A re-evaluation of relationships between fish size, acoustic frequency, and target strength

Abstract

There are many measurements of dorsal aspect target strength of fish, but relatively few studies compare estimation methods or attempt to combine data from different studies into general relations between fish size, acoustic frequency and target strength (or acoustic cross-section). We edited and updated earlier summary regressions relating fish size, acoustic frequency and acoustic cross-section. Experimental measurements on marine fish were separated into swimbladder and non-swimbladder species, model results compared with experimental data, target strengths of marine, and freshwater fish were contrasted, and previous and new target strengths of commercial New Zealand fish species were placed in the context of the new regressions. Analysis of variance was used to show significant effects of species, freshwater vs. marine, swimbladder vs. non-swimbladder fish, model vs. experimental, and dead vs. alive fish on the relationship between maximum dorsal aspect target strength and fish length. For experimental results on gadoids we found significant species and live vs. dead (or stunned) fish effects on the target strength to length relationship. The quadratic dependence of target strength on fish length was also tested and found to be the exception rather than the rule. Existing pitch tilt angle data was compiled and a normal distribution with standard deviation of at least 15° was required to describe most distributions.