Quantitative Assessment of Salmonid Escapement Techniques

Abstract

Most reviews of salmonid escapement estimation techniques have been based on logistical considerations or site-specific applications and not on statistical first principles. We reviewed six categories of salmon escapement techniques: area-under-the-curve, carcass abundance, mark-recapture, passage count, peak count, and redd count methods, based on statistical accuracy (i.e., unbiasedness), precision, and the ability to meet model assumptions. Within each of these categories of escapement techniques, we make recommendations on the best approaches to use for valid estimates and suggest five considerations when selecting an escapement estimation method. Currently in the Pacific Northwest, peak spawner counts are the most commonly employed technique and least defensible on a statistical basis than other methods. We recommend statistical accuracy and precision be given higher consideration when monitoring often increasingly scarce salmon resources.

Keywords:

• escapement
• area-under-the-curve
• carcass abundance
• mark-recapture
• passage count
• peak count
• redd count

ACKNOWLEDGMENTS

We thank the Bonneville Power Administration for the funding of this research and publication through Project 1989-107-00.