Southern Flounder Research Articles

Consumer likelihood to purchase farmed marine finfish with potential for commercialization in the United States

Local aquaculture production of marine finfish has potential to meet the domestic seafood demand and contribute to reduction of the United States (U.S.) seafood trade deficit. The United States Department of Agriculture-Agricultural Research Service, along with other research programs, has developed aquaculture production technologies for warmwater marine finfish species with potential for commercial production. To understand the marketing opportunities for the candidate species, an online survey of 818 seafood consumers in the southeastern U.S. was conducted to explore their awareness, familiarity, frequency of consumption, location of purchase, and likelihood of purchasing the species of interest. A binary logit model was specified to explore the factors that influenced consumers likelihood to purchase Atlantic cod, black sea bass, California flounder, California yellowtail, Florida pompano, redfish, red snapper, southern flounder, spotted seatrout, striped bass, summer flounder, and white seabass, the 12 species for which there were at least 100 survey responses. This study focused on consumers likelihood to purchase the candidate species at grocery stores and restaurants. The results show that consumers who placed high importance on source of the fish and quality were more likely to buy various candidate species including red snapper, striped bass, Atlantic cod, southern flounder, Florida pompano, California yellowtail, black sea bass, California flounder, and white seabass. Respondents who considered price to be important were more likely to buy California flounder, redfish, red snapper, white seabass, black sea bass (at grocery stores only), and summer flounder (at grocery stores only). Frequent consumers of Atlantic cod, southern flounder, California flounder, redfish, summer flounder (at grocery stores only) and California yellowtail (at grocery stores only) were more likely to purchase these species. Frequency of consumption, seasonality in consumption, and demographic characteristics, including income, age, race, and state of residence, influenced consumers likelihood to purchase various species of interest.

Combining biotracer and stomach contents analysis to understand trophic dynamics in the northern Gulf of Mexico

The northern Gulf of Mexico (nGOM) is a taxonomically rich ecosystem. Previous work based on a meta-analysis of stomach contents data has shown the trophic connectivity of predators and prey to be substantial. However, the trophic dynamics of many economically and ecologically important species are still not well understood. Sportfish, such as Spotted Seatrout (Cynoscion nebulosus), Red Drum (Sciaenops ocellatus), and Southern Flounder (Paralichthys lethostigma), support recreational fisheries throughout the region. Gulf Menhaden (Brevoortia patronus), a high biomass forage fish with the region's largest commercial fishery, is considered an important forage species. In this study, we use information from meta-analysis of stomach contents and stable isotope analysis to investigate the importance of prey taxa, including Gulf Menhaden, for nGOM nearshore predators. Stomach contents and stable isotope analyses are generally evaluated independently, with stomach contents used to directly identify trophic interactions, while stable isotopes of carbon (δ13C) and nitrogen (δ15N) provide insight into a consumer's long-term feeding habits. We used a multispecies trophic model, EcoDiet, developed by Hernvann et al. (2022), that integrates information of both stomach contents and stable isotopes into a single framework to estimate trophic link probabilities and diet proportions. Data in the model include n = 41 predators, n = 173 prey, and n = 497 unique predator and prey interactions. The results indicate that nGOM nearshore predators are generalists using the diverse prey base, and in concordance with previous findings, there is no single Menhaden-dependent predator. Our findings better quantify the trophic interactions of the highly diverse nGOM region and have important implications regarding future ecosystem modeling and management considerations for the Gulf Menhaden stock.

Analysis of the Skin and Brain Transcriptome of Normally Pigmented and Pseudo-Albino Southern Flounder (Paralichthys lethostigma) Juveniles to Study the Molecular Mechanisms of Hypopigmentation and Its Implications for Species Survival in the Natural Environment.

