Comparative Survival [Rate] Study (CSS) of Hatchery PIT-tagged Chinook; Migration Years 1996-1998 Mark/Recapture Activities, 2000 Annual Report.

摘要

The Comparative Survival Rate Study (CSS) is a multi-year program of the fishery agencies and tribes to measure the smolt-to-adult survival rates of hatchery spring and summer chinook at major production hatcheries in the Snake River basin and at selected hatcheries in the lower Columbia River. The CSS also compares the smolt-to-adult survival rates for Snake River basin chinook that were transported versus those that migrated in-river to below Bonneville Dam. Estimates of smolt-to-adult survival rates will be made both from Lower Granite Dam back to Lower Granite Dam (upriver stocks) and from the hatchery back to the hatchery (upriver and downriver stocks). This status report covers the first three migration years, 1996 to 1998, of the study. Study fish were implanted with a PIT (Passive Integrated Transponder) tag which allows unique identification of individual fish. Beginning in 1997, a predetermined proportion of the PIT tagged study fish in the collection/bypass channel at the transportation sites, such as Lower Granite and Little Goose dams, was purposely routed to the raceways for transportation and the rest was routed back to the river. Two categories of in-river migrating fish are used in this study. The in-river group most representative of the non-tagged fish are fish that migrate past Lower Granite, Little Goose, and Lower Monumental dams undetected in the bypass systems. This is because all non-tagged fish collected at these three dams are currently being transported. The other in-river group contains those fish remaining in-river below Lower Monumental Dam that had previously been detected at one or more dams. The number of fish starting at Lower Granite dam that are destined to one of these two in-river groups must be estimated. The Jolly-Seber capture-recapture methodology was used for that purpose. Adult (including jacks) study fish returning to the hatcheries in the Snake River basin were sampled at the Lower Granite Dam adult trap. There the PIT tag was recorded along with a measurement of length, a determination of sex, and a scale sample. The returns to the hatchery rack were adjusted for any sport and tribal harvest to provide an estimate of total return to the hatchery. Adult and jack return data from return years 1997 through 1999 are covered in this status report. Only the returns from the 1996 migration year are complete. A very low overall average of 0.136% survival rate from Lower Granite Dam and back to Lower Granite Dam was estimated for the 1996 migrants. The outcome expected for the 1997 migrants is much better. With one year of returns still to come, the overall average Lower Granite Dam to Lower Granite Dam survival rate is 0.666%, with the McCall Hatchery and Imnaha Hatchery fish already producing return rates in excess of 1%. With 635 returning adults (plus jacks) from the 1997 migration year detected at Lower Granite Dam to date, and one additional year of returns to come, there will be a large sample size for statistically testing differences in transportation versus in- river survival rates next year. From the conduct of this study over a series of years, in addition to obtaining estimates of smolt-to-adult survival rates, we should be able to investigate what factors may be causing differences in survival rates among the various hatchery stocks used in this study.