PEACE REGION Williston Watershed Kokanee Spawner Distribution and Enumeration Surveys (2002 – 2006) A.R. Langston December 2012 FWCP – Peace Region Report No. 357 The Fish & Wildlife Compensation Program – Peace Region is a cooperative venture of BC Hydro and the provincial fish and wildlife management agencies, supported by funding from BC Hydro. The Program was established to enhance and protect fish and wildlife resources affected by the construction of the W.A.C. Bennett and Peace Canyon dams on the Peace River, and the subsequent creation of the Williston and Dinosaur Reservoirs. Fish and Wildlife Compensation Program ––– Peace Region 9228 – 100 th Avenue, Fort St. John, BC, V1J 1X7 Website: www.fwcp.ca This report has been approved by the Fish and Wildlife Compensation Program – Peace Region Fish Technical Committee. Citation : A.R. Langston. 2012. Williston Watershed Kokanee Spawner Distribution and Enumeration Surveys (2002 – 2006). Fish and Wildlife Compensation Program – Peace Region Report No. 357. 11 pp plus appendices. Author: A.R. Langston, BC Hydro Correspondence: BC Hydro - Fish and Wildlife Compensation Program – Peace Region 9228 – 100 th Avenue, Fort St. John, BC V1J 1X7 Williston Reservoir Kokanee Spawner Surveys 2002-2006 A.R. Langston ABSTRACT Kokanee ( Oncorhynchus nerka ) were stocked into Williston Reservoir from 1990 to 1998 to create a kokanee sport fishery and a prey source for large piscivorous fish species. The status of the kokanee population in Williston Reservoir and success of the kokanee stocking program is unknown. Therefore, a five-year study (2002–2006) was conducted to determine trends in Williston Reservoir’s kokanee population. The study had four objectives: (i) to determine the peak spawning period of kokanee; (ii) to determine if kokanee populations are increasing; (iii) to identify kokanee spawner distribution and limits to upstream migration; and (iv) to propose candidate streams for a long-term population trend monitoring program. Survey flights to locate and enumerate spawning kokanee were conducted annually by helicopter over all suspected and reported spawning streams. Kokanee spawners were most abundant in the tributaries in mid-September. The observed number of spawners increased from 81,000 in 2002 to 1,011,000 in 2006. This change suggests a dramatic increase in the Williston Reservoir kokanee population and a successful result to the 1990–1998 kokanee stocking program. Kokanee were found to be distributed throughout the watershed, but their abundance varied. The Peace Reach tributaries had the lowest number of kokanee spawners (<1% of all spawners), and the Parsnip tributaries had the second lowest (<8%). The greatest distribution and highest numbers were observed in the Omineca Arm (60–89%, depending on the year) and Finlay Reach (2–36%) tributaries. During the survey, information was recorded about upstream migration barriers. These barriers are not believed to limit kokanee spawning success, because accessible spawning habitat appeared to be abundant in lower reaches. The barriers have prevented kokanee access to some locations, most notably the Nation Lakes, Germansen Lake, and the Finlay River upstream of Cascade Canyon. Based on the five years of aerial surveys, a long-term population trend monitoring program is recommended for up to nine identified index tributary streams. Annual monitoring of the index streams is recommended with an evaluation of the monitoring in 2010. In addition, biennial aerial surveys beginning in 2008 are recommended for Parsnip River tributaries in the vicinity of Arctic and Tacheeda lakes. These biennial surveys will determine if non-native kokanee are expanding their range closer to native kokanee populations. Whole watershed surveys similar to those conducted in 2002 to 2006 are recommended every fourth year (beginning in 2010) to document colonization of new habitat and range expansion of kokanee. i Williston Reservoir Kokanee Spawner Surveys 2002-2006 A.R. Langston INTRODUCTION Background and Scope The Peace/Williston Fish and Wildlife Compensation Program (PWFWCP), created in 1988, compensates for impacts to fish and wildlife associated with the formation of Williston Reservoir. Williston Reservoir was formed in 1968 by the construction of the W.A.C. Bennett hydro-electric dam on the Peace River. The goals and objectives of the PWFWCP are available in Bergmann et al. 2003. Williston watershed, prior to reservoir formation, supported localized native kokanee populations, in at least three locations: Thutade Lake (Finlay River headwaters), Arctic Lake (upper Parsnip River tributary) and Tacheeda Lakes (mid Parsnip River tributary). Small numbers of native kokanee have always existed in Williston Reservoir, most likely from