|Engineered logjam on the Hoh River during the winter 2010|
Both approaches have been used to stabilize eroding banks, especially when infrastructure such as roads and houses is threatened. Several reports, however, suggest that the more commonly used method of stabilizing river banks, rock riprap, negatively impacts fish habitat complexity and aquatic communities including fish. Additionally, several reports suggest that wood is an important ecological component of aquatic systems, and fish and other aquatic life often occur in greater densities and diversity at locations associated with wood. As a result, large wood complexes, such as engineered logjams, are viewed as an alternative tool for bank stabilization and stream restoration. Therefore, bank stabilization with engineered logjams may provide the dual benefit of protecting infrastructure and conserving aquatic natural resources, such as fish populations, when compared to alternative stabilization techniques.
|Looking for fish sampling locations|
In August 2010, we plan to PIT tag more fish at both sites. We are also preparing to collect habitat information in order to describe differences in the habitat quality and quantity from the perspective of fish in the study areas. Check back for postings of our upcoming fieldwork!
|River otters take a rest at one of the engineered logjams|
Field Work - Part 1
|Seining at Hoh River Site I|
We implanted PIT tags in 933 fish that were over 65mm (2.55 inches) in length. The purpose of this tagging is to compare fish survival at the two sites over the next couple of months. We plan to return to the sites in September to conduct a habitat survey, perform a fish survey to look for the fish we just PIT tagged, and determine the total number of fish in both sites.
|Hoh River Site II|
Field Work - Part 2
|Measuring habitat at Hoh II|
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|
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.
Field Work - Part 3
|Seining in the Hoh River|
At each of the two sites, we captured and marked fish with Bismarck Brown on one night, then recaptured fish the following night. We caught a total of 419 fish during the surveys. Recapture rates for coho and Chinook salmon at Hoh I and Hoh II sites were 11% and 13%, respectively. From these numbers, we will be able to make rough population estimates. Additionally, we recaptured 1 fish that we had PIT-tagged at the Hoh I (ELJ) site last year.
It was a fun-filled but hectic couple of days as we scrambled to get everything done before forecasted rain increased river discharge to a point where we couldn’t work, which would have washed away all of our sampling efforts. We compressed all of our work into two nights; one night for marking at both sites and one night for recapture at both sites. The work was completed just in time, with river discharge increasing to 5,000 cfs the day after we finished.
Data entry, checking, and analysis will be completed from April through May. A final report will be completed by June 30, 2011.