In Situ Target Strength of Alewives in Freshwater

Abstract

Abstract Acoustic estimation of absolute fish abundance depends on knowledge of the relationship between target strength (TS) and size for the species of interest. We have derived a relationship between in situ TS and both length (L, cm) and mass (W, g) for alewives Alosa pseudoharengus in Lake Ontario and eight inland lakes in New York to provide equations for predicting one variable from the other. The pelagic fish community in these lakes was dominated by alewives (≥80% numerically). Target strength distributions from fish populations investigated in 25 surveys were multimodal, whereas those for individual fish were unimodal, indicating that each mode for the populations corresponded to a size-group of alewives (range, 2.5-15.2 cm). The positive relationship between mean TS and mean length was highly significant (TS = 20.53 log10 L− 64.25), as was the relationship between mean TS and mean mass (TS = 6.98 log10 W− 50.07). These equations are similar to one often-used TS-length relationship but differ su...