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(Top panel) Map of Lake Chelan, Washington, USA, showing principal sampling sites (asterisks), and hydroacoustic transects (straight lines within Lake Chelan). (Bottom panel) Longitudinal depth profile of Lake Chelan shows the depth difference between lake basins. The horizontal axis represents the distance from lake outlet along the primary axis of the lake.
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In many food webs, species in similar trophic positions can interact either by competing for resources or boosting shared predators (apparent competition), but little is known about how the relative strengths of these interactions vary across environmental gradients. Introduced Mysis diluviana shrimp interact with planktivorous fishes such as kokan...
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... Chelan is a deep, glacially carved lake (maxi- mum depth 453 m) located in the Cascade Range in north-central Washington (488 N, 1208 W [ Fig. 2]). The lake is composed of two basins joined by a narrow channel. Wapato Basin is moderately deep and bowl- shaped (mean depth 43 m and maximum depth 122 m), while Lucerne Basin is extremely deep and steep-sided (see Plate 1, mean depth 180 m and maximum depth 453 m [ Kendra and Singleton 1987]). The lake is ultra- oligotrophic and ...
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... conducted standardized seasonal sampling from August 2004 through August 2006. We sampled water temperature, zooplankton, Mysis, and lake trout at five sites in the lake: two in Wapato Basin and three in Lucerne Basin (Fig. 2). We recorded surface water temperatures six times daily with temperature loggers (iBCod type Z, Alpha-Mach Incorporated, Ste-Julie, Quebec, Canada) deployed at 1 m depth near the midpoint of each basin. We collected vertical tempera- ture profiles seasonally with a Hydrolab Datasonde (Hach Environmental Incorporated, Loveland, Colora- ...
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... The annual mean density of kokanee was similar in both basins (0.1% less in Wapato Basin; 95% confidence interval: 43% less to 14% greater). Thus, kokanee abundance averaged 72% less (95% CI: 84-69% less) in the smaller Wapato Basin. Older kokanee migrated between basins seasonally, as indicated by reciprocal changes in abundance (Appendix B: Fig. B2). Many age- 1 and older kokanee moved into Wapato Basin during May and June, and many age-2 and older fish also used Wapato Basin during November. Greater abundances in Lucerne Basin during August were largely driven by kokanee aggregated near the mouth of the Stehekin River as maturing adults staged to spawn. Kokanee were distributed ...
Citations
... Alternatively, if establishment reflects strong selection and rapid adaptive evolution, genetic-environment association analyses would result in evidence for adaptive genomic divergence between populations occupying different environments independent of any neutral genetic divergence. shown Mysis to be impacted by water depth (Schoen et al., 2015), light (Boscarino et al., 2010), and temperature (Berrill & Lasenby, 1983;Dadswell, 1974;Degraeve & Reynolds, 1975) and exhibit poor tolerance to low oxygen environments (Horppila et al., 2003;Sherman et al., 1987). Furthermore, Mysis undergo a daily vertical migration from the bottom of the water column to the top at night to feed (Beeton & Bowers, 1982). ...
... It could be that the interaction between the number of stocking events, or local lake conditions such as lake depth (Schoen et al., 2015), light penetration (Boscarino et al., 2010), temperature (Berrill & Lasenby, 1983;Dadswell, 1974;Degraeve & Reynolds, 1975), or density of zooplankton prey (Caldwell & Wilhelm, 2012;Chess & Stanford, 1998) impact the overall population size and demographics of Mysis, which in turn could affect the effective population size (Waples, 2022). ...
The successes of introduced populations in novel habitats often provide powerful examples of evolution and adaptation. In the 1950s, opossum shrimp (Mysis diluviana) individuals from Clearwater Lake in Minnesota, USA were transported and introduced to Twin Lakes in Colorado, USA by fisheries managers to supplement food sources for trout. Mysis were subsequently introduced from Twin Lakes into numerous lakes throughout Colorado. Because managers kept detailed records of the timing of the introductions, we had the opportunity to test for evolutionary divergence within a known time interval. Here, we used reduced representation genomic data to investigate patterns of genetic diversity, test for genetic divergence between populations, and for evidence of adaptive evolution within the introduced populations in Colorado. We found very low levels of genetic diversity across all populations, with evidence for some genetic divergence between the Minnesota source population and the introduced populations in Colorado. There was little differentiation among the Colorado populations, consistent with the known provenance of a single founding population, with the exception of the population from Gross Reservoir, Colorado. Demographic modeling suggests that at least one undocumented introduction from an unknown source population hybridized with the population in Gross Reservoir. Despite the overall low genetic diversity we observed, FST outlier and environmental association analyses identified multiple loci exhibiting signatures of selection and adaptive variation related to elevation and lake depth. The success of introduced species is thought to be limited by genetic variation, but our results imply that populations with limited genetic variation can become established in a wide range of novel environments. From an applied perspective, the observed patterns of divergence between populations suggest that genetic analysis can be a useful forensic tool to determine likely sources of invasive species.
