A comparison between acoustic and bottom trawl estimates to reconstruct the biomass trends of sardine and anchovy in the Strait of Sicily (Central Mediterranean)

We evaluated the information on stock abundance of sardine and anchovy collected during the MEDITS trawl survey in the north sector of the Strait of Sicily (central Mediterranean Sea). A comparison between the temporal trends in biomass, derived from the MEDIAS hydro-acoustic surveys carried out along the south coast of Sicily since 1998, and the corresponding MEDITS index of biomass of the two species was performed. The two time series appeared highly correlated (r=0.85) depicting a very similar temporal trend in biomass for both sardine and anchovy. We also used the biomass index calculated from the hydro-acoustic surveys to estimate the MEDITS catchability coefficient q for the two species per year. The annual variability of q was rather high. The average q value was 0.016 (CV = 60%) for sardine and 0.011 (CV = 55%) for anchovy, respectively, indicating that the bottom trawl net sampled only a very reduced fraction of the biomass of small pelagics (1.1-1.6%) available in the trawled area.