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.
"Because SRKW growth and salmon abundance data are observations of uncontrollable events obtained from an unknown sampling design, there is a high risk of incorrectly assigning causes to correlations and making weak inferences," concluded the report.
Rutter said officials at NOAA are studying the report and will have internal discussions before meeting with Canadian fishery officials over the issue.
He said a comment period will run until the end of January, allowing individuals who participated in the process and other interested parties to give input on the findings.
Officials in NOAA will then have to decide this winter if they'll make any fisheries' management decisions for the spring because of the report's findings, he said.
"The main question we have to decide is should fishing as we now manage it be modified in some way," Rutter said. "That's the central question."
Paul Macgillivray, a spokesman for DFO's Pacific region, said officials inside the department are now analyzing the report and trying to determine how it will be used to inform decision on killer whale recovery actions and salmon fisheries.
"We're in the process of looking through the report in more detail, and saying, 'OK, what do we glean from the advice that's provided,' and go from there," he said.
He said both agencies will then have a discussion and compare notes on whether the issue should be pursued further in the context of the Pacific Salmon Commission.
Macgillivray said it's too early to say if the report will impact salmon-fishing plans for 2013.
The panel included seven senior scientists from five Canadian and U.S. universities, as well as a non-university research institution.
Panel members were asked to evaluate the available scientific evidence and attended three workshops between September 2011 and September 2012 in Seattle, Wash., and Vancouver, B.C.
Their final report was made public on NOAA's website at the end of November.
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