Size and spacing rules can balance conservation and fishery management objectives for marine protected areas

Abstract

Marine protected areas (MPAs) are increasingly integrated into fishery management for coastal systems. Size and spacing rules (SSRs) have been proposed as simple MPA design guidelines, especially in regions where population connectivity data are limited. We assessed whether SSRs allow managers to design effective MPA networks under spatiotemporally varying dispersal patterns using a spatially realistic population model parameterized for a commercially‐exploited fish species on the Great Barrier Reef. SSRs are used to design MPA networks, and population simulations are used to measure the mean and variance of the resulting population size and fishery catch. We show that SSR performance is contingent on the extent of the MPA network, and whether species’ connectivity data can be used to target areas for protection. For example, in the absence of connectivity data, a “many small” MPAs rule provides the least variable management outcome. Synthesis and applications. We demonstrate that the performance and usefulness of size and spacing rules (SSRs) as guidelines for marine protected areas (MPAs) depend on the level of knowledge about larval dispersal, as well as the level of current exploitation in the fishery. These context‐dependent results offer particularly relevant guidance to future MPA design projects in regions with limited connectivity data.

Why do several small patches hold more species than few large patches?

“…Finally, some authors extrapolated across species the idea that a patchy environment reduces the risk of species extinction by spreading the risk over multiple sites (den Boer, ), to predict SS > SL. In a single species model, Fovargue, Bode, and Armsworth () predicted lower overall variability through time in population abundance over several small than few large patches . Although the median abundance across the two systems was similar, higher variability over few large patches than many small patches increased the predicted probability of extinction there.…”

Underestimating the benefits of marine protected areas for the replenishment of fished populations

“…Although these effects may be desirable from an ecological perspective, there are both benefits and costs for fishers (Fovargue et al . ).…”

“…Importantly, studies of the spillover effects of MPAs still assume isometry (eg Fovargue et al . ). Recent evidence, however, suggests that reproductive hyperallometry is in fact the rule across nearly all groups of marine fishes.…”

“…Higher survivorship will create reserve size distributions that have both higher averages and greater variance, because fish are more likely to grow older and become bigger when they are not subjected to fishing (Fovargue et al . ; Edgar et al . ).…”

“…Theory suggests that MPAs, if sufficiently widespread, can impede the evolution of harvesting-adapted phenotypes, maintaining the original phenotypic distribution of the exploited species (Baskett et al 2005). Although these effects may be desirable from an ecological perspective, there are both benefits and costs for fishers (Fovargue et al 2018). MPA advocates argue that MPAs benefit fishers, not only by maintaining the population of the exploited species within the MPA network but also by promoting "spillover", whereby some fish or larvae leave the MPA and are eventually caught (McClanahan and Mangi 2000).…”