Native Cutthroat Trout Oncorhynchus Clarkii Research Articles

Evaluating a Permeable‐Style Fish Barrier to Prevent the Upstream Recolonization of Nonnative Trout during an Eradication Project

AbstractIn the western United States, the introduction of nonnative Brook Trout Salvelinus fontinalis has had deleterious effects on native Cutthroat Trout Oncorhynchus clarkii subspecies, and often their populations must be controlled or removed if Cutthroat Trout are to persist. Man‐made fish migration barriers are integral components of stream restoration projects, and typical designs are intended to be permanent and to funnel water over a drop and onto a splash pad. The water elevation drop and the splash pad, which prevents a jumping pool, are mechanisms intended to prevent fish from navigating upstream past the structure. In this study, we installed a temporary, permeable‐style barrier that was designed to have water flow onto and through a horizontal, expanded steel panel. When fish attempted to move upstream, they would follow the water flow and end up underneath the barrier, with no opportunity to move further. The permeable barrier proved effective in preventing the upstream movement of Brook Trout, and additional advantages to this barrier style included straightforward permitting, low cost, ease of installation, and quick removal. The main disadvantage was the periodic cleaning (average of 7 trips/year) that was required to maintain its intended function. The permeable barrier separated stream reaches for 5 years, allowing biologists to (1) eradicate Brook Trout upstream through multiple‐pass backpack electrofishing while preserving native Yellowstone Cutthroat Trout O. clarkii bouvieri and (2) apply a successful piscicide treatment below the barrier.

Patterns of Hybridization of Nonnative Cutthroat Trout and Hatchery Rainbow Trout with Native Redband Trout in the Boise River, Idaho

AbstractHybridization is one of the greatest threats to native fishes. Threats from hybridization are particularly important for native trout species as stocking of nonnative trout has been widespread within the ranges of native species, thus increasing the potential for hybridization. While many studies have documented hybridization between native cutthroat trout Oncorhynchus clarkii and nonnative rainbow trout O. mykiss, fewer have focused on this issue in native rainbow trout despite widespread threats from introductions of both nonnative cutthroat trout and hatchery rainbow trout. Here, we describe the current genetic (i.e., hybridization) status of native redband trout O. mykiss gairdneri populations in the upper Boise River, Idaho. Interspecific hybridization was widespread (detected at 14 of the 41 sampled locations), but high levels of hybridization between nonnative cutthroat trout and redband trout were detected in only a few streams. Intraspecific hybridization was considerably more widespread (almost 40% of sampled locations), and several local populations of native redband trout have been almost completely replaced with hatchery coastal rainbow trout O. mykiss irideus; other populations exist as hybrid swarms, some are in the process of being actively invaded, and some are maintaining genetic characteristics of native populations. The persistence of some redband trout populations with high genetic integrity provides some opportunity to conserve native genomes, but our findings also highlight the complex decisions facing managers today. Effective management strategies in this system may include analysis of the specific attributes of each site and population to evaluate the relative risks posed by isolation versus maintaining connectivity, identifying potential sites for control or eradication of nonnative trout, and long‐term monitoring of the genetic integrity of remaining redband trout populations to track changes in their status.Received February 24, 2011; accepted August 4, 2011

Flow regime, temperature, and biotic interactions drive differential declines of trout species under climate change

Broad-scale studies of climate change effects on freshwater species have focused mainly on temperature, ignoring critical drivers such as flow regime and biotic interactions. We use downscaled outputs from general circulation models coupled with a hydrologic model to forecast the effects of altered flows and increased temperatures on four interacting species of trout across the interior western United States (1.01 million km(2)), based on empirical statistical models built from fish surveys at 9,890 sites. Projections under the 2080s A1B emissions scenario forecast a mean 47% decline in total suitable habitat for all trout, a group of fishes of major socioeconomic and ecological significance. We project that native cutthroat trout Oncorhynchus clarkii, already excluded from much of its potential range by nonnative species, will lose a further 58% of habitat due to an increase in temperatures beyond the species' physiological optima and continued negative biotic interactions. Habitat for nonnative brook trout Salvelinus fontinalis and brown trout Salmo trutta is predicted to decline by 77% and 48%, respectively, driven by increases in temperature and winter flood frequency caused by warmer, rainier winters. Habitat for rainbow trout, Oncorhynchus mykiss, is projected to decline the least (35%) because negative temperature effects are partly offset by flow regime shifts that benefit the species. These results illustrate how drivers other than temperature influence species response to climate change. Despite some uncertainty, large declines in trout habitat are likely, but our findings point to opportunities for strategic targeting of mitigation efforts to appropriate stressors and locations.

