Restored top carnivores as detriments to the performance of marine protected areas intended for fishery sustainability: A case study with red abalones and sea otters

摘要

Marine protected areas are possible solutions to the problems of protecting the integrity of marine ecosystems and of sustaining harvested marine populations. We report demographic data for red abalones ( Haliotis rufescens ) at nine sites along the California coast. Six of our sites are within marine protected areas, and four of those six sites are occupied by sea otters ( Enhydra lutris ). Sea otters are known abalone predators and are believed to have an important role in facilitating biodiversity within coastal kelp forest communities along the North Pacific Rim. We asked whether marine protected areas intended to conserve ecosystems are compatible with use of marine protected areas for abalone fishery sustainability. We found that both sea otters and recreational harvest alter the density, size distribution, and microhabitat distribution of red abalones in qualitatively similar ways. Red abalone populations in marine protected areas outside the current sea otter range have higher density, are composed of larger individuals, and occur in more-open microhabitats compared with populations in locations lacking sea otters but subject to harvest and with populations in locations with sea otters. The effects of sea otters are stronger than the effects of harvest. Characterization of harvest effects on density may be confounded by other uncontrolled factors. We conclude that coastal marine protected areas off California cannot enhance abalone fisheries if, in the interest of ecosystem integrity, they also contain sea otters. Where restored top carnivores limit the sustainability of commodity harvest, it may be possible to resolve conflicts with two categories of spatially segregated, single-use marine protected areas, one focusing on ecosystem restoration and the other on fishery development. [References: 62]