Southern flounder skin pigmentation is a critical phenotypic characteristic for this species' survival in the natural environment. Normal pigmentation allows rapid changes of color for concealment to capture prey and UV light protection. In contrast, highly visible hypopigmented pseudo-albinos exhibit a compromised immune system and are vulnerable to predation, sensitive to UV exposure, and likely have poor survival in the wild. Skin and brain tissue samples from normally pigmented and hypopigmented individuals were analyzed with next-generation RNA sequencing. A total of 1,589,613 transcripts were used to identify 952,825 genes to assemble a de novo transcriptome, with 99.43% of genes mapped to the assembly. Differential gene expression and gene enrichment analysis of contrasting tissues and phenotypes revealed that pseudo-albino individuals appeared more susceptible to environmental stress, UV light exposure, hypoxia, and osmotic stress. The pseudo-albinos' restricted immune response showed upregulated genes linked to cancer development, signaling and response, skin tissue formation, regeneration, and healing. The data indicate that a modified skin collagen structure likely affects melanocyte differentiation and distribution, generating the pseudo-albino phenotype. In addition, the comparison of the brain transcriptome revealed changes in myelination and melanocyte stem cell activity, which may indicate modified brain function, reduced melanocyte migration, and impaired vision.

Enhancement of southern flounder (Paralichthys lethostigma) sperm velocity and fertility by direct activation of sperm epidermal growth factor and adenylyl cyclase signaling pathways

Development of southern flounder commercial aquaculture is limited by poor sperm motility and fertility, but the underlying causes and mechanisms regulating sperm motility are unknown. In vitro treatment of southern flounder sperm with progestin hormones rapidly increases velocity (swimming speed), a major component of sperm motility, and also fertility through membrane progestin receptor alpha (mPRα) and increases in Acy (adenylyl cyclase)/cAMP signaling. The progestin-induced increase of Atlantic croaker sperm velocity is also mediated through epidermal growth factor receptor (Egfr) transactivation resulting in extracellular-regulated kinase 1/2 (Erk1/2) signaling, but its role in regulating southern flounder sperm velocity is unknown. The hypotheses that Egfr transactivation and Erk1/2 signaling mediates progestin-induced increases in sperm velocity and calcium levels in southern flounder, and that direct stimulation of sperm Egfr/Erk1/2 and Acy/cAMP pathways increases sperm fertility in strip spawning trials were tested in the present study. Golf, Egfr, Erk1/2, and protein kinase A were detected on southern flounder sperm by immunocytochemistry. Involvement of Egfr/Erk1/2 signaling in increasing sperm velocity and calcium levels was investigated by preincubating sperm with two EGFR inhibitors, AG1478, and AG825, a matrix metalloproteinase inhibitor, Ilomastat, and two ERK1/2 inhibitors, PD98059, and U0126, for 30 min prior to 1 min treatment with progestins. Sperm swimming speed was observed under a microscope after activation with a hyperosmotic medium and recorded for 1 min. Whereas treatment with the inhibitors did not alter basal sperm velocity and calcium levels, all of them significantly attenuated velocity and calcium increases in response to progestins. Treatment in vitro for 1 min with the Egfr agonist, recombinant human EGF (0.1 nM and 100 nM), mimicked the stimulatory effects of progestins on sperm velocity, the increase in calcium, and also fertility in a strip spawning trials with ovulated southern flounder eggs. The results suggest Egfr/Erk1/2 signaling is involved in sperm velocity and fertility responses to progestins in southern flounder. Direct in vitro treatment with the Acy activator, forskolin (10 μM) for 1 min mimicked the stimulatory action of progestins on sperm calcium levels, velocity, and fertility, suggesting that Acy/cAMP signaling also mediates increased sperm swimming speed and fertility. Importantly, both EGF and forskolin also directly stimulated southern flounder sperm velocity and fertility at the end of the reproductive season when sperm were no longer responsive to progestins. The results suggest that EGF and forskolin could potentially be used as pharmacological agents to enhance reproductive performance of male southern flounder broodstock.

Modeling potential consequences of climate‐driven sex reversal on Southern and Summer Flounder population dynamics

AbstractObjectiveWe investigate the interacting effects of fishery selectivity and sexual dimorphism by using the fisheries for Southern Flounder Paralichthys lethostigma and Summer Flounder P. dentatus as case studies. In both species, females are larger than males, and temperature‐sensitive sex determination can lead to an increased proportion of males at sexual differentiation in warmer temperatures.MethodsWe developed a size‐, age‐, and sex‐structured population dynamics model for each species to understand how temperature‐induced sex reversal will interact with harvesting to impact population productivity. We considered scenarios with realistic sex ratios and varying levels of fishing pressure.ResultOur models of these species show that population egg production, abundance, biomass, and catch will all be constrained if sex ratios at differentiation become more male‐biased. For both species, climate‐induced changes to the sex ratio in early‐life stages could have a greater impact on relative catch than fishing mortality. We demonstrate that the spawning potential ratio may not be sensitive to climate‐induced changes in the sex ratio unless we account for changes in the sex ratio at differentiation in the historic baseline reproductive potential.ConclusionThese findings underscore the importance of utilizing sex‐specific stock assessments for species with temperature‐sensitive sex determination mechanisms.

