Is it possible to fill the vast North Pacific Ocean with too many salmon? Hard to fathom, but apparently so.
And what does that mean for fisheries management in the Northwest, Canada and Alaska, where the goal each year is to prompt millions of young, healthy salmon and steelhead — hatchery and wild – to move out of the freshwater and into the ocean?
Are we capable of thinking of the ocean as a finite habitat for fish? Recent studies suggest there may not be a choice.
It wasn’t so many years ago when hatchery managers figured the ocean has unlimited carrying capacity for both wild and hatchery salmon. But studies now indicate that salmon compete for food at sea. And that competition means those species with the short end of the stick will experience reduced growth and survival.
Last week’s story about sockeye salmon in Alaska’s Bristol Bay said some interesting and startling things. Due to climate change, these fish are altering their life history and moving into the ocean after one year in birth lakes rather than two to three years.
That doesn’t sound so bad. An extra year in the ocean to get fat and happy before returning home. Except that’s not what’s happening.
Researchers say these wild sockeye are getting stressed by competing for food with 6 billion hatchery salmon, a number that has grown steadily since the 1970s, when only about 500 million hatchery fish fed in these grounds.
Indeed, a 2015 study said as pink salmon abundance in the ocean off British Columbia and Alaska climbs, sockeye salmon abundance and size is declining and the competition for food between the two species is the reason.
Pink salmon in the North Pacific Ocean, said the study, reached 640 million adult fish in 2009. At the same time, many Fraser River sockeye populations in British Columbia saw significant declines.
Pinks — humpback salmon — are the smallest and most abundant of the Pacific salmon species. The rising number of pinks in the northern ocean are due to an increasing number of hatchery salmon – about 1.4 billion hatchery pinks a year — that are produced in British Columbia, Alaska and Russia.
Researchers said that the rise of pinks and decline in sockeye suggests that there is a limit to the number of salmon the northern ocean can support. Scientists have called for international discussions to talk about a possible cap on industrial scale releases of hatchery salmon.
So it’s getting crowded up there. But scientists don’t really know many salmon the North Pacific can actually support.
In other words, as this ocean fills with hatchery salmon, where is the tipping point for wild salmon? Scientists see the trend, but they don’t have the answer.
Eventually, I suppose, the answer will show itself in the nature of returns to freshwater spawning grounds and hatcheries. The ocean, at some point, may reveal itself as too full of salmon — hatchery and wild. Or maybe just hatchery.
— Bill Crampton, firstname.lastname@example.org
For more on this topic, see these stories from the CBB archives: