EISEVIER Fisheries Research 31 (1997) 11-17 Bioeconomics and catchability: fish and fishers behaviour during stock collapse Steven Mackinson a, *, Ussif Rashid Sumaila b, Tony J. Pitcher ’ a Fisheries Centre, 2204 Main Mall, University of British Columbia, Vancouver, B.C., Canada, V6T 124 b Department of Economics, University of Bergen, Norway and Christian Michelsen Instihde, Fantoftvegen 38, Fantoft, Bergen, Norway ’ Fisheries Centre, 2204 Main Mall, University of British Columbia, Vancouver, B.C., Canada, V6T 124 Accepted 10 February 1997 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON Abstract During periods of stock collapse, an increase in the catchability exhibited by many small pelagic fish is a consequence of two factors: their schooling habit and the remarkable efficiency of today’s technology intensive fishing fleets. The net result is that a virtually constant catch per unit effort may be achieved regardless of stock size. Three models of catchability used to highlight the consequences of fish behaviour and fishing technology during stock collapse (Pitcher, 1995) are extended to examine the effects of incorporating profit motivated economic behaviour of fishers. Three scenarios are examined: (1) cooperation by fishers to achieve maximum economic yield (MEY); (2) non-cooperation resulting in open access equilibrium; (3) non-cooperation with allocation of subsidies allowing fishers to increase effort beyond the open access equilibrium. Incorporating economic behaviour in the density-dependent catchability models may result in an alarming increase in the rate of stock depletion, since fishers maintain high profits even during low stock abundance. We discuss the consequences of using a model where catchability is assumed constant for the management of fisheries on small schooling pelagic fish. 0 1997 Elsevier Science B.V. Keywords: Constant CPUE model; Csirke-MacCall model; Schaefer model; Density-dependent catchability; Investment; Disinvestment; Small schooling pelagic fish 1. Introduction Fisheries which exploit small schooling pelagic fish are intrinsically unstable since they target the species in such a way as to weaken the very features that they have evolved for persistence in a variable environment. Beverton et al. (1984) classified fish- eries on small schooling pelagics as high risk, being * Corresponding author. Tel.: (604) 822 2731; Fax: (604) 822 8934; E-mail: smackin@fisheries.com considered exceptionally unreliable and vulnerable to unrestrained fishing. The catalogue of examples of pelagic stock collapse more than justifies this classi- fication. The technology and techniques employed in mod- em fishing fleets ensures they are very efficient at detection and capture of fish schools. Compounding this effect, small schooling pelagic fish may exhibit two behavioural responses that makes them remain vulnerable to capture, even during declining abun- dance. They reduce their range (Winters and Wheeler, 1985) whilst maintaining the same average school 0165-7836/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PI1 SO165-7836(97)00020-9