The Spatial Overlap Analysis (SOA, previously Risk Assessment) forms part of the three-part management approach endorsed by CCAMLR in 2019. We have implemented the SOA in the proposed candidate Management Units (MUs) described in Warwick-Evans et al. (2024, Scenario 1) and in two slightly modified versions of these candidate MUs (Scenarios 2 and 3). We also conducted a sensitivity analysis to assess the impact of one of the assumptions of the SOA: that fishing will be equally spread within a management unit, whereby we implemented the SOA assuming that catch within a candidate MU where the fishery has previously operated would be taken from within the footprint of previous fishery operations.
Our results show that in the baseline implementation for Scenarios 1, 2 and 3 the majority of catch is assigned to DP1 and Gerlache Strait during winter. However, in Scenario 3 the allocations to DP1 is slightly lower, with additional catch assigned to Elephant Island and Bransfield Strait. This results in a slightly more even distribution of catch between candidate MUs than Scenarios 1 and 2. In the desirability implementation, the majority of catch is assigned to the Bransfield Strait and Gerlache Strait during winter in all three scenarios. Regional risk is similar for Scenarios 1 and 2 and increases in the desirability implementation. It is not possible to compare regional risk with Scenario 3 as the spatial extent of the SOA footprint is different.
The sensitivity analysis showed differences in the catch allocation if the SOA is run assuming that fishing will concentrate within a management unit compared with if catch is equally distributed within a management unit. In particular, the proportion of catch allocated to the Gerlache Strait during winter is considerably lower if the SOA is implemented assuming that fishing will concentrate.
Our results provide a means of apportioning the krill catch under various scenarios. However, we highlight that by assuming catch will be equally distributed within an MU we may underestimate the risk to the ecosystem and may assign the proportion of catch allocated to each candidate MU in a way that does not minimise risk, if the fishery does indeed concentrate within MUs.