Multiaxial Shark Conservation: How vertical distribution can inform marine management

Abstract

Understanding how sharks are spatially and temporally distributed is critical to formulating effective conservation and management strategies. Many shark species are threatened around the world, and knowledge on diving behaviours and vertical habitat use remains limited, hindering the development of contemporary, multiaxial management strategies. The recent advent of satellite technology facilitates the investigation of vertical habitat use by pelagic sharks through the analysis of diving behaviours. Comparing temperature profiles and track analyses between shortfin mako (Isurus oxyrinchus), white (Carcharodon carcharias), and porbeagle (Lamna nasus) sharks tagged with pop-off satellite archival tags (PSATs) in Atlantic Canada indicates potential seasonal and species-specific characteristics of the local shark community. The explicit comparison of interspecific shark species distribution to understand the extent of their overlap on the vertical plane is novel, and vertical habitat characteristics such as preferred temperature and depth are rarely incorporated into vertical distribution and range using species distribution models (SDMs). Through developing an understanding of species-specific vertical habitat characteristics, depth-specific fisheries gear and bycatch mitigation regulations can be formulated to reduce the incidental capture of individual species instead of targeting sharks more broadly. In addition, periodically updating the Policy on Managing Bycatch to reflect contemporary data availability and establishing a centralized document outlining bycatch management for sharks beyond the implementation of recommendations by ICCAT are recommended paths to progress in the context shark conservation, bycatch mitigation, and species at risk recovery objectives in Canada.