Size selectivity of Muller's pearlside (Maurolicus muelleri), glacier lanternfish (Benthosema glaciale) and krill in trawls targeting the mesopelagic fish

The growing interest in harvesting mesopelagic fish increases the need for knowledge about trawl designs with high catch efficiency. Limited swimming ability of small mesopelagic species makes it important to consider potential net selectivity along the entire trawl body. Net makers designing trawls for harvesting mesopelagic species need to know which mesh sizes can be used in the low tapered belly sections and in the codend of trawls to avoid catch loss due to size selectivity. Therefore, we used an experimental design that enabled us to quantify both aft belly and codend size selection of Muller's pearlside (Maurolicus muelleri), glacier lanternfish (Benthosema glaciale), and krill (Euphausiidae) for three different mesh sizes relevant to the mesopelagic fishery. Our results confirmed that size selection needs to be considered in both the belly section and codend of the trawl but that the size selection in the codend is much more effective than that in a short, low tapering belly section. Further, predictions based on the estimated size selectivity showed that the catch efficiency can be low with the currently used mesh sizes in trawls targeting mesopelagic species, demonstrating that the choice of mesh size in the codend is a critical parameter.