Kootenay Lake kokanee (<i>Oncorhynchus nerka</i>) collapse into a predator pit

Warnock, Will G.; Thorley, Joe; Arndt, Steven K. A.; Weir, Tyler J; Neufeld, Matthew D.; Burrows, Jeff A.; Andrusak, Greg

doi:10.1139/cjfas-2020-0410

Cited by 4 publications

(10 citation statements)

References 60 publications

(10 reference statements)

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“…Effective conservation and management strategies require an understanding of population trends, genetic structure, and mechanisms influencing compensatory responses (Andrusak et al 2000;Askey 2016). Ill-informed management decisions could result in unexpected or unanticipated consequences (Peck et al 2019;Bassett et al 2020;Warnock et al 2021). For instance, fish populations that are locally adapted to a region could be eradicated through genetic introgression (Veale and Russello 2016), intrapopulation competition (Crowder 1984), densityrelated predation pits (Warnock et al 2021), or through the degradation of key spawning habitats (Frazer and Russello 2013).…”

Section: Prologuementioning

confidence: 99%

“…Ill-informed management decisions could result in unexpected or unanticipated consequences (Peck et al 2019;Bassett et al 2020;Warnock et al 2021). For instance, fish populations that are locally adapted to a region could be eradicated through genetic introgression (Veale and Russello 2016), intrapopulation competition (Crowder 1984), densityrelated predation pits (Warnock et al 2021), or through the degradation of key spawning habitats (Frazer and Russello 2013). Rather than adopting broad or static regulations, as is typical of traditional fisheries systems, care should be taken to consider locally-adapted subpopulations when implementing management strategies at the watershed level (Taylor et al 2000;Askey 2016).…”

Section: Prologuementioning

confidence: 99%

“…Two long-term British Columbia nutrient restoration programs, in Kootenay Lake (since 1992) and in the Upper and Lower Arrow Lakes Reservoir (since 1999), have resulted in abundant zooplankton resources and entirely different compensatory growth responses. In the Kootenay Lake system, the Kokanee that survived to sexual maturity in recent years reached record sizes (>36 cm), but the overall population remained in a state of nearcollapse due to intensive top-down predation from piscivorous species (Peck et al 2019;Warnock et al 2021). Density-dependent growth responses in the form of larger sizes at maturity were apparent, but also coincided with a shift to later maturation (age 4 spawners) rather than the predicted rapid growth and age 2 spawners (Peck et al 2019).…”

Section: Factors Affecting Growthmentioning

confidence: 99%

“…Askey 2016), and highlighted the remarkable habitat plasticity that has allowed Kokanee to repeatedly colonize regions in a pattern of parallel adaptive radiation since the last glaciation period (Wood et al 1994;Taylor et al 1996;Beacham and Withler 2017). Understanding the degree to which native and introduced Kokanee populations have responded to changes in fish density and the addition of exogenous stocks is crucial for effective fisheries management at a time when many populations of Kokanee in British Columbia are experiencing human-related population declines or outright collapse (Askey and Johnston 2013;Taylor et al 2014;Peck et al 2019;Bassett et al 2020;Grant et al 2021;Warnock et al 2021).…”

Section: Epiloguementioning

confidence: 99%

“…and Bull Trout (Salvelinus confluentus) has kept the Kokanee population in a state of collapse (Peck et al 2019;Warnock et al 2021). It has been theorized that favorable nutrient and rearing conditions elevated the Kokanee population past the carrying capacity of the Kootenay Lake system (Warnock et al 2021). Okanagan Lake and Wood Lake in the south-central region of B.C.…”

Section: Epiloguementioning

confidence: 99%

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Extirpation of a native population following a stocking program: genetic population structure and demographics of kokanee (Oncorhynchus nerka) in a large impounded watershed

