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Lab Report: Chinook Conservation

Twenty-four tanks at the University of Idaho Aquaculture Research Institute are full of immature Chinook salmon as Nick Hoffman takes notes. Hoffman is a first-year graduate student in Biological Sciences under the mentorship of Professor James Nagler.

 “We are trying to reduce the occurrence of premature maturation or ‘minijacks’ in the male fish,” Hoffman said. “Our hypothesis is that, if we can slow down their maturation, they will have a higher survival rate, resulting in higher abundances of wild fish in the rivers.”

Since Chinook salmon are a threatened species, conservation hatcheries are trying to increase the population. However, three factors are needed for salmon to thrive. Chinook need to become sexually mature, have a high energy store and the right environmental factors and genetics.

“The issue conservation hatcheries are facing,” Hoffman said, “is that they are feeding the fish a lot to give them the energy to survive once they are released, but the high amount of stored energy is being invested into premature maturation instead of investment into normal life cycle behaviors.”

The 29-year-old Twin Falls native spent three years studying the reproductive physiology of steelhead and salmon with Andy Pierce, whose U of I lab is a collaboration with Columbia River Inter-Tribal Fish Commission (CRITFC). That inspired him to take on his research.

 “I’m a fisherman and an outdoorsman,” he said, “so working on ways to improve fish conservation really appealed to me.”

While premature maturation happens to fish in the wild, it is not common. Hatcheries, on the other hand, can produce a huge number of minijacks in certain instances.

“We are trying to find a cost-effective way of stopping this because it negatively impacts the species,” Hoffman said.

James J. Nagler

Professor and Director, Center for Research on Invasive Species

According to Hoffman, minijacks don’t go through the complete lifecycle of a normal Chinook. They stay nearly exclusively in fresh water and they have a low survivability between spawning seasons. This can lead to too many females and not enough males. They also provide no economic value as they are not harvested by fisherman because of their small size.

Hoffman is looking at the environmental cues in hatchery fish. He said fish detect daylight change. They are genetically programmed to use this change in daylight as a cue to become sexually mature.

Christine Kozfkay, Idaho Fish and Game natural resource program coordinator, said salmon are highly adaptive.

“This work can have important implications for how Chinook are reared in conservation hatcheries and provide managers with an alternate tool besides growth rate adjustments to reduce early maturation,” Kozfkay said.

Hoffman hopes by using light to disrupt their internal clock, the fish will take longer to sexually mature. 

“We are really hoping to come up with something that hatcheries can easily adopt because right now the situation is a conservation nightmare, especially for a threatened species,” he said.

The Lab Report: Chinook Conservation

Nick Hoffman’s research is timely given the ongoing conversation about salmon and steelhead recovery across Idaho. This includes Gov. Brad Little’s Salmon Workgroup, which is meeting across Idaho. The goal is to bring together diverse participants to develop a unified policy recommendation that will assist Little as he shapes state policy on salmon and steelhead recovery.

When told of Hoffman’s research, Little stated: “I am interested in creative solutions that help bolster our anadromous fish populations in Idaho. Where better to look than our own universities and bright students such as Nick. I look forward to hearing how Nick’s approach may help us ensure that abundant and sustainable populations of spring Chinook exist for present and future generations to enjoy.”


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