A study of white sharks ( Carcharodon carcharias ) off the northern coast of California (United States) has found an adult population and a slight increase in the number of subadult sharks, totaling 300 individuals. The researchers used a seal lure to lure predators into their boats so they could photograph and count white sharks.
Investigation Development
According to Taylor Chapple, a marine ecologist at the University of Oregon (United States), these animals are fundamental to the marine ecosystem. For this reason, it is not only good news for white sharks, but also for the waters that wash the Californian coast.
White sharks are found in coastal waters around the world. However, according to the World Wildlife Fund, they are currently threatened by overfishing. Furthermore, its world population is in decline.
This team of researchers published in 2011 a study of the shark population in northern and central California. Now this new research updates the previous estimate with longer-term observations. According to scientists, sharks usually spend half the year in the northeast Pacific, between Mexico and Hawaii. Then they spend the other half of the year closer to the coast, reaching as far north as Washington and as far south as Mexico.
Also, the largest populations of white sharks are found near Guadalupe Island (off Mexico) and in the California Current. This current runs from Monterey Bay (in the south) to Bodega Bay (north of San Francisco).
Likewise, from 2011 to 2018 the team of researchers has carried out observations from a boat at three different sites (the southeast island of Farallón, New Year Island and Tomales point off the coast of California). Thus, they were able to collect underwater images of great white sharks and more than 1,500 photographs.
To carry out the count the sharks looked at their dorsal fins. This is because, according to Chapple, each great white shark has a unique dorsal fin. In the words of the researcher “it is like a fingerprint with a barcode”. This individual identification also allowed the researchers to follow male and female sharks for a long period of time.
Population increase
This potential growth could indicate that measures to protect sharks in the region are working, the researchers note. In particular, restrictions on gillnets (fishing nets that are left in the water to entangle fish) could be improving the survival rate of young sharks. However, more still needs to be done to protect white sharks along their migratory path, as researcher Chapple says.
