California is a hotspot for shark strandings, and scientists suspect pathogens in the water combined with favorable oceanic conditions may be to blame.
Marine wildlife strandings are a global phenomenon where animals are found washed up on beaches, unable to return to the water. In most cases, the animals die.
For some species, including whales and dolphins, strandings are well-documented. However, for sharks, information is lacking.
A study by researchers at the Federal University of Paraná, Brazil, has now tracked global shark strandings to get a better understanding of the issue. Their findings are published in the journal Fish and Fisheries.
Species affected included great white sharks, whale sharks, hammerheads and catsharks. The species most impacted—by a significant margin—was leopard sharks.
They found that out of 3,150 reports dating back to 1880, 2,409 happened in the U.S. Over half of these—58.8 percent—happened along the coast of California.
Study co-author Natascha Wosnick told Newsweek that there are several reasons why California has such a high number of shark strandings.
She said pathogens in California waters can cause diseases that kill sharks, while oceanographic conditions and the movement of the tides in the region help carcasses get deposited on the state’s beaches. In other areas, carcasses may simply get washed away by the tide.
A mass stranding event involving leopard sharks in California in 2019 was thought to be down to a pathogen called scuticociliate, which caused meningoencephalitis in the sharks—a serious neurological condition resembling meningitis and encephalitis.
Wosnick told Newsweek that leopard sharks were the species with the highest number of strandings. Not so coincidentally, these sharks live close to the shore and form large schools. “This could explain why most stranded individuals that are evaluated by pathologists are affected by meningoencephalitis, a disease that can spread very fast within a population,” Wosnick said.
Not only do the findings show California is a hotspot for the phenomenon, but Wosnick said it shows the number of shark standings far greater than scientists originally thought.
The study found survival rates of stranded sharks extremely low. Of all reports, only 9.9 percent of sharks were found alive. This indicates that sharks are more vulnerable to stranding than other animals, Wosnick said.
“This phenomenon has been systematically neglected resulting in significant knowledge gaps and decades of poor-quality data,” she said. “As a result of such neglect, responses to shark strandings are inefficient with little chance of success in rescue and rehabilitation.
“It is imperative to have shark specialists leading rescue and rehabilitation initiatives. A database of professionals and experts willing to help is also necessary, to build connections, assist rescue groups, and share resources.”
Going forward, Wosnnick said experts must gather more data on shark strandings in order to better protect them.