Scientists were surprised to find that the population of white sharks has not decreased, but instead remains steady. The number is estimated around 300 animals and there are signs that it may be growing.
Between 2011 and 2018, researchers were able to identify hundreds of individual adult and subadult white sharks, which are not fully mature but are old enough to prey on marine mammals. They used that information to develop estimates of the sharks’ abundance.
“The finding, a result of eight years of photographing and identifying individual sharks in the group, is an important indicator of the overall health of the marine environment in which the sharks live,” said Taylor Chapple of the Coastal Oregon Marine Experiment Station at Oregon State University’s Hatfield Marine Science Center and a co-author of the study.
White sharks, sometimes known as “great” white sharks; are apex predators that prey on large marine mammals such as elephant seals and harbor seals. As important players in the health of our oceans, they work to balance food chain levels through their predation habits.
White shark populations have been declining for years due to fishing practices and habitat loss but researchers like Dr. Chapple hope we can reverse these trends by using long-term data sets from underwater monitoring devices deployed near seal colonies or by studying great whites’ stomach contents when a carcass is recovered at sea – though both approaches carry risks associated with them which need consideration before undertaking any new research program.
“Robust populations of large predators are critical to the health of our coastal marine ecosystem,” said Chapple, a marine ecologist who specializes in the study of marine predators. “So our findings are not only good news for white sharks, but also for the rich waters just off our shores here.”
The findings were just published in the journal Biological Conservation. The study’s lead author is Paul Kanive of Montana State University. Additional co-authors are Jay Rotella of Montana State University; Scot Anderson of the Monterey Bay Aquarium; Timothy White and Barbara Block of Stanford University; and Salvador Jorgensen of University of California, Santa Cruz and the Monterey Bay Aquarium.
The great white sharks have a tendency to congregate in an area of the California Current spanning from Bodega Bay along the coast north of San Francisco all the way south to Monterey.
These formidable ocean dwellers are now being tracked by researchers for the first time. These sharks spend about half of their year in offshore waters that stretch halfway between Hawaii and Baja, Mexico, with more than 20 years worth of research showing how they travel as far north as Washington and south to Guadalupe Island off the coast of California or even closer.
Monitoring animal populations and determining trends is important to understanding the health of the population and making decisions about population management. In 2011, Chapple published a first estimate for California sharks with Jorgensen and Block which provides new insight into what these animals go through in their natural habitat.
Researchers have been monitoring white sharks off the coast of California for years, but it has always been difficult to identify individual animals. The researchers were able to use this data collected in 2011-2018 and get a better understanding of their movements by focusing on adults and subadults at three different sites: Southeast Farallon Island; Año Nuevo Island; Tomales Point. They lured them with seal decoys before capturing more than 1500 photographs which they used as identifying markers that helped scientists understand where these particular individuals travel during winter months along the coastal waters just outside San Francisco Bay Area’s Golden Gate Bridge.
“Every white shark has a unique dorsal fin. It’s like a fingerprint or a bar code. It’s very distinct,” Chapple said. “We were able to identify every individual over that eight-year period. With that information, we were able to estimate the population as a whole and establish a trend over time.”
Researchers were able to identify the sharks as either male or female by using underwater video. They found that following a shark from year to year, they could learn about their age and survival rates between males and females. About half of all sightings were repeat sightings while the other half was new appearances for those particular sharks in question.
Overall, the researchers found that white shark populations are on the rise and have potentially increased by as much as 20%. The number of adult sharks is up modestly while subadults remain steady. Both males and females were counted but female population estimates showed 60 in this region an increase – albeit small one-of around 300 remaining white sharks since 2000. There was even evidence suggesting their numbers had nudged substantially upward for adults (~20%) with only minor changes observed among subadult individuals (0%).
“That underscores the need for continued monitoring of white sharks, as there are relatively few reproductively active females supplying the population with additional sharks,” said Kanive, the study’s lead author.
“Losing just a few animals can be really critical to the larger population,” he said. “It’s important that we continue to protect them and their surroundings.”