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he Working Group on Acoustic and Egg Surveys (WGACEGG) coordinates pelagic surveys for a number of stocks and provides monitoring for the two major sardine and anchovy stocks in ICES areas 6, 7, 8, and 9. The group evaluated small pelagic fish biomass indices derived from acoustic and Daily Egg Production Method (DEPM) surveys in ICES areas 6, 7, 8 and 9. These indices have been provided to the ICES Working Group on Southern Horse Mackerel, Anchovy and Sardine (WGHANSA), the Working Group on Widely Distributed Stocks (WGWIDE) and the Herring Assessment Working Group for the Area South of 62ºN (HAWG) stock assessment group, to serve as fishery-independent input for analytical assessment purposes. DEPM and acoustic indices were derived based on data collected using independent methods. Acoustic- and DEPM-derived biomass indices from quasi-synoptic surveys conducted in the Bay of Biscay in spring were compared, to assess the presence of potential bias and to improve the precision of fish stock biomass estimates. The DEPM-based anchovy biomass index was 22% higher than the acoustic index in 2019. Unusual concentrations of anchovy in Eastern Cantabrian Sea, an area not covered by the acoustic survey, and the presence near the sea surface of actively spawning individuals possibly under-sampled by acoustics in central Bay of Bay had been postulated as potential causes of this discrepancy. No significant difference was found between sardine biomass indices derived from DEPM and acoustics in 2019. The group has updated its database of standard gridded maps covering the European Atlantic area. This initiative continues to inform on the spatial dynamics of various parameters collected during the surveys coordinated under the auspices of the group (fish acoustic densities, anchovy and sardine egg abundance, surface temperature and salinity). Results of an analysis of the time series of gridded maps (anchovy and sardine acoustic density, surface salinity and temperature) showed quantitative changes in the spatial and temporal distribution of anchovy and sardine over the last 15 years, and further define their habitats in European Atlantic waters in spring. The timing and spatial coverage of DEPM and acoustic surveys that will be conducted by group members in 2020 were planned to optimise the monitoring of anchovy and sardine populations and their pelagic environment in the European Atlantic area. The synoptic nature of the survey components has been assessed for each target species. A manual describing the protocols used during the DEPM surveys coordinated by the WGACEGG group was reviewed, and writing of a manual of WGACEGG acoustic surveys continued. Both manuals will be available in 2020. The final results of the 2017 sardine DEPM assessment were endorsed by the group.

The majority of the drifting fish aggregating devices (DFADs) used by the industrial tropical tuna purse seine fishery are deployed with satellite linked echo-sounder buoys. These buoys provide information on the accurate geo-location of the floating object and estimates of fish biomass underneath the DFAD. However, current echo-sounder buoys do not provide information on species or size composition under the DFADs. The aim of this study is to progress towards improved remote biomass estimates using the previous models proposed in the field, based on existing knowledge of the vertical distribution of non-tuna and tuna species at DFADs and mixed species target strengths (TS) and weights. Aiming to this objective, we use 287 fishing set information and their corresponding acoustic samples from echo-sounder buoys prior to the fishing set in the Indian Ocean. Results show that manufacturer’s biomass estimates generally improve, being this improvement more pronounced in NW Seychelles and in Mozambique Channel. However, the improvement of the biomass estimates is not as large as expected, so it can be further improved, indicating that the large spatio-temporal variability in the Indian Ocean is not easily considered with a single model. Potential reasons driving echo-sounder buoy estimates variability, as well as the limitations encountered with these devices are discussed, including the lack of consistent TS values for tropical tunas, among others

Expedición MALASPINA-2010, With a current estimate of about 1000 million tons, mesopelagic fish dominate the world total fish biomass. However, recent acoustic observations show that mesopelagic fish biomass could be significantly larger than the current estimate. We combined modeling and a sensitivity analysis of the acoustic observations from the Malaspina2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher biomass. We show that there is a close relationship between the open ocean fish biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fish in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fish on the oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring in deep waters around 10 % of the primary production., Consolider-Ingenio 2010, CSD2008-00077