Diet composition and resource overlap of sympatric native and introduced salmonids across neighboring streams during a peak discharge event.

Species assemblages composed of non-native and native fishes are found in freshwater systems throughout the world, and interactions such as interspecific competition that may negatively affect native species are expected when non-native species are present. In the Smith River watershed, Montana, rainbow trout were introduced by 1930. Native mountain whitefish and non-native rainbow trout have presumably occurred in sympatry since the introduction of rainbow trout; however, knowledge about how these two species compete with one another for food resources is sparse. We quantified diet compositions of rainbow trout and mountain whitefish in the mainstem Smith River and in a tributary to the Smith River-Sheep Creek-to determine the degree of overlap in the diets of mountain whitefish and rainbow trout in the Smith River and between the mainstem Smith River and a tributary stream. Rainbow trout and mountain whitefish had generalist feeding strategies, which probably contribute to the amicable coexistence of these species. Diet overlap between rainbow trout and mountain whitefish was high (Pianka's index value = 0.85) in the Smith River and moderate in Sheep Creek (Pianka's index value = 0.57). Despite overlap in diets, some resource partitioning may alleviate resource competition (e.g., rainbow trout consumed far more Oligochaeta than mountain whitefish but fewer Brachycentridae and Chironomidae). Diet composition of rainbow trout and mountain whitefish did not differ greatly between the Smith River and Sheep Creek. Prey categories most commonly used by mountain whitefish at the population and individual levels (i.e., Ephemeroptera and Trichoptera) are sensitive taxa and many species within these orders have experienced extinctions and population declines. Therefore, future changes in resource availability or competition could be of concern.

Landscape assessment of side channel plugs and associated cumulative side channel attrition across a large river floodplain.

Determining the influences of anthropogenic perturbations on side channel dynamics in large rivers is important from both assessment and monitoring perspectives because side channels provide critical habitat to numerous aquatic species. Side channel extents are decreasing in large rivers worldwide. Although riprap and other linear structures have been shown to reduce side channel extents in large rivers, we hypothesized that small "anthropogenic plugs" (flow obstructions such as dikes or berms) across side channels modify whole-river geomorphology via accelerating side channel senescence. To test this hypothesis, we conducted a geospatial assessment, comparing digitized side channel areas from aerial photographs taken during the 1950s and 2001 along 512 km of the Yellowstone River floodplain. We identified longitudinal patterns of side channel recruitment (created/enlarged side channels) and side channel attrition (destroyed/senesced side channels) across n = 17 river sections within which channels were actively migrating. We related areal measures of recruitment and attrition to the density of anthropogenic side channel plugs across river sections. Consistent with our hypothesis, a positive spatial relationship existed between the density of anthropogenic plugs and side channel attrition, but no relationship existed between plug density and side channel recruitment. Our work highlights important linkages among side channel plugs and the persistence and restoration of side channels across floodplain landscapes. Specifically, management of small plugs represents a low-cost, high-benefit restoration opportunity to facilitate scouring flows in side channels to enable the persistence of these habitats over time.

Now Hiring! Empirically Testing a Three-Step Intervention to Increase Faculty Gender Diversity in STEM.

Workforce homogeneity limits creativity, discovery, and job satisfaction; nonetheless, the vast majority of university faculty in science, technology, engineering, and mathematics (STEM) fields are men. We conducted a randomized and controlled three-step faculty search intervention based in self-determination theory aimed at increasing the number of women faculty in STEM at one US university where increasing diversity had historically proved elusive. Results show that the numbers of women candidates considered for and offered tenure-track positions were significantly higher in the intervention groups compared with those in controls. Searches in the intervention were 6.3 times more likely to make an offer to a woman candidate, and women who were made an offer were 5.8 times more likely to accept the offer from an intervention search. Although the focus was on increasing women faculty within STEM, the intervention can be adapted to other scientific and academic communities to advance diversity along any dimension.

A packed-bed filtration system for collection of Myxobolus cerebralis triactinomyxons.

Information on the distribution and abundance of Myxobolus cerebralis triactinomyxons in natural systems is limited because direct and accurate sampling methods for this life stage have not been developed. Existing methods are based on indirect measures of triactinomyxon densities and are therefore confounded. Direct estimation of triactinomyxon concentrations would more exactly pinpoint the ambient infection risk to wild fish and allow evaluation of management strategies designed to mitigate the effects of the disease. We developed a mobile packed-bed filtration system that quickly, accurately, and precisely collects, concentrates, and quantifies triactinomyxons. The system includes pumping, prefiltration, two rounds of packed-bed filtration, and centrifugation. Laboratory tests of the completed system using known quantities of triactinomyxons resulted in a mean recovery rate of 91% with a minimum detectable concentration of triactinomyxons of 0.04/L. We subsequently field-tested the system at a site known to be positive for the parasite and recovered triactinomyxons at densities of 0.7-1.4/L. The packed-bed filtration system has the potential to quickly determine the temporal and spatial variation in infection risk and to test the efficacy of various management strategies.

Effects of fish age versus size on the development of whirling disease in rainbow trout.

We examined the effects of both fish age and size on the development of resistance to whirling disease in Erwin strain rainbow trout. Previously, we demonstrated that juvenile rainbow trout became resistant to development of the disease when first exposed to triactinomyxons of the parasite Myxobolus cerebralis at about 9 wk post-hatch when raised at 12 degrees C, but ages and sizes of fish used in that experiment were confounded (Ryce EKN, Zale AV, MacConnell E [2004] Dis Aquat Org 59:225-233). In this study, rainbow trout of the same age and different sizes, and the same size and different ages, were exposed to the parasite to distinguish the influences of age and size. Fish were reared at 3 different water temperatures prior to exposure to produce groups with different growth rates and were exposed to the parasite at 7 or 9 wk post-hatch. Disease severity was affected by both age and size at first exposure, but the effects were not independent. An increase in fork length from 36 to 40 mm among fish exposed at 7 wk post-hatch did not confer increased resistance, but the same increase in size at 9 wk post-hatch did. Similarly, an increase in age from 7 to 9 wk post-hatch among fish exposed at 36 mm fork length did not confer increased resistance, but the same increase in age at 40 mm did. Rainbow trout must be both 9 wk post-hatch or older and at least 40 mm in fork length at time of exposure to exhibit enhanced resistance to whirling disease. Resistance to disease was not associated with the level of skeletal ossification.

Effects of fish age and parasite dose on the development of whirling disease in rainbow trout.

We determined the ages at which juvenile rainbow trout Oncorhynchus mykiss became resistant to the effects of whirling disease following exposure to a range of parasite doses. Heretofore, the development and severity of whirling disease in salmonids was known to be generally dependent on the age or size of fish when first exposed to the triactinomyxon spores of Myxobolus cerebralis; larger, older individuals tended to be less diseased. However, no systematic determination had been made of the exact age at which fish become resistant to the development of the disease. We exposed rainbow trout at 9 ages (1 to 17 wk post-hatch) to 4 parasite dose levels (0, 100, 1000 and 10,000 triactinomyxons per fish). Disease severity was measured using mortality, clinical signs, microscopic pathology, and myxospore counts. Disease and mortality were substantially reduced when exposure to the parasite occurred for the first time at 9 wk post-hatch (756 degree-days at 12 degrees C) or older. High doses elicited more disease among the younger age groups, but the effect was dampened in groups exposed at about 9 to 11 wk post-hatch and absent thereafter. Rainbow trout reared in M. cerebralis-free waters for 9 wk post-hatch or longer, whether in the wild or in a hatchery situation, should experience greater survival and less disease than fish first exposed to the parasite at younger ages.