Analysis of krill fishery behaviour in the southwest Atlantic: potential signals for moving fishing activities amongst SSMUs

This paper outlines the difference in fishing patterns between regions (Subareas) and seasons by analyzing CPUE (catch per hour) patterns towards the end of their sets of operations before leaving a SSMU, as well as its timing of the day, diurnal pattern of CPUE and fishing depth. Vessels tend to move between SSMUs frequently in summer, especially in SSMUs in Subarea 48.1 mostly spending less than a day to explore the fishing grounds from multiple options for the start of the fishing season. Vessels move around less frequently in Subarea 48.2 during the summer season because of only one viable SSMU, but in autumn, there appear to be some opportunistic fishing on the way to Subarea 48.1 to 48.3. Continuous operations in a single SSMU are longer later in the fishing season, especially for winter operation in Subarea 48.3, however forced to be relatively short in Subarea 48.1 due to changing ice conditions etc. Skippers tend to allow a day to decide before leaving a SSMU after over days of continuous operations. This behaviour suggests there are two types of tactics employed within an SSMU. The first set of tactics is to optimize factory supply. When factory supply diminishes, the skipper may initiate a second set of pre-departure tactics over one day to determine if factory supply can be regained. CPUE and towing depth generally showed clear diurnal patterns. It was not possible to outline vessel patterns of pumping methods due to small amount of data accumulated so far. More detailed data is need to be obtained to improve these analyses and models in the future.