OREGON COAST — A die-off of several hundred gray whales last year might, in fact, represent a promising future for the creatures, according to an expert in marine mammals.
According to NOAA Fisheries, there were 215 gray whale strandings on the Pacific coasts of the United States, Canada and Mexico during 2019, which the administration classified as an unusual mortality event, defined as “a stranding that is unexpected, involves a significant die-off of any marine mammal population and demands immediate response.” A previous gray whale mortality event in 1999 saw an even higher number of strandings.
Bruce Mate has researched marine mammals for more than 50 years and is the former director and endowed chair of the Marine Mammal Institute at Oregon State University.
He said the gray whale population had been reduced to between 1,000 and 2,000 animals by 1900 due to commercial whaling. The 20th century brought protections against over-exploitation of whales, first through the League of Nations and, later, by the International Convention for the Regulation of Whaling. The United States also protected them though the Marine Mammal Protection Act of 1972 and the Endangered Species Act of 1973, all of which helped reduce risks for the population.
Mate said at the time of the 1999 mortality event there had been annual counts by the National Marine Fisheries Service that estimated the gray whale population was about 20,000 animals, which may be close to the original population prior to its decimation by commercial whaling.
Researchers thought the 1999 strandings might indicate the species had possibly reached its carrying capacity, the maximum population its then mostly Bering Sea food (of bottom-dwelling, shrimp-like creatures of the order amphipod) could sustain, Mate said.
The whale biologist and his colleagues developed a method to track endangered species of whales by satellite to determine their migrations and habitat requirements. In 2005, his research group tagged mothers with calves at breeding grounds in Mexico and tracked them to their feeding grounds.
Gray whales, like several other whale species, feed heavily and then fast during long migrations to breed and calve. Gray whales were known to feed in Alaska’s Bering Sea and migrate to lagoons in Mexico to bear young, then travel all the way back to their feeding grounds, all without eating.
Mate said, “We found that any animals we tracked in 2005 for more than 100 days went up through the Bering Sea through the Bering Strait to the high arctic to the Cuckchi and Beaufort seas. It seemed as though the gray whales were exploring more environments to find food.”
The OSU researchers also tagged western gray whales feeding along the east coast of Russia in 2010 and 2011, where the international research community expected the whales would migrate north-south along the Asian coast to the China Sea for winter, much the way eastern North Pacific gray whales migrate along North America to Mexico. Instead, the “Russian” whales traveled east across the Bering Sea and then south to Baja Mexico like the eastern North Pacific whales.
“One of those animals traveled 12,500 miles round trip without stopping to feed substantially anywhere. That’s the longest migration of any mammal in the world. It is hard to imagine, but this female was away from her Sea of Okhotsk feeding grounds for five months,” Mate said.
“Last year, we saw fewer gray whales show up in some of the Baja lagoons, the whale migration was late, and there were fewer calves born. This is consistent with a possible food limitation, which seems consistent with the northbound die offs. This year, there are again fewer mothers with calves in San Ignacio Lagoon, where I have been visiting annually for more than 30 years, again suggesting that most females didn’t have the body condition to carry a calf to term.”
He said many of the animals found stranded along the north-bound migration last year were emaciated, another sign that they were running out of fuel during their long journeys back to their feeding grounds.
“The population is currently estimated at about 27,000, so it continued to grow after it ate itself out of house and home in the Bering Sea, and most whales moved farther north into alternate feeding areas where smaller numbers of gray whales had been feeding for decades. Now the larger population may not have any alternative areas to find food, so I am expecting the gray whale population to level out at a number that will likely be substantially lower than the current population.” he said.
“Yes, I think there may be more whales die offs this year. In my opinion this isn’t ‘woe for the gray whales.’ Instead, we should think about this ‘adjustment’ as the result of the species’ successful recovery and having overshot their carrying capacity as they find a population that is sustainable over an extended period of time. I see it as a celebration of this animal returning to its proper place in the marine ecosystem.”