... We estimated the mean monthly density (organisms/L), standing stock biomass (MT, metric tonnes), and production (MT) of adult Epischura and Diaptomus based on the sample counts and volumes interpolated among sampling months, BLs, mean temperatures in each depth layer, and depth-specific estimates of lake volume to characterise the predominant food supply available to kokanee and Mysis Schoen et al., 2015;Sorel et al., 2016). ...
... A tow depth of 100 m or near the bottom was always well below the Mysis scattering layer as determined by a 200 kHz digital echosounder prior to each tow. We counted and measured the TL (mm) of all Mysis in each sample and calculated the corresponding density (number per m 2 ) based on the surface area of the net opening and assuming a 100% capture efficiency (Nero & Davies, 1982;Schoen et al., 2015). ...
... This result aligned with theoretical and empirical expectations for the relative strength of top-down versus bottom-up regulation of planktivorous fish in large, deep lakes (Schoen et al., 2015;Tessier & Woodruff, 2002), but is still partially dependent on the density of piscivorous lake trout. To that end, the high degree of cannibalism observed by lake trout and stable catch rates from fishing charter services suggest that the population may be self-regulating, despite the potential early feeding and survival benefits Mysis afford juvenile lake trout (Clarke et al., 2005;Ellis et al., 2011;Stafford et al., 2002). ...
A series of species introductions, overexploitation, and habitat modification preceded the extirpation of Lahontan cutthroat trout (Oncorhynchus clarkii henshawi; LCT), historically the apex predator, from Lake Tahoe, California-Nevada, USA. Studies evaluating limiting factors for LCT emphasise the need to elucidate food web interactions, yet important knowledge gaps regarding trophic interactions among nonnative pelagic fishes and invertebrates remain. We quantified the abundance and consumption demand of planktivores with an emphasis on kokanee (Oncorhynchus nerka) and Mysis diluviana. We synthesised this new information with existing information for lake trout (Salvelinus namaycush). The seasonal supply of copepods satisfied the consumption demand of kokanee, but only supported low feeding and growth rates. Kokanee relied heavily on Mysis as prey, an unusual result. Mysis exhibited a high degree of herbivory initially followed by heavier consumption on copepods by larger individuals. Consumption demand for Mysis on copepods exceeded that of kokanee during all seasons. Mysis contributed to over 50% of the annual energy budget for lake trout up to 625 mm. Consumption of Mysis by lake trout and kokanee represented a significant source of mortality when compared to the production of Mysis. Predation on kokanee was sustainable, only involved lake trout >625 mm, and was focused on prespawning aggregations. Despite the presence of Mysis-fueled lake trout, kokanee have persisted; a noteworthy pattern when considering the negative responses of kokanee to nonnative lake trout and Mysis observed elsewhere. This pattern suggests that there may still be an effective niche for LCT in the invaded Lake Tahoe ecosystem.
... The effects of planktivorous fish on M. diluviana are not shown for better visualization clarity. Reproduced from[10], c National Oceanic and Atmospheric Administration, P. Olsen, K. Hambright, with kind permission from John Wiley and Sons. ...
The previous chapters have focused on the direct effects of resource loss on consumers. From that perspective, co-extinction events occur (either locally or globally) whenever a consumer runs out of resources, such as in the case of a plant left with no pollinators, a parasite left with no hosts, or a predator left with no prey. However, such direct “bottom-up” effects might not be the only way diversity loss can trigger further extinctions. Indeed, top-down regulatory effects (such as, for example, how a predator affects indirectly plant diversity by modifying plant–herbivore interactions) can have significant consequences at the ecosystem level. Higher-order interactions, which occur when the (pairwise) interaction between two species is modulated by either a third species or by other interactions, might play a fundamental role in the emergence and maintenance of diversity in natural communities, as supported by theoretical and, to a lesser extent, empirical work. This poses the interesting question of whether (and to what degree) higher-order interactions can generate additional paths through which the effects of species loss can propagate across ecological systems in detrimental ways and possibly result in further extinctions. Simulations conducted on a simple multispecies population dynamics analytical framework suggest that higher-order interactions can substantially amplify primary extinctions and that higher-order co-extinctions might represent a fundamental, yet largely neglected, driver of global diversity loss.
