Assessments of species in the Australian South East Fishery can be sensitive to the method used to convert from size-to age-composition data

Abstract

Information about the age-structure of the catch is one of the primary inputs to many of the methods of stock assessment currently applied to SEF species. Two methods for calculating the catch-, mean length-, and mean mass-at-age matrices from the data collected from the fishery are outlined. These methods are illustrated by applying them to data for blue grenadier, Macruronus novaezelandiae, and eastern school whiting, Sillago flindersi. The assessment and risk analysis results for blue grenadier are highly sensitive to the choice of method, whereas those for eastern school whiting are not. It is recommended that a method that allows for inter-annual variation in mean length- and hence mass-at-age should be the standard for SEF stock assessments but that sensitivity to alternative methods needs to be examined routinely.