Investigations of squid stocks using acoustic survey methods

Acoustic survey methods are now widely used for stock assessments of finfish, both those with and without swimbladders, but their application to squid stocks has been limited in the past, probably because squid are not particularly strong targets for detection with echosounders. Experience with acoustic stock assessment of krill (Euphausia superba) has revealed that it is possible to survey effectively for a species that is a weaker target than squid; this is partly due to the tendency for krill to form dense aggregations. This paper discusses examples of acoustic studies on different squid species from the South Atlantic (Loligo gahi, Martialia hyadesi) and demonstrates that squid detection is possible in widely differing locations. L gahi observed during a survey on the Falkland Shelf were shown to have acoustic characteristics in common with smaller organisms which may enable them to be distinguished acoustically from finfish encountered in these waters. When a species has been characterised acoustically, the technique permits rapid surveys of large areas to determine the geographic range of a population, both outside the usual area that can be surveyed using fishing methods and within areas that are inaccessible to nets for some reason. Crown Copyright (C) 2001 Published by Elsevier Science B.V. All rights reserved.