When wolves on an Alaskan island drove a population of deer to the brink of extinction, they decided change your nutritional regimen and have shifted to eating mostly sea otters, according to an article published this week in the journal Proceedings of the National Academy of Sciences (PNAS). This occurred over the course of a few years, according to scientists from the Oregon State University and the Alaska Department of Fish and Game, who were stunned to discover that sea otters had become the primary food source for a land-based predator.
To reach this conclusion, the researchers followed some wolves – equipped with GPS collars – and analyzed their droppings over the course of five years. Thus, they found that, in 2015, deer were the preferred food of wolves (they represented 75% of their diet, while the remaining 25% corresponded to otters).
Sea otters are a known predator in nearshore ecosystems, and the sea lion is among the most famous predators in terrestrial systems.
taal levi
Later, in 2017, they observed that sea lions consumed mostly sea otters (57% of their total diet), while the percentage of what had been their main prey, deer, dropped to 7%. This last dietary pattern was maintained until 2020, the end of the study period.
“Sea otters are a known predator in nearshore ecosystems, and the sea lion is among the most famous predators in terrestrial systems,” he says. taal levi, associate professor at the University of Oregon. Thus, in his opinion, it was “quite surprising” that sea otters have become the main source of food for sea lions, as it is a “large predator serving as food for another top predator”.
an inaccessible island
The researchers hypothesize that wolves and otters have a possible common history in the study area, Pleasent Island, an area adjacent to Glacier Bay (about 60 kilometers west of the city of Juneau). It is an island of approximately 50 square kilometers, uninhabited and accessible only by boat or seaplane.
During the 19th century and part of the 20th century, sea otter populations in this region were wiped out by the uncontrolled hunting that fueled the fur trade.
During the 19th century and part of the 20th century, sea otter populations in this region were decimated by uncontrolled hunting that spurred the fur trade. Instead, wolf populations in Southeast Alaska have survived because they have not been hunted to extinction.
In recent decades, especially after the reintroduction and legal protection of sea otters, populations of both species have recovered and coexisted again, providing new opportunities for predator-prey interactions.
This renewed coexistence has made possible the specific study of the wolf pack on Pleasant Island and the adjacent mainland. So biologist Gretchen Roffler and a team of researchers from the state of Alaska collected 689 wolf droppings, many along the coast of the island.
A wolf drags the carcass of an otter near the coast in Alaska. / Alaska Department of Fish and Game
it is samples were examined in the laboratory in Oregon, using molecular diagnostic tools, such as genetic characterization (the so-called DNA barcoding) and genotyping of feces, to identify individuals and determine their diets. In addition, GPS trackers were attached to a dozen wolves, both on the island and on the mainland, to learn whether the wolves swam between the mainland and island territory (something they used to do elsewhere). With this data, they determined that the wolf pack on the island was stable and that mainland wolves did not breed to hunt there.
Wolves that swim sometimes
Another piece of information that became evident thanks to the study was that wolves hunted sea otters when they were in shallow water or resting very close to the shore, exposed by low tide. Roffler argues that, until the wolves’ diet changed drastically, they would “occasionally” eat an otter that washed up dead on the beach. However, the fact that sea lions started chasing their marine prey (even dragging them ashore, above the tide line) indicates that what they learned so quickly became a widespread pattern of behavior across the entire planet. flock.
In monitoring the wolves, molecular diagnostic tools, such as genetic characterization and faeces genotyping, were used to identify individuals and determine their diets.
Recent history says that after wolves colonized Pleasant Island in 2013, the island’s deer population plummeted. The teacher Levi He admits that, at the time, he believed the wolves would leave the island or eventually disappear. To his surprise, the wolves remained and the pack grew to a density never seen before in their populations. According to the scientist, the main reason for this increase has been the availability of sea otters as a food source.
This phenomenon has been documented by the research team throughout the Alexander Archipelago, the southeastern Alaska archipelago that is home to Pleasant Island, work that is now expanding into Katma National Park and Preserve.youlocated in southwestern Alaska (just over 1,000 kilometers from Pleasant Island), to study their populations of sea lions and sea otters.