Estimating the Effects of Smolt Transportation from Different Vantage Points and Management Perspectives

Abstract

Smolt transportation is a major mitigation strategy in the Columbia River hydrosystem, yet measures of its effects on adult return rates are often unclear. Managers use a variety of transportation effect measures that need to be clearly defined and easy to understand. We develop eight alternative transportation effect measures based on a release–recapture model of juvenile and adult passive integrated transponder tag data and relate the measures to different management perspectives. The performance measures include site-specific transport−in-river ratios (T/Is) that view the effect of transportation operations at a site either separate from (“isolated”) or in the context of (“contextual”) the rest of the transportation system. Both relative and absolute systemwide measures of transportation effects are developed, as well as measures for fish in the release group had they been untagged. All performance measures are calculated by the program ROSTER. Transportation effect measures for summer Chinook salmon Oncorhynchus tshawytscha from the McCall and Pahsimeroi hatcheries released in the Snake River in 1999 range from the isolated site-specific relative value at Lower Granite Dam of 2.015 (SE = 0.152) to a systemwide relative value of 1.232 (SE = 0.036). This paper explains how these two estimates and the others are correct depending on perspective and management intent.