Correlation of environmental attributes with histopathology of native Yellowstone cutthroat trout naturally infected with Myxobolus cerebralis

Infection by the invasive parasite Myxobolus cerebralis (causing whirling disease in salmonids) is strongly influenced by a stream's physico-chemical characteristics, which might affect host pathology. We examined whether environmental variables of a M. cerebralis-positive tributary to Yellowstone Lake, Yellowstone National Park, U.S.A., correlated with the histopathology of naturally infected native cutthroat trout Oncorhynchus clarkii bouvieri. Host inflammatory response and cranial cartilage lesions were the main correlates with whirling behavior. Canonical correlation analyses showed that the prevalence of trout with severe lesions in the cranial and jaw cartilages was highest in stream sites with a combination of high temperature and low specific conductivity. Our results reveal that environmental components can affect when and where a pathogen resides within the host, and manifestation of disease. Recognition of the synergism among environmental and histopathology factors most conducive to whirling disease will increase our prediction and detection abilities for M. cerebralis in salmonid hosts.

Do Nonnative Salmonines Exhibit Greater Density and Production than the Natives They Replace? A Comparison of Nonnative Brook Trout with Native Cutthroat Trout

AbstractThe replacement of native species by nonnative species has been widely documented. In aquatic ecosystems, nonnative trout often replace native trout species to which they are closely related. For example, nonnative brook trout Salvelinus fontinalis have replaced native cutthroat trout Oncorhynchus clarkii throughout western North America. We hypothesized that when brook trout replace cutthroat trout, they exhibit greater density, biomass, and annual production than were achieved by the cutthroat trout before replacement. We tested this hypothesis in five paired streams in the Teton River drainage, Idaho, over a 4‐year period. Streams were paired based on similar habitat characteristics and the presence of brook trout or cutthroat trout as the dominant species. Fish were surveyed annually by means of multipass depletion along representative stream reaches. Consistent with our hypothesis, brook trout exhibited 2.4 times greater density, 1.7 times greater biomass, and 2.5 times higher annual production than cutthroat trout. Because age‐0 fish were difficult to capture during electrofishing, we also analyzed the data without this age‐class. When age‐0 fish were excluded, brook trout exhibited 1.3, 1.6, and 2.1 times greater density, biomass, and annual production, respectively, than cutthrout trout. These results are consistent with the hypothesis that nonnative salmonines exhibit greater density and production than the native fishes they replace, though the generality of this finding remains to be tested. The differences that we observed not only testify to the success of brook trout as an introduced species in western North America but also point to likely changes in ecosystem function that may accompany their replacement of native cutthroat trout.

Morphological Patterns of Hybridization between Yellowstone Cutthroat Trout and Introduced Rainbow Trout in the South Fork of the Snake River Watershed, Idaho and Wyoming

AbstractHybridization between native and introduced species is considered a serious threat for many native fish populations. In western North America, native cutthroat trout Oncorhynchus clarkii subspecies are declining dramatically across their ranges; competition and hybridization with nonnative rainbow trout O. mykiss are recognized as key factors in their decline. Presently, identification of cutthroat trout × rainbow trout hybrids is commonly made using molecular genetic markers because morphological differences are thought to be inaccurate. We sampled trout from the South Fork of the Snake River and 10 tributary streams to test for morphological differences that could predict genetic identity of individual Yellowstone cutthroat trout O. clarkii bouvieri, rainbow trout, and their hybrids. We found distinctive body shape differences among the three groups: Yellowstone cutthroat trout and hybrids had larger heads than rainbow trout. Yellowstone cutthroat trout had shallower bodies and caudal peduncles than rainbow trout, whereas hybrids exhibited intermediate body depth and caudal peduncle depth. Using logistic regression with a suite of morphological measurements, we found an overall rate of 92% for correctly classifying trout as Yellowstone cutthroat trout, hybrids, or rainbow trout. Over 99% of Yellowstone cutthroat trout and 80% of rainbow trout were correctly categorized; however, the correct classification rate for hybridized individuals was considerably lower. This study demonstrates that consistent morphological differences exist between Yellowstone cutthroat trout and rainbow trout in the wild, and the degree of introgression accounts for a significant portion of morphological variation in Yellowstone cutthroat trout × rainbow trout hybrids, thus causing difficulty in the use of morphology alone to classify trout.

