Stehekin River kokanee expanded spawning surveys, 2000 and 2010

Anthony, Hugh; Glesne, Reed

To effectively manage the kokanee population in Lake Chelan, data needs to be gathered regarding adult escapement and the extent of natural reproduction within Lake Chelan tributaries. The need for a comprehensive assessment of the kokanee spawning populations was documented in preliminary FERC relicensing study plans and again in the 2009 Lake Chelan Fishery Forum (LCFF) Work Plan. As a result of these planning efforts, funds were provided in 2000 and 2010 to conduct expanded kokanee escapement surveys in the Stehekin River drainage to complement data collected annually from the existing Chelan PUD kokanee index reach surveys within the Stehekin River. The objectives of these surveys were to determine the distribution and total escapement of kokanee in side channels and mainstem habitats of the Stehekin River.A probabilistic sample of suitable kokanee spawning habitat was used to estimate total kokanee escapement for all side channel habitat in the Stehekin River during 2000, and for all mainstem and side channel habitat in 2010. Expanded Stehekin River kokanee spawning surveys occurred on three occasions between September 12 and October 9, 2000 and on four occasions between August 30 and October 15, 2010. In the 2000 survey, 13 fish sample segment groups representing 6.2 km of the 19.8 km of suitable fish habitat (31.3%) were sampled. In 2010, 16 fish sample segment groups representing 3.4 km of 9.6 km of suitable fish habitat (35.4%) were sampled. Kokanee surveys were also conducted on six of twelve 500 m sections of the mainstem Stehekin River depositional zone habitat in 2010. Two surveyors worked in tandem; one on each side of the channel counting live and dead kokanee from the stream bank as they walked upstream.A total of 33,050 kokanee were counted in side channels during 2000 and 49,614 were counted in 2010. The majority of kokanee counted were located in the Blackberry and Company Creek side channel complexes and accounted for 84.8% (2000) and 91.4% (2010) of the total kokanee counts for all sampled side channel habitat. In 2010, a total of 27,872 kokanee were counted in mainstem sample segments with 53% of them observed in upstream sample reaches between river kilometers 9.5-15.0. Using Area-Under-the-Curve (AUC) methodology with a spawning fish residence time of 15 days, a total escapement of 120,447 was calculated for side channel habitat in 2000. Total escapement of kokanee during 2010 was estimated at 141,651 fish for side channel habitat and 53,812 for Stehekin River mainstem habitat. The total 2010 kokanee escapement for side channel and mainstem habitat combined was 195,463.

Stehekin River kokanee expanded spawning surveys, 2000 and 2010

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