title: Size-based hydroacoustic measures of within-season fish abundance in a boreal freshwater ecosystem.
abstract: Eleven sequential size-based hydroacoustic surveys conducted with a 200 kHz split-beam transducer during the summers of 2011 and 2012 were used to quantify seasonal declines in fish abundance in a boreal reservoir in Manitoba, Canada. Fish densities were sufficiently low to enable single target resolution and tracking. Target strengths converted to log2-based size-classes indicated that smaller fish were consistently more abundant than larger fish by a factor of approximately 3 for each halving of length. For all size classes, in both years, abundance (natural log) declined linearly over the summer at rates that varied from -0.067 x day(-1) for the smallest fish to -0.016 x day(-1) for the largest (R2 = 0.24-0.97). Inter-annual comparisons of size-based abundance suggested that for larger fish (>16 cm), mean winter decline rates were an order of magnitude lower (-0.001 x day(-1)) and overall survival higher (71%) than in the main summer fishing season (mean loss rate -0.038 x day(-1); survival 33%). We conclude that size-based acoustic survey methods have the potential to assess within-season fish abundance dynamics, and may prove useful in long-term monitoring of productivity and hence management of boreal aquatic ecosystems.
authors: Centre for Fisheries Ecosystems Research, Fisheries and Marine Institute of Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
authors: Riley A
authors: RA
authors: Pollom
authors: Centre for Fisheries Ecosystems Research, Fisheries and Marine Institute of Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
authors: George A
authors: GA
authors: Rose
mesh_terms: D000162:Acoustics / Q000295:instrumentation*; D000818:Animals; D049628:Body Size; D017753:Ecosystem; D005399:Fishes / Q000033:anatomy & histology / Q000502:physiology*; D005618:Fresh Water / Q000032:analysis; D057446:Hydrodynamics; D008350:Manitoba; D011157:Population Dynamics; D012621:Seasons