Acoustic Telemetry Measurements of Survival and Movements of Adult Steelhead (Oncorhynchus mykiss) within the Bulkley River, 2009

Summary

The Moricetown Canyon on the Bulkley River is the site of yearly steelhead (Oncorhynchus mykiss) mark-recapture studies done by Wet’suwet’en Fisheries. In 2008, a pilot scale acoustic telemetry study was conducted where adult steelhead were tagged with acoustic tags and released back into the river along side fish used the annual mark-recapture study. A drop back rate of 18% was measured for acoustically tagged adult steelhead (we define “drop-back” as fish going downstream after release, rather than continuing to migrate upstream past the recapture site, as conventionally assumed). In 2009, the acoustic study was expanded in Moricetown Canyon, and drop back rates were assessed more closely. … Key findings of the 2009 Bulkley River study:

  • Only between 56 and 59% of fish passed the recapture site during active recapture efforts (excludes: Fish that remained below (33%), undetected tagged fish (5%), and fish passing recapture site after the recapture efforts were terminated (3-6%))
  • 2009 drop-back rate (<0.7 km): 83% of all tagged fish (n=66)
  • 2009 drop-back rate (<11 km): 35% of all tagged fish (18% in 2008)

    Average time from release to passing the Moricetown Canyon recapture site (300 m upstream of release): 13.5 days (range: 0.9-52.5 days)

  • Twenty-two (33%) of all tagged steelhead remained below 123 the Moricetown Canyon release site and were never exposed to recapture at the recapture site

    Between two to four (3-6%) of the tagged steelhead passed the recapture site after termination of the recapture effort and were never exposed to recapture at the dip net site.

This evidence coupled with the extensive movements that a substantial proportion of the tagged steelhead made downstream and then upstream past the release site is potentially of major importance for the interpretation of data from the Moricetown mark-recapture analysis.

–Excerpt from the report’s Executive Summary