Acoustic detection of larval fish aggregations in Galician waters (NW Spain)
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AuthorsGarcía Seoane, E.(Eva); Álvarez Colombo, Gustavo; Miquel-Batle, J. (Joan); Rodríguez, J.M. (José María); Guevara Fletcher, C. (Carlos); Álvarez, P. (Paula); Saborido Rey, F. (Fran)
An acoustic study was conducted on the Galician shelf (NW Spain) during late winter 2012 to detect and assess larval fish abundance. An echo sounder operating with 18, 38, 70, 120 and 200 kHz split-beam, hull-mounted transducers was employed. We analysed the acoustic records in order to describe vertical and horizontal distribution patterns of larval fish aggregations. Regressions between acoustic backscattered energy and density of the most abundant species (Micromesistius poutassou) indicated that larvae with a swimbladder incremented notably the acoustic response at 38, 70 and 120 kHz. However, the predicted acoustic resonance at larval size and depth shows that the frequency of 120 kHz was likely ineffective in detecting fish larvae. The contribution of zooplankton (fish larvae excluded) to total scattering was negligible, even at the higher frequencies, except for several groups of fluid-like zooplankton, such as chaetognaths and polychaetes. Horizontal and vertical distributions ...
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