Mobile hydroacoustic surveys are routinely used to estimate pelagic fish abundance. In the Great Lakes, alewife are commonly surveyed with mobile hydroacoustics, however, their behavior often has them associated with epilimnetic habitats which increases the potential for vessel avoidance to bias hydroacoustic observations. Abundance estimates from mobile hydroacoustic surveys are typically made using depth and size thresholds to classify targets to species. In hydroacoustic surveys, fish can appear to be smaller when oriented off horizontal axis, as is common with fish displaying vessel avoidance behaviour. This presents a problem where alewives that are diving may appear too small to be correctly classified. We compared alewife swimming behaviours and target strength distributions between stationary up-looking and mobile down-looking hydroacoustics to quantify how vessel avoidance may bias hydroacoustic observations. Alewives from the mobile survey were found to be diving away from the surface, moving faster and in more linear paths than the undisturbed fish from the stationary survey. In the mobile survey, alewives were observed at smaller target strength values than would be expected if boat avoidance was not occurring. Our results suggest that alewife behavioral changes associated with vessel avoidance affect the number and size of targets classified as alewife from mobile hydroacoustic surveys in Lake Ontario.

流动水声调查通常用于估算中上层鱼类的丰度。在大湖地区，一般对alewife进行流动声水调查，但是，它们的行为常常使它们与易上岸生境相关联，这增加了避免船只使水声观测产生偏差的可能性。通常使用深度和大小阈值对目标进行分类，以进行流动水声调查的丰度估计。在水声调查中，鱼偏离横轴时可能看起来较小，这与鱼显示出回避船只的行为很常见。这带来了一个问题，正在潜水的虾仁看起来太小而无法正确分类。我们比较了固定式向上看和移动式向下看水声之间的阿勒威夫游泳行为和目标强度分布，以量化避开船只可能如何偏向水声观察。从流动调查中发现的拟议鱼类比从静止调查中未受干扰的鱼类迁移出水面，移动速度更快，并沿更线性的路径移动。在流动调查中，观察到的副渔民的目标强度值比未避免躲避船只的预期目标强度值小。我们的研究结果表明，与避开船只有关的alewife行为变化会影响安大略湖流动水声调查分类为alewife的目标的数量和大小。从流动调查中发现的拟议鱼类比从静止调查中未受干扰的鱼类迁移出水面，移动速度更快，并沿更线性的路径移动。在流动调查中，观察到的副渔民的目标强度值比未避免躲避船只的预期目标强度值小。我们的研究结果表明，与避开船只有关的alewife行为变化会影响安大略湖流动水声调查分类为alewife的目标的数量和大小。从流动调查中发现的拟议鱼类比从静止调查中未受干扰的鱼类迁移出水面，移动速度更快，并沿更线性的路径移动。在流动调查中，观察到的副渔民的目标强度值比未避免躲避船只的预期目标强度值小。我们的研究结果表明，与避开船只有关的alewife行为变化会影响安大略湖流动水声调查分类为alewife的目标的数量和大小。