Cold Summer Temperature Regimes Cause a Recruitment Bottleneck in Age‐0 Colorado River Cutthroat Trout Reared in Laboratory Streams

AbstractNative salmonids are increasingly restricted to upstream habitats that may be too cold to sustain recruitment, and recruitment limitation owing to cold temperatures is a main hypothesis to explain translocation failures of native cutthroat trout Oncorhynchus clarkii in high‐elevation streams in the southern Rocky Mountains. We subjected Colorado River cutthroat trout O. c. pleuriticus fry to one of three temperature regimes (cold, intermediate, or warm), which averaged 7.0, 8.5, and 10.0°C during the warmest summer month, in each of 2 years. The regimes mimicked those of natural streams where translocated fish had died out or produced populations of cutthroat trout of low or high abundance. The mean fry survival rate from hatching through swim‐up was high during both experiments, ranging from 97% in the warm regime to 85% in the cold. After swim‐up, fry in the warm regime grew more than 60% more on average than those in the cold regime by the onset of winter in 2003 during a 22‐week period. Survival rates through midwinter were also higher in the warm regime (76%) than in the intermediate (62%) and cold (29%) regimes. A similar pattern of temperature‐related growth and mortality was apparent in the 2004 experiment (12 weeks), in which survival rates to early winter ranged from 44% in the warm regime to 10% in the cold. Most mortality in all three treatments occurred during a recruitment bottleneck encompassing a 4‐6‐week period following swim‐up. Analyses of size and percent dry weight indicated that the energy content of fry after swim‐up was lower in colder regimes and declined during the recruitment bottleneck in all three regimes. Our findings indicate a strong recruitment bottleneck after swim‐up when temperature‐related energy deficits apparently cause significant mortality. Managers may increase the viability of these translocated populations by selecting sites that accumulate more than 900 degree‐days during summer.

Experimental Effects of Nonnative Brown Trout on the Individual‐ and Population‐Level Performance of Native Bonneville Cutthroat Trout

AbstractIn western North America, nonnative trout invasions threaten the persistence of native cutthroat trout Oncorhynchus clarkii subspp. through competition, predation, and hybridization. While small‐scale individual‐level studies on nonnative–native fish interactions have helped elucidate mechanisms of impact, very few investigations have occurred at a scale consistent with that of species replacement. Thus, large‐scale population‐level studies are needed to understand the effects of nonnative fish as well as to more effectively conserve native fishes in the presence of nonnative fish. For this reason, we conducted an evaluation of the effects of nonnative brown trout Salmo trutta on the individual‐ and population‐level performance of native cutthroat trout using a field‐experimental approach. We studied local populations of cutthroat trout in the presence and absence of brown trout in long stream reaches and subsequently compared growth, condition, stable‐isotope‐based measures of dietary habits, movement, and survival between treatment groups. We found clear evidence for reduced cutthroat trout growth owing to the presence of brown trout. Additionally, we observed differences in cutthroat trout dietary habits based on δ13C signatures resulting from our experimental manipulation of brown trout abundance. Finally, brown trout suppressed cutthroat trout movement but had no apparent effect on their survival. Considering previous studies, we concluded that the individual‐level effects of brown trout on cutthroat trout are scale invariant. Higher‐level impacts (i.e., on movement and survival), in contrast, appear to be more sensitive to the scale at which the investigation is conducted. Overall, our results indicate that brown trout can have strong negative effects on cutthroat trout performance and should therefore be more explicitly considered in native fish conservation plans.

How High Can Brook Trout Jump? A Laboratory Evaluation of Brook Trout Jumping Performance

AbstractQuantitative data on how high brook trout Salvelinus fontinalis can jump are crucial for efforts by fisheries managers to exclude brook trout from streams containing native cutthroat trout Oncorhynchus clarkii subspp. and to build effective fishways for brook trout migration. We identified factors that could influence brook trout jumping ability and demonstrated how this knowledge could be applied to improve the design of barriers to brook trout migration or fishways to facilitate their migration. Our objective was to measure brook trout jumping performance under laboratory conditions to identify design features for constructing waterfall‐type barriers or pool‐and‐weir‐type fishways. We used flashboard‐type and flume‐type adjustable waterfall devices to measure brook trout jumping performance at various combinations of vertical or waterfall height (13.5–93.5 cm in 10‐cm increments) and plunge pool depth (10–60 cm in 10‐cm increments) over a 24‐h interval. We tested three size‐classes of brook trout: 10–15 cm total length (TL) (mean ± SD: 13.09 ± 1.67 cm), 15–20 cm (19.30 ± 1.19 cm), and 20 cm or more (26.52 ± 2.13 cm). The 10–15‐cm brook trout could jump a 63.5‐cm‐high waterfall, equivalent to 4.7 times their body length, from a 50‐cm‐deep plunge pool, which was 3.7 times their body length. Larger size‐classes were capable of jumping 73.5‐cm waterfalls, or 2.9–4.0 times their body length, provided the plunge pools were at least 40 cm deep (>1.6 times their body lengths). Shallow plunge pools (10 cm) prevented brook trout from all size‐classes from jumping waterfalls 43.5 cm or more in height. Small fish were capable of jumping a greater number of body lengths over vertical obstacles than large fish. The data analyses identified vertical height, plunge pool depth, fish total length, and fish condition as factors important in predicting brook trout jumping performance.