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Squalus clarkae est un requin Squaliformes décrit à partir de spécimens collectés dans le nord-est du golfe du Mexique, et dont la répartition, selon des études génétiques, inclurait aussi l'Atlantique nord-ouest. Sa répartition méridionale dans le golfe restait inconnue. Quatre spécimens (deux femelles et deux mâles) d'une longueur totale de 54,2 à 61,4 cm ont été collectés parmi les captures de la pêcherie artisanale dans le sud de Veracruz, Mexique, sur le talus continental du sud-ouest du golfe du Mexique en juillet 2021. Cet article rapporte ce premier signalement de S. clarkae dans le sud-ouest du golfe du Mexique et dans les eaux mexicaines, ainsi que des données morphométriques et morphologiques. [ABSTRACT FROM AUTHOR]

In order for a comparison of shark bite numbers across locations to be meaningful, the locations must share a common feature or available statistic. One such statistic, which we called the "bite rate" in earlier projects, is the ratio between the human population and the number of bites within a given region. In the past, estimates of the total "beach population"--that is, the total number of individuals populating the beaches--for a given location throughout a year have served as the denominator for the purpose of calculating this ratio. However, such estimates are not always available, as is the case for regions within the United States, such as states that border the Gulf of Mexico including the west coast of Florida. In order to compensate for this gap in the data, we have been exploring the use of the "resident population" as a proxy for beach population numbers to determine bite rates. For the present study, we explored whether the two population values, beach population and resident population, are indeed interchangeable by analyzing the data for the east coast of Florida, for which both sets of population values are available. More specifically, we relied on SaTScan, a software package designed for geospatial cluster analysis, to determine whether the two data sets identified the same potential low- and high-significance clusters for bite rates. Next, we identified significance clusters for bite rates using resident population from Florida's west coast, a region where beach population numbers were not available, and compared the results with the east coast. We found that, despite its longer shoreline, Florida's west coast experienced a lower annual bite rate over the period of the study than the east coast. Several possible explanations are offered for these differences. [ABSTRACT FROM AUTHOR]

We investigated the effects of hook soak time on targeted reef species and shark bycatch in the reef fish bottom longline fishery in the Gulf of Mexico. Beginning in 2010, capture time and catch per unit effort (CPUE) for the primary target species red grouper ( Epinephelus morio ) in the fishery were evaluated using hook timers. Findings indicated that typical duration of hook soak times is longer than necessary to efficiently harvest red grouper and a reduction in gear soak times to less than one hour would result in minimal or no reduction in red grouper CPUE. The mean capture time of sharks and red grouper differed significantly, suggesting that a reduction in soak time would likely reduce the bycatch of sharks in the fishery. The study also revealed barometric pressure, lunar phase, and fish size were significant covariates with red grouper capture times and that different bait types significantly affected CPUE. Implementing shorter hook soak times would likely improve fishery profitability and potentially reduce discards of unwanted species in the fishery. [ABSTRACT FROM AUTHOR]

Background: Barrier islands are dynamic features of the northern Gulf of Mexico that are affected by natural processes and more frequently, anthropogenic disturbances. In addition to providing a barrier from storms, these islands offer habitat for many marine species. In an effort to prevent oiling of the Alabama coastline following the Deepwater Horizon oil spill, an artificial rock-rubble berm was constructed in 2010 to reconnect two portions of Dauphin Island, a northern Gulf of Mexico barrier island that was separated during Hurricane Katrina. An acoustic array established prior to the closure of "Katrina Cut" was used to investigate the potential effect of this anthropogenic alteration on the movement patterns of acoustically tagged Bonnetheads (Sphyrna tiburo). Results: Across the entire acoustic array, the largest proportion of detections occurred on receivers before construction at Katrina Cut (0.55), followed by the period after the construction (0.25), and the period during the construction (0.20). Focusing on the area near Katrina Cut, the two hydrophones in this area had the highest proportion of detections before construction (0.10), followed by the period during construction (0.02), and then the period after construction and closure of Katrina Cut (<0.01). The post-closure location of highest activity for Bonnetheads shifted westward following the closure of Katrina Cut. Salinity values from a hydrographic model were higher at the Katrina Cut location in 2010 when the cut was open compared to 2011 and 2012 when the cut was closed, a potential explanation for the observed changes in Bonnethead distribution. Conclusions: Fluctuations in salinity post-closure of Katrina Cut may effect Bonnethead movements, although other factors, including seasonal migrations and/or the redistribution of their preferred prey, may also be important. Regardless of the mechanism, this rapid shift in distribution of Bonnetheads highlights the potential effect of anthropogenic activities on sharks using coastal environments. [ABSTRACT FROM AUTHOR]

Deep-water sharks are abundant and widely distributed in the northern and eastern Gulf of Mexico. As mid- and upper-level consumers that can range widely, sharks likely are important components of deep-sea communities and their trophic interactions may serve as system-wide baselines that could be used to monitor the overall health of these communities. We investigated the trophic interactions of deep-sea sharks using a combination of stable isotope (δ 13 C and δ 15 N) and stomach content analyses. Two hundred thirty-two muscle samples were collected from elasmobranchs captured off the bottom at depths between 200 and 1100 m along the northern slope (NGS) and the west Florida slope (WFS) of the Gulf of Mexico during 2011 and 2012. Although we detected some spatial, temporal, and interspecific variation in apparent trophic positions based on stable isotopes, there was considerable isotopic overlap among species, between locations, and through time. Overall δ 15 N values in the NGS region were higher than in the WFS. The δ 15 N values also increased between April 2011 and 2012 in the NGS, but not the WFS, within Squalus cf. mitsukurii . We found that stable isotope values of S. cf. mitsukurii , the most commonly captured elasmobranch, varied between sample regions, through time, and also with sex and size. Stomach content analysis ( n =105) suggested relatively similar diets at the level of broad taxonomic categories of prey among the taxa with sufficient sample sizes. We did not detect a relationship between body size and relative trophic levels inferred from δ 15 N, but patterns within several species suggest increasing trophic levels with increasing size. Both δ 13 C and δ 15 N values suggest a substantial degree of overlap among most deep-water shark species. This study provides the first characterization of the trophic interactions of deep-sea sharks in the Gulf of Mexico and establishes system baselines for future investigations. [ABSTRACT FROM AUTHOR]

The movement of bonnetheads, Sphyrna tiburo, within an estuarine system on the Gulf of Mexico coast of Florida was examined to define response to salinity change. Shark presence and movements were evaluated by acoustic monitoring and gillnet sampling. Acoustic monitoring data were used to investigate active selection of different zones within the estuary based on differences in salinity among zones. Sharks were monitored for 187 days in 2003 and 217 days in 2004 in salinities ranging from 11.0 to 31.0 ppt in 2003 and 15.8 to 34.6 ppt in 2004. Monitoring data supported the hypothesis that salinity played a role in the distribution and movement of S. tiburo. Catch per unit effort (CPUE) data obtained from gillnet sampling from 1995 to 2004 were examined to determine affinity or avoidance of specific salinities within the study site as calculated using an electivity index. Electivity analysis showed almost no affinity or avoidance for specific salinity values. The difference in results between the CPUE and acoustic monitoring in relation to the potential effects of salinity likely relate to the nature of the data, with acoustic monitoring providing continuous data and CPUE providing snapshot location data. The results of this study suggest that although S. tiburo are collected within a wide range of salinity levels, salinity may affect movement and distribution. Salinity effects may be more pronounced during periods of prolonged and/or large changes in salinity as detected by long-term monitoring. [ABSTRACT FROM AUTHOR]