... Predator impacts on prey populations can be strongly influenced by habitat characteristics and environmental conditions (Carey et al., 2012;Hein et al., 2014;Schoen et al., 2015). Of particular interest in the AYK region is whether habitat type and streamflow affect predation risk of juvenile Chinook salmon. ...
Predation on anadromous salmon can have important consequences for both predators and prey. Salmon provide large seasonal pulses of energy and nutrients via carcasses, eggs and juveniles to many freshwater consumers, and conversely, predation can represent a significant source of mortality for juvenile salmon. Recent declines of Chinook salmon (Oncorhynchus tshawytscha) populations in Alaska have raised concern that predation might inhibit their recovery. Here, we quantify patterns of predation by freshwater fishes on juvenile salmon across seasons, habitats, predator sizes and streamflow levels in the Arctic-Yukon-Kuskokwim region of Alaska. We analysed piscivore stomach contents and identified prey using DNA sequence “barcoding.” In coastal rivers, juvenile pink (O. gorbuscha) and chum (O. keta) salmon contributed heavily to Arctic grayling (Thymallus arcticus) and Dolly Varden char (Salvelinus malma) diets, coho salmon (O. kisutch) prey were rare, and Chinook salmon were not detected. In interior rivers, Arctic grayling, burbot (Lota lota) and northern pike (Esox lucius) consumed small numbers of Chinook salmon. Predation on Chinook salmon was documented disproportionately in sloughs during a summer of exceptionally high streamflow. Dietary and distributional patterns suggested northern pike and burbot may exclude salmon from sloughs in low-gradient river reaches that would otherwise provide suitable rearing habitat. The data also provided tentative support for the hypothesis that high streamflow induces juvenile Chinook salmon to move from mainstem habitats into sloughs, where they face an increased risk of mortality. Incorporating predation risk into climate adaptation, fisheries management and habitat restoration decisions may help to facilitate Chinook salmon recovery.
... However, we found the results plausible because they were based on ecological mechanisms that influence Chinook salmon populations in other regions (e.g., fall flooding: Greene et al., 2005; extreme temperatures: Richter & Kolmes, 2005). Furthermore, by integrating environmental indicators and productivity time series for 15 populations, we reduced the possibility of identifying spurious "false-positive" correlations (Mueter et al., 2002;Myers, 1998 In addition to its direct effects, climate can influence salmon populations indirectly via their food supply (Schindler, Rogers, Scheuerell, & Abrey, 2005), competitors (Schoen, Beauchamp, Buettner, & Overman, 2015), predators (Lawrence et al., 2014), and pathogens (Kocan, Hershberger, Sanders, & Winton, 2009). Our analysis did not include multi-species interactions due to a lack of time-series data, but we recognize they could have contributed to Chinook salmon population declines. ...
The ecosystems supporting Pacific salmon (Oncorhynchus spp.) are changing rapidly as a result of climate change and habitat alteration. Understanding how—and how consistently—salmon populations respond to changes at regional and watershed scales has major implications for fisheries management and habitat conservation. Chinook salmon (O. tshawytscha ) populations across Alaska have declined over the past decade, resulting in fisheries closures and prolonged impacts to local communities. These declines are associated with large‐scale climate drivers, but uncertainty remains about the role of local conditions (e.g., precipitation, streamflow, and stream temperature) that vary among the watersheds where salmon spawn and rear. We estimated the effects of these and other environmental indicators on the productivity of 15 Chinook salmon populations in the Cook Inlet basin, southcentral Alaska, using a hierarchical Bayesian stock‐recruitment model. Salmon spawning during 2003–2007 produced 57% fewer recruits than the previous long‐term average, leading to declines in adult returns beginning in 2008. These declines were explained in part by density dependence, with reduced population productivity following years of high spawning abundance. Across all populations, productivity declined with increased precipitation during the fall spawning and early incubation period and increased with above‐average precipitation during juvenile rearing. Above‐average stream temperatures during spawning and rearing had variable effects, with negative relationships in many warmer streams and positive relationships in some colder streams. Productivity was also associated with regional indices of streamflow and ocean conditions, with high variability among populations. The cumulative effects of adverse conditions in freshwater, including high spawning abundance, heavy fall rains, and hot, dry summers may have contributed to the recent population declines across the region. Identifying both coherent and differential responses to environmental change underscores the importance of targeted, watershed‐specific monitoring and conservation efforts for maintaining resilient salmon runs in a warming world.
