Acoustic assessment and distribution of the main pelagic fish species in the ICES Subdivision IXa during the ECOCÁDIZ 0710 Spanish survey (July 2010).

Abstract

The present working document summarises the main results from the Spanish acoustic (pelagic ecosystem‐) survey conducted by IEO between 25th July and 1st August 2010 in the Portuguese (but with an incomplete coverage) and Spanish shelf waters (20‐200 m isobaths) off the Gulf of Cadiz onboard the R/V “Cornide de aavedra”. The survey season was coincident with the anchovy (Engraulis encrasicolus) peak spawning to achieve an acoustic estimate of its SSB in the study area as well. This year the surveyed area was reduced to an area limited by the waters placed between Cape Trafalgar and Cape Santa Maria. Abundance and biomass estimates are given for all the mid‐sized and small pelagic fish species susceptible of being acoustically assessed according to their occurrence and abundance levels in the study area. The distribution of these species is also shown from the mapping of their back‐scattering energies. In the sampled area, anchovy was distributed all over the shelf of the study area with the densest concentrations being recorded over the middle‐outer shelf in the westernmost area. The total biomass estimated for anchovy was 12.3 thousand tonnes (954 million fish) and sustained, as an average, by maller anchovies than those observed the last year. Sardine (Sardina pilchardus) occurred all over the inner‐middle shelf, in shallower waters than anchovy, and also showing the highest densities in the westernmost coastal waters of the sampled area. The species was the most important one in terms of both biomass (67 thousand tonnes) and abundance (2 thousand million fish) and showed vidences of a relatively good recruitment. Chub mackerel (Scomber colias) was almost absent in the shallower waters and in the whole central part of the sampled area. This species was amongst the species which less contributed to the total biomass and abundance of the pelagic species assemblage, with almost 3 thousand tonnes and 43 million fish only. Acoustic estimates for jack and horse‐mackerel species (Trachurus spp.), and bogue (Boops boops) are also given in the WD. No acoustic estimates either for mackerel S. scombrus or round sardinella (Sardinella aurita) were computed because their incidental occurrence or even absence in the study area during the survey. Because of the problems with the acoustic sampling coverage, results from this survey are not directly comparable with those provided by IPIMAR from its PELAGO10 spring survey, although some inferences on the most recent trends in the population levels of the main species may still be raised.