Acoustic estimation of the nycthemeral variability, of pelagic icthiofauna and plankton abundance in the Bay of Biscay: application to fisheries resources assessment and ecosystemic management
Supervisor: Guillermo Boyra (AZTI-Tecnalia Marine Research Division)
Anchovy (Engraulis encrasicolus) is one of the main commercial species in the Bay of Biscay. Every year a Total Allowable Catch (TAC) is set by the ICES and shared between France and Spain. In order to provide proper advice on the fishery management, annual monitoring and population estimates need to be conducted. Actually, anchovy biomass estimation is calculated from two different surveys, an acoustic survey and a plankton and adult survey based on the Daily Egg Production Method (DEPM). The objective of this project was the development of a methodology for acoustic estimation of abundance of Bay of Biscay anchovy and sardine using the acoustic data collected in the “Bioman” survey. These data differ from the typical acoustic data for abundance estimation in several aspects. First, the data were collected 24 hours a day, thus, about half of the acoustic data were collected during the night, when schooling aggregations disappear and fishes disperse increasing the difficulty of discriminating them from the plankton. Therefore, for the species discrimination, in addition to the typical pelagic trawls, a mask based on the different frequency response of the different organisms has been configured and applied to separate acoustic echoes in coarse taxonomic groups: fish (intended to refer to swimbladder bearing fish even though constraints are still to be refined), fluid-like (euphausiids, copepods, salps, siphonophores without gas inclusion and other large crustacean zooplankton) and others (mainly fish larvae and gelatinous and gas-bearing siphonophores). Also, the anchovy and sardine eggs collected for the DEPM were used to help to delimitate the positive areas of each species. The work has been based on the data of year 2012. The results obtained are consistent with the values expected according to both 2012 spring estimates obtained from the two methods: DEPM and Acoustics.