Traditional acoustic surveys evaluate the biomass of small pelagic species in the shelf and slope areas. However, an unbiased acoustic survey needs to consider other species with a significant echo in the water column, such as krill, jellyfish, or lantern fish. There is also a growing interest for the migrating mesopelagic species that participate in the carbon flux between the surface areas and deeper waters (projects MAFIA and SCAPA). In order to acoustically differentiate these species, a better understanding of their acoustic signature (echo variability with frequency) is needed. New broadband systems are being developed worldwide with this goal.
This project will study mesopelagic species (micronekton and macroplankton) by acoustic methods, employing the new SIMRAD broadband system EK80. Collaboration between the Spanish institute (IEO), the University of Bergen, the Norwegian institute (IMR) and SIMRAD will allow to develop algorithms to extract the acoustic signatures of the targeted species (mainly Northern krill, myctophidae species and Cyclothone spp). Different denoising and clustering techniques will be tested to improve their identification.
The main scattering models to be compared with the observed signatures will be the gas bearing model by Andreeva (1964) and Weston (1967) for mesopelagic fishes, and the Stochastic Distorted Wave Aproximation (SDWBA) for Northern krill. Other scatterers considered will be cephalopods, pteropods, siphonophores and jellyfish.
Marian Peña, Instituto Español de Oceanografía. Centro oceanográfico de Baleares, Spain
Equipment kindly lent by Lars Andersen , SIMRAD, Norway
Migration of mesopelagic species at sunset. Marian Peña, IEO.