Don’t blame salmon fishermen for the plight of some endangered killer whales off the Pacific coast, says a newly released report.
After three international conferences and nearly 15 months of reflection, members of a joint Canada-U.S. panel studying Southern Resident Killer Whales have concluded there’s no simple, linear, cause-and-effect relationship between the number of salmon available to the orcas and the population’s growth.
The Independent Science Panel was struck by the Department of Fisheries and Oceans and the U.S. National Oceanic and Atmospheric Administration in 2011 and was asked to answer whether fishing reduced the supply of food to the whales and if that impeded their recovery.
The population is listed under the Species at Risk Act in Canada and under the Endangered Species Act in the U.S., and since the 1970s the numbers have been growing by less than one per cent.
“It’s not a given that … their health is being hindered by the fishery,” said Larry Rutter, fisheries policy assistant with the U.S. National Oceanic and Atmospheric Administration.
“There are many other competing hypothesis as to what’s constraining the growth of the population, everything from toxins to noise to boat traffic to all kinds of things.”
Southern Resident Killer Whales live almost exclusively in the Salish Sea and the Juan de Fuca Strait in the waters off British Columbia and Washington state between July and September.
But the report says between April and June, only about 32 per cent of the population lives in the area, with the remainder of sightings during those spring and early summer months taking place in waters off northern Oregon and Vancouver Island.
During the winter, members of the population are sometimes found off the coast of central California but more frequently appear off the coast of Washington state.
Between 1974 and 2011, the group’s population has fluctuated between 67 and 95 animals, growing by a rate of 0.71 per cent a year. In contrast, members of another population, the Northern Resident Killer Whales, have increased from 120 animals in 1975 to more than 260 currently.
The report confirms chinook are an important part of the southern residents’ diet, and evidence collected since 1994 indicates some pod members have been in poor condition, which is associated with higher mortality rates.
Yet the report cautions against concluding a reduction in the salmon catch would mean more fish for the killer whales.
That’s because other orcas, and predators like seals and sea lions, feed on chinook at the same time as the Southern Residents, and harvest levels for chinook are already low, so there’s limited opportunity to further reduce the catch, states the report.
The report said there is a statistical correlation between the population’s survival rates and the abundance of chinook.
However it also said there is limited evidence linking the growth of the killer whale population with salmon availability.
2012 BellMedia