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In this study we use stable isotope analysis of lake sediments to investigate the historic presence
of anadromous salmonids in the Ash River watershed. Our objectives were to assess whether anadromous salmonids were historically present above Elsie Dam, whether presence or absence was correlated with timing of dam construction, and whether flow regulation has influenced downstream distribution ofanadromous salmonids. We use a recently developed model to place bounds on escapements to each lake.
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Author: Hatfield, T.; Solander Ecological Research
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Old Reference Number: 06.Ash.04
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Old Reference System: FWCP Fish Wildlife Compensation Program - Coastal
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Date Published: Oct 2007
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Report ID: 40970
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Audience: Government and Public
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We used stable isotope analysis of lake sediments in conjunction with radioisotope dating techniques to help resolve an ongoing controversy regarding presence of anadromous salmonids prior to hydropower development in the Ash River watershed, British Columbia. Profundal sediments were sampled from Elsie and Oshinow Lakes, upstream of Elsie Dam, Dickson and McLaughlin Lakes, downstream of the dam, and Nahmint and Nimnim Lakes, which are outside the Ash River watershed but nearby. Reductions in ∂15N are apparent in Elsie, Oshinow and McLaughlin Lakes and are approximately coincident with hydropower
development in the Ash watershed. There is a hint of a similar trend in Dickson Lake, and trends in Nimnim and Nahmint Lakes do not appear to be correlated with timing of hydropower development. Statistical comparisons of ∂15N concentrations in sediment samples
prior to vs. after the year of dam formation indicate statistically significant declines of 15N in Elsie, Oshinow and McLaughlin Lakes. Using a model to estimate escapement, Oshinow and Dickson Lakes both show lower levels of escapement after dam formation. In Oshinow this change is very dramatic, falling from escapements that were commonly 500 to 1100 fish, to 60 or fewer fish. Pre-dam escapements for Dickson Lake are occasionally above 100 fish, while postdam records are usually below 50 fish. Inferred escapement for Elsie Lake suggests that predam abundance was commonly higher than 400 fish and up to almost 900 fish. Post-dam escapements for Elsie Lake are likely to be confounded by the direct effects of damming.
Nahmint, Nimnim and McLaughlin Lakes show relatively little change in escapement over time. Based on salmonid life histories and migration patterns in nearby watersheds, the most likely candidates for species that accessed lakes in the Ash watershed are steelhead, coho, chinook and possibly sockeye. Pacific lamprey are also known to have ascended the Ash watershed prior to hydropower development. Our results support the hypothesis of a loss of anadromous salmon production from the Ash River system as a result of dam construction and operation. Alternate hypotheses are discussed and rejected.
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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 - Salmon (General) - Oncorhynchus spp. |
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Region - Vancouver Island |
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Fish and Fish Habitat - Habitat and Stream Assessment |
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Fish and Fish Habitat - Management |
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Fish and Fish Habitat - Research |
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Watershed Groups - 930 - Vancouver Island (West) Rivers |
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Water Information - Storage Inventory -Lakes and Reservoirs |
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