Wednesday, August 10, 2022

The inner workings of the world’s largest sockeye salmon hatchery

East Bank of Gulkana River – At the end of summer, 40-down wind through a crystal-clear pool among fragrant green vegetation a few months before this moss valley, will feel the sting of a bright red salmon dart. Gulkana Hatchery has a Garden of Eden feel, which has been fitting for millions of sockeye salmon every year since the beginning of their lives.

“There are seven waterfalls in the canyon,” said Gary Martinek, the former manager of this salmon hatchery just off the Richardson Highway between Summit and Paxson Lakes, during an interview in 2011. “Water temperature varies only 3 degrees from summer to winter. This water is the key to the hatchery.”

For most of the summer, fishermen heading to the Tamar River pass this group of small buildings in a shallow valley to catch salmon. Very few people realize that many of the fish they will catch originated here.

At Gulkana Hatchery, some people working for the Prince William Sound Aquaculture Corp raise a herd of 35 million red salmon each year and release them into the Gulkana River system.

“It’s the biggest sockeye hatchery in the world,” Martinek said. “Two hundred and sixty miles from the sea.”

The inner workings of the world's largest sockeye salmon hatchery

Martinek, now retired, had the exuberant tone of a proud father as he showed off long rows of more than 100 plastic fish filled with gravel and fertilized salmon eggs. Running spring water keeps the tots immobile during the coldest days of winter, allowing 97% of their eggs to hatch into young sockeye, or red, salmon.

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In April and May, hatchery workers stock small fish at Summit, Paxson and Crosswind Lakes. They accomplish the first two transfers by truck and hose, the latter airdropping about 10 million fish by a small plane.

This seeding of the Gulkana River system with red salmon—bred from the eggs and sperm of wild and hatchery salmon from the hatchery’s “egg-take pond”—raises one of the richest fisheries in Alaska. Commercial fishermen take thousands of Copper River raids to the Gulf of Alaska, and personal use and subsistence fishermen catch thousands with dipnets and fishwheels.

Managers estimate that two out of every 10 dipping Copper River raiders were born at the Gulkana hatchery.

The inner workings of the world's largest sockeye salmon hatchery

Even the most experienced fisheries biologists cannot attribute their full five-year life in the wild to a red salmon born at the Gulkana hatchery. To sort the fish, managers use a method born out of years of trial and error—the otolith of each Gulkana hatchery fish is a bright band on the bone that can only be seen with a sophisticated microscope.

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The otolith is an inner ear bone found in salmon and other fish that develops a new layer every year. In other hatcheries, managers mark by collecting salmon fry in a tank and varying its water temperature, which leaves distinct marks on the fish’s otoliths.

Because the Gulkana hatchery is off the grid and operates on gravity-powered water, the managers there decided that heating the spring water was impractical and potentially dangerous – they envisioned if stored fuel oil leaked into the upper Gulkana. If it happens, what can happen?

The inner workings of the world's largest sockeye salmon hatchery

Instead, they mark each hatchery by holding the fish in a tank enriched with strontium chloride for 24 hours. Strontium chloride, a salt present in seawater, does not harm the fish or fish eater, yet leaves a mark on the otolith indicating that the fish was born at the Gulkana hatchery.

Beginning in June, biologists from the Alaska Department of Fish and Game collect otoliths from fish caught in both the Gulf of Alaska and the Copper River. In the Cordova lab, they chop up bones — about the size of a grain of rice — mount them on slides, and send them to the University of Alaska Fairbanks. The workers there tell whether the bone samples came from a fish born in the Gulkana hatchery. Just days after the fish was caught, the researchers relayed the information to fisheries managers in Cordova.

Red salmon originate from more than 100 different spawning grounds along the Copper River System, but many of the fish are enjoyed in restaurants in San Francisco and in dining rooms throughout Alaska, which is home to Gulkana Hatchery.

The inner workings of the world's largest sockeye salmon hatchery

Nation World News Desk
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