Isotopes and otolith chemistry provide insight into the biogeochemical history of mercury in southern flounder across a salinity gradient.

Methylmercury (MeHg) continues to pose a significant global health risk to wildlife and humans through fish consumption. Despite numerous advancements in understanding the mercury (Hg) cycle, questions remain about MeHg sources that accumulate in fish, particularly across transitional coastal areas, where harvest is prominent and Hg sources are numerous. Here we used a unique combination of Hg and nutrient isotopes, and otolith chemistry to trace the biogeochemical history of Hg and identify Hg sources that accumulated in an economically important fish species across Mobile Bay, Alabama (USA). Fish tissue Hg in our samples primarily originated from wet deposition within the watershed, and partly reflected legacy industrial Hg. Results also suggest that little Hg was lost through photochemical processes (<10% of fish tissue Hg underwent photochemical processes). Of the small amount that did occur, photodegradation of the organic form, MeHg, was not the dominant process. Biotic transformation processes were estimated to have been a primary driver of Hg fractionation (∼93%), with isotope results indicating methylation as the primary biotic fractionation process prior to Hg entering the foodweb. On a finer scale, individual lifetime estuarine habitat use influenced Hg sources that accumulated in fish and fish Hg concentrations, with runoff from terrestrial Hg sources having a larger influence on fish in freshwater regions of the estuary compared to estuarine regions. Overall, results suggest increases in Hg inputs to the Mobile Bay watershed from wet deposition, turnover of legacy sources, and runoff are likely to translate into increased uptake into the foodweb.

Long-Term Climate Impacts on the Phenology of Southern Flounder Spawning Migrations

Long-Term Climate Impacts on the Phenology of Southern Flounder Spawning Migrations

Diet–egg relationships and equilibration of fatty acids in eggs of southern flounder, Paralichthys lethostigma

There is increasing interest in the transfer of nutrients from broodstock diets to eggs due to the consequences for egg and larval quality. Analyses were conducted with southern flounder Paralichthys lethostigma to identify which fatty acids (FAs) in eggs are influenced by broodstock diet and how long it takes for the FA composition of eggs to equilibrate to the broodstock diet. Data were obtained from a laboratory experiment and from hatchery production operations. For each source, two populations of adult flounder were given one or the other of two diet treatments. In the laboratory experiment, the diets differed markedly in FA composition. In the hatchery, a base diet was supplemented on two different schedules. Each of the four diet treatments produced eggs with significantly different mean FA compositions. Of the 27 FAs measured, 19 differed significantly between diets and had corresponding significant differences in eggs (direct diet–egg relationships). Combining results with data from a prior study showed that equilibration of eggs to a change in adult diet takes 8–16 weeks for southern flounder. These findings will be useful for improving broodstock diets and feeding protocols for captive flounder being used by stock-enhancement programs that are designed to mitigate the long-term and widespread population declines of this species.

Estuarine-coastal connectivity and partial migration of southern flounder in the Gulf of Mexico

Southern flounder (Paralichthys lethostigma) from an estuarine complex in the Gulf of Mexico were tagged with acoustic transmitters (n = 60) from 2016 to 2018 to assess estuarine-coastal connectivity during fall/winter spawning runs. Both egress and residency behaviors were observed for adult southern flounder caught in the Galveston Bay Complex (GBC), and individuals were classified as migrators or residents based on their maximum distance detected (MDD). Migrators (MDD >5 km; mean 13.8 km) displayed directed egress out of the GBC, with individuals moving through the tidal pass in November and December, peaking in mid to late December. In contrast, residents (MDD <5 km; mean 0.6 km) showed limited movements and were often detected in the same general area throughout the fall, winter, and spring, indicating overwintering in the GBC. Conventional tagging was also performed on over 1300 southern flounder and mean MDD for all recaptured fish was 5.7 km. Mean monthly MDD of conventionally tagged fish was also highest in December and linked to egress from the GBC. Although directed migrations into the Gulf were observed for southern flounder with both tagging approaches, a meaningful fraction of the population displayed sedentary tendencies with MDD less than 1–2 km and retention within the GBC. The coexistence of two migratory contingents with contrasting estuarine-coastal migration behaviors is symbolic of partial migration by southern flounder, which may influence the resilience and stability of the population. Given that the timing and magnitude of peak egress out of this estuarine complex did not align with management regulations intended to protect spawning adults (i.e., peak movement after reopening of fishery), our findings also indicate the need to extend future closures to protect migrators during the primary egress period.

