A high country paradise for sockeye salmon | Alaska Science Forum
In late summer, months before this mossy valley feels the sting of sub-40°C air, bright sockeye salmon pass through a crystal-clear pool amidst fragrant green vegetation. Gulkana Hatchery has a Garden of Eden feel to it, which is fitting since millions of sockeye start their lives here every year.
“There are seven springs in the canyon,” said Gary Martinek, former manager of this salmon hatchery just off the Richardson Road between Summit and Paxson lakes in a 2011 interview. in winter, the water temperature only varies by 3 degrees, and this water is the key to the hatchery.
Most days in the summer, anglers heading to the Copper River to catch salmon pass this group of small buildings nestled in a shallow valley. Few people realize that many of the fish they will catch were born here.
At the Gulkana Hatchery, a few people working for the Prince William Sound Aquaculture Corporation raise up to 35 million sockeye each year and release them into the Gulkana River system.
“It’s the largest sockeye salmon hatchery in the world,” Martinek said. “Two hundred and sixty miles from the ocean.
Martinek, now retired, had the exuberant tone of a proud father as he showed off long rows of more than 100 plastic fish boxes filled with gravel and fertilized salmon eggs. Flowing spring water keeps the bins unfrozen during the coldest days of winter, allowing 97% of those eggs to mature into young sockeye (red) salmon.
In April and May, hatchery workers stock small fish in Summit, Paxson and Crosswind lakes. They make the first two transfers by truck and pipe, the last by dropping about 10 million fish from a small plane.
This stocking of the Gulkana River system with sockeye salmon – born from the eggs and sperm of wild and hatchery salmon from the hatchery’s ‘egg catch tank’ – enhances one of the world’s richest fisheries. ‘Alaska. Commercial fishermen catch thousands of reds from the Copper River in the Gulf of Alaska, and personal and subsistence anglers catch thousands more with dip nets and fish wheels.
Managers estimate that about two out of 10 dip-net Copper River Reds are born at the Gulkana Hatchery.
Even the most experienced fisheries biologists cannot distinguish a sockeye salmon born in the Gulkana hatchery from one that has lived its entire five-year life in the wild. To sort the fish, managers use a method born out of years of trial and error – every fish at Gulkana Hatchery has a shiny band on its otolith that can only be seen with a sophisticated microscope.
An otolith is an inner ear bone found in salmon and other fish that grows a new layer every year. At other hatcheries, managers have marked salmon fry by herding them into a tank and varying the water temperature, which leaves distinct marks on the fish’s otoliths.
Because the Gulkana Hatchery is off-grid and runs on gravity-fed water, officials decided that heating the spring water was impractical and potentially dangerous (they considered what might happen if stored fuel oil leaked in upper Gulkana).
Instead, they mark each hatchery fish by holding it for 24 hours in a tank enriched with strontium chloride. A salt found in seawater, strontium chloride does not harm the fish or those who eat it, but leaves a mark on the otolith that shows the fish was born in 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. At a lab in Cordoba, they slice the bones — the size of a grain of rice — mount them on slides and send them to the University of Alaska Fairbanks. Workers there say if the bone samples were from a fish born at Gulkana Hatchery. Just days after catching the fish, researchers relay the information to fisheries managers in Cordoba.
Sockeye salmon emerge from more than 100 distinct spawning grounds along the Copper River system, but many of the fish enjoyed in San Francisco restaurants and dining halls across Alaska originated in the small, green valley that is home to Gulkana hatchery.
Since the late 1970s, the Geophysical Institute at the University of Alaska Fairbanks has provided this column free of charge in cooperation with the UAF research community. Ned Rozell is science editor at the Geophysical Institute. A version of this story aired in 2011.