Mainstem Stehekin River and Side Channel Kokanee Spawning Escapement Surveys. NPS Annual kokanee spawning surveys have been conducted by CPUD on index reaches of Lake Chelan tributaries since 1983 (Xxxxxxx 2000; Xxxxx and Xxxxxxx 2004). However, there is significant kokanee production emanating from the mainstem and side channel habitat of the Stehekin River that is not being assessed using current survey methods (DES 2000a). North Cascades National Park Service (NOCA) personnel conducted expanded kokanee spawning surveys in 2000, 2010, and 2015 on all fish accessible side channels in the lower 16 km of the Stehekin River (Table 17). Table 17. Amount of side channel habitat assessed, habitat suitable for kokanee spawning and migration, and number of fish sample segments in the Stehekin River expanded kokanee spawning surveys; 2000, 2010 and 2015. Year of Survey Habitat Assessed (km) Suitable Habitat (km) Habitat Selected for Survey (km) Percent of Suitable Habitat Surveyed (%) Number of Fish Sample Segments 2000 22.8 19.8 7.2 36.4 17 2010 14.9 9.6 3.4 35.4 16 2015 19.4 16.9 3.8 22.5 15 In 2010 and 2015, the mainstem Stehekin River was also surveyed for spawning kokanee. The river was partitioned into thirty-two 500 m reaches eight of which were considered poor kokanee habitat as the river channel is deeply incised and substrate consists of large cobbles and boulders. These reaches were identified in a 2007 NOCA large woody debris survey as “transport zones”. Of the remaining 24 reaches, in 2010 12 were randomly selected for sampling, and seven were selected in 2015. All randomly selected mainstem and side channel reaches were sampled four times between August 30 and October 15 in 2010 and five times between September 1 and October 28 in 2015. Extrapolation of spawner survey counts to all suitable mainstem and all suitable side channel habitat was determined using the Area-Under-the-Curve Method (Xxxxxxx and Xxxxxxxxx 1980). The 2015 escapement estimate was 32,620 kokanee, only 17% of the 2010 escapement estimate of 195,463 fish (Figure 4).
Mainstem Stehekin River and Side Channel Kokanee Spawning Escapement Surveys. NPS Kokanee spawning surveys conducted during the previous license focused on a set of important subjectively selected index reaches of tributaries to Lake Chelan and the Stehekin River (Xxxxxxx 2000; Xxxxx and Xxxxxxx 2004). The continuity of this important long-term survey has been maintained in the new license period (Section 2.3.1). However, there is significant kokanee production emanating from the mainstem and side channel habitat of the Stehekin River that is not being assessed using current survey methods (DES 2000b). An expanded kokanee survey, including a probability sample of all potential kokanee spawning habitat in the mainstem, side channels, and tributaries, was completed in 2010. The intent of the survey was to develop a better estimate of the total escapement of kokanee spawners in the Stehekin River and to track changes in distribution of spawners in the watershed. In the spring of 2010 North Cascades National Park Service (NOCA) personnel conducted habitat surveys on all fish accessible side channels in the lower 16km of the Stehekin River. These surveys were based on Forest Service Level 2 habitat surveys with additional criteria for defining suitable kokanee spawning habitat. A total of 9.60 km were deemed suitable for kokanee spawning based on substrate data and channel depths. Of this 9.60 km of suitable habitat, 3.40 km were randomly selected as kokanee spawning survey reaches. Additionally, the mainstem Stehekin River was partitioned into thirty-two 500m reaches. Of these 500m reaches, 8 were considered poor kokanee habitat as the river channel is deeply incised and substrate consists of large cobbles and boulders. These reaches were identified in a 2007 NOCA large woody debris survey as “transport zones”. Of the remaining 24 reaches, 12 were randomly selected for sampling. All randomly selected mainstem and side channel reaches were sampled four times (two week intervals) between August 30th and October 15th. Extrapolation of spawner survey counts to all suitable mainstem and all suitable side channel habitat was determined using the Area Under the Curve Method (Xxxxxxx and Xxxxxxxxx 1980). Preliminary results show a total of 50,580 kokanee using the mainstem Stehekin channel and 131,568 kokanee using the side channel habitat. Total kokanee escapement was estimated at 182,148 fish. A detailed report incorporating the 2010 results and the results from the 2000 expanded kokanee side channel spawner survey is currently in preparation...
