Patterns of genetic variation reflect interactions among microevolutionary forces that vary in strength with changing demography. Here, patterns of variation within and among samples of the mouthbrooding gafftopsail catfish (Bagre marinus, Family Ariidae) captured in the U.S. Atlantic and throughout the Gulf of Mexico were analyzed using genomics to generate neutral and non-neutral SNP data sets. Because genomic resources are lacking for ariids, linkage disequilibrium network analysis was used to examine patterns of putatively adaptive variation. Finally, historical demographic parameters were estimated from site frequency spectra. The results show four differentiated groups, corresponding to the (1) U.S. Atlantic, and the (2) northeastern, (3) northwestern, and (4) southern Gulf of Mexico. The non-neutral data presented two contrasting signals of structure, one due to increases in diversity moving west to east and north to south, and another to increased heterozygosity in the Atlantic. Demographic analysis suggested that recently reduced long-term effective population size in the Atlantic is likely an important driver of patterns of genetic variation and is consistent with a known reduction in population size potentially due to an epizootic. Overall, patterns of genetic variation resemble that of other fishes that use the same estuarine habitats as nurseries, regardless of the presence/absence of a larval phase, supporting the idea that adult/juvenile behavior and habitat are important predictors of contemporary patterns of genetic structure.

Context Nursery areas provide refuge from predators, rich foraging grounds, and physical conditions conducive to growth and development of juvenile inhabitants. Specifically, the Mississippi Sound in the northern Gulf of Mexico is likely a nursery ground for multiple large and small coastal sharks. Aims and methods Using over a decade of shark survey catch data, we employed habitat modelling approaches to identify preferred environmental conditions and spatial distribution, and quantify core habitat overlap within the Mississippi Sound for young-of-year (YOY), juvenile and adult life stages of four coastal shark species. Results YOY Atlantic sharpnose (Rhizoprionodon terraenovae), blacktip (Carcharhinus limbatus) and finetooth (Carcharhinus isodon) sharks showed a preference for a combination of shallow, warm, low salinity, low dissolved oxygen and turbid waters. Corresponding to shared environmental preferences, spatial distributions of YOY sharks showed a high degree of overlap, particularly in the northern portion of the Mississippi Sound where few adult sharks were observed, suggesting that these life stages partition themselves to avoid predation. Conclusion and implications With a continued rise in US coastal shark populations, we hope this study can help further refine essential fish habitat for these coastal species and provide a framework analysis that can be used to understand habitat partitioning in other regions.

Production by macrofauna associated with oyster reefs offers a multi-purpose indicator of ecosystem function, ecological integrity, and restoration success. We examined responses by oyster-reef-associated macrofauna to a hypoxic event across three subtidal oyster-reef complexes in western Mississippi Sound as part of a large-scale restoration program. Four hypotheses within the context of a Linear mixed model examined differences in the following: (1) the macrofauna relative to the hypoxic event; (2) subregions relative to the severity of hypoxia; (3) responses by key macrofaunal taxa; and (4) short-term macrofaunal recovery. Densities and production potential of the entire oyster-reef macrofaunal community as well as for six key taxa all abruptly decreased in connection with the hypoxic event. Overall, total production potential and total density were four-fold lower in the summer of 2015 during the hypoxic event than in the summer of 2014. The degree of macrofaunal impact corresponded with the severity of hypoxia on the landscape scale. Total density and total production averaged nearly three-fold lower and more than eight-fold lower respectively across two critically hypoxic reef complexes compared to the least affected reef complex. Taxon-specific responses depended on tolerances to hypoxia as well as modes of reproduction and dispersal. Short-term macrofaunal recovery indicated surprising ecological resilience relative to the hypoxic interruption. Detrimental macrofaunal effects ameliorated substantially within several months when total production potential was comparable to that of the previous year. However, the short-term recovery of key taxa varied with respect to the hypoxic event. Hypoxia-induced seasonal directionality reversed between summer 2015 and fall 2015, as evidenced by lower values for total density, total production, and the density and production of the larger-bodied crustaceans, Eurypanopeus and Palaemonetes. Secondary production offers a key functional indicator of multiple ecosystem services and an informative gauge of ecological disturbance. Associated macrofauna should be used more widely to assess the ecological function and recovery of oyster reefs. This study expands our understanding of a productive oyster reef ecosystem that is threatened by multiple environmental challenges.

Four new records of the ragged-tooth shark ( Odontaspis ferox , i.e., smalltooth sand tiger), are reported from recreational and commercial fisheries in the western North Atlantic Ocean. Two specimens of unknown sex were caught in the recreational swordfish ( Xiphias gladius ) fishery in the northern Gulf of Mexico [about 225 and 250 cm total length (TL)], a mature male was caught in the South Atlantic Bight (about 200 cm TL) by an angler targeting barrelfish ( Hyperoglyphe perciformis ), and another mature male was caught in the Sargasso Sea off Bermuda (about 275 cm TL) by a commercial fisher targeting Atlantic wreckfish ( Polyprion americanus ). All four specimens were incidentally caught on rod-and-reel and released alive. The Gulf of Mexico and South Atlantic Bight specimens reported herein contribute to the limited number of ragged-tooth shark interactions in these regions, while the observation in Bermuda is the first documented record for this locality.

