Wednesday, October 6, 2010

Hoh River Project - Field Work 2

Measuring habitat at Hoh II
We continued field work for the Hoh River habitat study in September. Habitat surveys were conducted to identify the distribution of habitat types within Hoh I (engineered logjam) and Hoh II (riprap) sites. Fish abundance, density, and diversity were assessed using seining and mark-recapture methods.

At each of the two sites, we captured and marked fish with Bismarck Brown on one night, then recaptured fish on the following night. Recapture rates for coho and Chinook salmon at Hoh I and Hoh II sites were 12% and 9%, respectively. From these numbers we will be able to make rough population estimates, as well as compare habitat use at the two sites. Additionally, we recaptured 46 previously PIT-tagged salmonids at Hoh I and 16 at Hoh II. We also tested the effectiveness of a fixed PIT tag reader for detecting previously PIT-tagged fish by placing it at the base of a logjam at Hoh I.

Prototype mobile PIT tag reader installation at Hoh I
Prototype mobile PIT tag reader installation at Hoh I
It was a fun-filled but hectic week as we scrambled to get everything done before forecasted rain increased river discharge to a point that we couldn’t work, which would have washed away all of our sampling efforts. On the second night, we compressed two nights’ work into one by recapturing at Hoh I and also marking at Hoh II--working from 7:30pm to 5:00am.

Data entry, checking, and analysis will be completed from October through December. In January, we will return to the Hoh River to do another population assessment of the two sites.