Combining control measures for more effective management of fisheries under uncertainty: quotas, effort limitation and protected areas

Abstract

We consider combinations of three types of control measures for the management of fisheries when the input information for policy decisions is uncertain. The methods considered include effort controls, catch quotas and area closures. We simulated a hypothetical fishery loosely based on the Icelandic cod fishery, using a simple spatially explicit dynamic model. We compared the performance with respect to conserving the resource and economic return for each type of control measure alone and in combination. In general, combining more than one type of primary direct control on fishing provides a greater buffer to uncertainty than any single form of fishery control alone. Combining catch quota control with a large closed area is a most effective system for reducing the risk of stock collapse and maintaining both short and long-term economic performance. Effort controls can also be improved by adding closed areas to the management scheme. We recommend that multiple control methods be used wherever possible and that closed areas should be used to buffer uncertainty. To be effective, these closed areas must be large and exclude all principal gears to provide real protection from fishing mortality.

Figure 1

Quota control only. Probability of (a) stock collapse and (b) long-term economic yield as a function of target fishing mortality for different levels of uncertainty (CV) in the quota.

Figure 2

Probability of (a) stock collapse and (b) long-term economic yield versus target effort for different levels of uncertainty when using effort control alone.

Figure 3

Effect of controls using only permanently closed areas, linking (a) short-term (15 year) economic yield, (b) long-term economic yield and (c) collapse probability with the initial proportion of biomass within closed areas. Default feeding migration rate, 20% emigration from each area to adjacent areas.

Figure 4

Comparing individual control systems used in isolation in terms of average inflicted fishing mortality rate and long-term yield. Open circles denote a quota-based system, filled diamonds denote an effort-based system and crosses denote closed areas alone.

Figure 5

Effect of quota control and closed areas on probability of (a) stock collapse and (b) long-term yield. CV in quota fixed at 0.6. The x-axis indicates the target removal rate for the quota control whereas each line type corresponds to a fraction of protected biomass (B_safe).

Figure 6

Effect of effort control and closed areas on (a) probability of stock collapse and (b) long-term yield. The x-axis indicates the target effort for the effort control whereas each line type corresponds to a fraction of protected biomass (B_safe).

Figure 7

Q and MPA control. Economic yield and collapse probability as uncertainty and closures vary. Q_CV=30, dashed line; Q_CV=60, solid line; Q_CV=100, dotted line).

Figure 8

Effects of combinations of quota and effort controls on (a) short-term and (b) long-term profits. Each curve represents one effort level.