...management marine conservation areas, covering many million square nautical miles, have been mandated. monitor the recovery of the rockfish stocks in these areas, scientists are faced with the following challenges: 1) multiple species of rockfish exist in these areas; 2) the species reside near or on the bottom at depths of 80 to 300 m; and 3) they are low in numerical density. To meet these challenges, multifrequency echosounders, multibeam sonar, and cameras mounted on remotely operated vehicles are frequently used (Reynolds et al., 2001). The accuracy and precision of these echosounder results are largely dependent upon the accuracy of the species classification and target strength estimation (MacLennan and Simmonds, 1992).

Broad bandwidth characterization of sound scatter from marine organisms has some potential for remotely classifying fish species (Conti and Demer, 2003), shapes and sizes (Conti et al., 2005), behaviors (Conti et al., 2006b), and to validate models for target strength estimation (Demer and Conti, 2003). All of these studies have employed variants of a new method for measuring the broad bandwidth total scattering cross section ([[sigma].sub.T]) of animals moving in a reverberant tank.

With the new method, the total scattering cross section ([[sigma].sub.T]) of live animals in tanks is obtained from a comparison of the coherent and incoherent acoustical intensities reverberated in a tank (de Rosny and Roux, 2001, 2003). The accuracy of this measurement technique was shown by using standard metal spheres (Demer et al., 2003). This technique was successfully used on krill (Demer and Conti, 2003; Conti et al., 2006a), fish (Conti and Demer, 2003), and humans (Conti et al., 2004). In our study, we explored the potential and limitations of the method to characterize the broad bandwidth sound scattering from bocaccio (Sebastes paucispinis).

Materials and methods

The total scattering cross section, ([[sigma].sub.T], of bocaccio was measured over acoustic frequencies ranging from 10 to 150 kHz with a group of fish (n=20) swimming freely in a large, insulated fiberglass tank at Hubbs-SeaWorld Research Institute, San Diego, CA, on 1 and 2 July 2004. The tank had 5.1 cm of foam insulation on the exterior, measured 2.44 m in diameter, and was filled with seawater to a depth of 1.37 m (V [volume]=6.4 [m.sup.3]). The pool was thermostated at...

NOTE: All illustrations and photos have been removed from this article.



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