The good, the bad and the ugly of marine reserves for fishery yields

Abstract

One contribution of 16 to a theme issue 'Measuring the difference made by protected areas: methods, applications and implications for policy and practice'. The good, the bad and the ugly of marine reserves for fishery yields Marine reserves (MRs) are used worldwide as a means of conserving biodiversity and protecting depleted populations. Despite major investments in MRs, their environmental and social benefits have proven difficult to demonstrate and are still debated. Clear expectations of the possible outcomes of MR establishment are needed to guide and strengthen empirical assessments. Previous models show that reserve establishment in overcapitalized, quota-based fisheries can reduce both catch and population abundance, thereby negating fisheries and even conservation benefits. By using a stage-structured, spatially explicit stochastic model, we show that catches under quota-based fisheries that include a network of MRs can exceed maximum sustainable yield (MSY) under conventional quota management if reserves provide protection to old, large spawners that disproportionally contribute to recruitment outside the reserves. Modelling results predict that the net fishery benefit of MRs is lost when gains in fecundity of old, large individuals are small, is highest in the case of sedentary adults with high larval dispersal, and decreases with adult mobility. We also show that environmental variability may mask fishery benefits of reserve implementation and that MRs may buffer against collapse when sustainable catch quotas are exceeded owing to stock overestimation or systematic overfishing.

Effects of fish movement assumptions on the design of a marine protected area to protect an overfished stock

“…When scaled to the proper size or combined as an interconnected network, they can effectively protect fisheries stocks and increase fisheries yields [1–3]. Yet, to be successful for both conservation and fisheries goals, MPA designs must adequately address the consequences of species movement, including swimming behavior of adults and dispersal of larvae [4,5].…”

“…Theoretical studies suggest that a well-designed MPA can provide comparable benefits to those obtained with perfect management of the catch or they can even exceeded under the right conditions [3]. For example, Hasting and Botsford [6] showed that for species with sedentary adults and larval dispersal, the optimal MPA size can offer identical stock protection and yields to those provided by the optimal fishing mortality rate.…”

“…To overcome this limitation, simulation approaches have been proposed as a complementary way to compare potential MPA designs, but they are not exempt from challenges. For example, simulations are highly sensitive to the assumptions describing the biology of larval dispersal, juvenile/adult and fisheries movement [2,3,5,7,9,10], and to the complexity of the natural environment and of human driven systems [11]. Furthermore, most MPA simulations have historically been done for benthic organisms with slow or sessile adults, where the assumption of simple diffusive or advective movement is a rational approach to depict passive dispersal of particles like eggs or larvae [12–16].…”

Measuring the difference made by conservation initiatives: protected areas and their environmental and social impacts

“…However, achieving an integration of retrospective and prospective impact studies in a unified scientific architecture will take substantial communication and collaboration among evaluators, planners and modellers. Initial steps towards this integration are outlined in three articles in this issue [20][21][22].…”

“…When we attempt to isolate the effects of protected areas on ecological indicators, we must disentangle the effects caused by protected areas from the effects caused by the productivity of the landscapes or seascapes that are typically protected. In both retrospective and prospective studies, the answers to the question about selection identify moderators and mechanisms of protected area impacts (see [17,[19][20][21]23]). The ways in which these factors shape impacts must be elucidated if we are to have a sound evidence base for guiding protected area management.…”