Abundance and life history characteristics of steelhead (Oncorhynchus mykiss) and Coho Salmon (Oncorhynchus kisutch) smolts in two direct ocean tributaries on the central Oregon coast, Information Report 2018-07

Identification Information

Citation

Originator: Lorion, C. M., E. Suring, J. L. Gerding and E. T. Leonetti

Publish Date: October 2018

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Erik Suring

Job Position: Salmonid Life Cycle Monitoring

Telephone: 541-286-5328

E-Mail Address: erik.suring@odfw.oregon.gov

Description

Abstract: In 1991, the Oregon Department of Fish and Wildlife (ODFW) began an intensive research study at Tenmile Creek on the central Oregon coast to evaluate the effects of a large wood addition on juvenile salmonid populations. Nearby Cummins Creek served as a reference site. Annual monitoring of juvenile salmonid out-migrants began in 1992 at the two sites, continued through 2012 at Cummins Creek, and is ongoing at Tenmile Creek. These data offer an unusually long time-series of smolt abundance and life history characteristics for steelhead and Coho Salmon at monitoring sites located less than a kilometer from the point of ocean entry. Annual estimates of steelhead smolt abundance ranged from 740 to 3,236 smolts at Cummins Creek, and from 2,464 to 19,602 smolts at Tenmile Creek. For Coho Salmon, annual estimates ranged from 319 to 3,164 smolts at Cummins Creek, and from 1,637 to 11,553 smolts at Tenmile Creek. Steelhead smolt production at Tenmile Creek appeared to increase significantly relative to Cummins Creek following the large wood addition in 1996, but there was no evidence of a similar effect on Coho Salmon smolt production. Most steelhead smolts spent 2 years rearing in freshwater before out-migration, and we observed a higher proportion of age-1 smolts and lower proportion of age-3 smolts than several other studies in Oregon coastal streams. Coho Salmon smolt out-migrants were dominated by age-1 individuals at both sites, but there was evidence that some juvenile Coho Salmon out-migrated as age-0 smolts. Smolts of both species tended to be larger at Tenmile Creek than at Cummins Creek, and negative relationships between mean smolt size and smolt abundance suggest that rearing density may influence growth for juvenile salmonids in these streams. The median migration date of steelhead smolts was consistent over time and tracked closely between the two sites. Coho Salmon smolt out-migration timing was more variable and tended to be slightly later than for steelhead, particularly at Tenmile Creek. During peak migration, a high proportion of steelhead migrants classified as smolts based on length had body coloration consistent with smoltification. External signs of smoltification were not as prevalent among steelhead captured early in the season, particularly among smaller migrants. This long term out-migrant monitoring at the ocean entrance illustrates the variation that occurs in freshwater production and the patterns that occur in salmonid smolt life history but also shows that without spawner abundance data conclusions about freshwater production are limited.

Purpose:

Time Period of Content: 1992-2018

Geographic Extent: Tenmile Creek, Cummins Creek, Oregon Coast

Status: Final

Use Constraints:

Format: PDF file

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