... In this study, we modeled the direct effects of temperature on juvenile salmon growth; however, changes in temperature can also influence salmon indirectly through their prey (Schindler et al. 2005), competitors (Schoen et al. 2015), and predators (Lawrence et al. 2014). Although warmer temperatures appear to provide growth benefits for salmon in the Chena River, warming could also reduce salmon survival rates by allowing warm-adapted predators such as Northern Pike to expand their distribution upstream and enhance their consumption rates. ...
Climatic variation is a key driver of freshwater physical processes that in turn control stream fish growth and population dynamics at fine spatial scales and species distributions across broad landscapes. A recent downturn in Chinook Salmon Oncorhynchus tshawytscha returns across the Yukon River basin, Alaska, USA and Yukon Territories, Canada has led to hardship among user groups and increased interest in understanding how freshwater processes affect population persistence within this important commercial, recreational, and subsistence fishery. Here, we present results for the Chena River basin, interior Alaska, where we used field observations and riverscape-scale spatially explicit models to assess the influence of stream temperature on juvenile Chinook Salmon growth potential among years (2003-2015) and across 438 stream kilometers. We ran bioenergetic simulations for warm and cool year scenarios and contrasted temperature model precision and growth among different habitat types (small and large tributaries, main stem, and side channels) based on field estimates of growth, size, diet, and measured stream temperatures. Stream temperature regimes predicted from remotely sensed land surface temperatures were precise during the open water season (R^2 > 0.87; root-mean-squared error < 1.1°C), although the relationship was weakest in groundwater-mediated tributary habitats. Field observations revealed salmon were 67% larger by mass (g) in September during a warm year versus a cool year from main-stem sites. Bioenergetic simulations predicted that, on average, growth potential was 42% higher in warm years, although growth potential varied across the riverscape as much as 60% between cool upstream and warm downstream habitats. Climate variability is clearly an important driver of freshwater habitat conditions and has a large role in controlling freshwater growth of juvenile salmon. A better understanding of how climate influences growth conditions in different habitat types and across broad landscapes will be critical for conservation and management of Alaskan Chinook Salmon stocks under an expected warmer and more variable climate.
... Mysis establishment in the 1970s was likely the catalyst that led to an eventual increase in the lake trout population (i.e., Bowles et al., 1991;Stafford et al., 2002). Lake trout predation on Mysis is likely far less efficient in Lake Pend Oreille, as compared to shallower lakes, because steep-sided deep lakes provide profundal refuge for Mysis during daylight hours and more diffuse scattering during low-light conditions (Schoen et al., 2015). Nonetheless, as in other waters where they were introduced, Mysis are an important food source for juvenile lake trout in Lake Pend Oreille (Clarke et al., 2005), which increases survival (Stafford et al., 2002;Ng et al., 2017). ...
... We found that kokanee production was a densitydependent process and that the collapse of Mysis corresponded to a shift in the expression of that process. While we did not model the influence of environmental factors, which may influence interannual variability in the strength of competition between Mysis and kokanee (Schoen et al., 2015), our models nonetheless suggest Mysis are an influential driver of kokanee productive capacity in Lake Pend Oreille. The kokanee production-biomass relationship since 2011 illustrated the conditions required to sustain the extraordinary production that historically supported kokanee harvests exceeding one million fish annually in the 1950s and 1960s. ...
Research on Lake Pend Oreille, Idaho, has focused on the influence of two potential limiting factors for kokanee Oncorhynchus nerka (Walbaum, 1792): competition for food with Mysis diluviana (Loven, 1862, hereafter Mysis) and predation by lake trout Salvelinus namaycush (Walbaum, 1792). Population fluctuations of Mysis and lake trout have resulted in substantial heterogeneity in food web conditions, apparently altering both bottom-up and top-down dynamics. Therefore, relative importance of predation and competition were evaluated as drivers of kokanee abundance, biomass, and production. A series of general linear models was used to evaluate relative influences of Mysis and lake trout on kokanee. Kokanee production was a density-dependent process and the collapse of Mysis corresponded to an increase in the modeled maximum annual production of kokanee from 224 tonnes to 408 tonnes. Lake trout also negatively influenced kokanee biomass. A Mysis-mediated, predator-induced kokanee biomass collapse occurred when lake trout and Mysis abundances were both high. Sustainable management of this fishery requires recognition that competition with Mysis will define the scope of kokanee production and therefore the scope of sustainable predation.
