Salmon in Alaska are shrinking, study says. How does that affect us?

People in Alaska have seen it for years.

Wild salmon that venture out into the ocean from Alaskan rivers have grown smaller in the last 60 years, a new study from the University of California, Santa Cruz confirmed.

That could have drastic impacts on ecosystems, including people, according to the study published Aug. 19 in Nature Communications.

Researchers analyzed data on 12.5 million fish from 1957 to 2018, the university said. That analysis helped researchers recognize that Chinook, chum, coho and sockeye salmon from all regions of Alaska have been shrinking, according to the university.

The reason?

Wild salmon have been returning to their spawning grounds at younger ages, which means they’re taking less time to feed and grow to maturity in the North Pacific Ocean, the study found. Salmon from all species and regions seem to be doing this for two primary reasons — climate change and growing competition, according to the study.

“We know that climate drives changes in ocean productivity, and we see a consistent signal of climate factors associated with decreasing salmon size,” Eric Palkovacs, professor of ecology and evolutionary biology at UC Santa Cruz, said in a news release. “Another consistent association is with the abundance of salmon in the ocean, especially pink salmon. Their abundance in the North Pacific is at historic highs due in part to hatchery production in Alaska and Asia, and they compete with other salmon for food.”

The impact of commercial fishing only affected some salmon populations, the university said. More research needs to be done to better understand the exact reasons for salmon spending less time in the ocean, but this study implies the ocean is becoming a riskier place for them to be, according to the university.

But the effects of this phenomenon on people and ecosystems is more obvious, the university said. The smaller the fish, the smaller the meal, plus lower profits for commercial fishers, fewer eggs to sustain existing populations and an overall shift in the biodiversity of freshwater ecosystems, according to the university.

“Salmon go up into these small streams, and whether they are caught by predators or die after spawning, their nutrients are transferred into the forests and freshwater ecosystems,” Palkovacs said. “It’s a classic salmon ecosystem service, and the amount of nutrients they deliver depends on their body size.”

Smaller salmon means less commercial value as well, the study says.

“Socioeconomic impacts of declining salmon size have long been of concern for Alaskans, especially those whose well-being, food security, and economic livelihoods depend on salmon,” according to the study.