For these reasons, the sea otter remains classified as an endangered species. The recovery of the sea otter is considered an important success in marine conservation, although populations in the Aleutian Islands and California have recently declined or have plateaued at depressed levels. A subsequent international ban on hunting, sea otter conservation efforts, and reintroduction programs into previously populated areas have contributed to numbers rebounding, and the species occupies about two-thirds of its former range. Sea otters, whose numbers were once estimated at 150,000–300,000, were hunted extensively for their fur between 17, and the world population fell to 1,000–2,000 individuals living in a fraction of their historic range. Its diet includes prey species that are also valued by humans as food, leading to conflicts between sea otters and fisheries. In most of its range, it is a keystone species, controlling sea urchin populations which would otherwise inflict extensive damage to kelp forest ecosystems. Its use of rocks to dislodge prey and to open shells makes it one of the few mammal species to use tools. Its foraging and eating habits are noteworthy in several respects. It preys mostly on marine invertebrates such as sea urchins, various mollusks and crustaceans, and some species of fish. The sea otter inhabits nearshore environments, where it dives to the sea floor to forage. Although it can walk on land, the sea otter is capable of living exclusively in the ocean. Unlike most marine mammals, the sea otter's primary form of insulation is an exceptionally thick coat of fur, the densest in the animal kingdom. Adult sea otters typically weigh between 14 and 45 kg (30 and 100 lb), making them the heaviest members of the weasel family, but among the smallest marine mammals. It's hard to predict what will happen.The sea otter ( Enhydra lutris) is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. They ended up attacking livestock. Bringing back predators can be tricky. Brown bears ( Ursus arctos) were brought back to the Pyrenees mountains in Europe. In Yellowstone, bringing back predators has been successful. But in other cases, top predators have caused problems. With fewer elk, there was more plant growth. ![]() The wolves had a big effect on the ecosystem and food web. ![]() They brought wolves back into Yellowstone National Park in the 1990s. Not Always Successful Scientists have tried bringing some top predators back. Fewer trees and plants meant fewer beavers and birds. The elk ate too many plants, including young trees. Wolves hunt elk ( Cervus canadensis). Without wolves around, the elk populations exploded. Something similar happened with gray wolves ( Canis lupus) in the 1900s. These changes are called a trophic cascade. The changes trickle all the way down the food chain. Many changes happen when a top predator is taken away. Without the kelp, the fish had to leave the ecosystem. Without otters, there were too many sea urchins. Otters eat small animals like sea urchins. When the otter population dropped during the fur-trade era, it initiated a cascade of events that altered the region's food web. Due to overhunting, the sea otter population off the California coast dropped from more than 10,000 in the 1700s to less than 100 by the early 1900s. The ecosystem changed a lot when the otters were gone. By the early 1900s, fewer than 100 were left. Without Top Predators, Entire Ecosystems Change In the 1700s, there were more than 10,000 sea otters off the coast of California in the United States. Due to the changes in their ecosystem, sea otters have had a hard time bouncing back. ![]() The effects trickled down to other animals. When many sea otters disappeared, it affected the whole ecosystem. Top predators hunts other animals for food. Sea otters are a top predator or apex predator. Sea otters ( Enhydra lutris) sit at the top of their food chain. A food web is made of all the food chains in an ecosystem. They are linked together in the order of the food they eat. It also hurt entire food chains. A food chain is a group of organisms. The fur trade didn't just harm the hunted animals. People used to hunt sea otters for their thick and warm fur.
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