Alexander V. Zale

Effect of Temperature on Growth and Survival of Bull Trout, with Application of an Improved Method for Determining Thermal Tolerance in Fishes

Abstract Elevated temperature is considered an important factor in the decline of the threatened bull trout Salvelinus confluentus, but the thermal requirements of this species have not been defined. We used the acclimated chronic exposure (ACE) method to assess the upper thermal limits and growth optima of bull trout fed daily to satiation over test temperatures ranging from 8°C to 28°C during 60-d trials. Survival of age-0 bull trout was at least 98% at 8, 10, 12, 14, 16, and 18°C, but 0% at 22, 24, 26, and 28°C after 60 d. The predicted ultimate upper incipient lethal temperature for these trout was 20.9°C. Peak growth, as estimated by regression analysis, occurred at 13.2°C (95% confidence interval, 10.9–15.4°C). Feed consumption declined significantly (P < 0.001) at temperatures greater than 16°C, and fish held at temperatures of 22°C and above did not feed. Feed, lipid, and protein efficiencies were similar at 8–18°C but declined significantly (P < 0.001) at 20°C. Our results corroborate field inves...

Comparative Thermal Requirements of Westslope Cutthroat Trout and Rainbow Trout: Implications for Species Interactions and Development of Thermal Protection Standards

Abstract Water temperature appears to play a key role in determining population persistence of westslope cutthroat trout Oncorhynchus clarkii lewisi, but specific thermal performance and survival criteria have not been defined. We used the acclimated chronic exposure laboratory method to determine upper thermal tolerances and growth optima of westslope cutthroat trout and rainbow trout O. mykiss, a potential nonnative competitor that occupies much of the former range of westslope cutthroat trout. Rainbow trout had a distinct survival advantage over westslope cutthroat trout at water temperatures above 20°C. The ultimate upper incipient lethal temperature of rainbow trout (24.3°C; 95% confidence interval [CI] = 24.0–24.7°C) was 4.7°C higher than that of westslope cutthroat trout (19.6°C; 95% CI = 19.1–19.9°C). In contrast, both species had similar growth rates and optimum growth temperatures (westslope cutthroat trout: 13.6°C; rainbow trout: 13.1°C) over the temperature range of 8–20°C, although rainbow tr...

Temperature and competition between bull trout and brook trout : A test of the elevation refuge hypothesis

Abstract We tested the elevation refuge hypothesis that colder temperatures impart a competitive advantage to bull trout Salvelinus confluentus and thus account for increased biotic resistance to invasion and displacement by brook trout S. fontinalis in headwater streams. Growth, survival, and behavior were compared in allopatry and sympatry at temperatures of 8-20°C in the laboratory. In allopatry, age-0 bull trout and brook trout grew at similar rates at temperatures of 8.0-14.3°C, but brook trout grew significantly faster at higher temperatures. In sympatry, bull trout grew significantly less than brook trout at all test temperatures, with growth differences increasing linearly with increased temperature. Age-1 brook trout had significantly higher feeding and aggression rates than did similar-sized bull trout at 8°C and 16°C. The modeled growth of age-0 bull trout and brook trout based on tributary temperature data from a high-elevation site (mean summer temperature, 10°C) and a low-elevation site (14°...

Effects of Surgically Implanted Transmitter Weights on Growth and Swimming Stamina of Small Adult Westslope Cutthroat Trout

Abstract The generally accepted 2% ratio of transmitter weight to body weight constrains or precludes telemetry studies examining the timing and location of spawning of small adult westslope cutthroat trout Oncorhynchus clarkii lewisi in headwater streams. We empirically determined effects of surgically implanted dummy transmitters ranging in weight from 1 to 5 g on the swimming stamina and growth of small (81.3–206.9 g) adult westslope cutthroat trout in the laboratory to establish acceptable transmitter weights for field studies on this species. Mean growth rates and swimming stamina were not significantly different among treatments, including controls. No precipitous decline or threshold beyond which performance deteriorated markedly was observed. Data collected using telemetered westslope cutthroat trout implanted with transmitters less than about 4% of body weight should therefore approximate information about untelemetered individuals without significant bias. However, we also detected subtle effect...

Development and Evaluation of a Fish Assemblage Index of Biotic Integrity for Northwestern Great Plains Streams

Abstract Quantitative indicators of biological integrity are needed for streams in the Great Plains of North America, but it was not known whether the index of biotic integrity (IBI) approach would be effective in this semiarid region. Great Plains streams have a depauperate and tolerant ichthyofauna and highly variable physicochemical conditions that may mask the effects of non-point-source pollution and stream habitat degradation. We developed an IBI based on fish assemblages by screening metrics for range, responsiveness to human influence, precision, and lack of redundancy; we then tested the IBIs ability to detect anthropogenic effects by validating the index with an independent data set. The IBI was composed of 10 metrics based on species richness and composition, trophic and reproductive guilds, and age structure. These 10 metrics had many significant correlations with substrate and water chemistry variables but had fewer significant correlations with riparian condition and watershed variables. Of...

