Antarctic krill are robust and can withstand capture and escape from a trawl, according to a new study by the Institute of Marine Research in Norway. Only a small percentage (4.40%) of krill escaping through the trawl meshes.
‘We knew from previous studies that krill of many different sizes can escape even the smallest meshes in a commercial trawl. The question was how this affects the krill, and whether or not they suffer damage and eventually die because of the interaction with fishing gear,’ said Bjorn Krafft, a researcher at the Institute of Marine Research (IMR) and lead author of krill study.
Antarctic krill is considered one of the least exploited fisheries resources worldwide. Exploitation levels are modest and there is significant potential for this to be increased. Norway is the largest fishing nation active in the Southern Ocean, and in 2015 Norwegian vessels caught approximately 150,000 tonnes of Antarctic krill.
Antarctic krill are a key food source for fish, marine mammals and seabirds, and strong concerns about the impact the fishery might have on the krill-dependent species have been expressed. The concern is further strengthened because of observed environmental changes, with temperature increases in some parts of the Southern Ocean, that may affect the production, distribution and life cycle of krill.
Krill that dies after being in contact with fishing gear contributes to the indirect mortality in the krill population, and establishing figures for this is important for calculating overall fishing mortality.
Assessment was carried out using an outer collection bag fixed around the usual codend, retaining the animals that had initially escaped through the meshes. These escaping krill were kept on board for observation to assess whether they had suffered stress in the process and to establish effects on survivability.
‘We found that mortality was low. In our study only 4.40% of krill escaping trawl meshes died. Many pelagic species show very low tolerance and high mortality under these circumstances. We can say that krill are robust animals that are able to tolerate a process in which they first captured and then escape the trawl,’ said Bjorn Krafft.
‘Using these studies, we can now more accurately calculate how extensive krill loss actually is. We can also more reliably calculate the effects on the species that feed on krill.’
The studies were carried out in collaboration with SINTEF, DTU Aqua in Denmark, and with financial support from the Norwegian Research Council. The commercial krill harvesting companies Aker BioMarine AS and Rimfrost AS contributed vessels and facilities.
Quantifying the Escape Mortality of Trawl Caught Antarctic Krill (Euphausia superba), by Bjorn A. Krafft, Louis A. Krag, Arill Engås, Sigve Nordrum, Inge Bruheim and Bent Herrmann can be found here.
