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Adult Returns of Subyearling and Yearling Fall Chinook Salmon Released from a Snake River Hatchery or Transported Downstream
Author(s) -
Bugert Robert M.,
Mendel Glen W.,
Seidel Paul R.
Publication year - 1997
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/1548-8675(1997)017<0638:arosay>2.3.co;2
Subject(s) - chinook wind , fishery , hatchery , oncorhynchus , environmental science , biology , fish <actinopterygii>
We compared the release‐to‐adult returns of coded‐wire‐tagged groups of fall chinook salmon Oncorhynchus tshawytscha in a 2 × 2 factorial experimental design: subyearlings and yearlings released directly from a hatchery versus those barged below two main‐stem hydroelectric dams on the Snake River, Washington. Releases comprised six brood years over a 6‐year period. In every release year, chinook salmon released as yearlings performed better than subyearlings; this was true both for returns to the Snake River and for their contribution to Pacific Ocean and lower Columbia River fisheries. We found no significantly consistent differences in rates of return between transported and on‐station releases for either age‐class. Return rates of both subyearlings and yearlings varied significantly with year of release. Median migration speeds of branded chinook salmon released on‐station varied directly with Snake River flows. However, there was no general relation between flow (and attendant spill) in the Snake and lower Columbia rivers and subsequent release‐to‐adult returns, both for subyearlings and yearlings. Likewise, transportation past two dams did not improve the adult returns of yearlings in low‐flow conditions, and it had limited but inconsistent benefits to subyearlings when Snake River flow and spill were low. The advantages of transportation past two main‐stem dams were probably offset by (1) additional handling stress of loading and unloading fish for transportation and (2) the short duration of transport relative to the time required to acclimate to barge hauling. Most notable was the significant variation in annual rates of return: 1,500% for subyearlings and 700% for yearlings. Both age‐groups that migrated in 1985 returned at high rates. Transported chinook salmon strayed to freshwater areas outside the Snake River basin at a significantly higher rate (5.9%) than those released on‐station (0.3%). Conversely, chinook salmon released on‐station strayed to locations upstream of the hatchery in the Snake River basin at a higher rate (7.8%) than chinook salmon that were transported (2.4%). Overall, the stray rate for all treatment groups to locations outside the Snake River basin was 1.8%.