Observation on the interactions between marine mammals and mid-water krill trawl

An observation on the interaction between marine mammal and krill midwater trawl was carried out onboard the Chinese krill fishing vessel Fu Rong Hai during the 2018/19 fishing season. The inner-trawl observation was made using an Underwater IP Camera, while sea surface observation was conducted visually with the aid of a SLR Camera and a Marine Binocular. Sea surface observation in Subarea 48.3 showed that the number of fur seal (Arctocephalus gazelle) around the fishing vessel increased from late July to August then decreased in September, and over 85% of the fur seals was observed chasing the trawl behind the codend during retrieving of the net. Although large number of Antarctic fur seal were observed at sea surface around the vessel during fishing operation, none seal by-catch was found during this fishing season and none identifiable marine mammal was observed inside the trawl either. Simultaneous observation of krill swarms detected by the echosounder revealed a linkage between the behavior of the seal and the depth of krill swarms. It is speculated that when krill swarms were available in reachable shallow depth (less than 50 m), Antarctic fur seal would feed on this krill and thereby was not attracted extensively by the presence of the fishing vessel. Chasing after the krill-filled trawl at sea surface seems to be a foraging related phenomenon.