Sustainability

Most juvenile great white shark deaths 'due to fishing'

Written by Oceanographic staff

Most juvenile great white shark deaths occur due to unintentional capture in fishing gear, a new study reveals.

The report, “Juvenile survival, competing risks, and spatial variation in mortality risk of a marine apex predator,” published today (9 May, 2018) in the Journal of Applied Ecology, used 20 years’ worth of data from pop-up archival tags (PAT tags) – which have been used worldwide to track tens of thousands of individual ocean animals – to determine the fate of juvenile great whites in the coastal waters of the Northeastern Pacific.

The research team, from the US and Mexico, suggests the report is the first empirical estimate of annual survival rates for young white sharks, a protected species in both countries.

Dr John Benson, an assistant professor at the University of Nebraskawho had previously used such modelling on land-based animals, conducted the white shark study as a postdoctoral researcher at Monterey Bay Aquarium. The aquarium, together with colleagues at California State University, Aquatic Research Consultants and the Ensenada Center for Scientific Research and Higher Education, has been tagging and tracking juvenile white sharks since 2002.

“We always learn things from adjacent fields,” said Dr Salvador Jorgensen, principal white shark scientist at the Monterey Bay Aquarium and senior coauthor on the paper. “Before coming to the aquarium, John made his name studying mountain lions in Southern California. We were excited to see how the methodologies John was using for land-based predators could be applied in the ocean.”

The paper revealed the overall estimated annual survival rate for young white sharks is 63 percent. Though the study did not address broad trends in the white shark population in the Northeastern Pacific, the researchers note that protection of white sharks in 1994 has likely resulted in a reduction in fishing-related mortality. The increase in juvenile shark sightings over the last 15 years may be an early indication of a positive sign for population recovery.

Researchers suggest the study highlights the need to follow best practices related to incidental catch in coastal commercial and sport fisheries. Only two young white sharks tagged by researchers died of natural (non-fishing) causes.

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