The current study examined 93 Swordfish, Xiphias gladius, (64 females, 27 males, 2 unknown) ranging in size from 77.6–246.3 cm lower jaw fork length (LJFL) from the northern Gulf of Mexico (GOM). Samples were collected between March and August in 2005–2007, 2017–2019 and 2021. Age estimates of 51 Swordfish resulted in a maximum observed age of 11 years (205.0 cm LJFL) and 7 years (190.4 cm LJFL) for females and males, respectively. Observed and back—calculated length—at—age data were fitted to 4 growth models (2— and 3— parameter von Bertalanffy, Gompertz, and logistic). The 2—parameter von Bertalanffy was the model that best fit the data (Linf = 210.2 cm LJFL, k = 0.25). Histological examination of gonadal tissue from 91 fish indicated that females reached 50% and 95% physiological maturity at 116 ± 6 cm LJFL and 143 ± 8 cm LJFL, respectively, corresponding to ages 2—3 years. All males >82 cm LJFL were physiologically sexually mature. Only 10% of females were reproductively active, with spawning capable females captured in June. Reproductively active females exhibited asynchronous oocyte development indicating batch spawning. Most males (96%) were spawning capable from April–August. Philometra sp. infection was found in all ovaries examined (n = 16) but with low abundance (2.25 ± 0.42); male philometrids were more prevalent than females (91.7% and 66.7%, respectively). Swordfish in the northern GOM appear to achieve sexual maturity at a younger age, grow faster, and have shorter theoretical longevity than previous reports from other regions world—wide.

Intraspecific variability in life-history patterns is well documented in elasmobranchs, and defining regionally specific parameters is essential for proper management and sustainability of species. Studies on the reproductive biology of finetooth sharks (Carcharhinus isodon) have noted a potential disparity in periodicity within North American waters. To better define regional variability, the current study collected 1490 finetooth sharks (831 female, 659 male) from the northern Gulf of Mexico. The size-at-maturity was determined to be 995- and 961-mm fork length for females and males respectively. In males, the peak gonadosomatic index (GSI) in March and presence of semen in the seminal vesicles in April suggested spermatogenesis occurs from March to April. In females, ovulation occurred from May to June, with a peak GSI occurring in May and maximum vitellogenic follicle diameter occurring in May and June. Gestation was found to be 11–12 months, with parturition occurring in May and June and a mean brood size was 3.8±0.1 embryos. Of the 50 females examined during the ovulatory period, 32 exhibited annual and 18 exhibited biennial reproductive periodicity. The results from this study will be impactful, because regionally distinct reproductive parameters can now be considered for future assessments.

Abstract The mechanisms underlying polyandry and female mate choice in certain taxonomic groups remain widely debated. In elasmobranchs, several species have shown varying rates of polyandry based on genetic studies of multiple paternity (MP). We investigated MP in the finetooth shark, Carcharhinus isodon, in order to directly test the encounter rate hypothesis (ERH), which predicts that MP is a result of the frequency of encounters between mature conspecifics during the breeding season, and should therefore increase when more time is available for copulation and sperm storage. Female finetooth sharks in the northern Gulf of Mexico (GoM) have been found to reproduce with both annual periodicity and biennial periodicity, while finetooth sharks from the northwestern Atlantic Ocean have only been found to reproduce biennially, allowing us to compare mating opportunity to frequency of MP. Our results show high rates of MP with no significant difference in frequency between females in the GoM (83.0%) and Atlantic (88.2%, p = .8718) and varying but nonsignificant rates of MP between females in the GoM reproducing annually (93.0%) and biennially (76.6%, p = .2760). While the ERH is not supported by this study, it remains possible that reproductive periodicity and other physiological factors play a role in determining rates of MP in elasmobranchs, with potential benefits to individuals and populations.

Species of Argulus (Branchiura Thorell, 1864) are common ectoparasites of freshwater, estuarine, and marine fishes. Argulid identification and taxonomy is often confusing because many species are reported to parasitize multiple host species, have similar morphological characters, and come from various salinity regimes. Gulf sturgeon is an anadromous fish natal to drainages in the north-central Gulf of Mexico, and as with many endangered species, has a poorly documented parasite community. During Gulf sturgeon tagging and monitoring studies (2016–2019) in the Pascagoula River, MS, USA, species of Argulus were collected from Gulf sturgeon as well as other incidentally captured fishes. Argulus flavescens Wilson, 1916 was found on Gulf sturgeon and flathead catfish, Argulus americanus Wilson, 1902 on bowfin, and Argulus bicolor Bere, 1936 on Atlantic stingray. We provide morphological details and measurements for these species as well as the first confirmed 28S rDNA molecular data. Argulus flavescens was more abundant and prevalent on larger Gulf sturgeon and on sturgeon captured in freshwater rather than estuarine habitats. Our results indicate that A. flacescens may not tolerate estuarine salinities and that the anadromous life-history pattern of Gulf sturgeon could help rid them of A. flavescens when they emigrate from their riverine habitats.

Alosa alabamae (Alabama Shad) is an imperiled anadromous species that reproduces in northern Gulf of Mexico drainages. To date, there have only been 4 vouchered specimens collected from marine waters, but none have been verified with molecular techniques. On 28 March 2013, we collected a single adult female in proximity to a barrier island (Petit Bois) off the coast of Mississippi. Microsatellite DNA analysis corroborated the identification of this individual and suggested that the specimen was most genetically similar to the group from the Pascagoula River drainage rather than other portions of the range. Thus far, research has been focused on the species' freshwater life history, and it is crucial that more effort be directed toward documenting and understanding the full life history of this threatened fish.