USE OF ELECTROMYOGRAM TELEMETRY TO ASSESS DIFFICULT PASSAGE AREAS FORRIVER-MIGRATING ADULT SOCKEYE-SALMON

We conducted laboratory respirometry trials using adult sockeye salmon Oncorhynchus nerka implanted with electromyogram (EMG) radio transmit ters to investigate the relationship between oxygen consumption and EM G pulse interval. The strong association that was observed suggested t hat EMG telemetry could be used to assess activity and, thus, relative energy expenditure in freely migrating sockeye salmon. Using EMG tele metry, we then assessed the relative energy costs of upstream migratio n by adult sockeye salmon through specific reaches of the Fraser River , British Columbia. Greatest energy costs were incurred during migrati on through Hell's Gate fish-ways, a known point of difficult passage. Another energetically demanding area was a gravel bar that had not bee n previously identified as difficult for passage. Three other areas th at historically had been identified as difficult for passage were ener getically less expensive to migrate through during our study. Our resu lts demonstrate that EMG telemetry identified features and reaches of the river that impeded upstream migration, and they provide insights i nto the behavioural responses of fish to areas of difficult passage.