Interactions between seals and trawl fishing gear often result in by-catch and incidental mortality. While by-catch rates are relatively well known, factors that contribute to these interactions, including seal behaviour whilst in the net, are poorly understood. In this study, mid-water trawl operations in the Commonwealth Small Pelagic Fishery were monitored using an underwater camera system. Video footage was available for almost 100 trawl shots.

Seals were observed inside the trawl net in 55% of tows, the interaction rate varying seasonally and peaking at over 70% between March and August. Seals entered the net through all phases of the trawl operation, with a significantly higher incident rate experienced whilst shooting the gear. There was a strong diurnal pattern in the occurrence of seals in the net that largely mirrored the distribution of fishing effort over the 24-h period. Seals entered and exited the net via the net mouth as well as the seal exclusion device escape hole. Not all seals escaped and mortalities were observed. By enlarging the escape hole it was possible to significantly reduce the mortality rate. In some cases interaction times substantially exceeded the maximum documented dive duration for fur seals, implying that not all seals that escaped would have survived.