Occurrence of the bigeye thresher shark, Alopias superciliosus (Lowe, 1841) (Elasmobranchii, Alopiidae) in the southwestern Gulf of Mexico

The bigeye thresher shark Alopias supeciliosus is a large epipelagic and mesopelagic species, and it has a wide distribution in the Atlantic. However, its record in the Gulf of Mexico is sporadic. A single adult female of A. superciliosus, measuring 360 cm total length and about weight 165 kg, was caught by artisanal fishers in Salinas Roca Partida, Veracruz, Mexico, on July 14, 2020. This study reports the first occurrence of this species in the southwestern of the Gulf of Mexico, which extends its geographical distribution in Mexico.

NEW RECORDS AND PRELIMINARY REPRODUCTIVE ASPECTS OF ELASMOBRANCHS OF THE TRINDADE-MARTIN VAZ INSULAR COMPLEX

Here we presented records of elasmobranchs obtained during a longline pelagic fishing monitoring around the Trindade-Martin Vaz insular complex, including one new record. New information on the reproductive aspects of the blue shark (Prionace glauca) and pelagic stingray (Pteroplatytrygon violacea) suggest the use of this area as mating and parturition ground for these species. The most abundant species was the P. glauca (N = 65), followed by shortfin mako shark Isurus oxyrinchus (N = 12). We also recorded for the first time the smooth hammerhead shark Sphyrna zygaena (N = 3) and the bigeye thresher shark Alopias superciliosus (N = 2), and other shark species previous reported for the insular complex, including the oceanic whitetip Carcharhinus longimanus (N = 2), and the tiger shark Galeocerdo cuvier (N = 1). Our findings highlight the importance of further studies at the Trindade-Martin Vaz insular complex considering the pelagic biodiversity and reproductive aspects of elasmobranchs.

Reproductive biology aspects of Alopias pelagicus and A. superciliosus (Lamniformes: Alopiidae) in the Ecuadorian Pacific

ABSTRACT The reproductive biology of thresher shark species of the Ecuadorian Pacific was analysed based on 1236 specimens of Alopias pelagicus (711 females and 525 males) and 354 of A. superciliosus (164 females and 190 males) landed in “Playita Mía”, from January to December of 2019. The length of A. pelagicus females ranged between 67.2 and 184 cm PCL (precaudal length) and the males between 69.0 and 178.4 cm PCL, A. superciliosus registered a minimum and maximum size of 76.0 and 202.2 cm PCL for females and 94.0 and 204.8 cm PCL for males. The most frequently captured size class for A. pelagicus was 147.2−157.2 cm PCL and for A. superciliosus was 156.0-166.0 cm PCL. The sex ratio (F:M) for A. pelagicus and A. superciliosus was 1.35F:1M and 0.86F:1M respectively. For A. pelagicus males the inflection point of the clasper length adjustment, was 134.2 cm PCL and size at first sexual maturity (L 50 ) was estimated at 136.0 cm PCL. For A. superciliosus males the inflection point of the clasper length adjustment, was 136.8 cm PCL, and the first sexual maturity (L 50 ) was estimated at 138.7 cm PCL.

Vertical movements of a pelagic thresher shark (Alopias pelagicus): insights into the species’ physiological limitations and trophic ecology in the Red Sea

The pelagic thresher shark Alopias pelagicus is an understudied elasmobranch harvested in commercial fisheries of the tropical Indo-Pacific. The species is endangered, overexploited throughout much of its range, and has a decreasing population trend. Relatively little is known about its movement ecology, precluding an informed recovery strategy. Here, we report the first results from an individual pelagic thresher shark outfitted with a pop-up satellite archival transmitting (PSAT) tag to assess its movement with respect to the species’ physiology and trophic ecology. A 19 d deployment in the Red Sea revealed that the shark conducted normal diel vertical migration, spending the majority of the day at 200-300 m in the mesopelagic zone and the majority of the night at 50-150 m in the epipelagic zone, with the extent of these movements seemingly not constrained by temperature. In contrast, the depth distribution of the shark relative to the vertical distribution of oxygen suggested that it was avoiding hypoxic conditions below 300 m even though that is where the daytime peak of acoustic backscattering occurs in the Red Sea. Telemetry data also indicated crepuscular and daytime overlap of the shark’s vertical habitat use with distinct scattering layers of small mesopelagic fishes and nighttime overlap with nearly all mesopelagic organisms in the Red Sea as these similarly undergo nightly ascents into epipelagic waters. We identify potential depths and diel periods in which pelagic thresher sharks may be most susceptible to fishery interactions, but more expansive research efforts are needed to inform effective management.