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Corvallis Research Lab
Alsea and Nestucca River Study Streams
Study Design

This study is designed to determine if habitat modification (placement of full channel width log structures, addition of woody debris in pools, and creation of off-channel rearing areas) would increase the smolt production of coho salmon in the Upper Mainstem of Lobster Creek (Alsea River) and East Creek (tributary of Moon Creek, Nestucca River). The study is a cooperative project with the Bureau of Land Management (BLM). The Oregon Department of Fish and Wildlife is responsible for collecting data on the fish populations and completing physical habitat surveys on the study streams. The BLM funded and completed the habitat modification in the treatment streams. We made estimates of; (1) the number of adult coho spawners, (2) the summer population size of juvenile salmonids (coho, steelhead, and cutthroat), and (3) the number of coho, steelhead, and cutthroat spring migrants (smolts) in each stream. Fish population estimates were made in the Lobster Creek treatment stream for four years (1988-1991) before habitat modification, and for three years (1988-90) in the East Creek treatment stream. The habitat modification was completed during July 1990 in East Creek and during July 1991 in Upper Main stem Lobster Creek. Monitoring of the adult spawners, the summer rearing population, and the spring migrant population will continue through at least 1995 to determine what influence the habitat modification has had on the fish populations.

Similar estimates of fish populations in two additional streams near the treatment streams have also been monitored since 1988 (East Fork Lobster Creek in the Alsea and upper Moon Creek in the Nestucca). No habitat modification was done on these streams during the study period. Fish population estimates from these streams act as a reference, helping us understand changes in fish populations that may be taking place in the river drainage as a whole. This information allows us to more clearly determine what changes have resulted specifically from the habitat modification.

The habitat modification was designed to increase overwinter rearing habitat, which our research indicated was limiting the smolt production in the upper Lobster Creek drainage and in the East Creek drainage. In East Creek, twenty seven full channel str uctures were placed in a 1.5 mile stream reach. These structures created dammed pools or served as scour agents to maintain pool depth. Rootwads and smaller trees were also added to increase the habitat complexity of the pools. Thirteen off-channel pools (alcoves) were also created to add additional overwintering rearing habitat for the juvenile salmonids. In Upper Mainstem Lobster Creek, twenty four dam pools and eight alcoves were created in a similar manner throughout a two mile long stream reach.

HABITAT CHANGES

Changes in winter habitat area in East Creek and in Upper Mainstem Lobster Creek as a result of the habitat modification work. Note the large changes in the surface area of dam pools (DM) and alcoves (AL) as a result of the habitat modification work. Dam pools and alcoves accounted for approximately 30% of the total surface area of each treatment stream during winter.

PRELIMINARY RESULTS

QUALIFICATIONS:

The preliminary results from this study should NOT be used as a general justification for instream habitat work. This project was designed to address a specific habitat limitation (winter) that was identified using a habitat limiting factors model. The model is described in:

Nickelson, T.E., M.F. Solazzi, S.L. Johnson, and J.D. Rodgers. 1992. An approach to determining stream carrying capacity and limiting habitat for coho salmon. Coho Workshop. May 26-28, 1992. Nanaimo, B.C. Canada. pp. 251-260. Abstract.

In addition to the changes in surface area of each habitat type, a large amount of woody debris was added to each dam pool and alcove to increase the complexity of the new habitat.

COHO SALMON

The text in this section has been updated to include the data from spring 1995 downstream migrant trapping.

Lobster Creek study streams

Coho Summer Population Estimates by year.

Average Summer Population Size (Pre vs. Post Treatment).

Coho Smolt Production Estimates by year.

Average Number of Coho Migrants (Pre vs. Post Treatment).

Coho Overwinter Survival Estimates by year.

