Potential for tube fishways to pass salmon upstream over high dams

Abstract

Disrupted freshwater fish migrations following river fragmentation by dams has been a major factor in internationally declining freshwater fish populations. High dams (>20 m) can eliminate upstream fish passage into extensive upper waterway networks, significantly reducing the habitats available to native species. Restoring upstream fish passage past high dams has proved extremely difficult and costly. Further, a major weakness of conventional fishways has been their design around fish of particular size and swimming ability. The tube fishway was developed with the overarching ambitions of restoring upstream passage for fish communities over high structures, with initial work focussed on slower-swimming species. Slatick’s (1970) studies of mature, upstream migrating Chinook salmon (Oncorhynchus tshawytscha), Sockeye salmon (O. nerka), Coho salmon (O. kisutch), and Steelhead (i.e. Rainbow) trout (O. mykiss) are reprocessed to demonstrate strong attraction into pipes. Log-normal forms reasonably represent his entrance-time distributions. More than half of the observed fish entered 0.6 m diameter horizontal pipes and 0.9 m entrance cones within 48 s. These results have significant implications for the application of tube fishways for endangered large salmonids. Extending Slatick’s work, this contribution quantifies potential upstream passage rates for large Chinook salmon based on a conceptual tube fishway design for a representative high Columbia River dam. Projections of tube fishway performance compare favourably with conventional fishways presently used on the Columbia system. Thereby, the tube fishway offers prospect of improved restoration of upstream passage and native fish access to extensive regions of catchments internationally that embrace both salmonid and non-salmonid species.