No abstract

White sharks, Carcharodon carcharias, are often described as elusive, with little information available due to the logistical difficulties of studying large marine predators that make long-distance migrations across ocean basins. Increased understanding of aggregation patterns, combined with recent advances in technology have, however,

Reliable estimates of mortality have been a major gap in our understanding of population ecology for marine animals. This is especially true for juveniles, which are often the most vulnerable age class and whose survival can strongly influence population growth. Thousands of pop‐up archival satellite tags (PAT) have been deployed on a variety of marine species, but analysis of these data has mainly been restricted to movement ecology and post‐handling survival following fisheries bycatch. We used PAT data to provide empirical estimates of annual survival and cause‐specific mortality for juveniles of a marine top predator. We tagged and tracked juvenile white sharks in the north eastern Pacific Ocean to (1) estimate survival rates and competing risks and (2) investigate intrinsic and environmental influences on mortality risk. We also evaluated the use of PAT data with respect to meeting assumptions of known‐fate survival models. Annual juvenile survival rate was 0.632 (SE = 0.15) and annual natural mortality rate (0.08, SE = 0.06) was lower than the rate of gillnet interactions (0.48, SE = 0.15). Mortality risk decreased with greater body length and was significantly greater (hazard ratio = 9.05, SE = 0.70) for juvenile sharks in Mexican waters, relative to California waters. The PAT data allowed for unambiguous determination of fate in most cases, aided by collaborative relationships with fishers and secondary tags deployed on a subset of sharks. Although caution must be exercised to establish whether assumptions are met, our work demonstrates that PAT data represent a widely available, untapped data source that could dramatically increase our understanding of marine population ecology. Synthesis and applications. Our research shows fisheries bycatch to be the main source of mortality for juvenile white sharks in the northeastern Pacific Ocean, highlighting the need for best practices, such as releasing sharks quickly following incidental capture. Furthermore, mortality risk for juveniles was greater in Mexican waters, such that survival may be lower in colder years when juveniles are likely to move south seeking warmer water. This could increase stochasticity in juvenile survival and negatively influence population growth for this apex predator.

A curated database of shark and ray biological data is increasingly necessary both to support fisheries management and conservation efforts, and to test the generality of hypotheses of vertebrate macroecology and macroevolution. Sharks and rays are one of the most charismatic, evolutionary distinct, and threatened lineages of vertebrates, comprising around 1,250 species. To accelerate shark and ray conservation and science, we developed Sharkipedia as a curated open-source database and research initiative to make all published biological traits and population trends accessible to everyone. Sharkipedia hosts information on 58 life history traits from 274 sources, for 170 species, from 39 families, and 12 orders related to length (n = 9 traits), age (8), growth (12), reproduction (19), demography (5), and allometric relationships (5), as well as 871 population time-series from 202 species. Sharkipedia relies on the backbone taxonomy of the IUCN Red List and the bibliography of Shark-References. Sharkipedia has profound potential to support the rapidly growing data demands of fisheries management, international trade regulation as well as anchoring vertebrate macroecology and macroevolution.

Juvenile white sharks distribute in coastal nursery areas, which are essential for population growth. Bahía Sebastián Vizcaíno (BSV), Mexico, is a white shark nursery area in the north‐eastern Pacific. Despite existing regulations forbidding the capture of white sharks, incidental catches still occur in some areas. Artisanal fisheries constitute one of the most important economic activities in BSV, yet no formal description of either these fisheries or the incidental catch of juvenile white sharks exists due to the poor data reporting system, thus preventing a clear understanding of the implications of these catches for the white shark population of the north‐eastern Pacific. Artisanal fishing activities and their interactions with juvenile white sharks in BSV are described based on fishermen's knowledge. Artisanal fisheries in BSV are multi‐specific, targeting mostly bottom‐related species (e.g. white seabass and California halibut) that are also common prey for juvenile white sharks. These activities are the only source of income for the majority of fishermen in BSV and are conducted throughout the year, with gillnets being the main fishing gear. White sharks are incidentally caught in bottom gillnets mainly during the summer, although another peak in incidental catch was recorded during winter, possibly related to the presence of juvenile white sharks from California, USA. The most common size of juvenile white sharks incidentally caught was <2 m in the nearshore areas close to the mouth of the Ojo de Liebre Lagoon; larger juveniles (~3 m) were caught in areas near Cedros, Natividad, and San Benito Islands. The multi‐specific nature of BSV artisanal fisheries and their socio‐economic value, and the high post‐release survival of juvenile white sharks suggest that future regulatory actions should focus on the release of incidentally caught live juvenile white sharks and the involvement of the BSV fishing community to increase the effectiveness of management efforts.