The Stream-Lake Ecotone: Potential Habitat for Juvenile Endangered June Suckers (Chasmistes Liorus)

Abstract

Potamodromous fish are poorly studied even though they are threatened often by human activities. The June sucker (Chasmistes liorus) is an endangered potamodromous species endemic to Utah Lake. Larval June suckers have not been collected from Utah Lake for at least 3 decades. Recruitment appears to be limited by low temperatures and scarce food, resulting in mass starvation of larval June suckers in the stream environment. We compared water temperature, Zooplankton food availability, and small fish abundance in the stream and in 3 habitats along the stream—lake ecotone (dense emergent vegetation, sparse emergent vegetation, and open lake) to test the hypothesis that all 3 factors would reach a maximum in the dense emergent vegetation of the stream—lake ecotone. We used the abundance of fathead minnows in each habitat type as a surrogate for small fish like juvenile June suckers. We found that temperature, food, and fathead minnows reached their maximums in the open lake rather than in vegetated habitats of the streamlake ecotone. The stream had the lowest average temperatures (15.1 °C) and the lowest Zooplankton concentrations (61 · L-1) over the growing season. Contrary to expectations, low temperatures (16.9 °C) and low food abundance (505 · L-1) also characterized the densely vegetated habitat, whereas the open lake had the highest temperatures (20.4° C) and highest concentrations of Zooplankton (2353 · L-1). Restoration should include a mechanism to transport larval fish through the densely vegetated portion of the stream—lake ecotone, which can be hundreds of meters wide, to the warm productive waters of the open lake. The braided planform of the terminal reaches of Hobble Creek should be replaced with shallow riffles to increase mean stream velocity and decrease the transport time of larval June suckers.