PARENT SESSION
Contributed Oral Session 136: Fish Communities, Management, and Recruitment
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal
"The Ecological Detective" investigates a declining trout population on Vermont's Batten Kill.
Omland, Kristian*,1, Parrish, Donna1, 1 USGS - Vermont Cooperative Fish & Wildlife Research Unit, Burlington, VT, USA
ABSTRACT- Ecologists who grapple with applied problems typically take on the role of "the ecological detective," i.e., we have to piece together bits of evidence that may have been collected for disparate purposes in our attempt to account for observed phenomena. The phenomenon with which we are concerned is the decline of the brown trout (Salmo trutta) population on the Batten Kill in southern Vermont. We first analyzed annual monitoring data collected by the Vermont Department of Fish & Wildlife and inferred that there appeared to be a bottleneck for population growth in the 150-200mm size class. That was consistent with hypotheses of increased predation and/or diminished cover (e.g., logs) and was inconsistent with hypotheses associated with disease, pollution, siltation, and a number of other potential causes. We conducted a mark-recapture study of trout survival using PIT tags, but found too few mid-size trout (200-300mm) to compare survival in the mark-recapture framework. We resorted to a simulation analysis of trout growth and survival, which suggested lower survival for trout under 200mm than for longer trout. We analyzed sightings of Common Mergansers (Mergus merganser) in the Breeding Bird Survey (BBS) using logistic regression and found increasing frequency of sightings over the years of the BBS, particularly in Western New England. Next, we sampled stomach contents of both Common Mergansers and large trout, as well as the "forage fish" community. We found greater representation of trout in Common Merganser stomachs and proportional representation in large trout stomachs relative to availability in the community. Finally, drawing on published information about Common Merganser diet as well as our own estimates of current Common Merganser abundance on Vermont trout streams, we used bioenergetics modeling to assess the plausibility of the hypothesis that predation by Common Mergansers has driven the decline of the trout population.
Key words: salmonid population decline, nonlinear regression for fitting population dynamics models, predator impacts on population growth, avian fish predator bioenergetics