Occurrence of Juvenile Paralichthys lethostigma (Southern Flounder) in Tributaries of Chesapeake Bay

Paralichthys lethostigma (Southern Flounder) inhabits the continental shelf and estuarine waters of the Gulf of Mexico and the east coast of the North Atlantic, from peninsular Florida to Albemarle Sound in North Carolina. Between 30 May and 20 August 2012, we collected 15 juvenile (71-192 mm) Southern Flounder in fyke nets in the Mattaponi River, a tributary of the York River, in southeastern Virginia. This is the first known documentation of juvenile Southern Flounder in any tributary of Chesapeake Bay. We confirmed our identification of the specimens as Southern Flounder morphologically and genetically by counting gill rakers and sequencing cytochrome oxidase subunit I, respectively

Environmental Drivers of Southern Flounder (Paralichthys lethostigma) Growth, Condition, and Juvenile Recruitment Along the Northern Gulf of Mexico

Southern Flounder (Paralichthys lethostigma) is an economically important species that uses habitats across salinity gradients along the Atlantic Ocean and Gulf of Mexico. During winter, adults spawn offshore, and larvae migrate to estuaries. During spring, larvae settle, grow, and metamorphose into juveniles. Juveniles and adults continue to use estuaries until adults mature and migrate offshore to spawn. This presumed, migratory life history indicates that Southern Flounder is an estuarine-dependent species. As with many estuarine-dependent species, growth, condition, and juvenile recruitment are highly variable across time and space. In response to declines across the species range, state managers have imposed a series of increasingly stringent regulations on Southern Flounder fisheries. However, recent stock assessments show no signs of recovery thus far, suggesting that factors other than fishing mortlity, such as environmental conditions and habitat-use patterns, may be contributing to the decline. My objectives were to 1) develop an index of juvenile Southern Flounder abundance to investigate relationships with environmental factors, and 2) use back-calculation and condition indices to investigate how observed patterns in growth and condition relate to habitat-use patterns. We developed an index of juvenile Southern Flounder abundance in Mobile Bay (1981 – 2018) and Perdido Bay (1988 – 2018) using historical Alabama survey data. Generalized additive models tested mechanistic hypotheses by relating environmental variables to juvenile abundance for short- and long-term analyses in Mobile and Perdido Bays. Models that included winter covariates were selected as best for all three analyses, suggesting that environmental conditions during spawning and larval stages explain the most variation in year-class strength. Specifically, westerly winds, river discharge, and intermediate winter durations were positively correlated with juvenile abundance, and recent suboptimal conditions helped to explain dramatic declines in juvenile recruitment. We used 313 otoliths from Southern Flounder collected in Alabama’s coastal waters in 2004 – 2007 and 2018 – 2019 to investigate how age-specific contingent types impacted age-specific back-calculated growth rates and condition. We used linear mixed effects models with various random effect structures to account for age, growth, year, and individual effects. Age-0 and first-year estuarine and transient contingents had higher growth rates than freshwater contingents, but there was no difference in growth among contingents during the second year of life. Age-0 and age-1 estuarine and transient contingents had higher condition than freshwater contingents, but there was no difference in condition for age-2 Southern Flounder. Over the next century, the Gulf of Mexico is expected to see increased drought conditions, more intense storms, and warmer winter temperatures. This could impact the amount of river discharge that enters the estuary, thus impacting growth rates and overall abundance of young Southern Flounder. Warmer winters could interfere with reproductive success and the number of recruits surviving to the juvenile stage. As recruitment dynamics strongly influence adult abundance, our results should help inform expectations for Alabama’s Southern Flounder fishery in response to changing environmental conditions. Growth and condition are products of good estuarine habitat, and our results could assist in identifying high-quality estuarine habitats that could be used for recently developed stocking programs and continued habitat restoration efforts in Alabama

Growth and Reproduction of Southern Flounder (\u3ci\u3eParalichthys lethostigma\u3c/i\u3e) in the North-Central Gulf of Mexico

Southern Flounder Paralichthys lethostigma is the most commonly harvested flatfish in the north-central Gulf of Mexico (GOM) and supports a major inshore recreational fishery, yet knowledge of the species’ life history is greatly limited. The objective of this research was to describe the growth and reproduction of Southern Flounder in the Mississippi stock. Fish were collected during September 2014 to March 2016 using primarily recreational fishing techniques. Otoliths (n = 313) were sectioned to estimate age, and multiple length-at-age models were fit to total length (TL, mm) and age estimate (y) data. Gonadal tissue samples (n = 221) were preserved for histological analysis and used to classify reproductive phases. Length-at-age model fit was evaluated using Akaike information criteria, revealing that the three-parameter von Bertalanffy growth function best described the female-specific data (L∞ = 509 mm, k = 0.70 y-1, t0= -0.46 y). By fitting a logistic model to binomial maturity data, the mean length-at-50% maturity was estimated as 303 mm TL and mean age-at-50% maturity was estimated as one year for females. Histological indicators and gonadosomatic index (GSI) data were used to estimate that the spawning season lasts from November to January, and to classify Southern Flounder as batch spawners. These results will inform future stock assessments and management decisions for the GOM Flounder fishery

