Target strength of an oily deep-water fish, orange roughy (Hoplostethus atlanticus) II. Modeling

Orange roughy consist of similar to 18% lipids by weight, mostly as wax est ers, and the lipids must be taken into account when modeling target strengt h. A deformed cylinder model incorporating the effect of temperature and pr essure on sound speed through wax ester was used to scale experimental meas urements of target strength to the temperatures and pressures where orange roughy live (similar to 6 degrees C, depths similar to 800-1300 m). The eff ect of decreasing temperature and increasing pressure is to increase the so und speed in orange roughy lipids. Modeling shows that the net effect of th is is to reduce tilt-averaged target strength, [TS], by similar to 2 dB. Ad justing experimental results to compensate for temperature and pressure eff ects gives a predicted [TS] for a 35-cm orange roughy of -48.3 dB. Adjustin g in situ estimates of orange roughy [TS] for avoidance behavior [McClatchi e et al., J. Acoust. Soc. Am. 106, 131-142 (1999)] suggests the correct [TS ] is similar to -47.5 dB, rather than -50 dB as previously reported [Kloser et al., ICES J. Mar. Sci. 54, 60-71 (1997)]. We conclude that experimental and in situ estimates now converge at a [TS] of similar to-48 dB for a 35- cm fish. (C) 2000 Acoustical Society of America. [S0001-4966(00)05302-9].