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Trawlers involved in the Antarctic krill (Euphausia superba) fishery use different trawl designs, and very little is known about the size selectivity of the various gears. Size selectivity quantifies a given trawl's ability to catch different sizes of a harvested entity, and this information is crucial for the management of a sustainable fishery. We established a morphological description of krill and used it in a mathematical model (FISHSELECT) to predict the selective potential of diamond meshes measuring 5–40 mm with mesh opening angles (oa) ranging from 10 to 90°. We expected the majority of krill to encounter the trawl netting in random orientations due to high towing speeds and the assumed swimming capabilities of krill. However, our results indicated that size selectivity of krill is a well-defined process in which individuals encounter meshes at an optimal orientation for escapement. The simulation-based results were supported by data from experimental trawl hauls and underwater video images of the mesh geometry during fishing. Herein we present predictions for the size selectivity of a range of netting configurations relevant to the krill fishery. The methods developed and results described are important tools for selecting optimal trawl designs for krill fishing.

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Fifteen experimental diets with five levels of medium chain triglycerides (MCT) (0, 39, 78, 117 and 156 g kg−1) and three levels of cysteine supplementations (0.0, 2.5 and 5.0 g kg−1) were fed ad libitum to Atlantic salmon (mean weight at start 846 g) in sea water for 71 days. Nutrient digestibilities and protein retention improved significantly with increasing dietary MCT level following simple linear regression models. Positive effects were also observed on proteolytic enzyme activities in chyme of the pyloric region with peak value around 117 g kg−1 MCT. However, strong inverse relationships were observed between MCT level and feed intake, growth, body lipid and energy retention, and these effects accelerated with increasing MCT level. Also chyme dry matter decreased with increasing MCT level which also seemed to stimulate pancreatic and bile secretion. MCT did not significantly affect condition factor, dress out percentage, relative liver size or pH in gastrointestinal contents. The only significant effects of dietary cysteine supplementation were increased enzyme activities in chyme of the pyloric region with peak values for the intermediate cysteine level. The results elucidate the importance of diet composition for digestive functions, production efficiency and composition quality.