Exploring the effect of installing collars on snow crab (Chionoecetes opilio) pots in Newfoundland and Labrador: Do collars improve size selectivity?

The snow crab ( Chionoecetes opilio ) fishery is the province of Newfoundland and Labrador’s most valuable fishery. The snow crab fishery is limited to land only hardshell (inter-molt) male adult crabs with a carapace width (CW) ≥ 95 mm. Bycatch consists of sublegal male (CW < 95 mm), softshell (post-molt), and rarely, female snow crabs. This manuscript documents a comparative fishing experiment evaluating the effects of installing external plastic collars on the tops of typically used conical pots. The goal of this work is to improve size selectivity by restricting the entry of bycatch while maintaining or improving the capture of target-sized snow crabs. Smaller (female and sublegal) or weaker (softshell) crabs were hypothesized to be unable to reach or climb beyond the distance of the collar. Four experimental conical pots with non-selective, small mesh jackets (40.5 mm mean; s. d. = ±1.4 mm; measured inside the knots) and collars of 180 mm, 240 mm, 300 mm, and 180 mm with a 51 mm lip, were compared with small mesh pots with no collar and traditional pots with traditional mesh (137.0 mm mean; s. d. = ±1.9 mm; measured inside the knots) and used in the fishery. Generally, results showed that adding a smaller collar to snow crab pots produced similar catches to traditional snow crab pots for target-sized snow crab, and that large amounts of target-sized snow crab were lost with the larger collars tested. Conversely, sublegal-sized crabs were generally caught more (except for the 300 mm collar) and had high retention for the smaller collars tested. The design, as tested, requires additional refinement as small male and female crabs were unable to escape once they entered the pot. Future research could investigate the additional use of escape gaps to assist the egress of these small crabs.