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Investigations confirm that basking shark sightings are declining sharply in California

A large dorsal fin is an important giveaway for identifying basking sharks, and a second small dorsal fin may also be visible. Their tails and noses may surface as they feed. And unlike most sharks’ more direct swimming patterns, basking sharks tend to zigzag or snake in the water. Credit: Irish Basking Shark Group

Basking sharks, about the size of a small school bus, are the second largest fish in the ocean and can be found in temperate and tropical waters around the world. Thousands of basking sharks were observed each year off the coast of California in the mid-1900s. It is rarely found in this area, now known as the California Current Ecosystem (CCE).


According to a survey by the University of California, Davis and the Southwestern Fisheries Science Center of NOAA Fisheries Basking shark Find out what we see in CCE since the 1970s and 1980s, and what drives their existence and distribution.The work is published in the journal Frontier of oceanology..

The findings are affecting the global protection of basking sharks, which are classified as endangered by the International Union for Conservation of Nature’s Red List.

Red flag

Little is known about basking sharks, such as their survival time, mating site, and birthing site. Populations have not been assessed at CCE, which extends from Baja to British Columbia, and there is no formal monitoring effort around the species. However, what data is present serves as a danger signal that the species needs further investigation.

“They are a rare sight,” said lead author Dr. Alexandra McInturf. He was a candidate for the Faculty of Wildlife, Fish and Conservation Biology at the University of California, Davis at the time of his research and is now a postdoctoral fellow at Oregon State University. “I want to know why the decline is happening. Is it climate change? Is it human-induced pressure? What environmental clues do they react to and how will they change in the future?”

In this study, the author investigated the longest available dataset. Systematic aerial surveys of small fish conducted by the NOAA fishery between 1962 and 1997, and additional information including fishery data, tagging and research efforts, and public observations between 1973 and 2018. The source.

In aerial survey, up to 4,000 basking sharks were witnessed in 1965. No sightings have been reported since the 1990s. Additional sources have reported less than 100 sightings annually since 1990. School size also decreased by about half from 57 to 24 per group between the 1960s and 1980s. In the decades that followed, no more than 10 schools were reported.

“While the aerial survey focused on small fish, the survey also collected data on basking sharks, which proved to be invaluable,” said the director of the Southwest Fisheries Science Center project. The author, Heidi Dewar, states. “Currently, basking shark fishing is banned in the United States, Mexico and Canada. If these protections are implemented, populations are expected to recover. Additional to understand the sources of death in international waters. Work is also required. “

Seasonal changes

The survey saw significant changes during the time of sightings. From the early fall and spring of the survey to the summer months since the 2000s.

Researchers have found a significant link between the presence of sharks and environmental factors such as sea surface temperature, prey presence, El Nino, and other climate change, driving these trends. What is still unknown.

Research states that lack of surveillance can also affect the reduction of sightings, and further research is needed to characterize their full range.

A sharp decline in basking shark sightings in California

Researcher Alexandra McInturf is looking for basking sharks during a research expedition in Ireland. Credit: Alexandra McInturf

Proposals for conservation

The study concludes with a proposal for species conservation, pointing out that the coastal area from Monterey Bay to Baja California continues to be an important habitat for basking sharks. The suggestions are:

  • Coordination of documents on basking shark death Witness Create more robust population estimates across the Pacific basin
  • Strengthening shark fin market surveillance
  • Development of region-specific genetic markers to ensure compliance with regulations on the international trade of endangered species

McInturf said raising public awareness of sharks may also help. For example, boating education is an important part of their protection, as they are susceptible to ship strikes when feeding on the surface of the water.

How to identify basking sharks

Basking sharks with huge mouths and bodies were once thought to be sea monsters, but because of their similar body structure, they were mistaken for great white sharks.

“I get questions like’Can they swallow people?'” McInturf said. “No, my throat is too small.”

Basking sharks have much smaller prey in mind. Like a whale, it filters feed small phytoplankton to fill its considerable belly.

A large dorsal fin is an important giveaway for identifying basking sharks, and a second small dorsal fin may also be visible. Their tails and noses may surface as they feed. And unlike most sharks’ more direct swimming patterns, basking sharks tend to zigzag or snake in the water.

After conducting a three-season field survey in Ireland to study basking sharks, McInturf saw the shark invading from the surface only once.

“It tells us what it’s like to work with a basking shark,” McInturf said. “I also want to see them underwater. I spent so much time looking for them, and they were incredibly hard to find.”

Additional co-authors of this study include Barbara Muhling and Joseph Bizzarro of the University of California, Santa Cruz and NOAA’s Southwestern Fisheries Science Center, David Ebert of the Moss Landing Marine Labs, and Nann Fangue and Damien Caillaud of the University of California, Davis. included.


New discoveries about basking sharks blow assumptions out of the water


For more information:
Alexandra G. McInturf et al, Spatial distribution, temporal changes, and knowledge gaps in sightings of basking sharks (Cetorhinus maximus) in the California Current ecosystem, Frontier of oceanology (2022). DOI: 10.3389 / fmars.2022.818670

Quote: A sharp survey of basking shark sightings in California obtained on February 22, 2022 from https: //phys.org/news/2022-02-sharp-decline-basking-shark-sightings.html. Decrease (February 22, 2022) confirmed

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Investigations confirm that basking shark sightings are declining sharply in California

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