Hydrological drought and the role of refugia in an endangered riffle-dwelling fish, Nooksack dace (Rhinichthys cataractae ssp.)

ArticleinCanadian Journal of Fisheries and Aquatic Sciences 71(11):1625-1634 · June 2014with 371 Reads
Abstract
Understanding the impacts of hydrological drought, and the role that refugia play in mitigating these impacts, is crucial to the conservation of freshwater fishes. This is especially true for species adapted to riffles, which are typically the first habitats to dewater at low discharge. We examined the relationship among decreasing stream discharge, abundance, and habitat use for Nooksack dace (Rhinichthys cataractae ssp.), an endangered riffle-dwelling species. A complementary experimental manipulation examined the effects of flow on growth rate across a discharge gradient in riffle and pool habitats. We found that low-velocity habitats and decreased discharge in experimental channels result in reduced dace growth and that decreasing stream flow was coincident with declines in Nooksack dace abundance. This study demonstrates the sensitivity of Nooksack dace to hydrological drought, and insofar as Nooksack dace are ecologically typical of small riffle-dwelling invertivore fishes, our results suggest that use of pools does not mitigate sublethal effects of declining flows on growth, although pools may provide refuge from the most negative effects of drought (i.e., stranding of fish).

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  • ... The flow regime is driven by direct precipitation, and stream discharge lags precipitation by a few days, with minimum flows occurring in August, shortly after the minimum precipitation in July and August (Berg and Allen 2007). The streams provide habitat for salmon and two fish species listed as endangered in Canada, the Nooksack Dace and the Salish Sucker (Pearson 2004), and summer low flows have threatened fish populations through loss of habitat, increased predation and decreased water quality (Avery-Gomm et al. 2014). These streams have been identified as having potentially variable interaction with groundwater both between them and along their lengths (Johanson 1988; Starzyk 2012). ...
    ... August (Berg and Allen 2007). The streams provide habitat for salmon and two fish species listed 166 as endangered in Canada, the Nooksack Dace and the Salish Sucker (Pearson 2004), and summer 167 low flows have threatened fish populations through loss of habitat, increased predation, and 168 decreased water quality (Avery-Gomm et al. 2014). These streams have been identified as having 169 potentially variable interaction with groundwater both between them, and along their lengths 170 (Johanson 1988; Starzyk 2012). ...
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  • ... During extreme low flows, shoals can contract substantially and population responses will depend on a species' ability to cope with environmental and biotic stressors associated with flow reductions (Davey et al. 2006 ). Fluvialdependent fishes that become concentrated in these diminished shoal habitats may experience increased stress and mortality caused by elevated stream temperatures, competition, and predation (Magoulick and Kobza 2003; Avery-Gomm et al. 2014 ). Consequently , fish may disperse (Albanese et al. 2004) or move into deeper-water refugial habitats (Magoulick and Kobza 2003; Roberts and Angermeier 2007) where survival depends on refuge quality. ...
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  • ... Effects of higher summer flow on growth and survival of non-salmonids tends to be poorly documented, and may range from positive (e.g. Avery-Gomm, Rosenfeld, Richardson, & Pearson, 2014) to negative ( Katz & Freeman, 2015). Notwithstanding the predictive value of flow-related changes in individual growth and survival, population change remain the definitive measure of biological response to altered flow ( Rosenfeld et al., 2016;Shenton, Bond, Yen, & Mac, 2012). ...
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    Flow alterations caused by reservoir storage, groundwater pumping, diversions, and drought are widespread in North American Great Plains streams and have altered and fragmented habitats and reduced native fish biodiversity. Early life stages of fish are particularly sensitive to altered flow regimes, and reduced growth and survival may negatively affect the persistence of native species and assemblages. We investigated how growth and survival of brassy minnow Hybognathus hankinsoni larvae in the Arikaree River, Colorado, varied among three 6.4-km river segments that differed in hydrology and how climate influenced drying rates of spawning and rearing habitats in these segments over 3 years. We found that brassy minnow spawned in backwater habitats within a discrete period from mid-April to late May, based on otolith increment analysis. The timing of spawning and growth of larvae were influenced by climate and the hydrologic context of the river segment. Brassy minnow spawned 2 weeks earlier under warm, dry conditions in 1 year, and both growth rates and survival were significantly lower than during two wetter years (growth: 0.25 mm/d versus 0.30 and 0.41 mm/d; survival: 0.8391/d versus 0.894 and 0.897/d). For cohorts of larvae in individual backwaters, survival was higher in spawning habitats that were larger and that dried more slowly, and among cohorts that hatched in the middle of the spawning period under a moderate thermal regime. Overall, we found that brassy minnow spawning and recruitment were strongly influenced by habitat drying driven by interactions among stream geomorphology, groundwater pumping, and climate across multiple spatial scales. We suggest that conservation efforts explicitly consider the adaptations of this fish to harsh environments and focus on providing flows to maintain the spawning, rearing, and refuge habitats that are critical to brassy minnow population persistence.
