Warm Ocean Not Good For Hungry Young Chinook

It’s a paradox in the Pacific that has scary ramifications for salmon runs in the near future.

In warmer-than-average ocean years, young Chinook eat 30 percent more food than they do during cold-water periods, but they end up scrawnier, “likely because they have to work harder to secure food and the prey they consume has less caloric energy.”

So reads a press release out from Oregon State University researchers who teamed up with the National Oceanic and Atmospheric Administration to pore over 19 years worth of survey data on the young salmon.

The study periods were 1981-85 and 1998-2011. Nine years represented cold phases while 10 were warm. Warm was considered 2 degrees Celsius, or 3.6 degrees Fahrenheit, above average.

Not surprisingly, the researchers found that the salmon off our shores mostly eat other fish.

But the diet varies between cold and warm years.

In the former conditions, they like krill, which are rich in lipids — the Omega-3 oils in Chinook flesh — and sandlance, but in the latter phase, they gnaw on young rockfish and crab larvae

The quality of copepods, which feeds the forage that Chinook feed on, also can vary depending on ocean temperatures, it’s been found previously. The amount of coastal upwelling bringing copepods up to the fish is dampened in warm years, according to the researchers.

“When the water is warm,” said OSU researcher Elizabeth Daly at the Cooperative Institute for Marine Resources Studies in Newport, “salmon are smaller and thinner.”

(OSU/NOAA)

(OSU/NOAA)

According to NMFS’s Richard Brodeur, that might be OK for Chinook for one year, but stretched out over two or three “could be disastrous – especially for wild fish populations. They may have to travel much farther north to find any food.”

Interestingly, the scientists found that hatchery salmon have a slight advantage during warm ocean years because of their larger size upon entering the salt.

Here’s where it gets kind of uh-oh. I’ll let the press release speak for itself:

During the last two years, an unusually large, warm body of water has settled into the ocean off the Pacific Northwest that scientists have dubbed “The Blob,” which is forecast to be followed this winter by a fairly strong El Niño event. Though recent spring Chinook salmon runs have been strong due to cooler ocean conditions in 2012-13, the impact of this long stretch of warm water on juvenile fish may bode poorly for future runs.

“So far this year, we’ve seen a lot of juvenile salmon with empty stomachs,” Daly said. “The pressure to find food is going to be great. Of those fish that did have food in their stomachs, there was an unusual amount of juvenile rockfish and no signs of Pacific sand lance or krill.

“Not only does this warm water make it more difficult for the salmon to find food, it increases the risk of their own predation as they spend more time eating and less time avoiding predators,” she added.

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