Chase the Rainbow (Smelt)

Kuskokwim River

Kuskokwim River

Individual Rainbow Smelt Eggs

Individual Rainbow Smelt Eggs

We got the call at 3:30 in the afternoon that they were 10 miles below Kalskag. At 6 a.m. the following morning we were on plane, bound for the Alaskan Bush on the Kuskokwim River in search of spawning rainbow smelt. These are river spawners and an important subsistence species for remote Alaskan villages. Concerns that proposed increases in barge traffic may disrupt or scour spawning areas prompted a study to identify where fish spawn and the types of habitats they use. And on the Kuskokwim, they travel fast; getting there in time to study them is one of the biggest challenges.

Rainbow smelt begin their spawning migrations shortly after the ice breaks up in spring. Through word of mouth, Alaskan villagers begin fishing as smelt move upstream. In 2014, smelt moved rapidly, moving upstream from village to village for nearly 200 miles at rate of about 30 miles per day. They spawn just as quickly and immediately leave the river for the ocean. Scientists must plug themselves into this word of mouth network and be ready to fly to remote areas on a moment’s notice.

Upon arriving, we began helicopter and boat surveys covering over 50 miles of river to find and follow the fish, and document the uppermost extent of the migration. This lasted a mere two days before the fish were gone, presumably having spawned and moving back downstream. Next, discrete spawning grounds needed to be identified in a river that flows more than 50,000 cubic feet per second. Eggs are also tiny (0.5 millimeter). Sampling included collecting and examining fish for spawn condition, collecting substrate samples, and sieving substrates for eggs and grain size to determine spawning locations and substrate preferences. All studies needed to be conducted in as little as two weeks before the eggs hatched and all traces of the fish were gone.

Despite all of the challenges, field efforts were successful. Results show that fish spawn on large, low gradient gravel bars in water between 5 and 14 feet deep. Gravel to cobble substrates were most commonly used. Data will be used to better define the potential impacts of barge routes and as a tool to help manage the resource. The ultimate goal is to allow the safe transport of commerce in the river while minimizing impacts to this unique resource for native Alaskans in this remote part of the state.

Rainbow Smelt

Rainbow Smelt

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