Habitat Suitability of Juvenile Smooth Hammerhead Shark (Sphyrna zygaena) off northern Peru

Abstract

El tiburón martillo (Sphyrna zygaena) está amenazado de extinción debido a las pesquerías del sudeste del Pacífico. Sin embargo, existen pocos esfuerzos para manejar sus pesquerías sosteniblemente, para lo cual se requiere conocer el uso de su hábitat. Por lo tanto, esta investigación tiene como objetivo predecir la distribución espacial del tiburón martillo en los escenarios actuales de La Niña y El Niño y su distribución en el cambio climático futuro. 2994 ocurrencias de tiburones juveniles (2009 y 2017), y ocho factores ambientales fueron modelados utilizando Maxent. Los resultados indican que los predictores ambientales de distribución más importantes fueron la profundidad, la temperatura de la superficie del mar y la clorofila-a (indicador disponibilidad de presas). La mayor idoneidad del hábitat se predijo en la región central oceánica durante La Niña y en zona costera del norte en El Niño. Estos hábitats presentan condiciones oceanográficas y batimétricas únicas que resultan en zonas de alta productividad marina. En escenarios futuros de cambio climático, se predice que la idoneidad del hábitat será más costera, aumentando su vulnerabilidad a la pesca. Para mejorar la conservación del tiburones martillo y su ecosistema, estas áreas de alta idoneidad deberían ser una prioridad para futuras investigaciones y manejo.

The smooth hammerhead shark (Sphyrna zygaena) is one of most captured shark species by southeastern Pacific fisheries. Their distribution and habitat use is poorly understood hindering the identification of critical habitats for their conservation and the possible impacts of environmental change on species distribution. The aim of this research was to predict the spatial distribution of smooth hammerheads based on habitat suitability from the Northern Humboldt Upwelling System (NHUS) off northern Peru. (06ºS-11ºS). To achieve this, three analyses were performed: i) characterize their population structure, ii) identify environmental factors that affect their distribution, and iii) predict their spatially and environmentally suitable habitat under current La Niña and El Niño scenarios and projected to a future scenario of ocean warming between the years 2040- 2050. Between the years 2009 and 2017, 7485 sharks were measured and georeferenced obtained from a small-scale driftnet fishery. Their ecological niche was modelled using the program MaxEnt. The results indicate that neonate and juvenile smooth hammerheads are the dominant life-stage in the northern part of NHUS where this area probably represents a nursery area. The spatial distribution of sharks varies according to their ontogeny, and at seasonal and El Niño Southern Oscillation (ENSO) conditions. Sharks were closer to the coast during warmer (summer and El Niño conditions) periods. Four environmental variables were identified as important predictors of species distribution: depth, sea surface temperature (SST), chlorophyll-a, as a proxy of prey availability-, and, to a lesser degree, salinity. During current conditions, the highest suitable habitat was predicted in the central-offshore and shifted to northern-coastal part of the study area (close to the ecotone zone; 6ºS) in La Niña and El Niño conditions- respectively- as the coastal upwelling area, during El Niño warm conditions, offers the coolest environment and the highest productivity. Unique bathymetric conditions are associated with these areas (i.e. shelf break, marine canyons, narrow continental shelf, and coastal topography) generating oceanographic conditions (i.e. marine fronts, upwelling) which result in zones of exceptional high marine productivity. Under future climate change scenarios, the habitat suitability of smooth hammerheads will shift to a more coastal distribution. To enhance the conservation of smooth hammerheads and their supporting ecosystem, these areas of high suitability should be a priority for fishery management and under future scenarios of climate change, their coastal distribution could increase their catchability. Furthermore, these areas of highest suitability should be considered as candidates for a dynamic pelagic marine protected area.