Page 8 - Donlin Newsletter Fall 2021

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Smelt Study continued from page 7
May 24. By May 27, they were found just below Big Bogus Creek all the way down to Kwethluk, in an approximately 45 mile stretch of river. On May 28, rainbow smelt
were being caught three miles below Lower Kalskag,
with females still spilling eggs. Dan Ausdahl Jr., with T
Bird Tours in Upper Kalskag, was a key member of the survey team. He provided smelt activity reports, boat transportation and lodging services. Dan also monitored river temperatures and relayed this information to the aquatic biologists. River temperatures during and after
the spawning event remained low throughout the egg incubation period, around 50 degrees Fahrenheit. This temperature was used to estimate that rainbow smelt eggs would hatch approximately 16 days later.
The field team began searching for larval smelt in the Kuskokwim River on June 12. Larval smelt are very small when they hatch, about half the length of a penny. Due to their size, aquatic biologists sampled for smelt using a seven-foot plankton net designed to catch tiny aquatic organisms. The net was towed behind the boat for two minutes at different depths in the river.
Some larval rainbow smelt were first seen on the night
of Sunday, June 13, while sampling near the Bluffs. By Monday, large numbers of larval fish were found between Bogus Creek and Tuluksak. Sampling continued daily as the team continued moving downriver following the bulk of the larvae as the rainbow smelt continued their voyage to the river mouth. By the end of Thursday, June 17, the bulk of the smelt had passed downriver of Bethel. Over the next week, the numbers of smelt in the river decreased slowly. However, low numbers of smelt were still being found from Tuluksak to Bethel through June 22.
Overall, this survey was a great success and is the
first larval smelt study ever completed in Alaska. We determined the day the larval smelt emerged from the gravel and tracked their progress downriver with the current. We found that the bulk of the smelt moved from spawning grounds located from Lower Kalskag, to the Bluffs and down to Kwethluk in three days. However, we also noted that larval smelt were still being found in low numbers in the river for over a week after most of the smelt had hatched.