Effect of gear soak time on size selection in the snow crab pot fishery

Abstract

In the commercial pot fishery for snow crab (Chionocetes opilio), size selection by the pots is important for reducing catch sorting and unintended mortality. In addition to mesh size and shape, selection in the pots relies on every crab contacting the netting meshes, which makes the process complex because the odour of the bait tends to keep all sizes of crab in the pots. Thus, soak time may affect the extent of the use of the selective potential of the pots. This study was designed to assess the influence of soak time on size selectivity, and the methodology was applied to snow crab data collected in the Barents Sea. The results showed that a minimum soak time is required to reach the full size-selective potential of the pots. Specifically, a fraction of the small crabs inside a pot will not attempt to escape through the pot meshes when the pots are soaked for short periods of time (under nine days). Further, with short soak time, some of the crabs inside a pot will not make selectivity contact with the netting. Therefore, some crabs will not utilize the escape options through the pot meshes. This finding confirms the need for using a selection model that explicitly accounts for such a process when assessing snow crab size selection. Lastly, this study outlines how the concept of selectivity contact can formally be applied to model the effect of soak time on the size selectivity of the snow crab pot fishery.