Changes in species compositions of fish in the bays of the Northwestern Gulf of Mexico

IntroductionLocal biodiversity is increasing in many temperate and subtropical waters due to climate change. It is often caused by shifting fish distributions, thus the biodiversity gradient, from lower to higher latitudes. However, these shifts in distributions do not occur uniformly across all species. Consequently, communities are not only shifting their spatial distributions, but species compositions are also changing. We investigated spatiotemporal differences in the compositions of fish species in the bays of the northeastern Gulf of Mexico and identified species that contribute to the temporal changes.MethodsWe used fish count data collected using gillnets in eight major bays, encompassing over 600 km of coastline, during spring and fall seasons from 1982 to 2019. The nonmetric multidimensional scaling (NMDS) on the Bray-Curtis dissimilarity index among species composition vectors was used to detect the differences in species composition, and the similarity percentages (SIMPER) were used to determine the contribution of species to the differences. ResultsThe result shows there was a gradual change in species composition in all bays over the years, and the composition was different among bays and seasons. The species contributing to the temporal changes included those that are expanding (e.g., Common snook, Centropomus undecimalis, and Smallscale fat snook, C. parallelus) as well as retracting (e.g., Southern flounder, Paralichthys lethostigma, and Spanish mackerel, Scomberomorus maculatus) their distributions toward the north. The species observed only in recent years in these bays tended to have a preference for warmer water (e.g., Gulf pipefish, Syngnathus scovelli, and Chain pipefish, S. louisiana). DiscussionThe results are consistent with the potential effects of climate change. However, the salinity of the bays in the study area generally exhibits an increasing trend from the northern to southern bays. The spatial salinity gradient has a substantial impact on species compositions, indicating that species distributions are influenced by multiple environmental conditions. This complexity makes our ability to accurately predict future species compositions under changing environmental conditions challenging.

Effects of anthropogenic noise and natural soundscape on larval fish behavior in four estuarine species.

The larval and post-larval forms of many marine organisms, such as oysters, crabs, lobster, coral, and fish, utilize ambient acoustic cues to orient, settle, or metamorphose. In this study, the effect of anthropogenic and ambient sounds on the orientation behavior of four larval estuarine fishes was examined in a controlled, laboratory experiment. Pre-settlement size red drum Sciaenops ocellatus, southern flounder Paralichthys lethostigma, spotted seatrout Cynoscion nebulosus, and Florida blenny Chasmodes saburrae larvae were exposed to four sound treatments-control, estuarine soundscape, seismic airguns, and large-ship passage-in a linear acoustic chamber. Initial significant (p < 0.05) avoidance of airguns was observed in three of the four species (all but the Florida blenny), but habituation to this sound occurred as the experiment progressed. All species avoided ship passage sounds; however, the avoidance behavior was not significant. Interestingly, none of the species studied were significantly attracted to the acoustic cues alone of the estuarine soundscape; in fact, three of the four species spent less time near the speaker when it was broadcast. These results suggest that larval fish can potentially habituate to anthropogenic noise relatively quickly (<10 min). Understanding how sounds affect larval behavior is necessary because successful recruitment ultimately affects a population's success.

