Evaluating Salmon Spawning Habitat Capacity Using Redd Survey Data

Abstract

Management and recovery goals for fish populations often rely on estimating the number of fish that can be supported by finite habitats. In the absence of direct measures of carrying capacity, management decisions are commonly informed by results of habitat models. However, the shortcomings and spatially explicit nature of most habitat models result in making assumptions, often preclude inclusion of important variables, and are rarely validated at the reach level. We analyze long-term, redd-count data for a population of Chinook Salmon Oncorhynchus tshawytscha to evaluate spawning habitat capacity of a major river. Adult escapement generally increased during the years 1994–2012; consequently site use and total redd counts also increased. Together, the annual use of spawning sites and the redd counts (as functions of adult escapement) provided evidence for density-dependent changes in the availability and capacity of spawning sites. Redd counts exceeded one recovery criterion specific to one spawning aggregate of the population during 11 years of our survey data, supporting the conclusion that adequate spawning habitat is available to attain a management goal set for this aggregate.

Received May 31, 2012; accepted March 27, 2013

ACKNOWLEDGMENTS

For almost two decades, Snake River basin fall Chinook Salmon research has been a highly cooperative venture involving an interagency and tribal team of scientists and managers. We thank our team members, especially those who have accumulated flight time. Bill Arnsberg, Jay Hesse, Yetta Jaeger, and several other anonymous reviewers improved this paper. Costs were covered by the Idaho Power Company and by the Bonneville Power Administration through projects 199102900 and 199801003 administered by D. Docherty. The use of trade names does not imply endorsement by the U.S. Government. The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.