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.

Monitoring of the status of eleven bony and cartilaginous fish populations in the Malpelo Sanctuary of Fauna and Flora, Colombian Pacific

To determine trends over time in the relative abundance of species prioritized in the Malpelo Fauna and Flroa Sanctuary Management Plan, underwater visual censuses were done from April 2009 to August 2019. Data were collected for five species of bonefish: bluefin trevally (Caranx melampygus), longfin yellowtail (Seriola rivoliana), yellowfin tuna (Thunnus albacares), leather bass (Dermatolepis dermatolepis) and sailfin grouper (Mycteroperca olfax), and six cartilaginous fish: spotted eagle ray (Aetobatus laticeps), silky shark (Carcharhinus falciformis), Galapagos shark (Carcharhinus galapagensis), whitetip reef shark (Triaenodon obesus), whale shark (Rhincodon typus) and scalloped hammerhead shark (Sphyrna lewini). A negative non-significant trend in abundance through time was observed for most of the evaluated species, except A. laticeps and T. obesus, which showed positive non-significant trends. The hammerhead shark (S. lewini) was the only species that showed a statistically significant decrease in abundance over time. The results of this study highlight the urgent need to establish more effective fisheries management and regulation measures that promote the conservation of important fish species, not just inside the sanctuary but also within the Tropical Eastern Pacific.

SEBARAN UKURAN DAN PERTUMBUHAN HIU MARTIL (BY CATCH) YANG DIDARATKAN DI PANGKALAN PENDARATAN IKAN (PPI) UJONG BAROH MEULABOH

Hammerhead shark is a type of predator shark belongs to the family of Sphyrnidae. This shark is so aggressive in hunting prey such as fish, squid, and shrimp. The hammerhead shark in Indonesia is included in Appendix II of CITES and has been a special concern in the field of capture fisheries. The aim of the study was to see the size spread, the number of catches, the first size caught, the age growth and the genital ratio of the hammerhead sharks caught with the base fish net. The study was conducted from October to December 2019. The shark measurement was performed once in 2 weeks. Sharks caught by the gills of the base (buttom gilt net) were measured using a roll meter. The collection of hammerhead sharks included total length (TL), number of catches and genital ratio. The analysis was done descriptively using the ELEFAN I existing on Sofwere FiSAT II. The results showed that the hammerhead sharks caught with an gill net of 65 tails from October to December 2019 were taken on the male genital. The total size spread of female malletic sharks were between 61.5-131.5 cm and male hammering sharks between 61.5-111.5 cm. The morphologically spread of the female hammerhead was relatively longer than the male shark. The male hammerhead shark was first captured at a length of 117.9 cm and a female hammerhead shark at a size of 106.2 cm. Hammerhead shark growth by following the curve of von Bertalanffy mallet were male Lt = 138,08 (1-exp (-0.480 (t + 0.0487)) and female mallet shark Lt = 138,08 (1-exp (-0.430 (t + 0.0434)). Such equations can be known by using the relationship curve model between the age and length of fish.