Physiological Effects of Collecting and Transporting Emigrating Juvenile Chinook Salmon past Dams on the Columbia River

Abstract

Emigrating juvenile salmonids are collected at McNary Dam on the Columbia River and transported past the three downstream dams to avoid mortalities caused by passage through power-generating turbines. During the 1982–1984 seaward migrations of juvenile fall and spring chinook salmon Oncorhynchus tshawytscha, we used an array of physiological measurements (plasma cortisol and glucose, white blood cell counts) and challenge tests (saltwater challenge, secondary stress, and swimming endurance) to identify the stressful elements in these activities. Sequential increases in plasma cortisol titers offish sampled at the physically separable points in the collection system led us to conclude that the elements of the system stressed fish cumulatively. Furthermore, there were decreases in numbers of white blood cells, in osmoregulatory ability, and in swimming endurance during the first 24 h after fish were collected. Increasing the water flow rate in the system after the 1982 season seemed to reduce total stress. The most stressful event in transportation appeared to be the loading of fish into a tank truck or barge, Fish recovered from the stress of loading while en route, and thus recovered more fully during the 16-h trip by barge than during the 3-h trip by truck. Physiological responses did not differ in fish transported in trucks at densities of 0.02–0.36 kg·L–1. Although there were no significant differences in responses of fish collected at various times during the migrations, apparent differences between the responses of fall and spring chinook salmon suggested that the latter were more sensitive to the stresses of collection.