Brown Trout (Salmo trutta) Status, Trends and Current Distribution in the Clearwater River, 2005
Author(s)
Kevin Gardiner
Summary
The Clearwater River drainage has been stocked with over 1.35 million brown trout (Salmo trutta) since 1927. However, formal analysis of brown trout populations or stocking evaluations within the drainage are limited. A review of the historic fishing regulations for this drainage suggested that the Clearwater River has been managed historically and is still being managed as a bull trout (Salvelinus confluentus) fishery. Bull trout are listed as a species of special concern (Berry 1994) in Alberta and competition from exotic species such as brown trout hasbeen suggested as a deterrent to their recovery (Berry 1994). Therefore, an assessment of brown trout status, trends and current distribution within the Clearwater River drainage may prove invaluable to fisheries managers from Alberta Sustainable Resource Development (ASRD). The specific objectives for this project were: 1) Compare the results of brown trout population estimates from historic surveys to those conducted during the Clearwater River Bull Trout Study in 2004/2005, 2) Compare brown trout fork length data collected in 2004 to that collected in past studies and, 3) Use current catch-per-unit-effort data to demonstrate current brown trout distribution in the Clearwater River drainage and code tributary streams of the Clearwater River as having high, moderate or low populations of brown trout.
The study area for this project included the Clearwater River and all tributaties (except for Alford Creek) located downstream of the Banff National Park boundary and upstream of the intersection of the Clearwater River and Highway 54. For population analysis purposes and in keeping consistent with hisotric surveys, the Clearwater River was broken into three sections; 1) Ricinus, 2) Corkscrew and 3) Elk Creek reaches. The primary data source for this project came from the report named, "Upper Clearwater River Bull Trout Status Assessment - 2004" (Rodtka and Gardiner, in prep.). In addition, all hisotric brown trout population data available that have been collected on the mainstem Clearwater River and all electrofishing catch-per-unit-effort (CUE) data collected within the past eight years on tributary streams to the Clearwater River were also used.
Population estimates from 2004, 1987 and 1977 and from 2004 and 1977 were compared for the Ricinus and Corkscrew reaches, respectively. The population estimate prepared for the Elk Creek reach in 2004 is the first formal population estimate ever been established in that section of the Clearwater River. Therefore, comparisons to other years were not possible. Fork length frequency bar charts were compared between the years of 2004, 1995, and 1977 in the Ricinus reach, 2004, 1993 and 1977 in the Corkscrew reach and 2004 and 1993 in the Elk Creek reach. The statistical program Jump-InTM (SAS) was used to group the list of all brown trout CUE's from the entire province into three groups. Brown trout populations were considered to represent a high-density population if their CUE's were within the upper 75th percentiles (>=.8.32 brown trout per 100 m), moderate-density if within the 26th to 74th percentiles (8.31 to .98 brown trout per 100 m) and a low-density when in the 25th and lower percentiles (>=.97 brown trout per 100 m). These codes were then used to code tributary streams to the Clearwater River, where CUE data were available.
Brown trout population densities in 2004 were very similar to 1977 and higher than those from 1987 in the Ricinus reach and similar to 1977 in the Corkscrew reach; though seasonal population variations from brown trout migrations limit the strength of the 2004 data. Brown trout population densities derived on the Ricinus Reach in 2004 were 144.3 brown trout per kilometre. This is lower than that documented on the Bow River (ASRD unpublished data) but higher than what has been documented on the Little Red Deer River (Buchwald 1992). In 2004, individual brown trout sizes ranged from 76-610 mm and a relatively even size distribution was observed. In 1977 and 1987 the most dominant size calsses were near 200 mm and in 2004 fork lengths near 400 mm were dominant. The dominant coding for tributary streams was, "no brown trout collected". Cutoff Creek and the lower portions of Elk Creek were both coded as high-density brown trout streams, despite the fact that Cutoff Creek has never been stocked with brown trout. The middle reaches of Elk Creek and the greater length of Idlewilde Creek were coded a having a moderate density of brown trout. The lower section of the Tay River was coded as having a low density of brown trout. Specifically, within the Tay River drainage in the past eight years, only one brown trout has been collected.
The author believes that catch-and-release regulations in place on Elk Creek and size restrictions and the seasonal closures that are in place for brown trout in the rest of the Clearwater River drainage are maintaining healthy brown trout population levels and that stocking is no longer required. Despite extensive stocking historically and the current reduced (10,000/5-years) level of stocking in the Tay River drainage only one brown trout has been documented in that drainage from the 28 surveys that have been completed there in the past eight years. Stocking may in fact only be augmenting brown trout populations in other streams that are important for bull trout such as Cutoff Creek and Elk Creek. Both of these streams have been documented as bull trout spawning streams (Rodtka and Gardiner, in prep.).
Two recommendations resulted from this project. Recommendation number one is to doscontinue brown trout sotcking within the Clearwater River drainage. Recommendation number two is that future research should be conducted in competition between brown trout and bull trout. This research should provide insight into whether or not established exotic brown trout population are acting as a detriment to bull trout recovery in the Clearwater River drainage.