University of Tasmania

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Estimating illegal and unreported catches from marine ecosystems: A basis for change

journal contribution
posted on 2023-05-17, 17:06 authored by Pitcher, TJ, Reginald WatsonReginald Watson, Forrest, R, Valtysson, HP, Guenette, S
To evaluate the impacts of fishing on marine ecosystems, the total extraction of fish must be known. Putting a figure on total extraction entails the difficult task of estimating. in addition to reported landings, discards, illegal and unmandated catches. Unreported catches cast various types of shadow. which may be tracked and estimated quantitatively. Some shadows of unreported catches are reviewed, for example, an innovative, well-funded NGO publicizes illegal catch in the Southern Ocean. For various reasons. official figures often have the implicit but unacceptable assumption that such categories are null. We present an estimation procedure based on adjustment factors taken from observer reports, correspondents and published information that track changes in a regulatory regime, and hence reflect incentives and disincentives to misreport. Monte Carlo simulations address uncertainty using multiple sources of information to provide upper and lower estimates. Once in place, this method provides preliminary estimates that may be refined without disruption. The method is demonstrated for fisheries in Iceland and Morocco. We use a 'by-species' approach for Icelandic cod and haddock, while the Morocco catch is divided into demersal and pelagic categories. Results suggest that Icelandic cod catches may have been under-estimated by between 1 and 14% at different times, and haddock by between 1 and 28%. Underestimation of Moroccan catches appears to have been as much as by 50%. These case studies show that it is possible to obtain estimates of misreporting. even when direct data are lacking. Our method encourages transparency because sources of information are presented so that uncertain values are easily identified, offering a basis for comment. collaboration and refinement in estimating illegal and unreported fishing.


Publication title

Fish and Fisheries








Institute for Marine and Antarctic Studies


Wiley-Blackwell Publishing Ltd

Place of publication

United Kingdom

Repository Status

  • Restricted

Socio-economic Objectives

Wild caught fin fish (excl. tuna)