Research on three Bristol Bay area rivers could eventually provide managers with more information when they generate run forecasts each year.
The Alaska Department of Fish and Game has counting projects on several rivers throughout Bristol Bay to determine how many fish enter rivers to spawn, but less is known about the juvenile fish migrating out of those rivers in spring, called smolt. Previous smolt studies took place from the 1970s to 1990s, but ended, leaving a gap in the information.
The Bristol Bay Science and Research Institute is working with Fish and Game on smolt abundance projects on three rivers, the Kvichak, Ugashik and Egegik.
Institute smolt program manager Matt Nemeth says the smolt studies offer scientists a glimpse of how salmon are doing in the freshwater.
"It's important to study smolt because it gives us an opportunity to see how the fish are doing halfway through the life cycle, instead of waiting until the very end when they come back as adults," Nemeth said.
Nemeth has worked on smolt research since 2002 and studied juvenile salmon for 20 years in Alaska.
Last year, Nemeth and his team estimated that 61 million sockeye smolt swam by the first of two sonar sites, which is closer to the village of Igiugig, and Lake Iliamna, where the juvenile salmon spend their early years.
That estimate is based on data collected by eight sonar pods sitting on the bottom of the river for about a month in the spring. The sonar pods face upward and send out a signal that hits the smolts' swim bladders. Later in the summer, the signal information is used to estimate the number of smolt swimming by.
For the Kvichak project, there's a second sonar site farther downriver with 12 pods and a fish trap in between the two that the field crew uses every night to catch about 600 smolt for sampling. At that site, the project has been going since 2008.
The sonar provides the abundance estimate, while samples done on the fish caught at the trap provide an idea of the condition fish are in when they swim downstream toward the ocean.
A three-person field crew operates the Kvichak fish trap almost every night while the project is going. Dirk Middleton and Chris Sewright pull the trap into the middle of the river, while Logan Reveil keeps a second boat ready in case it's needed to help move the trap.
Sewright compared the incline trap to a kind of fish-specific sluice box that smolt swim into and can't leave.
The trap fishes about 3 feet deep in a pretty fast section of river. Smolt typically run close to the surface at night, when predators aren't out, so the crew operates the trap around 1 a.m.
The crew takes about 100 smolt at a time, aiming for 600 smolt in two hours or less. If the trap is filling up too fast, they release some and wait five minutes before taking the next bucket.
By waiting, Sewright said the goal is to get more diversity in the sample, hopefully meaning it's more representative of all the fish that swim downstream.
The smolt are used to collect fish scales for aging, clip fins for genetics and gather data on the length and weight of the smolt.
The scales are used to age the fish. By knowing how old the fish are, and recording their length and weight, the team eventually gets a sense of the condition the smolt were in as they swam downstream.
In the fall, Nemeth and his colleague Justin Priest will produce a report on the smolt. The 2014 report said that smolt that year were in pretty good shape, and the genetics showed that they came from four different stocks in the Kvichak watershed.
Eventually, the smolt information can be paired with data on returning sockeye, and provide a sense of how fish swimming downstream correlate with those that return. That information can be incorporated into forecasts.
"If we have smolt data paired with the adult data that come back, then we can start to learn a lot more about the fish," Nemeth said.
The project also provides a time stamp of how many smolt were there during the study and where in the watershed they come from, he said.
"We have a much better sense of how the fish, the smolts, are distributed as they go downstream," Nemeth said. We know when they're running, we know what part of the river they use, we know how compressed their run timing is, and we know how deeply they're distributed."
That information can serve as both a baseline on how smolt were doing during the study years, and can inform other research projects on smolt in general, Nemeth said.
This story first appeared in The Bristol Bay Times/Dutch Harbor Fisherman and is republished here with permission.