Estimating unaccounted fishing mortality using selectivity data: an application in the Hauraki Gulf snapper (Pagrus auratus) fishery in New Zealand

Unaccounted fishing mortality has been the focus of a growing body of resea rch. Its importance as both an input to stock assessment models and as info rmation to be presented to fishery managers is now being realized. Such inf ormation is usually gathered by expensive at-sea sampling programmes and th rough complex experiments. Proposed here is a modeling approach that use es timates of selectivity to estimate discard and escapee mortality through a series of simple equations. The probabilities of first, being caught by a f ishing gear, and second, retained to become part of the landings, are model ed as a function of fish length. A Variety of methods have been proposed fo r the presentation of information about unaccounted fishing mortality and a n example of both a graphical presentation of the fate of fish encountering fishing gear and a tabulated set of efficiency indices are described. As a n example the proposed approach is applied to the Hauraki Gulf snapper (Pag rus auratus) fishery off the northeast coast of New Zealand. It is found th at overall the fishery is quite efficient when compared to reported oversea s fisheries and that unaccounted fishing mortality may not be a significant component of total fishing mortality. (C) 2000 Elsevier Science B.V. All r ights reserved.