Increase of pink salmon may be leading to the decline of kings

Apr 17, 2018

Credit Photo KBBI.

Pink, chum and sockeye salmon have been doing really well over the past few decades. A new study published in Marine and Coastal Fisheries finds in the North Pacific, those species’ abundance levels have been peaking over the past 25 years. But more salmon can be a bad thing. Evidence suggests that more pinks, chums and sockeye are contributing to declining king salmon stocks.

Greg Ruggerone is a scientist with Natural Resources Consultants INC., and he’s been studying levels of salmon in the North Pacific.

“Pink, chum and sockeye salmon average 721 million each year from 2005 to 2015,” Ruggerone said. “That was about 36 percent more salmon than in the previous peak that we documented back in the 1930s.”

These species are flourishing for a number of reasons, but it’s climate change that seems to be giving these fish a helping hand by increasing their food supply.

“Their key prey are zooplankton and so that early marine life sets the stage for pinks and sockeye salmon and those ocean conditions have been quite favorable for producing zooplankton abundance,” he said.

The most abundant species, by far, is pinks, which Ruggerone said accounts for 70 percent of returns to the North Pacific. He said hatcheries are adding to their numbers.

“I calculated roughly about 66 million hatchery-origin pink salmon returning from the North Pacific Ocean each year and that's just phenomenal,” he said. “It’s almost as many hatchery pink salmon as wild sockeye salmon returning from the North Pacific.”

Young pinks benefit from zooplankton, but later in their life stages, they start feeding on squid and small fish, which is the same food supply kings also feed on in their later life stages.

While there are other factors to blame for the overall decline of king salmon, Ruggerone hypothesizes that pink salmon are the primary culprit. He said pinks outcompete older kings with their sheer numbers. He adds that hatchery pinks are adding to the problem and with declining king populations, he said hatcheries may be having a negative effect on the overall value of Alaska’s salmon fisheries.

“The hatchery production is not simply adding to the existing wild production,” he said. “There's interaction between the two species: the hatchery and wild pink salmon in this case. The net benefit is actually much less than what people might expect. Hatchery fish just don’t simply add on to wild salmon production.”

Ruggerone said hatcheries need to keep limited resources in the marine environment in mind before releasing more fish, suggesting a tax on hatcheries as a way to keep their numbers in check.

He is also studying other impacts increasing pink salmon numbers might have on the environment.