Each year, the Cook Inlet Aquaculture Association (CIAA) collects salmon eggs and fertilizes them to produce the next generation of salmon. Hatcheries call this process “egg take” or “gamete collection” — and it’s one of their busiest times of the year.
Back in the spring, hatcheries released salmon and cleaned out the raceways and mended net pens to get ready for next year’s round of fish. Egg take is a shift back to this year’s returning adults.
How do you get the salmon to spawn?
When we release hatchery-raised salmon as fry or smolt, they have a lifetime memory of the waters where they are released called “imprinting.” These fish use chemical signatures in the water to make it back to their release site.
Depending on the location of the egg take, we might install weirs to direct the salmon to the spawning grounds. These weirs aid in the capture and sorting of the adults. In some lakes where the spawning is going to take place, hatchery staff take boats around the lake to find where the salmon are milling around. When they spot a school of salmon, they use seine nets to carefully capture the fish and transfer them into holding pens.
At this point, we can sort salmon into male and female groups, which will make the spawn go much smoother than if we mixed them all together. Having the salmon in holding pens also allows for easy access to check their ripeness.
How do we know when the salmon are ready?
The timing of spawning is entirely dictated by the fish. Hatchery staff use a simple, direct method to tell if female salmon are ripe: they gently feel the bellies of the females. A salmon that is “green” or not ready to spawn will have a hard belly whereas the “ripe” or ready-to-spawn fish will have a soft belly. Applying slight pressure to a ripe female will cause the ovipositor (a small protrusion at the anus where the eggs come out of when laid) to become more prominent.
After we declare fish as ripe, hatchery staff can help the salmon get down to business.
The act of spawning
In order to spawn salmon, we need to humanely dispatch them. We either use a swift blow from a fish bat or from a dose of electricity. Once we have euthanized the salmon, crews get to work because the eggs and milt will not be viable for long after.
Depending on the species of salmon, there are different spawning procedures.
We can spawn pink salmon in a big lot, with multiple males to multiple females. This is because there is limited disease concern with pinks. We combine pink salmon eggs directly at the spawning location, then take them into the hatchery to be fertilized and rinsed in freshwater. This removes impurities that could harm the growth of the baby salmon.
Sockeye salmon need to be spawned in a strict 1:1 female to male ratio. We clean our spawning tools in iodine between each fish to control the spread of disease. We then take sockeye eggs and milt back to the hatchery, where we combine them to fertilize the eggs. We track these lots of sockeye in their incubators as well. That way, if any disease issue comes up, we can dispose of the appropriate eggs.
As they grow
After the eggs are fertilized, they go into incubators that mimic the substrate in the wild. As they develop throughout the winter the hatchery staff keeps a close eye on them. The eggs will be cleaned and picked during incubation. This process removes the dead eggs from the incubators. Once the eggs are picked, they are returned to the incubators. The pre-hatch otolith markings will be made using a temperature change in the air or the water.
After baby salmon, called alevin, hatch from their eggs, they live in incubators as they consume nutrients from their yolk sacs. When they’re big enough they swim through pipelines to raceways or net pens. At some locations fish are moved by hatchery staff. Once they have matured, we release salmon into their natal lakes or streams to head out to the ocean, or we release them directly to the ocean. Our hatchery staff then await their return to continue the circle of life.