Douglas J. Austen

Importance of the Guild Concept to Fisheries Research and Management

Abstract The concept of the guild has appealed to fisheries researchers and managers for simplifying analysis and assisting in the prediction of community change. Guilds have been developed based on reproduction, feeding, habitat use, and morphology. In most published accounts, guilds were used to describe a community change in response to some environmental perturbation (e.g., stream habitat modification or siltation). Members of a guild are often expected to react similarly to environmental change. However, little evidence exists to support the extrapolation of population changes in one guild member to that of other members of the same guild. It may be more reasonable to assume that the combined abundance of all species in a guild can more accurately reflect changes in their primary resource or a limiting factor. Thus, we suggest that guilds reflect the characteristics of a super-species—a unit that responds to environmental change in a more predictable manner than individual species. We recommend that ...

Comparison of Detonating Cord and Rotenone for Sampling Fish in Warmwater Impoundments

Abstract Fish sampling with detonating cord (Primacord) in blocked areas of warmwater impoundments or drainable ponds was inferior to sampling with rotenone (followed by detoxification) in terms of efficiency of fish retrieval, cost, personnel, and convenience. Twenty-one enclosures, including 13 blocked areas in impoundments and 8 experimental ponds, were treated with either rotenone at 3 mg/L (active ingredient) or with Primacord laid in parallel with spacing of 4 m between lines. Marked fish were added to blocked areas and experimental ponds were stocked with known populations prior to detonation or rotenone treatment. Retrieval efficiency with either method depended on fish length but not on species. When similar enclosures were compared, fish retrieval efficiency was always greater for rotenone samples than for Primacord samples. Draining of the experimental ponds indicated that the difference in efficiency could be accounted for by the quantity of fish surviving the Primacord detonation. Primacord i...

Modeling the Sampling Efficiency of Rotenone in Impoundments and Ponds

Abstract Fish were sampled in 25 coves or ponds treated with a 3-ppm concentration of a rotenone formulation. Before rotenone treatment, each site was enclosed by a block net, and fish were captured, measured, marked by fin-clipping, and returned to their appropriate habitats. In all, 2,907 marked fish were released at an average density of 368 fish/hectare. Efficiency was calculated as the percentage of marked fish retrieved during 3 d. With all fish combined within length-groups, three factors explained 63% of the variance in efficiency (residual SE = 15.5): the inverse of fish length (P < 0.00001; 4–49 cm, total length), water temperature (P < 0.00001; 11–28°C, and area of enclosure (P = 0.001; 0.09–5.09 hectares). Area was uncorrelated with depth, and depth was not a significant factor. Allowing for the effect of the significant factors, we found no differences in retrieval efficiency between major species and species groups. A multiple-regression model based on all species combined is proposed as a m...

The Multi-state Aquatic Resources Information System: An Internet system to access fisheries information in the upper midwestern United States

Abstract Traditionally, state agencies in the United States have invested millions of dollars to collect information on fish populations. Management of fisheries resources often necessitates the sharing of this information across political boundaries. Federal agencies need to share information on fish populations across political boundaries to complete the congressional mandates of the Resource Planning Act (U.S. Forest Service) and Resource Conservation Act (Natural Resources Conservation Service). Further, these data are needed for other analyses such as proposed listings under the Endangered Species Management Act and examinations of possible climate change effects. Since 1994, Illinois, Iowa, Michigan, Minnesota, Ohio, Wisconsin, the U.S. Fish and Wildlife Service, the U.S. Forest Service, the U.S. Geological Survey Biological Resources Division (formerly National Biological Survey), and the Natural Resources Conservation Service have collaborated to develop a system to share these data. The Multi-sta...

Usefulness of Structural and Condition Indices in Management of High-Mountain Stream Salmonid Populations

Abstract We assessed the utility of relative weight (Wr ), young-to-adult ratio (YAR), and a stock density index (SDI) calculated in a manner similar to the proportional stock density index as management tools for populations of brook trout Salvelinus fontinalis in six high-elevation streams. On each stream, estimates were made for production, biomass, production: biomass ratio, and brook trout density, as well as 14 environmental variables. The SDI varied substantially among streams and was significantly related to mean depth and conductivity, but not to any other environmental variables or to any of the population parameters. Values of Wr varied substantially over the growing season and were inversely related to mean depth for fish 100–150 mm and more than 150 mm total length, and directly (but marginally) related to production: biomass ratio for medium (>150-mm) and large (>200-mm) fish. Estimates of YAR were related only to the production biomass ratio. Structural indices, in general, were correlated ...