Initial Applications of Statistical Catch-at-Age Assessment Methodology to Atlantic redfish

Age structured production model assessments are explored for four redfish populations. The reason for introducing age-structure into the models is to allow a sounder reality check of the estimates of the survey catchability coefficients q that result when the models are fit to data. The data fitted are the survey abundance trends plus catch-at-length information from both surveys and the commercial catches. The catches-at-length are used to estimate selectivity-at-age relationships, though some assumptions are required, particularly for the commercial information which is not available in species disaggregated form. Only for S. fasciatus in Unit 3 is the survey trend compatible with the expected impact of past catches in terms of a simple density-dependent population model, and the associated assessment results could be used to inform reference point determination for this population. However for the other three populations considered (S. mentella and S. fasciatus in Units 1+2 and S. fasciatus in 2J3K) further assumptions are needed (e.g. regime shifts related to changes in productivity) to achieve compatibility between model output and survey trends, so that population model-based assessment of the current status of these populations is problematic. The most immediate concern for these three populations would seem to be whether or not current levels of catch are sustainable, and a suggestion is made as to how that might be addressed.