Are there sharks in Santa Cruz, CA.

Sea otters: shark attacks leave biologists puzzled

Sea otters were considered to be around 85 years ago (Enhydra lutris) on the California coast as extinct: fur hunters had exterminated them because of their coveted coat. Then, in the 1930s, a few dozen animals were rediscovered and strictly protected in an almost inaccessible part of Big Sur. Since then, their population has grown to around 3,000 animals - but their future is again uncertain, warn sea otter researchers such as Tim Tinker from the University of California in Santa Cruz. As the biologist reports to National Geographic, great white sharks in particular are a threat to the species' recovery today, and nobody knows why. According to the observations of Tinker and Co, the number of fatal attacks on sea otters has increased explosively in recent years, although the mammals do not actually fit into the predatory fish's range of prey.

Half of all sea otters found dead are now being bitten by young great white sharks (Carcharodon carcharias) back. So far, however, no case has been reported in which one of the fish also ate such a victim. "This cause of death far exceeds all other factors," Tinker told National Geographic. Sea otters are made up of many muscles and have extremely dense fur, which is why they are inadequate as a food source for sharks. In California the predatory fish mainly hunt sea lions and fur seals, which store a lot of energy-rich fat in their tissues. The biologists therefore suspect that the sharks mixed up their prey and actually wanted to kill sea lions. If they then notice their mishap, leave the sea otters dead or dying. In the case of attacks on humans, too, misunderstandings are usually suspected because surfers or swimmers are mistaken for marine mammals. Often the sharks let go of their victim when they discover after the first bite that it is not a seal.

Since sea otters live near the coast, but adult great white sharks mostly far out in the sea, they could be young sharks. They tend to swim towards the mainland and are less experienced, which is why they take test bites more often. The bite pattern in alluvial carcasses supports this thesis. The researchers do not yet know why the number of attacks has risen sharply since it was first detected in 2003. Perhaps it is slowly becoming apparent that great white sharks are strictly protected in California's waters and that their numbers are therefore increasing. At the same time, the population of sea otters has grown for a long time - as a result, both species could meet more frequently with fatal results. The warming of the Pacific could also play a role, as it ensures that the great white sharks spread northwards, where the main distribution areas of the sea otters are. And finally, the sea lions and bears populations have also recovered in recent decades, which also attracts predators. The affected sea otters would then be collateral damage.

In view of the frequent deaths among the sea otters, however, Tinker and colleagues fear for the population of the animals and their distribution. While in the past, before the hunt, at least 15,000 sea otters would have lived off California, there are currently at most 3,000. Above-average losses by a predator are more significant and could endanger the species regionally again in the long term.