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Wednesday, June 7, 2023
June 7, 2023

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Southern resident orcas are visiting us less often, new study shows


Finding fewer Chinook salmon to eat, the endangered southern resident orcas are visiting the San Juan Islands, their traditional summer home, less often.

That’s the main takeaway from a paper published in the journal Marine Mammal Science last week. Researchers documented a 75% drop in reported sightings of the southern residents from 2004 to 2020 around the San Juan Islands. That corresponded with a 50% decline in available Chinook, the orcas’ favorite food, from British Columbia’s Fraser River.

The southern residents, consisting of the J, K and L pods, are beloved in the Northwest but are struggling to survive. Only 73 remain.

“The reason these whales are these cultural icons of the Pacific Northwest is because people can see them right from their doorsteps in the San Juan Islands,” said Joshua Stewart, the paper’s lead author. “They’re a huge draw for tourists. And that’s because this summer feeding area is a critical habitat for them.”

That was proved last year when for the first time in five years the southern residents were present in the Salish Sea for more than 150 days from April to September last year. The J pod was spotted on nearly 160 days last year, an increase from the average of 100 to 120 days in the previous four years. Sightings of the K and L pods remained consistent with their recent average of 30 to 40 days each year.

Stewart said his research, coupled with other recent studies, has made it clear that prey availability is a key driver of the health issues affecting the southern residents. “When there’s less food around it probably makes vessel disturbance more important and it might even make the impact of pollutants more acute when they’re skinny and starving,” Stewart said.

All of this combined has made the southern residents’ traditional foraging patterns less fruitful. The study shows how they are responding to human-driven change in the environment by seeking alternative food sources to their traditionally important salmon prey, but it’s not clear how long it will take them to adapt, or if they’ll even be able to replace these key resources with other salmon stocks.

The research also demonstrates a need to invest in Fraser River salmon recovery, but it’s only one piece of the puzzle. Scientists have known the river’s runs have been depressed for years. And it emphasizes the need to make it easier for the orcas to access their food, such as by reducing boat and ship noise.

Researchers used daily gill net catch data on Chinook salmon returning to the Fraser River from the Albion test fishery at the mouth of the river to measure relative salmon abundance. They chose the metric because it is most likely to represent the availability of Chinook to the southern residents in the San Juan Islands.

The salmon abundance data was paired with southern resident sightings recorded from April 1 to Oct. 31 each year from 2004 to 2020. The encounters were recorded through photo surveys, hydrophone detections, and firsthand reports by local nonprofits, the public and researchers.

The Center for Whale Research led data collection which was updated by Jane Cogan and Melisa Pinnow who collected additional observations from naturalists and the public. The late Ken Balcomb, founder of the Center for Whale Research and a champion of southern resident orca recovery, was an author on the paper.

During the summer months, Fraser River Chinook make up an estimated 40% to 50% of Chinook salmon in the Salish Sea, the transboundary waters between the U.S. and Canada. Accessing lots of thick adult Chinook then is important for the southern residents to build up body mass for the winter and early spring months when less food is available.

Chinook are the biggest, fattiest and highest-quality salmon. And Fraser River Chinook are the largest of the region’s Chinook, Stewart said. The southern residents rely on Chinook for the majority of their diet; they’re known to toss less desirable salmon, like pink or chum, out of their way on the hunt.

“If you’re going to expend all this energy chasing after individual fish, you need to get a good return on your investment,” said Stewart, who’s also an assistant professor at Oregon State University’s Marine Mammal Institute.

The southern residents have long pursued these fish as their main food source.

But things have changed. Humans have choked off salmon habitat with dams and culverts. Loud boats plow through the orcas’ home. The animals hunt with echolocation but the noise of cargo ships, ferries and other vessels mask the sounds they need to use to hunt. The orcas are also absorbing the region’s industrial and municipal pollution.

The fleet of whale watching boats in the Salish Sea has increased from fewer than 20 commercial boats in the 1980s to more than 80 boats serving about 500,000 people a year by 2015. A bill in Olympia could provide a greater buffer for the southern residents, increasing the distance recreational boaters must maintain from the orcas from 400 yards to 1,000 yards.

The study comes alongside recent research that found the southern resident females have less hunting success than their neighbors up north, and a shrinking, increasingly inbred population of southern residents could be plummeting toward extinction.

Both the northern and southern resident populations were devastated by the capture of orcas for theme parks. But while the northern resident population has grown by at least 50% since 2001, with more than 300 today, the latest census tallied one of the lowest population counts among the J, K and L southern resident pods since 1974: 73.

The northern residents have cleaner, quieter waters and access to more fish than the southern residents.

“Their future, their ability to continue and to avoid a path to extinction,” said Howard Garrett, founder of the Orca Network, “is based primarily on the availability of Chinook salmon.”