Adult Salmonid PIT-TAG Returns to Columbia River's Lower Granite Dam PDF Download

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Languages : en
Pages : 48

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Book Description
The results of an analysis of the returns of PIT-tagged Snake River spring chinook and steelhead detected at Lower Granite Dam are summarized. Included is theoretical work on statistical power calculations for tests of return rates. The phrase return rate will be taken to mean return and detection rate. Knowledge that a fish has returned depends upon it being detected at Lower Granite Dam. Some returns are unaccounted for because they go through the navigation lock or manage to go through the adult bypass undetected. (1) Adult PIT tag recoveries to date are informative at least from a qualitative perspective. (2) The tagging levels by geographic region, rearing type, and, for chinook, life history stage have varied considerably since PIT tagging began on the Columbia River system. Early tagging studies were directed at Juvenile problems rather than adult return rates. As a result, comparisons in adult return rates between years, regions, etc., are more difficult. Global conclusions about the effect of potential treatments and/or natural factors, such as region of origin, on adult return rates are difficult to make until a more balanced. more consistent tagging study is implemented. (3) Along the same lines, tagging levels will need to be increased considerably if experiments are to be conducted to determine factors that affect return rates. E.g., approximately 46,000 fish in both the control and the treatment groups need to be PIT-tagged to detect a statistically significant difference with 80% probability. (4) Analysis of the available data suggests that life stage (parr or smolt), rearing type (hatchery or wild), and geographic location all affect the return rates for spring chinook. The data are limited, however. (5) Return rates for Snake River steelhead are roughly an order of magnitude greater than Snake River spring chinook return rates.