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    Accurate low flow measurements are important in groundwater-fed streams in order to assess in-stream flow requirements and the nature of stream interactions with groundwater, as well as the potential impacts of climate variability and climate change. Variability in stream discharge was measured over the low flow season in Bertrand Creek, Pepin Brook and Fishtrap Creek, which drain the Abbotsford-Sumas aquifer in southwest British Columbia and northwest Washington State. Discharge was measured to quantify variability: (1) along the length of the stream and relate those variations to differing groundwater contributions over the low flow season, and (2) across a series of cross-sections, both repeating across a middle cross-section (at-a-station measurements) and along consecutive sections from upstream to downstream (downstream measurements), to assess the repeatability of the low flow measurements. Downstream increases in discharge in Fishtrap Creek and Pepin Brook are attributed to groundwater discharging into the channels along these sections, as supported by lower dissolved oxygen concentrations and stable water temperatures. Along Bertrand Creek, stream water interaction with groundwater appears to be variable, with the stream recharging the aquifer along some reaches, and discharging in others. Over the summer season, discharge decreased in all streams; on average the decrease was in the range 0.01 to 0.05 m3/s. As the flow decreased, the coefficient of variation of the mean discharge tended to increase when the flow was very low (i.e., <0.1 m3/s), although the trends for Fishtrap were weak. Overall, the variations in measured discharge are of sufficient magnitude that subtle changes in streamflow caused by some real effect may be difficult to detect.
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    The distribution, abundance, and habitat associations of juvenile anadromous coastal cutthroat trout (Oncorhynchus clarki) and coho salmon (Oncorhynchus kisutch) were evaluated using survey data from 119 sites in coastal British Columbia. Both cutthroat and coho occurred at their highest densities in very small streams (< 5 m channel width), and bankfull channel width was the single best predictor of cutthroat presence ( p = 0.0001) and density (R 2 = 0.55). Within a channel, densities of coho and larger (yearling and older) cutthroat parr were highest in pools, while densities of young-of-the-year cutthroat were significantly lower in pools and highest in shallower habitats. Abundance of larger cutthroat parr and pool habitat were positively correlated with large woody debris (LWD) within a subset of intermediate-gradient gravel-cobble streams, where pools appear to be limiting to larger cutthroat parr abun - dance. More than 50% of pools were formed by scour associated with LWD in streams ranging from 1.2 to 11 m channel width, and pools formed by LWD scour were on average 10% deeper than pools formed by other mechanisms. Disproportionate use of small streams by cutthroat indicates that protection of small stream habitat is important for long-term conservation of sea-run populations.
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    The American Fisheries Society herein provides an update of their now decade-old list of rare North American fishes. The 1989 list adds 139 new taxa to the list developed by Deacon et al. (1979) of 251 fishes and removes 26 for a total of 364 fishes in Canada, United States, and Mexico that warrant protection because of their rarity. The 26 taxa removed from the 1979 list include 16 removed because of better information on their taxonomy or status and 10 because they have become extinct. Not a single fish warranted removal from the list because of successful recovery efforts. In addition, 49 fishes have changed in status but remain on the list: 7 have improved in status, 24 have declined, and 18 have been reclassified because new information revealed that they were either more common or rarer than was earlier believed and, therefore, were incorrectly classified in 1979. Comparison of the 1979 and 1989 lists indicates that recovery efforts have been locally effective for some species, but are clearly lagging behind deterioration of the overall fish fauna. The health of aquatic habitats in North America continues to decay. A major commitment to conservation of entire ecosystems, rather than the inconsistent recovery efforts for individual species, is needed to reverse this trend.
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    abstract: This is the third compilation of imperiled (i.e., endangered, threatened, vulnerable) plus extinct freshwater and diadromous fishes of North America prepared by the American Fisheries Society's Endangered Species Committee. Since the last revision in 1989, imperilment of inland fishes has increased substantially. This list includes 700 extant taxa representing 133 genera and 36 families, a 92% increase over the 364 listed in 1989. The increase reflects the addition of distinct populations, previously non-imperiled fishes, and recently described or discovered taxa. Approximately 39% of described fish species of the continent are imperiled. There are 230 vulnerable, 190 threatened, and 280 endangered extant taxa, and 61 taxa presumed extinct or extirpated from nature. Of those that were imperiled in 1989, most (89%) are the same or worse in conservation status; only 6% have improved in status, and 5% were delisted for various reasons. Habitat degradation and nonindigenous species are the main threats to at-risk fishes, many of which are restricted to small ranges. Documenting the diversity and status of rare fishes is a critical step in identifying and implementing appropriate actions necessary for their protection and management.