The number of coho salmon smolts migrating out of the treatment stream (Upper Mainstem Lobster) has increased from an average of 1,737 smolts/year before the habitat modification, to 5,386 smolts/year after the habitat modification (a 3 fold increase). In the reference stream (E. Fork Lobster), there was little change in the pre and post treatment estimates of coho salmon smolts (2,690 fish/year in the pre treatment period, compared to 2,304 fish/year in the post treatment period). Much of the increased smolt production in the treatment stream has resulted from an increase in overwinter survival. In the treatment stream, the overwinter survival before the habitat modification averaged 14%, compared to 41% in the years after the habitat modification. In the reference stream, the overwinter survival was 23% for both time periods.

Moon/East Creek study streams

Coho Summer Population Estimates.

Average Summer Population Size (Pre vs. Post Treatment).

Coho Smolt Production Estimates by year.

Average Coho Smolt Production (Pre vs. Post Treatment).

Coho Overwinter Survival Estimates.

The number of coho salmon smolts migrating out of the treatment stream (East Creek) has increased from an average of 895 smolts/year before the habitat modification, to 1,811 smolts/year after the habitat modification. In the reference stream (Upper Moon Creek), the average number of smolts for the same time periods dropped from 601 smolts/year to 156 smolts/year. Again, the increase in smolt production in the treatment stream was due to increased overwinter survival. In the treatment stream (East Creek), the overwinter survival before the habitat modification averaged 11%, compared to 39% in the years after the habitat modification. In the reference stream (Upper Moon Creek), the overwinter survival was 19% and 10% for the same time periods.

CUTTHROAT TROUT

Lobster Creek study streamsCutthroat Summer Population Estimates by year.

Average Cutthroat Summer Populations (Pre vs. Post Treatment)

Cutthroat Smolt Production Estimates

Average Number of Migrants (Pre vs. Post Treatment)

The number of juvenile cutthroat migrating out of the treatment stream (Upper Mainstem Lobster) has increased from an average of 196 fish/year before the habitat modification, to 572 fish/year after the habitat modification. However, in the reference stream (E. Fork Lobster), the average number of cutthroat has also increased from 185 fish/year to 448 fish/year. Therefore, we cannot attribute most of the increase in cutthroat production specifically to the habitat modification in the treatment stream.

Moon/East Creek study streams

Cutthroat Summer Population Estimates by year.

Average Summer Population Size (Pre vs. Post Treatment)

Cutthroat Smolt Production Estimates by year.

Cutthroat Overwinter Survival Estimates by year.

Average Number of Cutthroat Migrants (Pre vs. Post Treatment)

The number of juvenile cutthroat migrating out of the treatment stream (East Creek) has increased from an average of 109 fish/year before the habitat modification, to 408 fish/year after the habitat modification. In the reference stream (Upper Moon Creek), the average number of cutthroat during the same time periods has declined from 211 fish/year to 120 fish/year.

STEELHEAD TROUT

Lobster Creek study streams

Average Summer Population Size (Pre vs. Post Treatment)

Steelhead Smolt Production Estimates by year.

Average Number of Steelhead Migrants (Pre vs. Post Treatment)

Steelhead Overwinter Survival Estimates

The number of juvenile steelhead migrating out of the treatment stream (Upper Mainstem Lobster) has increased from an average of 16 fish/year before the habitat modification, to 161 fish/year after the habitat modification (an 10 fold increase). In the reference stream (E. Fork Lobster), the average number of steelhead has increased from 28 fish/year to 61 fish/year (a 2.2 fold increase).

Moon/East Creek study streams

Steelhead Summer Population Estimates by year.

Average Summer Population Size of Juvenile Steelhead (Pre vs. Post Treatment).

Steelhead Smolt Production Estimates by year.

Average Number of Steelhead Migrants (Pre vs. Post Treatment).

Steelhead Overwinter Survival Estimates.

The number of juvenile steelhead migrating out of the treatment stream (East Creek) has increased from an average of 71 fish/year before the habitat modification, to 344 fish/year after the habitat modification. In the reference stream (Upper Moon Creek), the average number of juvenile steelhead migrating past the trap has decreased from 211 fish/year to 120 fish/year.


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