| Abstract/Description or Keywords |
During the summer and fall of 2005, the Wet’suwet’en Fisheries continued the Moricetown Canyon steelhead tagging program that was initiated in 1999, in conjunction 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 migrating from June to October 2005 are summarized in this report. Catch per unit effort information was summarized in a separate report prepared by Wet’suwet’en Fisheries. The continued objectives of this steelhead tagging program have been to standardize sampling methodologies, develop and evaluate in-season population estimates or indices and to monitor the run-timing and relative annual returns of steelhead migrating upstream of Moricetown Canyon. Between July 7th and October 3rd, 2005, 527 steelhead were tagged by beach seining and 1426 steelhead were tagged in the dipnet fishery. Steelhead catch rates obtained from dipnet and beach seine samples exhibited less temporal differences in 2005 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 beginning and peak time of steelhead migration through Moricetown Canyon, but that a later portion of the migration period may not have been sampled. A comparison of sex ratios was not conducted because gender identification of steelhead in the fall is notoriously difficult, and was found to be inconsistent during previous years of the study (1999, 2000 and 2001). Fork lengths were compared between dipnet and beach seine catches to investigate potential size biases in sampling gear. Fork lengths were not found to be significantly different, similar to previous years of the study except 2004 where steelhead captured in the dipnet fishery were significantly larger than the steelhead captured by beach seining. The number of steelhead tagged in 2005 is lower than the targeted number (600-1,000) for a markrecapture estimate, assuming a population size between 10,000 and 30,000 steelhead, and the recapture rates in 2005 were intermediate to recapture rates in previous years of the study, with 3.3% the steelhead examined in the dipnet fishery having been tagged by beach seining (54 of 1,636). 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 0.5% in 1999, where only eight steelhead were recaptured in a sample of 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 second highest number of tags applied in the beach seine fishery (656 tags) was in 2003, which corresponds to the highest proportion of recaptures. In 2005, 527 steelhead were tagged in the beach seine fishery downstream of Moricetown Canyon. The number of steelhead tagged in the beach seine fishery in 2005 was lower than the number tagged in 2003, and 2002, but was higher than the number of steelhead tagged in the beach seine fishery in 1999, 2000, 2001 and 2004. Fifty-four of the 527 steelhead tagged downstream of the canyon were recaptured in a sample of 1700 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 2005, and in previous years of the study. The adjusted Petersen estimate for steelhead moving through Moricetown Canyon between July 7th and October 3th, 2005 determined for this mark-recapture data is 14,912 steelhead (95% confidence interval = 11,289-18,535). 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 15,567 steelhead. The ML Darroch estimate for the Moricetown tagging project was 18,126 steelhead (95% confidence interval = 5,696-30,284). These estimates should be viewed in light of constraints of the study, including low recapture rates (3.3%), incomplete sampling of the steelhead run, 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 similar to the estimate for the same period in 2003 and 2004, and appears lower than the population estimates determined in 1999 to 2002. The population estimates for 2000 (Petersen estimate = 43,428; 95% confidence interval = 18,876-103,819) and 2001 (25,289; 95% confidence interval = 20,596-33,941) are significantly higher than the steelhead population estimates for 2003 (14,963; 95% = 12,390-17,535) and 2005 (14,912, 95% confidence interval = 11,289-18,535) as indicated by the lack of overlap in the confidence intervals. No further studies (e.g. snorkel counts) were conducted upstream of Moricetown Canyon in 2005. |
