Final Publication: Hinrichsen, R., J.J. Anderson, G.M. Matthews, and C.C. Ebbesmeyer. 1998. Effects of the ocean and river environments on the survival of Snake River stream-type chinook salmon. In Plan for Analyzing and Testing Hypotheses (PATH): Retrospective and prospective analyses of spring/summer chinook reviewed in fiscal year 1997, ed. D.R. Marmorek, C.N. Peters, and I. Parnell. Vancouver, BC, Canada: ESSA Technologies Ltd.
Executive Summary
The U.S. National Marine Fisheries Service (NMFS) studied the success of transporting spring chinook salmon smolts during the years 1983-1990 (excluding 1988) from Lower Granite Dam (river mile107.5 of the Snake River) to below Bonneville Dam (river mile 146 of the Columbia River). During this eight-year period, approximately 350,000 smolts were coded-wire tagged, and subsequently recovered as adults in a fish trap at Lower Granite Dam. To estimate survival, we calculated the recovery fraction (number recovered/number tagged). Our analysis revealed that survival was related to smolt migration timing and that survival varied among years.
Of the juveniles marked, those migrating earlier in the season (16-22 April) had an average adult recovery of 1 per 870; later migrants (19 April-8 June) had an average adult recovery of 1 per 349, representing a 2.5-fold increase over the migration season. The greatest contrast was seen in 1990, when there was a 5-fold increase in recovery for later versus earlier migrants.
We performed a generalized linear model (GLM) analysis using 18 physical and biological variables to determine which were the best predictors of adult returns. The age of return over the study period was the best explanatory variable, showing the percentage of total returns was 9%, 58%, and 33% for the 3-,4-, and 5-year-olds, respectively. This reflects the effect of age of maturity on the numbers returning. Three to five-fold more fish mature to make their spawning run at age 4 and 5 than at age 3. Of the riverine and oceanographic variables considered, the spring transition explained the most year-to-year variations in survival. It was also clear that smolts migrating later in a given year generally yielded higher adult returns. This was not related to an increase in fish size or discharge with the advance of the season, but may be due, in part, to a greater mix of wild outmigrants (compared to hatchery outmigrants) later in the season. However, a separate analysis of hatchery and wild fish in 1990 suggests that both experienced better survival as the season progressed. Alternatively, the increased survival over the season may indicate that lower smolt densities later in the season, or improved estuary/nearshore oceanographic conditions, produced greater survivals.
Finally, we incorporated our findings in a model of the survival of transported fish for use in CRiSP and other life-cycle models.