Monitoring Bull Trout in Select Tributaries to the Kakwa River Watershed
Author(s)
John Tchir and Tyler Johns
Summary
The bull trout (Salvelinus confluentus) is native to the Eastern slopes of Alberta. As a result of over exploitation and habitat loss, the bull trout has suffered significant decline and currently exists within only a fraction of its range. The Kakwa River watershed supports populations of bull trout that rely on tributaries for spawning and rearing. Among others, Lynx and Grizzly Creeks provide spawning and rearing habitat for Kakwa River fluvial bull trout. The adult spawning run on Lynx Creek has been monitored since 1995, while abundance of juvenile bull trout (based on an index site) has been monitored since 1996. The objectives of this study conducted in 2004 were to enumerate the bull trout spawning run in Lynx Creek and estimate juvenile abundance in Lynx and Grizzly Creeks.
Juvenile abundance estimation
A stratified random sampling design was employed to estimate juvenile bull trout densities in Lynx and Grizzly Creek. Streams were stratified by natural breaks in elevation, resulting in five strata in Lynx Creek and eight strata in Grizzly Creek. Sampling units that comprised each stratum were defined as 35 times the bank full width and samples were selected at random with a minimum of 200 m between sites. Sample size was allocated proportionately to stratum size. Within each stratum, a site was randomly selected to assess sampling efficiency (i.e., q). Mark-recapture techniques were used to determine q for each stratum. Sampling efficiency and catch of fish per unit of effort were then used to estimate abundance of fish in each stratum using simulation (i.e., bootstrapping) techniques. Estimates for each stratum were then added together to produce an estimate of juvenile bull trout abundance for all strata sampled. Estimated density of bull trout in Lynx Creek in the fall of 2004 was 5.8 fish /100 m2 (95% CI 3.2-8.2). While estimated density of bull trout in Grizzly Creek was less at 3.2 fish/100 m2 (95% CI = 2.1-4.1).
Enumeration of post spawn adult bull trout in Lynx Creek
A fence was constructed across Lynx Creek approximately 600 m upstream of its confluence with the Kakwa River to enumerate the bull trout spawning run, from 12-29 September 2004. However, as a result of high flow conditions and leaf litter accumulations, the fence failed to stop the downstream movement of fish during most of the out migration of adult fish. Over the period, a total of 12 adult bull trout were captured upstream of the fence.
Monitoring the adult spawning run and juvenile abundance will provide insight into changes that may occur as a result of industrial development. Future industrial developments in the Kakwa River watershed pose a risk to the health and abundance of bull trout and other natural populations within this watershed. Critical and valuable information on the natural variation and perturbations resulting from industrial and recreational activities can reduce uncertainty and aid in development of integrated resource management plans.