Deciphering the Journey of Bristol Bay Smolt

Sockeye. (Alaska Department of Fish and Game photo)
Sockeye. (Alaska Department of Fish and Game photo)

Every year, millions of sockeye salmon return to Bristol Bay, headed for spawning grounds in area rivers. The Alaska Department of Fish and Game has counting projects on several rivers throughout the region to give managers a sense of how many fish enter rivers to spawn, but less is known about what happens to outbound juvenile fish each spring. Research teams on three rivers that flow into Bristol Bay have been studying those baby fish, called smolt, for the past few years.

The team is studying smolt on the Kvichak River, near the village of Igiugig and Lake Iliamana.

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Matt Nemeth, Dirk Middleton and Chris Sewright get sonar pods ready to deploy in the Kvichak River near Igiugig on May 29, 2015. The pods are part of a smolt abundance study on that river conducted by the Bristol Bay Science and Research Institute and the Alaska Department of Fish and Game. Credit Molly Dischner/KDLG
Matt Nemeth, Dirk Middleton and Chris Sewright get sonar pods ready to deploy in the Kvichak River near Igiugig on May 29, 2015. The pods are part of a smolt abundance study on that river conducted by the Bristol Bay Science and Research Institute and the Alaska Department of Fish and Game.
Credit Molly Dischner/KDLG

It’s a little past 1 a.m. in Igiugig, and I’m headed down the Kvichak to a fish trap set up to catch sockeye salmon smolt.

Researchers from the Bristol Bay Science and Research Institute are working on a study of smolt abundance, and the trap is how they collect fish each night to take a fin for genetic samples, scales for aging, and record certain information about the smolt, including lengths and weights.

Smolt are juvenile salmon that have spent the first part of their life growing up in the freshwater.

This is one of three sites where BBSRI is studying smolt in Bristol Bay, in partnership with the Alaska Department of Fish and Game. The information collected here, and at similar projects on the Ugashik and Egegik rivers, provides a picture of the condition smolt are in as they swim downstream, leaving the lake where they’ve grown for the past year or two, headed for the ocean where they’ll spend the next phase of their lives.

Matt Nemeth is the project manager for BBSRI’s smolt program:

“Well, it’s important to study smolt because it gives us an opportunity to see how the fish are doing halfway through the lifecycle, instead of waiting until the very end when they come back as adults. And 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.”

Eventually, when there’s a better understanding of how smolt features correlate with the number of salmon swimming back, information on smolt could be used to help with run forecasts.

But for tonight, we’re just fishing in the dark. Nemeth says the crew captures smolt at night to try for a representative sample of the fish migrating downstream.

“We capture the fish at night because that’s when we can get the most representative sample of the fish that are going by. Most of the fish, most of the smolts, emigrate at night. And we know from the sonar data, that when they migrate at night, they’re distributed unusually close to the surface, and that’s where our trap is, and so we can capture the largest portion of the run.”

Back on the river, there’s one last band of pink light ahead of us, and a bright moon behind us. That’s about as dark as it gets in Igiugig this time of year.

Dirk Middleton and Chris Sewright pull the trap away from shore and start fishing. Logan Reveil keeps the second boat ready in case it’s needed to help move the trap. Once the trap is secured near the middle of the river, we pull in to wait. It’s warm tonight, and the crew keeps reminding me that I’ve lucked out on the weather.

“It’s called an incline plane trap, ‘cause it’s got the inclime that comes up right, so we’re fishing further down in the front than in the back. It’s almost like sluicebox.”

The trap fishes about three feet deep, in a pretty fast section of river. Smolt typically run close to the surface at night, when predators aren’t out.

“It’s pretty incredible there are that many fish going down. Every once in a while, we’ll have a night, you just look out with your headlamp, and the whole river is just fish. You feel like you could walk right across the water.”

The crew samples fish almost every night for the month that the project operates, trying to capture 600 sockeye smolt in two hours each night. Tonight they’re done much sooner. It’s probably about an hour from the time we head down the river to the time we get back to the bunkhouse carrying six buckets with smolt in them.

The trap is just for collecting samples and data. The count itself comes from sonar pods at two sites on the Kvichak. Last weekend, a sonar pod at one site had to be replaced, a project that involved taking all eight off the bottom of the river, changing one out, testing the array, and putting them back.

But most days, the sonar do their job on their own. The crew downloads the data each day. It’s read in the summer, and Nemeth and his colleague Justin Priest write a report by the fall that includes the number of smolt estimated to have swum done the Kvichak during the study period.

The report also includes size, age and genetic information about those smolt based on the fish captured each night. The field crew collects samples from the smolt to provide that information.

Back at the bunkhouse, the sun is getting ready to rise, and the crew is getting ready to start sampling the smolt.

Chris takes scales, Logan measures the smolt and clips off a fin, Dirk records the data. They get into a rhythm.

And they keep each other on track, Dirk says.

“So you really end up, you do look out for one another. Like if there’s something missing in part of the cycle, it’s like, he’ll catch i., Chris will say no, I think we’re on this one because of the scales, and the same for me.”