Effects of natal water dilution on the migration of Pacific salmon in a regulated river

Abstract

AbstractAdult salmon are guided by chemical cues from their natal water during the spawning migration. Consequently, hydroelectric activities can have negative effects on adult salmon navigation if they alter the chemical properties of the homing environment. We conducted riverside experiments to examine the effects of natal water dilution resulting from hydroelectric operations on upstream navigation in a British Columbia river and the efficacy of current dilution management in providing clear migratory cues for two local populations of sockeye salmon (Oncorhynchus nerka) and a population of pink salmon (Oncorhynchus gorbuscha). We found that both sockeye populations exhibited behavioural preferences for pure natal water when compared with various levels of diluted natal water, whereas pink salmon, which spawn throughout the system and exhibit lower levels of natal site fidelity, appeared unaffected by natal water dilution. Our findings confirmed that current management operations were appropriate for ensuring timely migration to spawning grounds and highlight the potential effects of alterations to water odour properties on salmon migrations.