the headwater Thutade Lake kokanee ( Oncorhynchus nerka ) population. In the late 1980s, the British Columbia Ministry of Environment made the management decision to stock kokanee into Williston Reservoir (Harvey Andrusak, pers. comm., Redfish Consulting Ltd., previously with Ministry of Environment). The intent was to hasten the establishment of kokanee as a significant pelagic population in Williston Reservoir to provide both sport fishery opportunities and a prey source for piscivorous fish species (Blackman et. al. 1990). Kokanee from Hill Creek and Meadow Creek, both in BC (Columbia River origin), provided the donor source of fish for stocking. The PWFWCP funded and managed the stocking into the Carbon, Davis, Dunlevy, Manson, and Nation (Williston tributaries) systems from 1990–1998 (Appendix A). Kokanee are a pelagic planktivore that survive exceptionally well in reservoirs despite large drawdowns. Kokanee were stocked and have survived and grown very well in southeastern BC reservoirs: Mica and Koocanusa (Harvey Andrusak, pers. comm.) and Kinbasket (Oliver 1995). The establishment of a Williston Reservoir kokanee population may be a success that benefits recreational anglers, potential First Nations fisheries, certain terrestrial wildlife species (e.g., bears, eagles), and most fish species. However, there are concerns about an expanding kokanee population of Columbia River origin having potentially negative impacts on some native species (e.g., Arctic grayling ( Thymallus arcticus ) and native Williston kokanee. Aerial surveys have previously been conducted to locate and enumerate spawning native kokanee. Presence/absence surveys were conducted in the lower Finlay River in 1989. In 1990 the entire Finlay River and 18 tributaries of Williston Reservoir were surveyed (McLean and Blackman 1991). Four of the 1990 surveyed tributaries were re-surveyed in 1994 (Langston and Zemlak 1998). The results of the 1990 and 1994 surveys (5,000 or less spawning kokanee observed) indicated that relatively low numbers of native kokanee inhabited Williston Reservoir. No further enumerations had been conducted until the current study, which used aerial enumeration of spawning kokanee, as described by Fleck 1992, to evaluate the results of the 9-year kokanee stocking program and to estimate relative changes in kokanee populations and spawner distribution in the Williston Reservoir watershed. 1 Williston Reservoir Kokanee Spawner Surveys 2002-2006 A.R. Langston Study Objectives This five-year study (2002–2006) in the Williston watershed had four objectives: (i) to determine the peak spawning period of kokanee; (ii) to determine if kokanee populations are increasing; (iii) to identify kokanee spawner distribution and limits to upstream migration; and (iv) to propose candidate streams for long-term population trend monitoring. Description of Study Area Williston Reservoir (56° N latitude, 124° W longitude) is located approximately 140 km north of Prince George in northeast British Columbia, Canada (Fig. 1). The reservoir was created in 1968 by impounding the Peace River in the canyon near Hudson’s Hope, B.C. for hydroelectric generation (W.A.C. Bennett Dam). A second dam, Peace Canyon, is located 22 km downstream of the W.A.C. Bennett Dam. The Peace River flows east to Lake Athabasca within the Mackenzie River drainage system, which flows north and discharges into the Arctic Ocean. Williston Reservoir has a mean depth of 44 m and a maximum depth of 166 m (BC Research 1977). The shoreline is dendritic in shape and estimated to be about 1,770 km long (BC Research 1977). With a surface area of 1,779 km 2 at a maximum, normal operating level of 672.1 m (BC Hydro 1988), Williston Reservoir is the largest lentic freshwater system in British Columbia. A comprehensive description of the watershed is available in Stockner et al. 2005. Thutade Lake Peace Reach Finlay Reach Omineca Arm Parsnip Reach Tacheeda Lakes Arctic Lake Fig. 1. Williston Reservoir watershed. The four areas with kokanee spawning tributaries (circled), the 3 known locations of native kokanee populations highlighted in yellow. 2 Williston Reservoir Kokanee Spawner Surveys 2002-2006 A.R. Langston METHODS Tributary selection The streams stocked with kokanee from 1990 to 1998 (Appendix A) were surveyed in 2002 to 2006. In addition, the streams surveyed in 1990 (McLean and Blackman 1991) and 1994 (Langston and Zemlak 1998) were re-surveyed in 2002 to 2006. Other streams were selected according to geographic area (so the survey would cover as much area as possible), habitat attributes, and reports from local area residents of kokanee presence. Not all streams were surveyed in each year of the 2002–2006 survey. Rain storms and shortage of time meant skipping some streams