SEATTLE — Reducing fishermen’s catch of chinook salmon may not increase the availability of prey for endangered Puget Sound orcas, a panel of U.S. and Canadian scientists have found.
Their draft report released last week finds that while killer whales feed on chinook salmon and their deaths are more likely to occur during years of low chinook runs, the limited fish runs may not be causing the orca’s decline, the Kitsap Sun newspaper in Bremerton reported. Another environmental factor could be affecting both the low runs and killer whale deaths
NOAA’s Fisheries Service and Canada’s Fisheries and Oceans convened the group of seven scientists to figure out whether the orca population would do better if salmon fishing were reduced or eliminated.
The study has important implications for the recovery plans for the killer whales that frequent the inland waters of Puget Sound and British Columbia, as well as salmon fisheries. The federal agency is taking comments on the draft report until June 15. A final report is expected in September.
Chinook salmon stocks are currently harvested at a roughly 20 percent rate, so there’s limited room to increase the salmon abundance by reducing fishing pressure, the draft report found. Reduced fishing also won’t necessarily mean more chinook salmon for the orcas, since other predators such as sea lions and harbor seals eat the fish and some of the fish would come nowhere near the orcas, the draft report found.
The issue is complicated by many assumptions, said panel chairman Ray Hillborn, a professor of fishery and aquatic resources at the University of Washington. At best, a reduction in fishing might slightly increase the orca population’s rate of growth, he told the Kitsap Sun.
Over the past four decades, the southern resident population has been growing an average of 1 percent per year, far short of the 2.3 percent listed as a recovery goal for the orcas. Based on the most recent analysis, Hillborn said, the rate might be bumped up to 1.5 percent, or it might not be improved at all.
“The decision makers will have to make decisions considering the effects of the uncertainty,” Hillborn said. “Some will say we should take the cautious approach and close all fisheries, and others will say the differences are too small to worry about.”
Food is one factor hindering the orcas’ recovery. Other factors include toxic chemicals and human disturbances, such as noise and boats.
“A lot of people originally concluded that orcas are in bad shape because Puget Sound chinook are in bad shape,” said Pat Pattillo, with the Washington Department of Fish and Wildlife. “We have discovered that maybe the orcas are not doing so badly (with an annual growth rate of 1 percent) and that they are not even eating Puget Sound chinook.”
Experts must consider the effects of fishing on killer whales, but the vast majority of chinook eaten by the orcas in summer are those bound for the Fraser River in Canada, where the overall chinook runs are quite healthy, he said.
He added that his agency’s strategy has been to recover chinook stocks wherever possible — both in Puget Sound and along the West Coast, where the killer whales go in winter. That strategy should also help the whales, he said.
“I’m not sure that there is any evidence showing that additional protections for chinook stocks … would improve the situation for the southern residents,” he added.
Ken Balcomb of the Center for Whale Research on San Juan Island said it is clear that chinook have declined from historical populations, so nobody can say the shortage of salmon has not affected the whales. “But the general feeling I’m getting from these fishery guys is that they are working as hard as they can,” he told the Kitsap Sun.
Balcomb agrees with the panel’s preliminary recommendations to better determine where the orcas go in winter and what they are eating during those lean times.