| Abstract/Description or Keywords |
During the summer and fall of 2008, Wet’suwet’en Fisheries continued the Moricetown Canyon steelhead tagging program that was initiated in 1999, in coordination with an ongoing coho, sockeye and chinook tagging program. Coho, sockeye and chinook data were analysed separately by Fisheries and Oceans Canada. The data collected for steelhead migration from July to October 2008 are summarized in this report in conjunction catch per unit effort information summarized in a separate report prepared by Wet’suwet’en Fisheries. The continued objectives of this steelhead tagging program have been to standardize the sampling methodologies, to evaluate in-season population estimates or indices and to monitor the run-timing and relative returns of steelhead migrating upstream of Moricetown Canyon. Between June 23rd and October 20th, 2008, 777 steelhead were tagged by beach seining and 1820 steelhead were tagged in the dipnet fishery. Tagging at the beach seine fishery ceased on October 6th, and tagging effort was reduced by one crew between October 6th and October 20th in the dipnet fishery. Steelhead catch rates obtained from dipnet and beach seine samples exhibited less temporal differences in 2008 than in the initial two years of the study (1999 and 2000), when capture rates by dipnetting decreased notably after September 1st (Labour Day). Catch rates indicate that the tagging program encompassed the fall steelhead migration through Moricetown Canyon. No comparisons of sex ratios was conducted because gender identification of steelhead in the fall is notoriously difficult, and has been found to be inconsistent during previous years of the study (1999, 2000 and 2001). Fork lengths were compared between dipnet and beach seine catches, and were found to be significantly different. Steelhead captured in the dipnet fishery were significantly smaller than those captured in the beachseine fishery in 2008, indicating a bias in capture techniques, and/or inconsistencies in recording fork length at the dipnet fishery where some fork lengths measurements were recorded in inches. The number of steelhead tagged in 2008 is second highest among the number of steelhead tagged since 1999, and is within the targeted number (600-1,000) for a mark-recapture estimate, assuming a population size between 10,000 and 30,000 steelhead. The number of recaptures in 2008 was similar to recaptures in previous years of the study, with 2.8% of the steelhead examined in the dipnet fishery having been tagged by beach seining (54 of 1923). Since 1999, the highest proportion of recaptures in the dipnet fishery was achieved in 2003, where 5.5% of the steelhead sampled by dipnetting were recaptures initially tagged in the beach seine fishery (100 of 1805). The lowest proportion of recaptures was in 1999, where only eight steelhead were recaptured in a sampled 1555 steelhead examined in the dipnet fishery. The varying proportions of recaptured steelhead in the dipnet fishery is in large part due to the varying number of tags applied in the beach seine fishery, with a low of 164 (in 1999) and a high of 834 (in 2002). The third highest number of tags applied in the beach seine fishery (656 tags) was in 2003, which corresponds to the highest proportion of recaptures. In 2008, 777 steelhead were tagged in the beach seine fishery downstream of Moricetown Canyon, and resulted in the recapture of 54 of these steelhead in the dipnet fishery. Fifty-four of the 777 steelhead tagged downstream of the canyon were recaptured in a sample of 1,923 steelhead examined for tags at the canyon. A 5% tag loss was assumed, based on tag loss estimates for beach seine and dipnet capture steelhead in 2008, and in previous years of the study. The adjusted Petersen estimate for steelhead moving through Moricetown Canyon between June 23rd and October 20th, 2008 determined for this mark-recapture data is 25,865 steelhead (95% confidence interval = 19,441-32,288). In addition, a Schaeffer estimate was calculated for steelhead migrating through Moricetown Canyon for the duration of the tagging project. The Schaeffer estimate for the tagging project was 19,039 steelhead. The ML Darroch estimate for the Moricetown tagging project was 27,474 steelhead (95% confidence interval = 15,487-39,461). These estimates should be viewed in light of constraints of the study, including low recapture rates (2.8%), and non-random sampling at the beach seine and dipnet locations. The estimated number of steelhead moving through Moricetown Canyon in the study period is the highest estimate since 2001, when the numbers of recaptures increased from very low initial recapture rates in 1999 and 2000. |