Southern Flounder Life History Diversity and Contributions to Fisheries from Differing Estuarine Salinity Zones

AbstractOtolith chemistry is a useful natural tracer for discerning habitat‐use of estuarine fishes. For Southern Flounder Paralichthys lethostigma, recent otolith chemistry studies have revealed a diversity of residency patterns across salinity gradients. However, the contribution of recruits with specific residency patterns to fisheries is poorly understood. The objectives of this study were to (1) use otolith chemistry from fishery‐independent and fishery‐dependent collections in Mobile Bay, Alabama, to classify lifetime residency patterns (i.e., freshwater, transient, estuarine) in Southern Flounder collected across a large estuarine salinity gradient (0–30 psu); (2) to test if Southern Flounder exhibited resident or migratory behavior by determining if lifetime residency patterns in fishery‐independent samples matched expected salinity patterns in the region of collection after accounting for annual variation in river discharge; and (3) to examine which residency patterns contributed to the commercial and recreational Southern Flounder fisheries in nearby coastal waters. Age‐0 residency patterns in fishery‐independent samples were strongly correlated with region of collection and annual river discharge, suggesting that the majority of Southern Flounder had resided in the same region in which they spent their age‐0 growth phase. Southern Flounder with a combination of freshwater and estuarine salinity signals and classified as “transient” did not appear to have conducted large‐scale movements across salinity gradients, but instead resided in regions of the estuary experiencing seasonal fluctuations in salinity. The majority (57%) of commercially and recreationally harvested Southern Flounder were transients, while a minority (39%) were estuarine residents and lifetime freshwater residents (4%) were rarely harvested. Results from this study suggest that Southern Flounder settle in and remain in the certain habitats during the estuarine residency phase. Given the lack of movement across habitats, future efforts to understand how habitat‐specific conditions (e.g., abiotic, biotic, fishing exploitation) affect vital rates seems warranted for a species currently experiencing population declines.

Determining spatiotemporal trends in hatch and metamorphosis timing of young-of-year southern flounder Paralichthys lethostigma) in Texas bays

It is important to monitor spatiotemporal shifts in the timing of key life history events (i.e., hatch and metamorphosis) since these can influence larval survival and juvenile recruitment success. We use otolith microstructure analysis to examine spatiotemporal trends in hatch and metamorphosis timing of a widespread and economically-valuable finfish, southern flounder Paralichthys lethostigma, in Texas. We use linear regressions that predict otolith-based age from length for young-of-year (YOY) individuals caught coastwide from 2019 to 2021 to calculate hatch and metamorphosis dates of YOY individuals caught coastwide across a 39-yr time series from 1980 to 2018. Also, we use YOY hatchery-reared individuals to indirectly validate the association between otolith accessory growth centers and larval metamorphosis. Our analysis reveals that on the middle coast average hatch timing is shifting toward earlier in the year across the 39-yr time series. In contrast, we find that coastwide, and especially on the middle coast, average metamorphosis timing is shifting toward later in the year across the 39-yr time series. On average, YOY individuals show similar hatch and metamorphosis timing coastwide. We find that on the middle coast and across the 39-yr time series, higher maximum water temperature correlates with earlier average hatch timing. In contrast, we find that coastwide, and especially on the lower and middle coast, higher average water temperature (later years in time series) correlates with later average metamorphosis timing across the 39-yr time series. Fishery-independent monitoring shows no concurrent evidence of individuals emigrating earlier in the fall to spawn offshore. We interpret the spatiotemporal trends in average hatch and metamorphosis timing as evidence of a narrowing survival window where (1) individuals caught on the middle coast that hatch earlier experience higher survival during years with higher maximum water temperature and (2) individuals caught coastwide that metamorphose later experience higher survival during years with higher average water temperature (later years in time series). We highlight the ecological and management implications of the impact of water temperature on hatch and metamorphosis timing and in turn, larval survival and juvenile recruitment success.

Ecological mechanisms generating variable first-year growth in Paralichthys lethostigma, a coastal flatfish

Determining the relative influence of, and possible synergistic relationships among, environmental and biotic processes on individual growth rates can identify key mechanisms that contribute to variation in body size observed among similar-aged individuals. The timing of ontogenetic shifts in diet or habitat, which themselves can be size-dependent, can have considerable impacts on individual growth trajectories, survival, and year class formation. The southern flounder Paralichthys lethostigma is a coastal flatfish species with juvenile cohorts that occupy diverse estuarine settlement habitats and commonly display 2-3 fold variation in body size by the end of the first growing season. We examined abiotic and biotic factors contributing to differences in early juvenile growth for the 2018 year-class of southern flounder in a North Carolina estuary. Following peak larval settlement (Febuary/March), flounder body sizes began to diverge by April, with differences between settlement habitats contributing to roughly 3-fold variation by August. Stomach content analyses indicated a greater occurrence of fish prey in the diets of southern flounder recovered in mesohaline versus oligohaline settlement habitats. Increased piscivorous foraging in mesohaline habitats was linked to nitrogen (δ15N)-enriched tissues and faster growth rates relative to fish collected in oligohaline habitats. Results from a controlled laboratory experiment provided evidence for the strong effects of diet, with only minor direct effects of salinity on juvenile southern flounder growth. Our findings support the critical role of ontogenetic shifts to piscivorous feeding for growth in young-of-the-year southern flounder and highlights the potential for growth-mortality tradeoffs to exist among estuarine settlement habitats.

