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Researchers Search for Methods to Reduce High
Numbers of 'Mini-Jacks' Produced by Hatcheries

by Staff
Columbia Basin Bulletin, December 11, 2009

Researchers continue to look for remedies for "an unforeseen byproduct" of hatchery supplementation of salmon populations -- an unnaturally high occurrence of so-called mini-jacks, male fish that have experienced a precocious maturation and urge to spawn.

A research team led by Don Larsen of the Northwest Fisheries Science Center in Seattle, as well as other Columbia River basin researchers, have shown that the hatchery-rearing environment can cause early maturation to occur more often than in wild populations. Genetics can also be a contributor to higher than normal occurrences of precocious parr, mini jacks and jacks, as compared to naturally produced fish,

That fact can lessen the benefits expected from supplementation, which involves the outplanting of hatchery reared juvenile fish in streams so that they will home in on those waters when they return as adults to spawn. The goal is to increase naturally spawning populations.

But having more mini-jacks in the population can have negative genetic and ecological consequences on wild populations and other native species because many of them don't survive the round trip and those that do may not be as capable spawners as older fish. That higher rates of early maturation mean fewer male salmon migrating to the ocean, the loss of adults available for harvest or broodstock, and a skewed sex ratio in favor of more females in a population.

Spring chinook salmon can spend anywhere from 1 to 5 years in the ocean before returning to their home rivers to spawn. After hatching from salmon eggs and approximately 18 months of growth in fresh water, juvenile fish migrate downstream undergoing the "smoltification" process in preparation for the ocean phase of their life-cycle, according to a feature article posted on the NWFSC web page,

Male chinook salmon that return to their fresh water stream a year or two earlier than their counterparts are known as jacks. Most chinook salmon mature at age 4 or 5 after spending 2 or 3 years in the ocean.

Some males, referred to as mini-jacks, have an even shorter life history strategy, skipping a trip to the Pacific Ocean altogether. Mini-jacks either remain near their natal waters or favor a short-term downstream migration in freshwater before heading back upstream a few months later to attempt reproduction at age 2.

Each March, Larsen and his team sample more than 1,000 juvenile spring chinook salmon just prior to their release from acclimation ponds high up in the Yakima River basin. The fish are produced by the Cle Elum Supplementation and Research Facility, one of the pioneers in large scale testing of supplementation techniques. The hatchery and research facility is operated by the Yakama Nation.

Larsen and his team since 1997 when the hatchery started production have tracked the smolt releases using PIT (passive integrated transponder) tag detection systems, which can identify individually-tagged fish as they pass through dam fish passage ladders downstream.

The research team has found over the 11 year course of the ongoing study that migrating mini-jacks are occurring at rates 10-20 times higher than observed in wild populations. An average of 40 percent of the male hatchery fish never migrate to the ocean, but rather mature early as mini-jacks.

Plasma is drawn from each captured male smolt to be tested for 11-ketotestosterone (11-KT), a reproductive steroid produced by the testes of adult male salmon. High levels of plasma 11-KT in juveniles at the time of release from the hatchery are one indicator of a precociously-maturing male -- one that is destined to mature earlier than its broodmates.

Laboratory-based studies led by Penny Swanson of NWFSC's Physiology Program helped develop the necessary tools for further study of the mini-jack phenomenon in the field. The NWFSC's Larsen and Brian Beckman, and University of Washington collaborators, are using those tools to better understand the physiology of the mini-jack and how hatcheries may be contributing to early maturation in male salmon.

Early maturation in male salmon is a naturally-occurring phenomenon, according to the NWFSC. Both genetics and environmental conditions (i.e., water temperature, food availability) can determine when a male sexually matures and can reproduce.

Larsen and his colleagues are testing to what extent hatcheries along the Columbia and Snake Rivers are contributing to a rise in the production of mini-jacks, as some studies have shown that the hatchery-rearing environment can cause early maturation more often than in wild populations. And the phenomenon has been witnessed across the Columbia basin.

"You'll find mini jacks everywhere you look," Larsen said. Most hatcheries use fish food that is high in lipids, which includes fats.

"It's cheaper than making fish food with protein, made of fish," Larsen said. The lipid-fueled diet promotes growth and provides the energy needed to start the physiological shift toward maturation.

"It seems to be that those conditions are conducive to having high rates of precocious maturation," Larsen said. Tests have shown that lipid levels in wild fish are typically 1 or 2 percent while hatchery fish tend to have lipid content of about 9 percent.

"The lipid content of bugs is very low," he said of a staple of wild fishes' diets.

Researchers tried to manipulate growth by cutting back rations of half of the Cle Elum spring chinook production in midwinter when the fish are about a year old, a time when fish in the wild would be feeding minimally. The long-standing hatchery feeding pattern promoted "high growth when you ought not," Larsen said.

For wild fish, "the getting is not good" during the winter when natural food production slows. And they idle in cold, cold water while the hatchery fish live in well water that is held at about 10 degrees C, which is believed to be optimal for growth.

The three-year experiment worked, reducing precocious maturation by about 50 percent. But a late winter boost in food failed to lift the juvenile to "production" size so they headed toward the ocean at a smaller size than their broodmates that were on a normal hatchery diet. And the juvenile survival and adult return rates were lower for smaller fish.

"When it comes to smolt production size does really matter," Larsen said.

The NWFSC scientists have been involved in studies of salmon life history at the Yakima River basin hatchery since the program first started rearing spring chinook salmon from wild broodstock in 1997. Each year, the program releases about 800,000 age 1-plus-year-old smolts, and anywhere from 3,000 to 10,000 (hatchery and wild) return each year as adults.

Many of the lipid-bolstered fish have by the spring of their second year already begun an "upramping of hormonal processes" and decide "I might as well start going to the ocean," Larsen said.

Some of the tagged fish are identified downstream each year at Prosser Dam on the Yakima River and some apparently never make that far before turning around. A large share of the fish that do proceed downstream ultimately disappear.

"Our guess is that they just die," Larsen said of missing mini jacks that continued to navigate the Columbia and/Yakima rivers' tepid waters in late summer.

Researchers Search for Methods to Reduce High Numbers of 'Mini-Jacks' Produced by Hatcheries
Columbia Basin Bulletin, December 11, 2009

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