Acoustic assessment and distribution of the main pelagic fish species in the ICES Subdivision IXa South during the ECOCADIZ 0813 Spanish survey (August 2013).

Abstract

The present working document summarises the main results from the Spanish (pelagic ecosystem‐) acoustic survey conducted by IEO between 2nd and 13th August 2013 in the Portuguese and Spanish shelf waters (20‐200 m isobaths) off the Gulf of Cadiz onboard the R/V “Cornide de Saavedra”. The survey dates were somewhat delayed in relation to the usual ones and to the anchovy (Engraulis encrasicolus) peak spawning as well. 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. The bulk of the anchovy population was concentrated in the Spanish shelf, with a residual nucleus to the west of Cape Santa Maria. A delay of the usual survey dates may be the reason of a higher relative importance of smaller anchovies in the population as a probable consequence of the incorporation of the first waves of recently recruited juveniles to the adult population. The total biomass estimated for anchovy was 8.5 thousand tonnes (609 million fish), the lowest estimate in its series. Sardine showed a distribution pattern almost complementary to that described for anchovy, with higher densities occurring over the inner‐middle shelf of both extremes of the surveyed area, mainly west to Cape Santa Maria, and in shallower waters than anchovy. Sardine yielded a total of 9.7 thousand tonnes (232 million fish). The 2013 sardine estimate was also the lowest one in its series and corroborates a clear recent decline in the population which has also been evidenced by the PELAGO surveys. Chub mackerel was present all over the surveyed area although showed a more “oceanic” distribution in the westernmost waters. The species was the most important in terms of assessed biomass, rendering estimates of 31.3 thousand tonnes (333 million fish). 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 in the study area during the survey.