Larry Greenberg

AVAILABILITY OF MICROHABITATS AND THEIR USE BY BROWN TROUT (SALMO TRUTTA) AND GRAYLING (THYMALLUS THYMALLUS) IN THE RIVER VOJMÅN, SWEDEN

Availability of microhabitats and their use by brown trout (Salmo trutta) and grayling (Thymallus thymallus)

Effect of an Artificial Pond on Migrating Brown Trout Smolts

Abstract In southern Sweden, nutrient runoff from agricultural areas causes extensive eutrophication of inland and coastal waters. To reduce nutrient transport, especially nitrogen, resource managers are creating wetlands and ponds within stream systems. During 1996 and 1997, we studied the migration of smolts of brown trout Salmo trutta through one of these artificial ponds, situated in Onnerupsbacken Creek in southern Sweden. Because the former migration route through the stream was severed, migration through the pond was compared with an upstream reference section in the stream. Smolts were captured by a smolt trap about 2 km upstream of the pond and marked with electronic passive integrated transponders before being released into the stream. Downstream of the smolt trap, loss rate, swimming speed, and timing of movements of the brown trout were measured in the reference stream section and in the pond as the smolts passed each of three submerged antennae placed in the stream and at the ponds inlet and...

Complex trophic interactions in freshwater benthic food chains

Complex trophic interactions play an important role in structuring benthic communities in lakes and streams. In this review of freshwater, benthic food chains, a variety of different types of complex interactions were identified, including trophic cascades, interaction modifications and indirect commensalisms. The strength of these interactions varied greatly among studies, depending on habitat complexity, the type and intensity of environmental stresses, the ways in which prey defended themselves from predators, and the degree of trophic omnivory in the food chain. Areas that deserve further study include the effect of trophic omnivory on interaction strength and indirect effects of piscivores in benthic communities. Future studies should include whole-system, long-term manipulations to deepen our understanding of the role of complex interactions in freshwater communities.

Effect of depth and substrate on use of stream pools by brown trout

Abstract We tested how depth and cobble clusters affected pool use by brown trout Salmo trutta in four enclosures in a seminatural, outdoor stream channel. Into each enclosure, which consisted of a shallow, cobble-filled habitat and a deeper pool, we stocked eight brown trout 9–19 cm long that had been tagged with passive integrated transponders (PIT). Receiver antennae for the PIT tags were placed between the two habitats to allow continuous monitoring of movements of individual fish. We found that trout used pools to a greater extent at night than during the day. Alterations of depth and substrate had no effect on pool use at night. During the day, increasing water depth either alone or together with adding cobbles increased pool use, whereas cobble addition alone had no effect on pool use. We suggest that evaluations of physical habitat modifications in streams should include measurements of population responses as well as information on how, when, and which fish use newly created habitat structures.