Scientists search for “disappearing” young Coho salmon

Humboldt researchers track the fate of Coho juveniles forced from their birthing grounds by poor water quality
March 09, 2015
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It’s not uncommon for a young angler, enthralled by the flash of silver scales and blue water, to dream of going pro. This is certainly what Darren Ward had in mind when he enrolled as a fisheries science major, thinking it would simply be a good way to catch more fish.

Three degrees and twenty years later, Ward has become a fish pro of another sort, an Assistant Professor of Fisheries Biology at Humboldt State University. The job puts him in close proximity to both his research subjects and his table fare: wild salmon.

Ward is the recipient of a 2015 Special Focus Award from California Sea Grant to study the state and federally endangered Coho salmon, working with graduate student Molly Gorman. Specifically, they are looking to track the fate of vast numbers of juveniles who seem to simply disappear.

Coho born in the cold, spring-fed headwaters of the Shasta River are able to remain for a year before emigrating downstream to the Pacific Ocean. Those born further downstream – where the water becomes too low and warm to survive in summer due to drought and extensive human use – are forced to emigrate early. Nobody knows where to, or how many survive.

“It’s possible that some of these fish are finding a refuge to survive in, such as cold water tributary streams. We just don’t know,” says Gorman.

To understand their fate, Ward and Gorman are tracking juvenile Coho in the Shasta River and Scott Rivers. Wild fish are netted and released with tiny transmitters called Passive Integrated Transponders, each the size of a grain of rice, a delicate operation Gorman recently demonstrated for ABC’s Nightline.

The transmitters signal a unique code for individual fish when they pass sensors maintained by the California Department of Fish and Wildlife (DFW). So far, Gorman has deployed more than 700 transmitters.

The team’s early results show the fish are on the move, with many Coho from the Scott River turning up in cold-water tributaries, including some newly restored pools created by DFW to protect the juveniles.

Whether young from poor habitat in the lower Shasta River are finding these refuges remains to be seen. If so, it could spell good news for the endangered fish.

“Variation in life history strategies can help stabilize populations,” says Ward, who explains that having a mix of successful emigration patterns gives Coho a better chance to survive changes to the river.

As spring nears and the juveniles prepare to enter the ocean, Ward and Gorman have their fingers crossed for a successful journey and healthy salmon runs in the future.

“I love being outside and getting to interact and do science with these tiny little fish,” says Gorman. “Knowing you’re going to be able to track where they’re going is pretty cool.”

And as for Ward’s first dream to be a pro angler?

“Now that I work with fish all day long, I’ve tried to branch out into other hobbies,” says Ward. He pauses. “Although I did just go fishing with my sons yesterday.”

About California Sea Grant

NOAA’s California Sea Grant College Program funds marine research, education and outreach throughout California. Our headquarters is at Scripps Institution of Oceanography, University of California, San Diego; we are one of 33 Sea Grant programs in the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce.