Data from: Size-based hydroacoustic measures of within-season fish abundance in a boreal freshwater ecosystem

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.day-1 for the smallest fish to -0.016.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.day-1) and overall survival higher (71%) than in the main summer fishing season (mean loss rate -0.038.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.2011年与2012年夏季，研究团队借助200 kHz分裂波束换能器（split-beam transducer）开展了11次连续的基于尺寸分级的水声调查（hydroacoustic surveys），以量化加拿大曼尼托巴省（Manitoba）某北方水库（boreal reservoir）内鱼类丰度的季节衰减趋势。该水域鱼类密度极低，可实现单目标分辨（single target resolution）与追踪。转换为基于log₂的尺寸分级的目标强度（target strengths）结果显示，每当体长减半，小型鱼类的丰度始终较大型鱼类高出约3倍。两年间所有尺寸分级的鱼类丰度（自然对数）均随夏季进程呈线性衰减，衰减速率范围为最小体型组的-0.067·天⁻¹至最大体型组的-0.016·天⁻¹（决定系数R²=0.24~0.97）。基于尺寸分级的鱼类丰度年际对比（inter-annual comparisons）结果表明，相较于夏季主捕捞季（平均损失速率为-0.038·天⁻¹，存活率为33%），大型鱼类（体长>16 cm）的平均冬季衰减速率低一个数量级（-0.001·天⁻¹），整体存活率更高（71%）。本研究得出结论认为，基于尺寸分级的水声调查方法具备评估季内鱼类丰度动态的潜力，或可用于北方水生生态系统（boreal aquatic ecosystems）的生产力长期监测，进而为该类生态系统的管理提供支撑。