The Life History and Population Dynamics of Southern Flounder

Southern Flounder, Paralichthys lethostigma, are a coastal, estuarine-dependent flatfish species that inhabits the Southeastern US Atlantic Ocean and Gulf of Mexico. Throughout their range, Southern Flounder are exploited by both commercial and recreational fisheries. Recently, numerous sources have expressed concerns about Southern Flounder populations, with stock assessments indicating declines in spawning stock biomass and recruitment. To estimate life history traits needed for informed management, such as age, growth, and maturity, I collected 327 Southern Flounder from Louisiana and obtained 14,184 historical records from the Louisiana Department of Wildlife and Fisheries. Using a von Bertalanffy growth equation in a Bayesian hierarchical framework, I found local-scale differences in growth between estuaries and parameter differences from previous studies. Logistic regression estimated an L50 of 353mm, which is over 100mm larger than a previous estimate for Louisiana. Finally, I evaluated the variability in life history estimates from historical studies throughout the range. I then used generalized additive models to quantify age-0 relative abundance trends in Texas, Louisiana, Alabama, Florida, South Carolina, and North Carolina. Of 31 estuaries modeled, a significant decline was found to be occurring in 19, indicating a range-wide population decline. Environmental covariates including growing degree days (GDD), wind, and winter severity were tested to explain the trends. GDD and winter severity appeared to have localized effects on Southern Flounder abundance, while wind was a significant explanatory factor in all 21 estuaries with available wind data. Additionally, I show that Southern Flounder are being exposed to warmer temperatures as they develop, which could cause sex ratios to masculinize. This research addresses fishery management needs and seeks to explain the population dynamics of Southern Flounder in the Gulf of Mexico and US Southeastern Atlantic

Relationships between Larval and Juvenile Abundance of Winter-Spawned Fishes in North Carolina, USA

We analyzed the relationships between the larval and juvenile abundances of selected estuarine-dependent fishes that spawn during the winter in continental shelf waters of the U.S. Atlantic coast. Six species were included in the analysis based on their ecological and economic importance and relative abundance in available surveys: spot Leiostomus xanthurus, pinfish Lagodon rhomboides, southern flounder Paralichthys lethostigma, summer flounder Paralichthys dentatus, Atlantic croaker Micropogonias undulatus, and Atlantic menhaden Brevoortia tyrannus. Cross-correlation analysis was used to examine the relationships between the larval and juvenile abundances within species. Tests of synchrony across species were used to find similarities in recruitment dynamics for species with similar winter shelf-spawning life-history strategies. Positive correlations were found between the larval and juvenile abundances for three of the six selected species (spot, pinfish, and southern flounder). These three species have similar geographic ranges that primarily lie south of Cape Hatteras. There were no significant correlations between the larval and juvenile abundances for the other three species (summer flounder, Atlantic croaker, and Atlantic menhaden); we suggest several factors that could account for the lack of a relationship. Synchrony was found among the three southern species within both the larval and juvenile abundance time series. These results provide support for using larval ingress measures as indices of abundance for these and other species with similar geographic ranges and winter shelf-spawning life-history strategies

The Life History of Southern Flounder (Paralichthys Lethostigma) in Louisiana Waters

The objectives of this study were to describe the life history patterns of the southern flounder (Paralichthys lethostigma) in Louisiana waters through determination of age, growth, and reproductive biology. A variety of sample sources were included to demonstrate how the southern flounder life cycle is dependent on both the estuary and offshore waters throughout the various stages of its life cycle. Females exhibited greater lengths then males reaching a maximum of 764mm total length and males a maximum of 414mm. Ages were estimated through examination of transverse sections of sagittal otoliths. Annuli were validated to form yearly in the winter months. Females lived longer then males reaching a maximum age of eight years while males reached a maximum of 4 years. Resultant Von Bertalanffy growth equations were shown to be significantly different between males and females. Males displayed a higher growth rate then females but had a much smaller U,. Histological evidence and gonadosomatic indices indicate that southern flounder spawn in December and January in offshore waters. Southern flounder are batch spawners indicated by the presence of multiple stages of oocytes throughout the spawning season. Mean batch fecundity was estimated for 1991 and 1993 as 62,000 and 44,000 ova per batch. Spawning frequency was estimated using the postovulatory follicle method as 3.6 days and 6.4 days. The time-calibrated method provided estimates of 2.3 days and 3.1 days. Females were found to reach fifty-percent maturity at 229mm and all females were mature above 509mm. Sex ratios indicate that males begin to migrate offshore as early as October in preparation for the spawning season. Female migration offshore takes place in November and December. Both males and females begin to move back into the estuaries as early as February as the spawning season comes to an end

Assessing Residency Patterns and Trophic Ecology of Southern Flounder in Alabama\u27s Coastal Waters

