A REEVALUATION OF RELATIONSHIPS BETWEEN FISH SIZE, ACOUSTIC FREQUENCY, AND TARGET STRENGTH

There are many measurements of dorsal aspect target strength of fish, but relatively few studies compare estimation methods or attempt to co mbine data from different studies into general relations between fish size, acoustic frequency and target strength (Or acoustic cross-sectio n). We edited and updated earlier summary regressions relating fish si ze, acoustic frequency and acoustic cross-section. Experimental measur ements on marine fish were separated into swimbladder and non-swimblad der species, model results compared with experimental data, target str engths of marine, and freshwater fish were contrasted, and previous an d new target strengths of commercial New Zealand fish species were pla ced in the context of the new regressions. Analysis of variance was us ed to show significant effects of species, freshwater vs. marine, swim bladder vs. non-swimbladder fish, model vs. experimental, and dead vs. alive fish on the relationship between maximum dorsal aspect target s trength 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 t arget strength on fish length was also tested and found to be the exce ption rather than the rule. Existing pitch tilt angle data was compile d and a normal distribution with standard deviation of at least 15 deg rees was required to describe most distributions. (C) 1996 Internation al Council for the Exploration of the Sea