Bull Trout Spawner Escapement in the Salmo River Watershed

Author: G. Nellestijn, S. Decker

Bull Trout escapement studies have been conducted annually in the Salmo River Watershed since 1998. BC Hydro conducted these studies until 2008 as part of their environmental monitoring requirements associated with the addition of the fourth turbine at the Seven Mile Power Plant. The Salmo Watershed Streamkeepers Society (SWSS) continued the project in 2010, 2011, 2016-2017, and 2012-2015 as volunteers, and in 2018, with support from the Fish and Wildlife Compensation Program (FWCP). The primary goal of this report is to summarize the results of the 2018 redd surveys and to provide an estimate of the aggregate (total) Bull Trout spawning escapement for the Salmo River watershed in 2018, and to compare this to previous years estimates (1998-2017). Specific objectives of the 2018 survey included: a) To continue the 1998 - 2017 time series of annual Bull Trout escapement estimates for the Salmo River watershed. b) To conduct Bull Trout redd counts in mid to late October (post spawning) in known spawning areas (Sheep Creek, South Salmo River, Clearwater Creek and the upper Salmo River mainstem) within the Salmo River Watershed. c) To conduct redd counts in potential spawning areas of Qua Creek and Curtis Creek. d) To ensure minimum error and bias of counts through continued utilization of highly experienced crew members who have been involved in conducting the redd counts in the Salmon system since 2003. The second goal of this report is to examine whether stream fertilization in Sheep Creek (Decker 2010; Decker and Nellestijn 2018) has had a positive effect on Bull Trout spawner abundance 15 years after the program began. During 2001-2009, a nutrient addition experiment was conducted in Sheep Creek to determine if this restoration technique could be effective in increasing the size and abundance of juvenile bull trout. The South Salmo River was selected as a control, and the treatment was applied to Sheep Creek during 2004-2009. Monitoring was based on a beforeafter- control-impact study design (BACI; Stewart-Oaten et al. 1986), with 2001-2003 serving as the control period, and 2005-2009 serving as the treatment period. The results of the experiment showed increases in the average size and abundance of juvenile Bull Trout in Sheep Creek as a result of nutrient addition that markedly increased standing crops of periphyton algae and benthic invertebrates (Decker 2010). There were insufficient years of data to test whether these increases in juvenile production were associated with increases in subsequent adult spawner abundance at the conclusion of the experiment in 2009, but this is no longer the case. During 2012-2018, stream fertilization continued in Sheep Creek as a management initiative (without the experimental monitoring) concurrent with annual Bull Trout red surveys in the Salmo watershed, providing the opportunity to examine whether the benefits of nutrient addition extended to the final stage of the Bull Trout life cycle.

In total, 62 redds were enumerated in 2018 (Table 2). Sheep Creek saw the highest concentration of spawning activity in 2018, with a total of 45 redds. There were 16 redds observed in the upper Salmo River mainstem, and one in the South Salmo River. Redd surveys of other Salmo River tributaries (Qua and Curtis Creeks) provided the location of upstream barriers, but no redds or spawners were observed.
The smoothed (5-year running average) time series of aggregate escapements (excluding South Salmo River) indicates a positive trend in adult abundance from 1998 to 2002, followed by a gradual decline from 2002 to 2014, and then a fairly strong increase in abundance over the last four years (2015-2018).
The mean abundance of Bull Trout spawners in Sheep Creek for years affected by nutrient enrichment (2008-2018) was 6% lower compared to that for years prior to enrichment (1998- 2007; 53 versus 57 spawners, respectively).

In total, 62 redds were enumerated in 2018 (Table 2). Sheep Creek saw the highest concentration of spawning activity in 2018, with a total of 45 redds. There were 16 redds observed in the upper Salmo River mainstem, and one in the South Salmo River. Redd surveys of other Salmo River tributaries (Qua and Curtis Creeks) provided the location of upstream barriers, but no redds or spawners were observed.
The smoothed (5-year running average) time series of aggregate escapements (excluding South Salmo River) indicates a positive trend in adult abundance from 1998 to 2002, followed by a gradual decline from 2002 to 2014, and then a fairly strong increase in abundance over the last four years (2015-2018).
The mean abundance of Bull Trout spawners in Sheep Creek for years affected by nutrient enrichment (2008-2018) was 6% lower compared to that for years prior to enrichment (1998- 2007; 53 versus 57 spawners, respectively).