Five key issues with implications for draft WCRL FCPs

The following are amongst the major issues raised the draft FCPs and associated deadlines put forward by WWF/SASSI. There are various inter-relationships amongst these issues. The intent of this document is to summarise these so that the current draft FCP deadlines can be re-assessed in this context

Responses to reservations raised concerning the GLM analyses of and inferences drawn from the results from the island closure feasibility study

This document provides responses to a number of reservations which have been raised locally over the past year to the GLM approach for analysis of the island closure feasibility study, and conclusions inferred from the results. The issues covered range from whether catch provides an index of local fish abundance, the Clark model of a relation between shoal size and predation, comparisons with what occurred in Namibia, the appropriate period for which islands need to be closed, an argued need to apply model selection methods when developing the basis for a power analysis, whether a step-function relationship is appropriate for describing the different results from closure vs non-closure of an area around an island to fishing, and what the default conclusion about the impact of fishing near to penguin colonies should be

Response to comments on Winker and Sherley’s brief reply to FISHERIES/NOV/2019/SWG-PEL/34

This document provides a point by point response to comments made by Winker and Sherley on paper FISHERIES/NOV/2019/SWG-PEL/34

A Draft Framework for Assigning Probabilities to Alternative Assumptions concerning the Contribution of Sardine Spawning Biomass on the South Coast to Recruitment on the West Coast

A draft framework is put forward, by way of giving examples, to provide a quantitative basis for the combination of information from the hydrodynamics model and ts to stock-recruitment relationships to provide weightings for alternative hypotheses for the proportion of South Coast sardine spawning biomass which contributes to recruitment on the West Coast, for use in revising the pelagic OMP. The intent is that this draft be re ned prior to full deliberation, including the International Panel, at the November 28| December 2 workshop. Some suggestions are provided for further work desirably conducted before that event to facilitate discussions there

Some comments on the suggested use of the “one third for the birds” measure as a pelagic OMP performance statistic threshold

Although Cury et al. (2011) provide valuable insight into seabird population dynamics, their suggested application of a “one third for the birds” threshold is considered premature for a number of reasons. Further research remains needed to develop population models for the seabird populations considered, to utilise the assessments of their prey species to infer their abundance distributions in the absence of harvesting, and to take account of size structure effects. Such thresholds are not pertinent when Management Procedures (MPs) are used to provide management advice; there the relevant performance statistics relate to projected seabird abundance trends. The role of analyses such as those by Cury et al. (2011) in such circumstances is to inform the specification of the predator-prey models included in the operating models used for testing those MPs

Clarification regarding population growth rate parameters used for Southern Hemisphere humpback whales analyses

Papers on the dynamics of Southern Hemisphere humpback whales have described their growth rates in different ways. To attempt a simple summary, the following have been used (sometimes with different symbols to denote them or different forms of words to describe them): d : instantaneous growth rate (units yr–1) (sometimes indicated as r) l : annual growth rate (units yr–1) r : intrinsic growth rate (units yr–1) (sometimes indicated as rmax

On the use of aggregated vs individual data in assessment models

The conventional two-step process in fisheries assessments, whereby data are first aggregated to provide typically annual values before those are input to the assessment model, is compared to a single-step process where the individual data are input directly to the assessment model. The key point at issue is whether or not the latter process would provide estimates of key parameters that are (and are reliably estimated to be) more precise in circumstances where there is non-independence in the individual data. Arguments are offered that this non-independence does not introduce bias into estimates of precision for the aggregated case when observation error variance in the data is much less than process error variance in the assessment model. The utility of the random effects approach for addressing non-independence through working with individual data in a single-step process is queried; this is because of uncertainty about the bias in estimates of precision that may arise because of a lack of knowledge in most situations whether the structure assumed for the random effects will adequately account for the actual (and usually unknown) sources of non-independence in the data. Some aspects of the issue are illustrated by quantitative examples

The approach recently developed by the IWC Scientific Committee for taking formal account of the results of robustness trials, together with their relative plausibilities, in assessing risk when selecting between alternative candidate management procedures

A particular raison d’etre for the management procedure (MP) approach for providing scientific recommendations on management measures such as TACs is that it takes formal account of scientific uncertainties in its assessment of risks (primarily to the resource, but also to the fishery). This is achieved by considering the results of simulation tests which project the resource forward under the MP’s TAC-setting algorithm, not only under a model seen to best reflect the resource’s dynamics, but also under other models consistent with alternative plausible explanations of the data availabl