Did a Winter Visit By Orcas Help Puget Sound Steelhead?

Transient whales in Puget Sound in 2010. Photo by tifotter via flickr.

Transient whales in Puget Sound in 2010. Photo by tifotter via flickr.

The Nisqually Indian Tribe – with help from the federal and state government – is trying to find out how much a winter-time visit of marine mammal eating transient orca whales might have benefited endangered steelhead.

The orcas preyed on marine mammals, whose numbers had been spiking around Puget Sound in recent years. Recent research has also indicated that those marine mammals may be taking a significant bite out of out-migrating steelhead populations.

King 5 also had a report on this project that aired last night. You can watch it here.

“We have a real opportunity here to see if transient orca predation on South Sound and Mid-Sound marine mammals eased the predation pressure of marine mammals on out-migrating Nisqually steelhead,” said Christopher Ellings, salmon recovery manager for the tribe.

Megan Moore, NOAA Fisheries biologist, inserts an acoustic tag into a Nisqually steelhead.

Megan Moore, NOAA Fisheries biologist, inserts an acoustic tag into a Nisqually steelhead.

According to research wrapped up last summer on Nisqually steelhead, the fish are dying at a higher rate the more time they spend in Puget Sound. One impact on these fish as they head out is predation by marine mammals, such as harbor seals.

The study was a combined effort by the Nisqually Indian Tribe, the National Oceanic and Atmospheric Administration Fisheries Service and the state Department of Fish and Wildlife as part of the Salish Sea Marine Survival Program coordinated by Long Live the Kings. Puget Sound steelhead were listed under the federal Endangered Species Act in 2007.

The study looked at the relative success of steelhead leaving the Nisqually and Green rivers. The project partners captured and fit juvenile steelhead from both rivers with acoustic transmitters. An array of acoustic receivers located throughout Puget Sound tracked the fish. When a steelhead carrying an acoustic transmitter passed between a pair of receivers, its individual frequency was recorded and tracked for several hundred yards.

The researchers also tagged a dozen harbor seals to find out how often they swam in the vicinity of tagged steelhead. It turned out, quite often.

“Our research partners found acoustic tags in places harbor seals would use to rest,” Ellings said. “The circumstantial evidence is that a lot of these fish are being eaten before they head out to the ocean. Ideally we would tag fish every year so we could track steelhead survival trends in response to environmental variables ranging from marine mammal abundance to sea surface temperature.

“We do not consider this a one and done research study but a monitoring necessity if we are going to address the sources of mortality and recover Puget Sound steelhead,” he said.

But, just because harbor seals are eating the steelhead doesn’t mean they’re automatically at fault. “What we’re looking at out there is an ecosystem out of whack,” said David Troutt, natural resources director for the tribe. “Because seals are not likely finding the prey they historically have, they need to focus on already weak stocks of juvenile steelhead.”

This is why the transient orca whales visiting South Puget Sound might have, at least temporarily, put things back into balance. While the whales visited Puget Sound, the tribe was scrambling to bring some funding to repeat the experiment.

Iris Kemp, Fisheries Research Biologist at Long Live the Kings, tests an acoustic tag.

Iris Kemp, Fisheries Research Biologist at Long Live the Kings, tests an acoustic tag.

“If there are fewer marine mammals out there now, we want to see if that lower number equals more steelhead getting out. There is a good chance we will not detect an impact on steelhead survival. This is also important information to have,” Ellings said. “We need to know if we can count on natural processes like orca predation on the resident seal population to increase survival of our threatened Nisqually steelhead.”

Puget Sound has been in decline for decades. “Shoreline armoring, things like bulkheads, is increasing, despite decreasing runs and endangered species listings,” said Troutt. “We know that 40 percent of Puget Sound is modified and that over a quarter is armored.” Armoring decreases the amount of food available to salmon and makes it more likely they’ll be eaten by predators.

“We also know that based on the most recent data, the problem is getting worse,” Troutt said. “We’re building new bulkheads faster than we’re restoring shoreline,” he said.

Based on earlier steelhead tracking studies the tribe was involved in, the major bottleneck for all steelhead leaving the deep southern Puget Sound seems to be between Tacoma and Seattle. “Nisqually steelhead do okay leaving the river and going through the Tacoma Narrows,” Troutt said. “But, once they hit around Seattle, all steelhead stocks drop off.”

The Nisqually steelhead population crashed almost 20 years ago. Tribal and state co-managers would like to see just under 2,000 steelhead return to spawn every year to the Nisqually, but since 1993, fewer than 1,000 have come back. Decades ago, the Nisqually River had one of the strongest runs of steelhead in Puget Sound; over 6,000 would return every year.

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