the great White shark The population off California’s northern coast is healthy and growing, according to a new study.
A survey of the great whites (Carcharodon carcharia) off the north coast found a stable adult population and a slight increase in the number of subadult sharks, totaling 300 individuals. The researchers used a seal decoy to lure predators to the top of their boats so they could photograph and count sharks.
The results are excellent for the region.
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“Robust populations of top predators are essential to the health of our coastal marine ecosystem,” study co-author Taylor Chapple, marine ecologist at Oregon State University, said in a press release. “So our findings are not only good news for white sharks, but also for the rich waters just off our shores here.”
Great white sharks are found in coastal waters around the world. They are threatened by overfishing, according to the World Wildlife Fund, and their world population is declining.
On the Pacific coast, by contrast, sharks seem to be doing well. Chapple and his team initially published an estimate of the shark population off northern and central California in 2011. The new research updates the previous estimate with longer-term observations. Sharks found in the region don’t stay in one place: they spend half the year in the northeast Pacific, between Baja, Mexico, and Hawaii, then spend the other half of the year closer from the shore, going as far north as Washington. and as far south as Mexico. The largest populations are found near Guadalupe Island off Mexico and in the California Current off northern California. This current extends from Monterey Bay in the south to Bodega Bay north of San Francisco.
From 2011 to 2018, Chapple and his colleagues carried out boat observations at three sites near the southeastern island of Farallon, the island of Año Nuevo, and Tomales Point off the coast of California. They collected more than 1,500 photographs as well as underwater video footage of great white sharks, using the dorsal fins to identify individual sharks and get a more accurate count.
“Every white shark has a unique dorsal fin. It’s like a fingerprint or a barcode,” Chapple said.
This individual identification also allowed researchers to track male and female sharks over a long period of time. Although the overall population numbers seemed strong, the researchers were slightly concerned that the adult population of white women is only around 60 years old.
“This highlights the need for continued monitoring of white sharks, as there are relatively few active breeding females providing the population with additional sharks,” said study co-author Paul Kanive, a doctoral student in ecology. at Montana State University, in the release.
The reproduction of the great white shark is largely a mystery, but scientists believe the gestation period is around 12 months, and females typically give birth to between two and 10 cubs at a time.
The possible population growth could be the result of a natural fluctuation, or it could indicate that shark protections in the region are working, the researchers wrote in the May issue of the journal. Biological conservation. In particular, restrictions on gillnets – fishing nets that are left in the water to entangle fish – could improve the survival rate of young sharks. More needs to be done to protect white sharks along their migratory journey, Chapple said.
“We can provide as much protection as possible when they are in coastal waters, but these sharks are highly migratory animals,” he said. “It will take international cooperation, agreement and enforcement to protect them.”
Originally posted on Live Science.