Acoustic properties of Salpa thompsoni.
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Salps are common members of the world oceans planktonic community (Madin, et.al., 2006). In the southern ocean, both krill (Euphausia superba) and salps (Salpa thompsoni) can occur in dense aggregations (Loeb et al, 2009, Atkinson et al. 2004, Woodd-Walker et al., 2003). Krill, an important part of pelagic food webs, are prey of many Antarctic marine mammal, sea bird, penguin, and fish species. They are also subject to a significant fishery. Each year there are krill surveys using high frequency acoustics scattering techniques supplemented by ground truthing with macrozooplankton nets and pelagic trawls to provide the data from which sound scientific advice about harvesting levels can be made (Madureira et al, 1993; Brierley and Waktins, 1996; SC-CAMLAR, 2000). While salps do not often form krill-like aggregations, they do aggregate and form dense layers like those that krill are also known to occur in. Recent studies suggest that the salps have an acoustic frequency response similar to that of krill and the ability to discriminate the two groups was a problem (Woodd-Walker et al., 2003). Our study was undertaken to understand how this might be possible.