Background information to support development of a feedback management strategy for the krill fishery in Subarea 48.1

Here we compile eight vignettes that, together, provide the background data and information needed to support development of a feedback management strategy for the krill fishery in Subarea 48.1. In this compilation, we provide support for combining SSMUs into groups of SSMUS (gSSMUs) to form larger management units. We believe that identifying management areas that are larger than SSMUs within Subarea 48.1 will both facilitate and expedite the allocation of a catch limit in the subarea without negatively impacting the krill fishery while simultaneously mitigating risks to krill-dependent predators. We review the logic for these gSSMUs and then use the gSSMU concept in many of the vignettes that follow. In the second vignette, we examine the influence of oceanic and shelf circulation on the distribution of krill biomass and commercial fishery catch and effort to better understand how retention and concentration mechanisms aggregate krill in fishable quantities above the background concentration. We use a circulation model and particle tracking to show that areas with high catches also tend to be areas of retention and are generally separated from the prevailing circulation. These findings indicate that local depletion within these areas is more likely when regional krill abundance is low.  In the third vignette, we examine the correlations between acoustic estimates of krill biomass and two measures of fishery performance, krill catches and nominal catch rates (CPUE), within and between gSSMUS and show that there is little correlation between biomass estimates from research surveys and either performance measure. In the fourth vignette, we examine how temporal variability in the seasonal sea-ice coverage of gSSMUs is related to krill catches. We show that krill catches decline rapidly when gSSMUs are more than 50% covered in ice, which acts as an environmentally-driven constraint on the duration of the fishing season in different gSSMUs. In the fifth vignette, we examine the overlap of krill catches and predator foraging distributions using data from a large telemetry study involving multiple species of birds and mammals during summer and winter. We show that direct overlap of krill-dependent predators with the krill fishery on small spatio-temporal scales is common throughout the Antarctic Peninsula region. Such overlap highlights the potential for competitive interactions between predators and the krill fishery and underscores the goal of the Commission to prevent concentration of fishing effort in small areas. In the sixth vignette, we show that fluctuations in krill size and biomass are related to changes in the durations of foraging trips made by Antarctic fur seals. In the seventh vignette, we quantify functional relationships both between local krill biomass and penguin performance and between local krill harvest rates and penguin performance. These functional relationships empirically demonstrate reduced penguin performance in the Antarctic Peninsula region when local krill biomass is low or when local krill catches are high relative to local biomass. The results further demonstrate that krill fishing in Subarea 48.1 may have already had negative impacts on penguin performance. In the final vignette, we evaluate three alternatives for allocating catch limits for krill among gSSMUs in Subarea 48.1. These alternatives are not exhaustive, and other alternatives can certainly be developed. Together, all eight vignettes provide background material referenced in other papers (AERD 2016b and 2016c) that Watters et al. (2016) use as the basis of a proposed feedback management strategy in Subarea 48.1.