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Report: Summary of Quesnel Lake Kokanee and Rainbow Trout Biology With Reference to Sockeye Salmon 00431QUES
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All available data on Quesnel Lake kokanee and rainbow trout are summarized to provide an updated assessment of the status of the lakes populations. It was concluded that recent increases in the numbers of sockeye and concurrent declines in abundance of kokanee may be the primary cause of declining size and size-atage of the Quesnel Lake rainbow trout.
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Author: Sebastian, D.; Dolighan, R.; Andrusak, H.; Hume, J.; Woodruff, P.; Scholten, G.
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Date Published: Jan 2003
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Report ID: 11874
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Audience: Government and Public
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All available data on Quesnel Lake kokanee and rainbow trout are summarized to provide an updated assessment of the status of the lakes populations. Kokanee data suggests there are two distinct populations that may well be reproductively isolated.----- Studies on kokanee in the 1950s and 1960s by the International Pacific Salmon Fisheries Commission (IPSFC) focused on the hypothesis that kokanee competed with sockeye juveniles for food and were the cause of cyclical dominance in Quesnel lake sockeye. This work concluded that kokanee did not compete for food, interspecific competition was not a factor causing cyclical dominance and some data indicated that large sockeye numbers could adversely impact kokanee. ----- There is evidence from the hydroacoustic and trawl survey data that suggests a decline in total numbers of kokanee during the 1990s and early 2000s. The total kokanee population in the 2000s has been estimated at only 1.5-2.2 million compared with 3.5 million in the early 1990s. In sharp contrast, the Quesnel Lake sockeye population has increased dramatically during the last decade with annual acoustic estimates ranging from 4-65 million fry.------ It is speculated that the decline in kokanee is in response to increased competition for food due to significantly increased numbers of sockeye fry. There is no evidence that kokanee spawning habitat has deteriorated to any degree to account for the decline in numbers. It is further speculated that the stream spawning component has declined while the shore spawners have not because stream spawner progeny emerge much later than sockeye fry and shore spawning kokanee fry.------Rainbow trout spawn in the Horsefly and Mitchell rivers with the former system appearing to support the largest numbers. While these trout reside in the lake for most of their adult life some also undertake migrations into Summary of Quesnel Lake kokanee and rainbow biology page i the two rivers to feed on emerging sockeye fry in the spring and on eggs later in the summer and early fall.----- A decrease in the average size of spawners may have been in part due to some over fishing in the past, however recent age analyses indicates that not only size but rainbow growth rates have declined over the past decade. Stomach sampling confirmed that their primary food source is age 1-3 kokanee which have been declining in numbers over the same period. Diet analysis showed that as the numbers of sockeye fry increased following dominant and subdominant (i.e. high) return years, the numbers of age 1 and 2 kokanee eaten declined and the total biomass of O. nerka consumed (per stomach) declined by up to 70%.It follows then that recent increases in the numbers of sockeye and concurrent declines in abundance of kokanee may be the primary cause of declining size and size-atage of the Quesnel Lake rainbow trout. Recommendations for further study include continuation of the annual kokanee trawl and acoustics survey in cooperation with DFO.
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Report Type
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Fish and Aquatic Habitat Information |
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Subject
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Fish Species - Coho Salmon - Oncorhynchus kisutch |
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Fish Species - Kokanee - Oncorhynchus nerka |
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Fish Species - Rainbow Trout - Oncorhynchus mykiss |
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Region - Cariboo |
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Fish and Fish Habitat - Lake |
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Fish and Fish Habitat - Stock Assessment |
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Watershed Groups - 160 - Quesnel |
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