Monitoring and managing the effects of environmental change on toothfish assessments

This paper presents a ‘first-step’ proposal for CCAMLR to consider the effects of environmental variability and change on management advice from toothfish assessments. We focus on changes to environmental conditions that are maintained over a number of years, which includes the effects of global climate change. The effects of environmental variability and change on toothfish population dynamics and productivity are largely unknown and are difficult to predict given our current understanding of the Southern Ocean environment and ecosystems. However, we note that existing information from toothfish fisheries can be used to identify changes that have occurred, or changes that may currently be occurring, as a consequence of environmental variability and change, including that due to global climate change.

We note that CCAMLR’s fishery reports may be revised to include a new section on changes in model parameters and productivity assumptions that have been found to have occurred, and that these may be related to the effects of environmental variability and change. We note that causal relationships between observed changes in stock productivity and environmental conditions are not required for this understanding to be useful. We propose that consideration of changes in biological parameters and work to understand the impact of these changes on yield assessment would reduce uncertainty in management advice. The parameters that could be evaluated to for the effects of environmental variability and change would include mean recruitment (ȳ), recruitment variability (σ_R), mean length at age, mean weight at length, natural mortality (m), and maturation ogives. Other factors that may impact assumptions underlying the assessments that could also be considered, including stock distribution (for example, for its impact on tagged fish distribution or research survey interpretation), sex ratio (indicating maturation or other sex specific changes), and the ages or lengths observed in the fishery (indicating changes in vulnerability patterns or mortality). Further, we recommend that methods be developed that can be used to evaluate the importance of observed changes in the toothfish productivity or distribution on resulting advice.