Preliminary 2017 Coho Smolt Trapping Results Are In; Juvenile Monitoring Underway

The coho salmon smolt trapping season ended in late May, and preliminary results are now available. These include production estimates, or estimates of the total number of coho that migrated out to sea from a given watershed, which are calculated based on the total number of coho captured as well as on our understanding of other factors such as trapping effectiveness. Trapping also reveals information about migration timing, fish size, and fish survival and growth rates since last summer when the smolts were first surveyed as juveniles.
Juvenile steelhead in a measuring tray
This juvenile steelhead is about to be measured to the nearest millimeter, from the tip of its snout to the fork of its tail fin. The data helps determine how fish size changes over time. In general, larger salmonids have a higher chance of survival than smaller ones both in the creek and at sea.

Madison Halloran / NPS

On Redwood Creek, this year’s preliminary smolt production estimate (897 smolts, SE 160) is lower than for the previous time smolts of this cohort were seen in 2014. Compared to historic averages, peak migration was a little later than usual, survival in the creek from summer to spring was typical, and fish size and growth were somewhat low.

Meanwhile, the smolt production estimate for Olema Creek (5,698 smolts, SE 587) was higher than for smolts of the previous generation. Peak migration timing and fish survival were normal, and fish size and growth were surprisingly high compared to historic averages. High fish growth from summer to spring indicates that conditions in Olema Creek must have been good for coho during the fall and winter months.

With the smolts now adjusting to life in the ocean, the Coho and Steelhead Monitoring Program has begun surveys of juvenile coho that hatched in the creeks this past winter. Surveys are underway on Pine Gulch Creek, where many juvenile steelhead have already been spotted. Based on spawner observations made this past winter, the monitoring team is also expecting to find juvenile coho in both Redwood and Olema Creeks as surveys continue. Data collected this summer will serve as the basis for estimating coho survival and growth between now and next spring, when these juveniles will be studied again as migrating smolts.

Check out more preliminary smolt season results, or contact Michael Reichmuth to learn more.