Evaluating the Conservation and Ecological Roles of Large Marine Protected Areas for Threatened Sharks

Abstract

Sharks are among the most threatened groups of vertebrates on the planet, in large part due to historical and ongoing overfishing, both via targeted exploitation as well as bycatch. In recent years, shark conservation has gained increased international attention, particularly with respect to spatial protection. Many of the marine protected areas in the ocean were created specifically with the goal of conserving shark species, despite equivocal evidence for their efficacy, particularly for broad ranging species. Here, I test a set of questions about the role of large marine protected areas in shark conservation using advanced spatial and quantitative analyses. In my first chapter, I investigate how bycatch jeopardizes the conservation goals of shark sanctuaries that continue to permit commercial fishing, by developing a data integration workflow to predict shark bycatch and incidental mortality from longline fishing in remote ocean sectors, based on the level of fishing effort observed via satellite. Next, I explore how the space use of mobile sharks varies over their ontogeny, using a dataset of more than 300 white shark (Carcharodon carcharias) tracks as a case study, highlighting rapid space use expansion in juveniles and early support for a novel pattern of space use refinement in adults. In my third chapter, I report a first of its kind satellite track from a juvenile shortfin mako shark (Isurus oxyrinchus) tagged in the Mediterranean Sea, detailing its rapid movements away from one proposed nursery area and toward another, again highlighting the broad space use of juveniles among mobile species. Finally, I use Bayesian point process species distribution models to analyze an unstructured, opportunistic, presence-only dataset of Mediterranean white shark records to characterize a nursery area for the Critically Endangered population. Overall, I highlight the broad space use of mobile shark species even at early ages, and note that simple targeting or retention bans, like those in many shark sanctuaries, are unlikely to be sufficient. This underscores the need for nesting spatial protections of critical habitat within integrated management frameworks at broader scales, such as gear restrictions or other technical measures, to balance conservation goals with socioeconomic impacts from fisher displacement.