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. 2015 Nov 5;370(1681):20140276.
doi: 10.1098/rstb.2014.0276.

The Good, the Bad and the Ugly of Marine Reserves for Fishery Yields

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Free PMC article

The Good, the Bad and the Ugly of Marine Reserves for Fishery Yields

Giulio A De Leo et al. Philos Trans R Soc Lond B Biol Sci. .
Free PMC article

Abstract

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.

Keywords: demographic and management models; large spawners; marine reserves; quota-based fisheries; total allowable catches.

Figures

Figure 1.
Figure 1.
Effects of marine reserves on the performance of a TAC-regulated fishery, measured in terms of incremental benefit (or loss, when negative) in mean catch and stock biomass with respect to a conventional TAC-regulated fishery (i.e. with no MRs) at MSY. In (a,b), larval dispersal range is 100 km; in (c,d), larval dispersal is 10 km. The fishery is overcapitalized (TE = 3TEMSY) and here TAC is computed on the whole stock inside and outside reserves. All other parameters are as in table 1.
Figure 2.
Figure 2.
Effect of fecundity of large spawners (a–d) and Goodyear compensation ratio (e–h) on fishery performance of a TAC-regulated fishery including MRs, relative to a conventional TAC-regulated fishery (without MRs) at MSY. Large spawner fecundity is normalized with respect to the fecundity of average-size adults. Shaded areas represent values of fecundity or GCR where the differences between fishery performance with MRs and under conventional management are not significant (p ≥ 0.05) at the level of environmental variability simulated in the model. All the other parameters as in table 1, with larval dispersal range equal to 50 km, adult dispersal 1 km, and 36% of the fishing ground set aside for protection in four MRs of 9 km each.
Figure 3.
Figure 3.
Mean harvest and biomass as a function of fishing mortality (scaled with respect to fishing mortality at MSY) for alternative management regimes. Continuous black line: conventional management (with no MRs); dark grey line: fishery management scheme, including a network of MRs with TAC computed on the whole stock inside and outside MRs; light grey line: fishery management scheme including a network of MRs with TAC computed only on the stock outside MRs. All the other parameters as in table 1, with larval dispersal range equal to 50 km, adult dispersal 1 km, and 36% of the fishing ground set aside for protection in four MRs of 9 km each.

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