The Effects of Climatic Variability on the Feeding Ecology of the Scalloped Hammerhead Shark (Sphyrna lewini) in the Tropical Eastern Pacific

Climatic variability changes ocean productivity and generates systematic cascading effects in marine food webs. Studying the feeding ecology of top predators, such as sharks, can provide insights into the overall health of marine ecosystems. We conducted a 4-year study to evaluate seasonal and inter-annual trophic variations and their relationship with El Niño Southern Oscillation (ENSO) on the largest aggregation of scalloped hammerhead shark (Sphyrna lewini) in the Tropical Eastern Pacific (TEP). We used δ13C and δ15N signatures to gain a better understanding of hammerheads’ feeding strategies as well as variations of their isotopic niche. Our results suggest that the hammerhead sharks in the Galapagos Marine Reserve respond to climatic fluctuations, with La Niña event potentially benefiting their trophic needs as the overall marine productivity increased in the region. This work is the first of its kind in the TEP and provides insights on how climate variability influences the feeding ecology of this critically endangered species. It also highlights the need to incorporate climate-related conservation strategies into the management of this species since ENSO events become more frequent and intense in the face of climate change.

Captura de peces elasmobranquios provenientes de la pesca artesanal en las playas de Poneloya y las Peñitas, León, Nicaragua

El presente trabajo se centro en evaluar la composición de la captura, la diversidad de especies, abundancia relativa y estructura de tallas de tiburones y rayas capturados por la pesca artesanal en las playas de Poneloya y Las Peñitas. Se analizaron los organismos desembarcados durante los meses de mayo a junio. Se registraron las especies capturadas, sitio de la captura, tallas, pesos y condición reproductiva. Se analizaron 216 organismos distribuidos en 7 especies y 6 familias. Siendo la de mayor abundancia el tiburón Sphyrna lewini (67.6 %), seguida de Dasyatis brevis (13 %) y Dasyatis longa (11 %), Rhinoptera steindachneri (3.2), Aetobatus narinari (3.2 %), Gymnura marmorata (1.4 %) y Rhinobatus leucorhynchus (0.5%). Las capturas fueron realizadas con dos artes de pesca, palangre (54.5%) y red agallera (45.5%) con capturas dirigidas hacia peces óseos de alto valor comercial Sphyrna lewini se encontró un 47.3% de hembras, 52% machos y un individuo desconocido (0.7%), el 100% de machos y hembras fueron juveniles por ende se encontraron inmaduros. Dasyatis brevis el 81.5 % fueron hembras y 18.5% machos, encontrándose diferencias significativas en la proporción sexual (X2 = 10.7 P < 0,05). El 80 % de machos fueron inmaduros y el 20% maduros, las hembras el 95% fueron inmaduras y un 5% maduras. Dasyatis longus el 35 % fueron hembras, 52 % machos y 13% individuos desconocidos. El 58% de los machos fueron inmaduros y el 42% maduros, en el caso de las hembras el 62.5% fueron inmaduras y el 37.5% maduras.

Observations of sharks (Elasmobranchii) at Europa Island, a remote marine protected area important for shark conservation in the southern Mozambique Channel

Sharks have declined worldwide and remote sanctuaries are becoming crucial for shark conservation. The southwest Indian Ocean is a hotspot of both terrestrial and marine biodiversity mostly impacted by anthropogenic damage. Sharks were observed during surveys performed from April to June 2013 in the virtually pristine coral reefs around Europa Island, a remote Marine Protected Area located in the southern Mozambique Channel. Observation events comprised 67 1-hour scientific dives between 5 – 35m depth and 7 snorkeling inspections, as well as 4 dinghy-based observations in the shallow lagoon. In a period of 24 days, 475 sharks were tallied. Carcharhinus galapagensis was most encountered and contributed 20% of the abundance during diving, followed by C. albimarginatus (10%). Both species were more abundant between 11-14h, and on the exposed sides of the island. Numbers of Sphyrna lewini were highest with 370 individuals windward and leeward, mostly schooling. S. lewini aggregations in the area are hypothesized to be attracted to the seamount archipelago offering favorable conditions for deep incursions and of which Europa Island forms part. C. amblyrhynchos, Galeocerdo cuvier and S. mokarran were uncommon, while there was an additional observation of Rhincodon typus. The lagoon of Europa was a nursery ground for C. melanopterus where it was the only species present. A total of 8 species was recorded, contributing to the shark diversity of 15 species reported from Europa since 1952 in the scientific and gray literature. Overall, with the occurrence of several species of apex predators in addition to that of R. typus, large schools of S. lewini, fair numbers of reef sharks and a nursery of C. melanopterus, Europa’s sharks constitute a significant reservoir of biodiversity, which contributes to preserve the functioning of the ecosystem. Our observations highlight the relevance of Europa Island for shark conservation and the need for shark-targeted management in the EEZ of both Europa and Bassas da India.