... However, care should still be taken if applying to populations whose body form deviates largely from W s due to ecological conditions different from those in Blue Mesa Reservoir. For example, application to kokanee inhabiting lakes influenced by Sockeye Salmon(Beauchamp et al. 1995), that are ultraoligotrophic(Buktenica et al. 2007), or contain invasive Mysis diluviana(Schoen et al. 2015) could be less appropriate depending on how these factors influence growth, body condition, and fish girth. ...
Recent studies evaluating the size‐selectivity of standard horizontal benthic gill nets for some common sport fish have demonstrated congruence across regions and gear configurations. Studies evaluating retention in gill nets designed to sample pelagic‐oriented fish (e.g., vertical and curtain nets) are rare, which has limited corresponding assessments of generality. This study estimated the retention of kokanee Oncorhynchus nerka in multimesh vertical gill nets using catch data compiled over three decades from a large montane reservoir in Colorado. The corresponding best fit retention model was compared to that developed for kokanee in Idaho using multimesh curtain nets. There was strong congruence (Pearson's r = 0.98) between the total retention values (integrated over all mesh sizes) estimated by the two models for kokanee 50‐430 mm total length and the values followed a 1:1 relationship. This result indicated that the retention of fish in pelagic gill nets may also be largely conserved across regions and gear configurations. Thus, the retention models for kokanee compared in this study should be flexible and broadly applicable. These properties enable practitioners to easily adjust length‐frequency distributions for bias arising from size‐dependent retention when minimally biased estimates of size‐structure are needed for addressing management or research questions. This article is protected by copyright. All rights reserved.
... Mysis establishment in the 1970s was likely the catalyst that led to an eventual increase in the lake trout population (i.e., Bowles et al., 1991;Stafford et al., 2002). Lake trout predation on Mysis is likely far less efficient in Lake Pend Oreille, as compared to shallower lakes, because steep-sided deep lakes provide profundal refuge for Mysis during daylight hours and more diffuse scattering during low-light conditions (Schoen et al., 2015). Nonetheless, as in other waters where they were introduced, Mysis are an important food source for juvenile lake trout in Lake Pend Oreille (Clarke et al., 2005), which increases survival (Stafford et al., 2002;Ng et al., 2017). ...
... We found that kokanee production was a densitydependent process and that the collapse of Mysis corresponded to a shift in the expression of that process. While we did not model the influence of environmental factors, which may influence interannual variability in the strength of competition between Mysis and kokanee (Schoen et al., 2015), our models nonetheless suggest Mysis are an influential driver of kokanee productive capacity in Lake Pend Oreille. The kokanee production-biomass relationship since 2011 illustrated the conditions required to sustain the extraordinary production that historically supported kokanee harvests exceeding one million fish annually in the 1950s and 1960s. ...
Research on Lake Pend Oreille, Idaho, has focused on the influence of two potential limiting factors for kokanee Oncorhynchus nerka (Walbaum, 1792): competition for food with Mysis diluviana (Loven, 1862, hereafter Mysis) and predation by lake trout Salvelinus namaycush (Walbaum, 1792). Population fluctuations of Mysis and lake trout have resulted in substantial heterogeneity in food web conditions, apparently altering both bottom-up and top-down dynamics. Therefore, relative importance of predation and competition were evaluated as drivers of kokanee abundance, biomass, and production. A series of general linear models was used to evaluate relative influences of Mysis and lake trout on kokanee. Kokanee production was a density-dependent process and the collapse of Mysis corresponded to an increase in the modeled maximum annual production of kokanee from 224 tonnes to 408 tonnes. Lake trout also negatively influenced kokanee biomass. A Mysis-mediated, predator-induced kokanee biomass collapse occurred when lake trout and Mysis abundances were both high. Sustainable management of this fishery requires recognition that competition with Mysis will define the scope of kokanee production and therefore the scope of sustainable predation.
... Assessing the indirect effects of Yellow Perch within the BMR food web was outside the scope of this study. However, indirect effects are important considerations for assessing the full threat of introduced species and may manifest in complex ways (Schoen et al. 2015). For example, Lake Trout now consume notable fractions of Yellow Perch during spring and autumn in BMR (Pate et al. 2014;B. ...