Seasonal Survival, Movement, and Habitat Use of Age-0 Rainbow Trout in the Henrys Fork of the Snake River, Idaho

Abstract We quantified seasonal abundances, apparent survival rates, movements, and habitat use of age-0 rainbow trout Oncorhynchus mykiss in a 25-km reach of the Henrys Fork of the Snake River, Idaho, to determine what factors limit recruitment to the population. Natural production of rainbow trout occurred in each year of the study (1995-1997) and ranged from 158,000 to 306,000 age-0 fish each summer. No significant loss of age-0 rainbow trout occurred between summer and autumn; suitable habitat was present throughout the channel in all reaches and supported large abundances of age-0 rainbow trout through this period. The greatest losses (77-100%) occurred during winter and primarily involved fish from center-channel macrophyte beds. Most river sections, which had only simple bank habitat, did not support any age-0 rainbow trout through the entire winter. Overwinter survival was greatest (18-23%) in Box Canyon, a river section characterized by complex bank habitat, high gradient, and large substrate. Fi...

Seasonal Movements, Habitat Use, Aggregation, Exploitation, and Entrainment of Saugers in the Lower Yellowstone River: An Empirical Assessment of Factors Affecting Population Recovery

Abstract Migratory barriers, habitat loss, entrainment in irrigation canals, and overexploitation, especially at times of aggregation, have been suggested to explain the failure of Yellowstone River saugers Sander canadensis to return to historical abundances after a late-1980s decline that was attributed to drought. These factors are thought to affect saugers throughout their range and migratory large-river fishes in general. We characterized the seasonal movement patterns, habitat use, and aggregation of saugers and estimated movement, exploitation, and irrigation canal entrainment rates to test these hypotheses. Saugers aggregated near spawning areas in spring and subsequently dispersed 5–350 km to upstream home locations, where they remained for the rest of the year. Upstream movement was not overtly restricted by low-head diversion dams. During the spawning period, terrace and bluff pools, which are unique geomorphic units associated with bedrock and boulder substrate, were positively selected, while...

Entrainment of lchthyoplankton by a Warmwater Hydroelectric Facility

Abstract We examined entrainment of ichthyoplankton associated with hydropower generation in 1988 and 1989 at the Pensacola Dam hydroelectric facility on Grand Lake in northeastern Oklahoma. To provide a basis for evaluating the effects of entrainment on the fish assemblage, we also estimated the total abundance of fish eggs and larvae in the top 10 m of the reservoir. Entrainment totaled about 10 million larval fish in 1988 and almost 100 million in 1989. Only nine taxa of larval fish were entrained during the study. Entrained eggs were almost exclusively those of freshwater drum Aplodinotus grunniens. Although estimates of entrainment were large, they were generally low compared with the estimates of total abundance of ichthyoplankton in Grand Lake.

Effectiveness of Fish Screens to Prevent Entrainment of Westslope Cutthroat Trout into Irrigation Canals

Abstract Irrigation canals entrain anadromous and potamodromous salmonids of all life stages during their annual migrations. Fish screens may reduce or eliminate entrainment, but few studies exist on their benefits and these studies have evaluated effects on anadromous populations only. The benefits of fish screens for nonanadromous salmonids are largely unknown. Postspawn adult and downstream-migrating juvenile westslope cutthroat trout Oncorhynchus clarkii lewisi are potentially entrained into irrigation canals on Skalkaho Creek, Montana. We quantified entrainment rates into the canals using telemetry and driftnetting before (2003) and after (2004) installation of fish screens on three canals. No radio-tagged adults were entrained in 2003, but most adults were residents and therefore did not migrate past the canals. In 2004, 79% of the radio-tagged adult migratory fish were entrained at either screened or unscreened canals, but all those entrained in screened canals were successfully bypassed back to Sk...

Temporal Reproductive Separation of Fluvial Yellowstone Cutthroat Trout from Rainbow Trout and Hybrids in the Yellowstone River

Abstract Yellowstone cutthroat trout Oncorhynchus clarkii bouvierii are genomically extinct throughout much of their historic range because of displacement by and introgression with introduced rainbow trout O. mykiss. However, fluvial Yellowstone cutthroat trout still retain their genetic integrity while coexisting with rainbow trout in the Yellowstone River. We assessed whether spatial or temporal reproductive isolation, or both, occurs between these taxa. Time and place of spawning was determined by radiotelemetry. We implanted 164 trout (98 cutthroat trout, 37 rainbow trout, and 29 cutthroat trout × rainbow trout hybrids) with radio tags before the 2001, 2002, and 2003 spawning seasons in four sections of a 140-km segment of the main-stem Yellowstone River. Of the 164 radio-tagged fish, 73 (44 Yellowstone cutthroat trout, 15 rainbow trout, and 14 hybrids) were assumed to have spawned; 55 (75.3%) used 16 tributaries, 17 (23.3%) used 7 river side channels, and 1 (1.4%) used the main channel of the Yellow...