Hoh River Project

Study Description

Engineered logjam on the Hoh River during the winter 2010 
USFWS and Washington Department of Transportation (WSDOT) are working together to investigate the response of fish and stream habitat to alternative riverbank stabilization techniques. The WSDOT Hoh River project is located on the western side of the Olympic Peninsula where WSDOT is attempting to protect U.S. Highway 101 from eroding into the Hoh River as a result of river channel migration during flood events. WSDOT has installed engineered logjams consisting of large pieces of natural wood and tree rootwads along the river bank in the first site called Hoh I. River bank in the second site (Hoh II) is currently treated with large angular rock, often called riprap. This riprap, which has continuously failed to protect the bank, will be replaced with engineered logjams during the summer of 2011 or 2012.

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
USFWS and WSDOT are conducting the Hoh River study to compare fish habitat diversity, fish density, growth, survival, movement, and species diversity in Hoh I and Hoh II. Fieldwork started in August 2009 with two study components. Fish survival in both Hoh I and Hoh II was estimated and compared between sites by capturing, tagging, and recapturing fish at a later date. A total of 495 fish were tagged with passive interrogated transponder (PIT) tags between the two sites. The second study component relied upon acoustic tagging technology to provide spatial information in order to identify how fish utilize the engineered logjams at the Hoh I site. In this second effort, USFWS technicians and biologists deployed a series of sound recorders called hydrophones on the river bottom. Twenty-nine fish were captured and surgically implanted with an acoustic tag. The hydrophones passively tracked the location and movement of the tagged fish over a couple of weeks. Preliminary results from Hoh River study indicate that engineered log jams are a valuable technique for bank stabilization projects and can provide favorable habitat for juvenile salmonids when compared to sites utilizing other bank stabilization methods.

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
Field work for the Hoh River habitat study has started for 2010. We used beach seines, minnow traps, and hook-and-line methods to capture more than 1,700 fish at the two study sites (974 at the engineered logjam site - Site 1 - and 785 at the riprap site - Site 2). Most of the fish captured were juvenile salmon and trout; however, we also caught other types of fish. Our catch included Chinook salmon, coho salmon, cutthroat trout, rainbow trout (steelhead), Mountain whitefish, dace, and lamprey. A few crayfish were also captured.

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
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
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.


Field Work - Part 3
Seining in the Hoh River
We continued field work for the Hoh River Engineered Logjam (ELJ) study in March 2011. 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 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. 





No comments:

Post a Comment

Post a Comment