Density-Dependent Catchability of Spot Prawns Observed Using Underwater Video

Abstract

Understanding how fishing gear catches target species is an important part of understanding the impacts of commercial fishing. Here, we use underwater video to investigate the catch dynamics of spot prawn (Pandalus platyceros) traps, a fishing gear used in a large commercial fishery in British Columbia, Canada. We report, for the first time, interactions that occur as prawns accumulate in traps during the first eight hours of trap deployment at depths between 75 and 100 m, and test whether catchability of prawns depends on the density of prawns in and around traps. We found that prawn catchability decreased as the number of prawns in the trap increased. This process was driven by a diminishing proportion of approaching prawns that made entry attempts, as well as a reduced likelihood of entry attempts being successful as traps filled with prawns. Very few prawns exited traps during observations, but final catch rates demonstrated that exits must have occurred after the termination of our videos. Recording and examining the full 24 hours of a typical soak would clarify how trap saturation is achieved.