79 research outputs found

    First Record of a Nurse Shark, Ginglymostoma cirratum, within the Mississippi Sound

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    Of all the coastal shark species in the northern Gulf of Mexico, the nurse shark, Ginglymostoma cirratum, is one of the few species not documented in the Sound. Unlike most coastal sharks, nurse shark distribution is confined to a relatively specific suite of abiotic characteristics. Hannan et al. (2012) demonstrated that the distribution of nurse sharks in the northern GOM is primarily limited to hard bottom habitats with relatively high temperature, salinity, dissolved oxygen, and water clarity. Herein, we provide support for the findings of Hannan et al. (2012) and report the first documented occurrence of a nurse shark in the Sound

    Diel Vertical Movements of a Scalloped Hammerhead, \u3ci\u3eSphyrna lewini\u3c/i\u3e, in the Northern Gulf of Mexico

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    Despite the circumglobal distribution of scalloped hammerheads, Sphyrna lewini (Griffith and Smith, 1834), little information is available regarding fine-scale movement and habitat use patterns for this species. Over a 27-d period, data were collected on diel habitat use and environmental preferences of a 240 cm (total length) female S. lewini. The shark exhibited a consistent and repeated diel vertical movement pattern, making more than 76 deep nighttime dives; the maximum depth reached was 964 m, where the temperature was 5.8 degrees C. The purpose of the nightly oscillatory deep diving pattern is unknown but could possibly represent feeding behavior. These findings represent the first detailed account of S. lewini diel vertical behavior and habitat utilization in the western North Atlantic Ocean

    Investigating Life History Differences Between Finetooth Sharks, Carcharhinus isodon, in the Northern Gulf of Mexico and the Western North Atlantic Ocean

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    The life history of the finetooth shark, Carcharhinus isodon, off South Carolina was studied by determining age, growth, and size and age at maturity. These data were compared to a recent study describing the same parameters for finetooth sharks in the northern Gulf of Mexico. Cervical vertebrae were extracted from 168 specimens (71 males and 97 females), ranging in size from 376 to 1,262 mm fork length (FL), and prepared for age analysis using standard techniques. Sex-specific von Bertalanffy growth models were generated and yielded the following growth equations: Lt = 1,311 mm FL (1 - e-0.19(t - (-2.17))) for females and Lt = 1,151 mm FL (1 - e-0.33(t - (-1.43))) for males. The oldest female and male aged were 12.4 yr and 10.4 yr, respectively. Median length where 50% of the population was mature was 1,021 mm FL for females, corresponding to an age of 6.3 yr and 1,015 mm FL for males, corresponding to an age of 5.0 yr. Finetooth sharks in the western North Atlantic Ocean had higher observed ages and there was a significant difference in size at age between neonate finetooth sharks in the western North Atlantic Ocean and the northern Gulf of Mexico; however, there were no significant differences among von Bertalanffy growth function parameters between regions examined. Results indicate lower amounts of regional variation in life history parameters for finetooth sharks when compared to other small coastal sharks

    Distribution and Length Frequency of Invasive Lionfish (Pterois sp.) in the Northern Gulf of Mexico

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    The purpose of this communication is to document continued spatial expansion of lionfish farther west into the northern Gulf of Mexico. Furthermore, we provide the first length— mass relationships and length frequency information for lionfishes captured within the northern GOM based on data collected as part of a broader on—going study of lionfish life history in this region

    Observations of a Feeding Aggregation of Whale Sharks, Rhincodon typus, in the North Central Gulf of Mexico

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    On 26 June 2006 an aggregation of 16 whale sharks was observed for a period of 4 hr in the north central Gulf of Mexico (GOM). The sharks remained within an area about 1.0 km2 in size and continuously ram filter fed at the surface. Visual analysis of a plankton sample collected from the study site revealed the presence of copious amounts of fish eggs in mid-embryonic development and a minor amount of other zooplankton. A second plankton sample (control) collected about 3.5 km from the study site in an area where no whale sharks were present contained few eggs, however other zooplankton were similar to the study site sample in species composition and abundance. Two egg morphs were identified, and samples of one of the morphs, which represented 98% of the eggs at the study site, were verified by genetic analysis as little tunny, Euthynnus alleteratus. The observed feeding behavior and the abundance of fish eggs at the study site indicated the whale sharks were feeding on recently spawned little tunny eggs. This represents the first confirmed observation of a feeding aggregation of whale sharks in the GOM

    Indication of Density-Dependent Changes in Growth and Maturity of the Barndoor Skate on Georges Bank