Social media shines light on the "hidden" impact of nighttime guided-gigging charters on Texas' Southern Flounder fishery: A stab in the dark.

Southern Flounder (Paralichthys lethostigma) populations are declining in the Gulf of Mexico basin. This is particularly true in Texas, where this unique and culturally important fishery has been in decline since the 1980s despite increasingly stringent regulatory measures. Current angler-intercept creel surveys used to estimate recreational flounder harvest levels are conducted during daylight hours and do not account for the high levels of nighttime flounder gigging (spearing) activity, a popular and efficient harvest method for this fishery. There are legitimate scientific and logistical concerns that have prevented the use of wide-spread nighttime creel surveys to monitor the flounder gigging fishery in the past, however this has made accurate catch and effort estimates difficult to obtain. Given the concern about this economically important fishery's status, we adopted a unique approach utilizing social media to provide unprecedented information into this fishery's impact during periods that are not traditionally monitored. Specifically, we reconstructed seasonal flounder harvest and effort metrics stemming from the nighttime recreational guided flounder gigging sector over 2.6 years using guided flounder gigging charter photo archives publicly available through Facebook. These metrics show large average client party sizes, large trip harvests, and near-perfect bag limit efficiencies. Temporal trends indicated peak recreational guided flounder gigging effort and harvest occurs during the summer months, a time not traditionally associated with flounder gigging. The addition of nighttime guided-gigging recreational harvest estimates from this study to traditional daytime harvest estimates and commercial harvest estimates resulted in total annual harvest estimates nearly two times greater than current estimates. Overall, this study demonstrates the high pressure guided-gigging charters are placing on Texas' flounder fishery and illustrates the critical need for additional information on the nighttime recreational flounder fishery for both guided and private gigging anglers. Moreover, our results also demonstrate the usefulness of mining social media platforms to capture catch and effort data that are otherwise unavailable.

Relationship of Microplastics to Body Size for Two Estuarine Fishes

In the northern Gulf of Mexico, microplastics are reported in very high concentrations, which are thought to be partly sourced from the Mississippi River. This study sought to quantify microplastics across body size in two fish species, the hardhead catfish (Ariopsis felis) and southern flounder (Paralichthys lethostigma), common to Gulf of Mexico estuaries. We hypothesized that counts of ingested microplastics would be higher in smaller fishes than larger fishes. Fish were sampled in 2018 and 2019 across coastal Louisiana and represented a balanced range of length classes. Both species in our study ingested microplastics—25% of southern flounder and 15% of hardhead catfish. There was a significant positive effect of total length on microplastic loads in hardhead catfish. Due to the biological importance and management relevance of fish length, the study of microplastic loads and effects on fish may need to move beyond aggregating a species to considerations of individual size.

Economic Values of Potential Regulation Changes for the Southern Flounder Fishery in Louisiana

AbstractPopulation declines of Southern Flounder Paralichthys lethostigma have reached levels that present management concerns in Louisiana waters. As the need for regulatory change in this fishery approaches, we conducted a survey to better characterize the Southern Flounder fishery in Louisiana, with two primary goals: (1) determining a value for the economic welfare provided by the fishery and (2) evaluating how this value might change in response to hypothetical regulation scenarios. Based on total travel cost estimates, the aggregate economic value of the Southern Flounder fishery among coastal Louisiana anglers reached an estimated US$119.7 million; however, this value primarily stems from anglers targeting multiple species during their coastal angling trips, as the value of the Southern Flounder fishery while only accounting for anglers that solely targeted this species amounted to an estimated $8.4 million. Respondents revealed strong levels of supportiveness for all regulation scenarios that increased limitations on allowable harvest for Southern Flounder. None of the hypothetical regulation scenarios led to significant behavioral responses in the expected number of coastal angling trips taken, leaving the economic value of coastal Louisiana fisheries unchanged. The results of our study illustrate the relatively inconsequential nature of Southern Flounder regulations upon the behavior of coastal Louisiana anglers. The information gathered by this survey can be used to guide the decision‐making process in developing a sustainable management strategy that is supported by stakeholders and that keeps the strong economic values of coastal Louisiana fisheries intact.

