Validating Bull Trout Redd Count Surveys Utilizing an Electronic Fish Counter Over Multiple Migration Years

During the summer of 2006 through 2009 portable resistivity counters were placed on the lower portions of the Kaslo River and in 2008-2009 on Crawford Creek in an effort to record downstream movements of spawned out adfluvial bull trout that inhabit Kootenay Lake. Run timing was well defined by the counters and the peak of spawning was determined after downstream movement increased at the end of September. This information signaled the timing of redd surveys on both systems that were conducted in the first week of October.

Redd counts per km were 16-27/km for the Kaslo River, 23/km in Keen Creek and 1/km in the main river below the counter. A similar survey on Crawford Creek counted a total of 268 redds with the majority (n=233) observed in the mainstem while the balance were located in the lower reaches of three tributaries. Redd densities were much lower in Crawford Creek compared to the upper Kaslo River with 8-11fish/km in the mainstem.

The Kaslo River resistivity counter recorded a total of 1,219 spawners in 2009 and 1,197 in 2008 while the Crawford Creek count was 486 in 2009 and 336 in 2008. Count efficiency based on video records was high (>95%). Comparing the 2009 redd counts to the counter numbers results in a conversion factor of 2.2 fish/redd for the Kaslo system and 1.8 fish/redd for Crawford Creek in 2009 and 2.5 and 1.8 fish/redd respectively in 2008. The differences in total spawner numbers between the two watersheds are attributed to far greater amounts of suitable spawning habitat in the upper Kaslo River compared either Crawford or Keen creeks. These derived expansion factors based on redd counts could be applied to other tributaries in an effort to evaluate spawner numbers where resistivity counters cannot be operated due to geography or cost but redd surveys are feasible.