A review of Fishery-Independent assessment models, and initial evaluation based on simulated data

fishery indipendent model



Large uncertainties in the catch data (official landings and discards) are undermining ICES'
ability to provide valid management advice based on the conventional approach of analytical
assessments. There is thus an urgent need to consider alternative tools that do not depend on long series of precise catches, with their age composition. This paper presents a few fisheryindependent assessment models developed by the EU project FISBOAT (Fishery Independent Survey Based Operational Assessment Tools). It also reports on rudimentary tests based on simulated data, following the same protocol as an evaluation study conducted by the US National Research Council in 1997. It appears that the survey-based assessment models at hand are able to reliably capture the major signal in biomass and recruitment, although they smooth out transient changes. However, they cannot provide absolute abundance estimates, but only relative values on an arbitrary scale. Their operationalisation in ICES would thus require an adaptation of the advisory framework, in terms of nature of the advice and definition of reference points; indeed, this might be needed anyway, if we were more lucid about the myth of VPA estimates being absolute. It is also noted that survey-based approaches have the potential to provide much more rapid updates of the state of stocks than catch-based methods.