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    Drastic increases or decreases in biomass often result in density-dependent changes in life history characteristics within a fish population. Acknowledging this phenomenon and in light of the recent biomass increase in Barndoor Skate Dipturus laevis, the current study re-evaluated the growth rate and sexual maturity of 244 specimens collected from 2009-2011within closed areas I and II on Georges Bank, USA. Ages were estimated using vertebral band counts from skate that ranged from 21 to 129cm TL. The von Bertalanffy growth function was applied to pooled age-at-length data. Parameter estimates from the current study of L = 155cm TL and k = 0.10 represent a significant decrease from previously reported parameters of L = 167cm TL and k = 0.14. In addition to changes in growth parameters, age at 50% maturity for both males (based on clasper length, testes mass, and percent mature spermatocytes) and females (based on data from shell gland mass, ovary mass, and follicle diameter) increased by 3years and 4years, respectively. Based on our results and the 10- to 12-year gap in the collection of samples, it is likely that Barndoor Skate within this region have exhibited pliability in life history parameters

    First Record of a Sleeper Shark in the Western Gulf of Mexico and Comments on Taxonomic Uncertainty Within Somniosus (Somniosus)

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    A sleeper shark, Somniosus (Somniosus) sp., is reported from Alaminos Canyon in the western Gulf of Mexico at a depth of about 2647 m based on observations made using a remotely operated vehicle. This is the first record of a sleeper shark (Somniosus, Somniosidae) from the western Gulf of Mexico and deepest record of any shark from the Gulf of Mexico. Despite claims to the contrary in the literature, no taxonomic character has been identified to date that can be used to unequivocally identify all representatives of Somniosus (Somniosus), and as a result, some species records must be considered dubious

    Seasonal Occurrence, Horizontal Movements, and Habitat Use Patterns of Whale Sharks (\u3ci\u3eRhincodon typus\u3c/i\u3e) in the Gulf of Mexico

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    In the northern Gulf of Mexico (GOM), whale sharks (Rhincodon typus) form large aggregations at continental shelf-edge banks during summer; however, knowledge of movements once they leave aggregation sites is limited. Here we report on the seasonal occurrence of whale sharks in the northern GOM based on over 800 whale shark sightings from 1989 to 2016, as well as the movements of 42 whale sharks tagged with satellite-linked and popup satellite archival transmitting tags from 2008 to 2015. Sightings data were most numerous during summer and fall often with aggregations of individuals reported along the continental shelf break. Most sharks (66%) were tagged during this time at Ewing Bank, a known aggregation site off the coast of Louisiana. Whale shark track duration ranged from three to 366 days and all tagged individuals, which ranged from 4.5 to 12.0 m in total length, remained within the GOM. Sightings data revealed that whale sharks occurred primarily in continental shelf and shelf-edge waters (81%) whereas tag data revealed the sharks primarily inhabited continental slope and open ocean waters (91%) of the GOM. Much of their time spent in open ocean waters was associated with the edge of the Loop Current and associated mesoscale eddies. During cooler months, there was a net movement southward, corresponding with the time of reduced sighting reports. Several sharks migrated to the southwest GOM during fall and winter, suggesting this region could be important overwintering habitat and possibly represents another seasonal aggregation site. The three long-term tracked whale sharks exhibited interannual site fidelity, returning one year later to the vicinity where they were originally tagged. The increased habitat use of north central GOM waters by whale sharks as summer foraging grounds and potential interannual site fidelity to Ewing Bank demonstrate the importance of this region for this species

    Notes on the Biology of an Adult Female Chimaera cubana Captured Off St. Croix, U.S. Virgin Islands

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    Within the western North Atlantic Ocean there are at least 4 genera and 5 species of chimaeroids occurring in deep waters generally associated with outer continental slopes or areas of high bathymetric relief (Didier 2002; Didier 2004). Two chimaeroids, Chimaera cubana and Hydrolagus alberti, are known to be indigenous to the Caribbean Sea in waters associated with the Greater and Lesser Antilles. While H. alberti occurs throughout the Gulf of Mexico and the Caribbean Sea, C. cubana is thought to be endemic to an area bounded by Cuba and Colombia (IUCN 2009). These two chimaeras are readily differentiated by the presence or absence of an anal fin and species–specific branching patterns of cranial lateral line canals (Didier 2004). Since the description of C. cubana by Howell–Rivero (1936), only 10 specimens have been reported in the primary literature with another 11 specimens located in museum collections (Bunkley–Williams and Williams 2004). The dearth of biological information on C. cubana led the International Union for the Conservation of Nature to recommend that “basic data be collected on all captures” (IUCN 2009)
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