Wilson¹

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Kokanee, the non-anadromous life history form of Oncorhynchus nerka, use lacustrine habitat in watersheds draining into the north Pacific Ocean. Kokanee have also been widely introduced into reservoirs following impoundment of rivers due to the construction of dams. Locally-adapted subpopulations of Kokanee, however, should be identified and evaluated when implementing watershed-level management strategies. In Chapter 1, I examined fork length, condition factor, and age at maturity for Kokanee in the Williston watershed of northern British Columbia to identify potential spatial and temporal trends in demographic structure following a large-scale stocking program that occurred in the 1990s. Adult spawning Kokanee that were native to the reservoir and collected prior to stocking events were significantly larger and maintained higher condition factors than Kokanee stocked from the Columbia River sampled in any year after 1991. Introduced Kokanee sampled in 2018 and 2019 were the smallest spawners and were significantly smaller than all fish collected between 1989 and 2018; the condition factors of these fish were also significantly lower than native Kokanee and the first spawning cohorts of Columbia-origin fish. The average age at maturity did not change across spatial or temporal scales (3 yrs.). My results indicate an ongoing trend of decreasing spawner size and condition factor for Kokanee in the Williston Reservoir since introduction events in the early 1990s. In Chapter 2, I analyzed the genetic population structure of Kokanee in the Williston watershed, including from the reservoir before stocking Columbia-origin fish and native populations from headwaters of the Williston Reservoir: Thutade, Arctic, and Tacheeda Lakes. Using microsatellite markers, I identified that all fish collected from 2006 to 2019 were introduced Columbia-origin genotypes, and there was no evidence of genetic divergence by spawning location. Native populations in Arctic and Tacheeda Lakes remained entirely separate from the reservoir populations, and there was no indication of past or current introgression with introduced stock. I identified that native Williston Reservoir Kokanee diverged from the Thutade Lake population; as native Williston fish have not been sampled since 2000, it is likely that this population has been extirpated in the reservoir by the successful Columbia-origin lineage. My results highlight an unfortunate consequence of underinformed management practices that failed to recognize the native Williston Kokanee as a distinct population. Strategies that incorporate knowledge of subpopulations of Williston watershed Kokanee, such as genetic populations or reproductive ecotypes, should be prioritized to conserve locally-adapted genetic diversity.

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Section: Prologuementioning

confidence: 99%

Section: Prologuementioning

confidence: 99%

Section: Factors Affecting Growthmentioning

confidence: 99%

Section: Epiloguementioning

confidence: 99%

Section: Epiloguementioning

confidence: 99%

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Extirpation of a native population following a stocking program: genetic population structure and demographics of kokanee (Oncorhynchus nerka) in a large impounded watershed

Wilson¹

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Genetic population structure of introduced and native lineages of kokanee in a large impounded watershed

Breault,

Wetklo,

Langston

et al. 2023

Trans Am Fish Soc

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Kokanee, the non‐anadromous life‐history form of Oncorhynchus nerka, use lacustrine habitat in watersheds draining into the north Pacific Ocean. Kokanee also have been widely introduced into reservoirs following impoundment of rivers consequent to the construction of hydroelectric dams. Genetically divergent subpopulations of Kokanee should be identified and evaluated when implementing watershed‐level fishery management strategies. We analyzed the genetic population structure of Kokanee in the Williston watershed, north‐central British Columbia, where native populations were present in the reservoir and headwater lakes prior to stocking Columbia River‐origin fish in the 1990s. Using microsatellite markers, we determined that native Williston Reservoir Kokanee were divergent from only one of the headwater lake populations. Native populations in headwater lakes remain entirely separate from the reservoir populations, and there was no indication of past or current introgression with the introduced stock. We identified all fish collected from 2006 to 2019 as introduced Columbia River‐origin genotypes, and there was no evidence of genetic divergence by spawning location. As native Williston Kokanee have not been sampled from the reservoir in survey efforts since 2000, it is likely that this population has been extirpated from the reservoir perhaps through competition with the introduced Columbia River‐origin lineage.

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Predation of Atlantic salmon across ontogenetic stages and impacts on populations

Falkegård

Lennox

Thorstad

et al. 2023

Can. J. Fish. Aquat. Sci.

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Managers and stakeholders increasingly ask whether predation is a driving force behind the poor status of many species, and whether predator control is likely to be a successful management action to intervene. We review existing literature on Atlantic salmon Salmo salar predation and predator control, as well as general ecological theory on the role of predation in the life cycle of this iconic fish. Many bird, mammal, and fish predators target salmon at different life stages. In healthy salmon populations, predation is likely compensated for by reduced intra-specific competition during the freshwater stage. There is little evidence that predation alone has been an underlying mechanism for driving salmon populations below conservation limits. However, depending on the predator’s response to salmon abundance, predation may keep decimated populations from recovering, even when the actual causes of decline have been removed. Under such a scenario, predation control may contribute to recovery, but there are no strong examples that clearly demonstrate the efficacy of managing predators to recover threatened salmon populations, challenging further applications.

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Kootenay Lake kokanee (Oncorhynchus nerka) collapse into a predator pit

Cited by 4 publications

References 60 publications

Extirpation of a native population following a stocking program: genetic population structure and demographics of kokanee (Oncorhynchus nerka) in a large impounded watershed

Extirpation of a native population following a stocking program: genetic population structure and demographics of kokanee (Oncorhynchus nerka) in a large impounded watershed

Genetic population structure of introduced and native lineages of kokanee in a large impounded watershed

Predation of Atlantic salmon across ontogenetic stages and impacts on populations

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