Southern Flounder (Paralichthys lethostigma) is an economically important species along the northern Gulf of Mexico. Over the last several years, Southern Flounder populations have experienced drastic declines. Analysis of natural tags, such as otolith chemistry and stable isotopes, can be used to examine habitat-specific contributions to commercial and recreational fisheries. A better understanding of habitat-use patterns and food web dynamics of this species could provide insight into habitat conservation and harvest regulations to promote sustainability of this species. Water and otolith chemistry were used to quantify the proportional contributions of various residency patterns to the commercial and recreational harvest of historic (2004 – 2007) and recent (2018 – 2019) Southern Flounder populations. Otolith strontium to calcium (Sr:Ca) values from laser ablation inductively coupled plasma mass spectrometry were used to quantify age-specific and lifetime residency patterns for Southern Flounder across Alabama’s seasonal salinity gradient. Flounder were classified into one of three contingent types: freshwater, estuarine, or transient. Our results suggest that contributions to the commercial and recreational fisheries were predominately from estuarine habitats, and freshwater habitats were important during the settlement phase. Specifically, 3% of commercially and recreationally harvested flounder were lifetime freshwater contingents, but 57% utilized freshwater during the first year of life. We used bulk carbon (δ13C) and nitrogen (δ15N) isotopes, compound specific δ15N isotopes (AA-CSIA), and stomach content analysis (SCA) to determine trophic ecology and food web dynamics of Southern Flounder. We assigned location of harvest for commercially and recreationally harvested flounder using δ13C and δ15N values from fishery-independent samples. In agreeance with otolith chemistry, isotope analysis results indicated greater contributions to commercial and recreational fisheries from estuarine habitats than freshwater habitats. Additionally, flounder harvested in lower portions of Mobile Bay appear to be consuming prey at higher trophic levels than other areas along Alabama’s coastal waters

Fatty acid composition of the maternal diet affects egg and larval quality of southern flounder, Paralichthys lethostigma

Yolk of marine fish eggs is highly concentrated in fatty acids (FAs) that are used for energy, hormone production, and membrane structure. Essential fatty acids (EFAs) are fatty acids that cannot be biosynthesized in physiologically sufficient amounts and must be obtained from the diet. Since EFAs in yolk must originate in the maternal diet, a study was conducted to determine whether changes in maternal dietary docosahexaenoic acid (DHA, an important EFA for proper larval development) during a spawning season had an effect on the proportion of DHA in eggs of Southern flounder, Paralichthys lethostigma. Adult flounder were conditioned on a common diet and then switched to a high DHA diet, low DHA diet, or no change (control) after the first spawn. Spawns were produced weekly and DHA content of the eggs was measured by gas chromatography. Females fed a high DHA diet produced eggs with a significantly higher proportion of DHA after 3 weeks on the experimental diet. DHA in eggs from females fed a low DHA diet decreased for 5 weeks, then increased, suggesting that those females first used dietary DHA to make yolk then shifted to DHA stored in liver or white muscle. In a second study, spawns from the first study were incubated and larvae were reared to 15 and 35 days post-hatching (dph) to determine whether there was a relationship between FA composition of the eggs, FA composition of the larval body, and responsiveness to a visual predatory stimulus. Ratios of DHA to other EFAs (DHA:ARA and DHA:EPA) were positively correlated with larval responsiveness to a simulated predator. The amount of omega-3 docosapentaenoic acid (DPA) in the egg was strongly correlated with the amount of DHA in the larval body at 15 dph, and was significantly correlated with the amount of DHA in the larval body at 35 dph. This research suggests that southern flounder follow a mixed breeding strategy to supply developing eggs with DHA during vitellogenesis, and variability in FA composition of eggs, specifically (n-3) DPA, may influence larval mortality from predation in the wild.Marine Scienc

Food Contents of Six Commercial Fishes from Mississippi Sound

Specific dietary contents from six fishes collected in Mississippi Sound are recorded. In order of their importance, primary components grouped in major taxonomic categories were fishes, penaeid shrimps, and other crustaceans for Cynoscion nebulosus; Crustaceans and fishes for C. arenarius; fishes and crustaceans for C. nothus; crustaceans, pelecypods, and polychaetes for Pogonias cromis; crustaceans, molluscs, polychaetes, and fishes for Archosargus probatocephalus; and fishes and penaeid shrimps for Paralichthys lethostigma. Principal items in the diets of most of the fishes included Anchoa mitchilli, Penaeus aztecus, P. setiferus, and Callinectes sapidus. Those crustaceans show that competition exists for commercial shellfishes in Mississippi Sound. Ratios among the different dietary items vary, according at least to species of fish, length of fish, season, specific location, and abundance of available prey. Some of these variations are documented and are additionally related to selected findings by other authors sampling different localities. We suggest that examination of food items in Archosargus probatocephalus can serve as a practical means to sample and assess seasonal prevalence and abundance of a wide range of invertebrates throughout different habitats in Mississippi Sound and elsewhere