Spatial ecology of blue shark and shortfin mako in southern Peru: local abundance, habitat preferences and implications for conservation

Abstract

While global declines of pelagic shark populations have been recognized for several years, conservation efforts remain hampered by a poor understanding of their spatial distribution and ecology. Two species of conservation concern are the blue shark Prionace glauca and the shortfin mako shark Isurus oxyrinchus. To improve management of these species, this study examined their local abundance patterns, habitat preferences, and distribution in the Southeast Pacific. Catch per unit effort (CPUE) data from an artisanal fishery in Peru were used to identify geographic hot spots and model abundance estimates as a function of environmental variables, including the El NiÒo Southern Oscillation (ENSO). A 10 yr data series revealed declining annual landings since 2012, despite no changes in management structures. Significant aggregations of both species were found in southwestern Peruvian waters (74-76∞W, 17-19∞S), with both species-specific hot spots targeted by major fishing efforts. P. glauca CPUE increased during La NiÒa conditions (i.e. low water temperature anomaly), and CPUE of both species declined when water depths exceeded 1000 m. Correlations with lunar illumination and chlorophyll a were revealed in P. glauca and I. oxyrinchus, respectively. Modeling explained 57 to 61% of the deviance, indicating that other factors not included in the present study might account for unexplained variance in CPUE (e.g. thermocline depth, location of marine fronts, dissolved oxygen, and gear characteristics). Given the importance of the examined area to shark fisheries and the exploitation of multiple species of conservation concern, the information presented here can be used to inform management strategies designed to limit the depletion of pelagic sharks.