Search

Pelagic fish distributed near the surface off Angola were sampled with a medium-sized pelagic trawl having a vertical opening of about 20m. Numerous trawls targeting on dense sardinella schools (Sardinella maderensis and Sardinella aurita) failed to yield large catches. Schools that were at the trawl depth as the vessel passed over them were often observed far below the foot rope of the trawl, indicating vertical avoidance. The net sonde transducer often recorded schools in the net mouth for long periods: it was assumed that these fast-swimming fish were able to swim along with the trawl, and escaped when the towing speed was reduced during hauling. No correlations were found, however, between towing speed (2.7–5.0 knots) and the total catch of sardinella. Increasing the two duration during the day to more than 2h also failed to yield consistently higher catches. A negative correlation at night between tow duration (15–60min) and catch size arose simply because the trawl was towed for a longer time to obtain adequate samples in areas with scattered recordings. During the day, sardinella was caught both inshore and further offshore, while horse mackerel (Trachurus trecae and Trachurus capensis) was caught further offshore only. Both species were well represented in catches made at night. There were substantial day and night differences in the length distributions of sardinella, with small sardinella being caught only at night. [ABSTRACT FROM PUBLISHER]