Open Collections

Gray, John

University of British Columbia

Nooksack dace (Rhinichthys cataractae sp. cataractae) are a federally endangered riffle specialist with a limited distribution in the lower Fraser Valley of British Columbia, Canada. Population declines have been associated with the loss and degradation of riffle habitat from stream dredging, channelization, and excessive sediment inputs. However, dace abundance may be further impacted by temporal and spatial variation in juvenile recruitment associated with deteriorating water quality and the degradation of rearing habitat. To assess the effectiveness of restoring riffle habitat as a recovery strategy for Nooksack dace, I constructed gravel and cobble riffles on two replicate tributaries of the Nooksack River as described in my second thesis chapter. In my third chapter, I report the results of visual field surveys and in-stream enclosure experiments designed to identify the factors driving variation in young-of-the-year dace recruitment. Dace abundance increased significantly within cobble addition treatment riffles but not in gravel addition treatment riffles, relative to unaltered control riffles, indicating that riffle habitat restoration has the potential to be an effective recovery strategy to increase dace abundance. Increasing dace abundance within riffle habitat restored with cobble substrate appeared to be associated with the increased availability of interstitial refuges large enough to be exploited by dace, rather than substrate effects on invertebrate prey abundance, suggesting that interstitial refuges may limit adult dace abundance. My results also indicate that juvenile growth rates increase with water temperature and that low juvenile recruitment is associated with the encroachment of invasive reed canarygrass, which is implicated in the loss of the shallow marginal bar habitat preferred by post-hatch fish. Together the results from these chapters fill key knowledge gaps in the biology of Nooksack dace that will directly inform management and conservation priorities.

Text

2023-10-19

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86230

Oceans and Fisheries

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/