© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Mixed and Multi-Stock Fisheries
a The Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory Pakefield Road, Lowestoft, Suffolk, NR33 OHT, England, UK
b Department of Agriculture and Rural Development for Northern Ireland River Bush Salmon Station, Bushmills, Co. Antrim, BT55 7BL, Northern Ireland, UK
c National Marine Fisheries Service, Northeast Fisheries Science Center 166 Water Street, Woods Hole, MA 02543, USA
*Correspondence to L. T. Kell: tel: +44 1502 524257; fax: +44 1502 513865. e-mail: l.t.kell{at}cefas.co.uk; walter.crozier{at}dardni.gov.uk; chris.legault{at}noaa.gov.
The September 2003 ICES Annual Science Conference was held in Talinn, Estonia, and Theme Session V was "Mixed and multi-stock fisheries – challenges and tools for assessments, prediction, and management." The theme session brought together researchers from the salmonid and marine fishery fields to address common problems faced when multiple fleets harvest a common stock, or multiple stocks are harvested by a common fleet. In all, 23 papers were presented during the theme session, prefaced by an invited plenary lecture by Randall Peterman that focused on challenges facing fisheries scientists and managers. The ten papers that follow represent the diversity of topics in the Theme Session, but all focus on approaches to overcome the uncertainty inherent in these complex situations.
Fleets and fisheries that harvest multiple stocks, and stocks harvested by multiple fisheries, face a number of complexities. Less productive stocks in a mix of stocks may suffer unsustainable mortality, while more-productive stocks continue to support sustainable catches. Stocks harvested together may be at a very different status relative to safe biological limits, which would make different harvest strategies necessary in the same fisheries. Where fisheries take multiple stocks of the same species, uncertainties about allocating catches to stocks present special assessment problems. Projections to guide advice on effort levels appropriate for different stocks in the harvested complex can also thwart traditional approaches, and can produce results that are either incompatible across stocks, or not straightforward for managers to apply. Therefore, the objectives for Theme Session V were to describe developments in assessment and projection methods for multi-stock and multi-fleet fisheries, and to discuss opportunities for applying new concepts more widely.
Management of complex systems is not necessarily facilitated by making stock assessment and management more complex. Ideally, simple rules should be devised that are robust to the pervasive uncertainties in such systems. However, the process by which these simple rules could be found would incorporate as much complexity as possible.
The papers presented here comprise Peterman's plenary lecture, five papers from salmonid research, and four from marine research. The plenary lecture itself posed six challenges for fisheries in general, and mixed fisheries in particular: pervasive uncertainties; probabilities for uncertain quantities; time-varying parameters; evaluating management options; communication management; and objectives and trade-offs. All of these six challenges except time-variance of parameters, and objectives and trade-offs, are addressed in the written version of the lecture that follows this Introduction. The salmonid papers progress from an overview of the mixed-stock fisheries for Atlantic salmon (Crozier et al.) to specific examples of problems faced by mixed-stock fisheries in estimating abundance pre-fishery (Potter et al.), and considerations in the use of spawner reference levels in mixed-stock fishery management (Chaput). A Bayesian hierarchical analysis example (Ó Maoiléidigh et al.) and genetic considerations in harvesting stocks in mixed aggregations (Hindar et al.) round out the salmonid papers. The marine papers examine the factors to be considered when transitioning from single-species to mixed-species management (Vinther et al., and Holley and Marchal) and provide case studies of management for a multispecies fishery (De Oliveira and Butterworth), and mixed-fisheries fishing strategies (Hutton et al.).
The timely publication of these papers owes much to the referees, who prepared comprehensive reviews, and the authors, who made the required revisions of their manuscripts within tight deadlines.
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