Upper North Saskatchewan River and Abraham Lake BLTR Study, 2002-2003
Marco Fontana, Kevin Gardiner and Mike Rodtka
Historically, bull trout (Salvelinus confluentus) have been the most abundant and widely distributed char species in Alberta. However, many native populations have declined in range and abundance due to overfishing and habitat loss. To prevent further decline in their populations, a province-wide ban (zero bag limit) on bull trout harvest wasfin 1994 by Alberta Sustainable Resource Development as part of Alberta’s Bull Trout Management and Recovery Plan. The current study is part of a larger study designed to generate data on the status of bull trout populations in the upper North Saskatchewan River region. Here, we evaluate the extent and timing of seasonal migrations and the distribution of spawning and over-wintering habitat using radiotelemetry.
A total of 38 bull trout ranging in fork length (FL) from 446 to 665 mm were implanted with radio-transmitters, 35 implanted in 2002 and three in 2003. Radio-tagged bull trout were located during 20 tracking events between 7 June 2002 and 25 September 2003. Forty-nine percent (17 of 35) and 47% (18 of 38) of tagged bull trout in 2002 and 2003, respectively, underwent fall migrations presumably to access spawning habitats. Ten of the 35 bull trout tracked both years (29%) did not undergo fall-migrations in either year. Of the 25 fall-migrants tracked both years, 17 (68%) underwent fall migrations in one year only and 8 (32%) migrated both years. There was no significant difference in mean length (FL) between fall-migrant and non-migrant bull trout. Overwintering migrations were observed for 77% of all radio-tagged fish.
Migrations to suspected spawning tributaries were detected as early as 7 July in 2002 and 13 June in 2003. All migrations into tributaries were completed by 18 September in both years. In 2002, all fall-migrant bull trout had departed from tributaries by 6 October, whereas in 2003 four fall-migrants still occupied tributaries during the last tracking event conducted 25 September. Over-wintering migrations began 8 August 2002, and by 6 December, 89% of winter migrants had moved to their winter locations.
The mean (± SD) distance of fall spawning period migrations was 25.2 ± 19.3 km. Maximum likelihood estimates of the average distances traveled during August, September, and October, by fall-migrant bull trout were 9.6, 14.6, and 17.4 km, respectively. The mean distance traveled for migrations to over-wintering locations was 16.0 ± 12.3 km. Mean winter movement between 6 December 2002 and 27 February 2003 was 1.5 ± 3.3 km, with 50% of fish showing no movement. Maximum likelihood estimates of mean monthly distance traveled by all radio-tagged bull trout, ranged from 2.6 to 5.8 km during the spring and summer months, 6.6 to 11.0 km during the fall months, and 2.8 to 4.6 km during the winter months.
Spawning locations were identified in Owen Creek and Unnamed Creek #22932. In addition, the Howse River, Siffleur River, Murchison Creek, and Whiterabbit Creek were identified through telemetry as fall-use tributaries, presumably for spawning purposes. Over-wintering locations used by 89% of radio-tagged bull trout were distributed throughout much of the main-stem in the upper North Saskatchewan River below the confluence of Owen Creek, and 11% of bull trout over-wintered in Abraham Lake.