…Recently, there has been interest in understanding the stock structure of Southern Flounder. Past research has focused on using genetics (Blandon et al 2001;Anderson and Karel 2012), otolith morphometrics (Midway et al 2014), tagging methods (Furey et al 2013;Craig et al 2015), and models of growth variability (Midway et al 2015) to better describe Southern Flounder stock structure. Based on these studies, the Southern Flounder population appears to exhibit homogeneity, with little structuring among or within GOM states.…”

Population Genetic Structure of Southern Flounder Inferred from Multilocus DNA Profiles

“…Thus far, we have no evidence that Southern Flounder from different locales within the Atlantic are biologically distinct. Based on otolith morphometric analysis, Midway et al (2014) also detected only weak evidence for differentiation among Southern Flounder populations within the Atlantic, including within NC. These results are consistent with our findings.…”