Report on progress made on the hake cannibalism and inter-species predation model

The purpose of this report is to provide an update on work done since IWS 2014 and to highlight areas where input from the panel would be useful.

In summary, this work aims to build on that undertaken by Punt and Leslie (1995) and Punt and Butterworth (1995) in the development of a multispecies model for the two Cape hake species, Merluccius capensis and M. paradoxus.

There, the authors aimed to construct a model which included hake, seals and "other predatory fish" and then to use this model to assess the consequences of different levels of consumption of hake by seals on the hake fishery in the context of the change in the size of sustainable hake TACs and catch rates. They also aimed to investigate the effect of seal culling on the fishery. In the years that have passed since, more data have become available, and the hake assessment models have been continuously developed. The aim is to update the work done by Punt and Leslie (1995) with new data, and to extend the model to the level of the current hake assessment model.

At the time of IWS 2013, the most notable problems surrounding the cannibalism model were extremely slow model runs as well as instability arising from the manner in which the initial population equilibrium setup was structured in the model. Suggestions made by the panel as well as interim modifications to the model have helped to resolve these issues. At IWS 2014, the greatest area of concern was that the model battled to fit all of the proportion of hake in diet, daily ration and trend data simultaneously, although the methodology and preliminary results showed promise for a reasonable base case model that takes hake predation and cannibalism into account.