The strange mass die-off of gray whales in the northeastern Pacific Ocean may finally have an explanation: Scientists are linking Arctic sea ice levels to major extinction events.
Three deaths affected gray whales, according to a new study (Eschrichtius SağmusA species that has been living off the coast of North America since the 1980s, decreasing the population by 15-25% each time. In total, more than 2,000 gray whales are known to have died. The first mass die-off occurred between 1987 and 1989 and was the largest of its kind, killing at least 700 whales. However, according to the study, reporting and research structures only expanded in the 1990s; This means the number of emissions associated with this fatality may be an underestimate. The second occurred between 1999 and 2000, and 651 whales were killed.
The most recent extinction began in 2019 and resulted in the deaths of more than 70 gray whales in just six months. It continues, and as of September 26, 2023, a total of 688 whales have died. It was unclear what caused each of the incidents.
“These are extreme population fluctuations that we did not expect to see in a large, long-lived species like gray whales,” lead study author Joshua Stewart, an associate professor at the Marine Mammal Institute at Oregon State University, said in a statement.
Commercial whaling drove the North Pacific gray whale population to near extinction in the mid-20th century, but it has since rebounded and now numbers around 14,500, according to the statement. Scientists previously believed that this successful recovery meant that whales periodically disappeared; because their numbers were greater than their habitat and prey could support.
But changing conditions and fluctuating sea ice levels in the Arctic may better explain what the National Oceanic and Atmospheric Administration (NOAA) calls “unusual mortality events,” according to a new study published Oct. 12 in the journal Science.
Sea ice cover and the amount of food available to gray whales can affect population survival. In some years, larger-than-usual ice cover can block passage to the Bering and Chukchi seas, where whales spend the summer months feasting on oily crustaceans before migrating south again. “When prey availability is low in the Arctic and whales are unable to reach feeding grounds due to sea ice, gray whale populations experience rapid and severe shocks,” Stewart said.
Gray whales recovered quickly after the first two deaths. But the latest extinction has been going on since 2019 and has thrown us into “uncharted territory,” Stewart said.
Unlike the previous two events, the historic loss of Arctic sea ice may be responsible for the latest gray whale extinction. That’s because the underside of the sea ice has a carpet of algae that degrades the seafloor and fills it with food for bottom-dwellers, including whales’ favorite crustaceans.
“With less ice you get less algae, which is worse for gray whale hunting,” Stewart said. Melting sea ice also opens up powerful currents that wash away sediment and leave benthic crustaceans and other creatures homeless. “All these factors combine to reduce the quality and availability of the food we rely on [сірі кити]”, – said.
Stewart said climate change may be the reason this die-off event lasted longer than the previous two. “We are seeing a much more bumpy ride in response to very variable and rapidly changing ocean conditions,” he said.
Climate change may mean there will be less food for gray whales, but it probably won’t put the Northeast Pacific population at risk of extinction, Stewart said. But “the significantly warming Arctic Ocean may not be able to support 25,000 gray whales as it did in the recent past,” he added.
Source: Port Altele
