Bioeconomics and catchability: Fish and fishers behaviour during stock collapse

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 stack 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. (C) 1997 Elsevier Science B.V.