Foraging by estuarine juveniles of two paralichthyid flounders: experimental analyses of the effects of light level, turbidity, and prey type

Juvenile summer flounder Paralichthys dentatus and southern flounder P. lethostigma inhabit turbid salt marsh estuaries. Predation rates by juveniles (50-90 mm) were examined at 5 daytime light levels (6 × 1011 to 2 × 1014 quanta s-1 cm-2) and in darkness and 4 turbidity levels (clear [≤1], 11, 20, and 40 NTU) at an intermediate light level. Both species fed equally well on benthopelagic mysid shrimp and benthic spionid polychaetes at all daytime light levels tested. However, predation on mysids was significantly reduced in the dark. Consumption of polychaetes was not reduced in the dark by either species, illustrating the effectiveness of non-visual foraging methods on benthic prey. Turbidity levels tested did not affect predation on either prey type by either flounder species. Locomotor behavior was examined at the same turbidity levels. P. lethostigma spent more time swimming in the water column than P. dentatus in lower turbidity (clear-20 NTU), and both species reduced swimming at 40 NTU. It appears that both species primarily use a benthic-oriented ambush foraging strategy under high turbidity conditions. This is a particularly pronounced switch in foraging style for P. lethostigma. Estuarine turbidity is increasing due to the impacts of climate change. When turbidity is elevated enough to eliminate light sufficient for visual feeding on mysids (between darkness and the lowest light level tested), feeding on this motile prey is negatively impacted for both species. Turbidity can thus alter foraging modes and types of prey consumed, affecting nursery habitat quality and the prey base supporting these young fishes.

Spatiotemporal Variability of Fishery‐Dependent Indices for the Declining Louisiana Southern Flounder Fishery

AbstractIn recent years, management agencies across the Gulf of Mexico and southern U.S. Atlantic have recognized Southern Flounder Paralichthys lethostigma as a declining fish stock. Population declines in coastal Louisiana are exhibited by indices of recruitment and biomass, which have reached levels that present management concerns. To develop a better understanding of this declining fishery, we examined fishery‐dependent data collected by the Louisiana Department of Wildlife and Fisheries’ recreational angler harvest survey (referred to as “LA Creel”). Data were modeled using generalized additive models to estimate temporal components of recreational Southern Flounder landings in both seasonality and trend. Over the study period (2014–2019), recreational landings exhibited a declining trend statewide. Strong seasonal peaks in the fall occurred statewide and regionally in every coastal management zone (i.e., estuary). Understanding the current fishery with the fine‐scale resolution provided by the LA Creel survey can be used to help guide future management decisions in the pursuit of a sustainable management strategy inclusive of fishery‐dependent information.

Disentangling complex genomic signals to understand population structure of an exploited, estuarine-dependent flatfish.

Interpreting contemporary patterns of population structure requires an understanding of the interactions among microevolutionary forces and past demographic events. Here, 4,122 SNP‐containing loci were used to assess structure in southern flounder (Paralichthys lethostigma) sampled across its range in the US Atlantic Ocean (Atlantic) and Gulf of Mexico (Gulf) and relationships among components of genomic variation and spatial and environmental variables were assessed across estuarine population samples in the Gulf. While hierarchical amova revealed significant heterogeneity within and between the Atlantic and Gulf, pairwise comparisons between samples within ocean basins demonstrated that all significant heterogeneity occurred within the Gulf. The distribution of Tajima's D estimated at a genome‐wide scale differed significantly from equilibrium in all estuaries, with more negative values occurring in the Gulf. Components of genomic variation were significantly associated with environmental variables describing individual estuaries, and environment explained a larger component of variation than spatial proximity. Overall, results suggest that there is genetic spatial autocorrelation caused by shared larval sources for proximal nurseries (migration/drift), but that it is modified by environmentally driven differentiation (selection). This leads to conflicting signals in different parts of the genome and creates patterns of divergence that do not correspond to paradigms of strong local directional selection.