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    Individual variability in body size provides a template for selective mortality processes during early life history stages of teleost fishes. This size variability has generated the logically intuitive hypothesis that larger or faster growing members of a cohort gain a survival advantage over smaller conspecifics via enhanced resistance to starvation, decreased vulnerability to predators, and better tolerance of environmental extremes. This review evaluates field and laboratory studies that have examined size-based differences in survival, with emphasis on the juvenile stage of teleost fishes. The results in general support the "bigger is better" hypothesis, although a number of examples indicate non-selective mortality with no obvious size advantages. The reverse pattern, with enhanced survival of smaller individuals, is rare with the notable exception of bird predation. Major size-selective processes during the juvenile stage include overwinter mortality for temperate species, associated with either starvation or intolerance of physical extremes by smaller members of the young-of-the-year cohort, and predation, with smaller fish more susceptible to successful capture by predators. Most studies examining these processes have used indirect methods to evaluate size-selective mortality, with interpretation of results dependent on several critical assumptions. For methods that track size distributions over time, unbiased samples collected from the same population are critical, and changes in size distributions associated with mortality must be distinguished from changes due to individual growth. The latter requirement can be met with the direct, "characteristics of survivors" method, but few studies have used this approach. Experimental methods isolating specific mechanisms of size-specific mortality must appropriately represent the natural context of environmental factors. Specific predator/prey combinations, for example, can elucidate size-based prey preferences but may be irrelevant compared to the natural, multi-species predator field. The composition of the predator field and its correspondence to size-spectrum theory is crucial to the probability of size-selective predation as a cohort progresses through the juvenile stage. Distinction of selection on body size vs. selection on growth rate has received little attention. However, a number of physiological constraints and ecological trade-offs can place restrictions on growth rates and apparently override the advantages of large body size. Identifying the major sources of mortality and how they operate in the juvenile stage has valuable applications in understanding population dynamics and recruitment variability.
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    Reductions in river discharge (water availability) like those from climate change or increased water withdrawal, reduce freshwater biodiversity. We combined two scenarios from the Intergovernmental Panel for Climate Change with a global hydrological model to build global scenarios of future losses in river discharge from climate change and increased water withdrawal. Applying these results to known relationships between fish species and discharge, we build scenarios of losses (at equilibrium) of riverine fish richness. In rivers with reduced discharge, up to 75% (quartile range 4–22%) of local fish biodiversity would be headed toward extinction by 2070 because of combined changes in climate and water consumption. Fish loss in the scenarios fell disproportionately on poor countries. Reductions in water consumption could prevent many of the extinctions in these scenarios.
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    Summary We evaluate the position of 50 previously published studies of fish and drought with respect to spatial scale of study (individual stream pools to subcontinents), length of the dry period (weeks to centuries), and level of system complexity (individual fish to ecosystems). Most papers address short (months to a year) droughts or dry periods, in local reaches of streams, and impacts on populations or local assemblages. In these 50 papers, the most frequently demonstrated effects of drought were population declines, loss of habitat, changes in the community, negative effects from changes in water quality, movement within catchments, and crowding of fish in reduced microhabitats. Thirteen other less frequent effects also were identified. Gaps in knowledge exist on effects of long-term droughts (decades to centuries), influence of drought on fish effects in ecosystems, and at the spatial scale of river basins to subcontinents. However, some of these gaps have recently been addressed, particularly additive effects of repeated drying episodes and whole-lake or basin-wide effects of drought, and in using molecular techniques to seek signals of drought at wide geographic scales because of events in the deep past. Gaps in knowledge remain for effects of very short dry periods, on drought effects on higher levels of complexity, and on the manner in which droughts at the scale of decades affect fish. Data from streams in Oklahoma and elsewhere in the south-western U.S.A. suggest that most droughts may leave little persistent signal in the existing fish fauna, i.e. that recovery from drought by fish populations or assemblages in the region can be rapid. However, species that are vulnerable to drought or water loss in streams may have disappeared from some basins in the region before the mid-1900s, and recent evidence also suggests that extreme droughts do sometimes alter fish assemblages. Little is known about mechanisms by which droughts have direct or indirect effects on fish, the roles of droughts in the evolution of fish species, and the ways droughts alter effects of fish in ecosystems. Global climate changes may have serious consequences for future local or regional fish faunas, but ongoing studies of fish experiencing drought may aid in future conservation of what will become species at risk under climate-change scenarios.