Exploring the effectiveness of Blue Water MPAs

The article “Ecological responses to blue water MPAs” is freely available online at https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0235129

New research published in July 2020 contributes to filling a substantial gap in evidence of ecological objectives achieved by very large Marine Protected Areas (MPAs) that include open ocean, blue water habitat. The study conducted the first-ever environmental performance assessment of the U.S. Pacific Remote Islands Marine National Monument. Established in 2009, this MPA encompasses 1.27 million square kilometers of the central Pacific Ocean. It is the largest no-take marine area in the world.

MPAs are increasingly used as components of management frameworks to govern marine activities, including fishing, and to protect marine biodiversity. Over the past two decades, the number of very large MPAs globally — those greater than 100,000 square kilometers — jumped from 2 to 35, and cover 4.6% of the ocean. These contribute substantially toward meeting the United Nation’s Sustainable Development Goal target 14.5 to conserve 10% of global marine areas.

While an extensive body of evidence has demonstrated the ecological changes that occur within and near coastal, benthic, mainly shallow-water MPAs, there is limited theoretical — and in particular empirical — evidence of ecological effects of very large MPAs that include blue water habitat.

As the United Nations nears the adoption of a much-needed new treaty on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction, it is timely to take stock of how spatial management of the open ocean, including through MPAs, can contribute to meeting these objectives.

The study evaluated a wide range of ecological attributes. Among the study’s main findings:

Fishing effort displaced by the Monument caused multispecies conflicts. Catch in Hawaii’s tuna longline fishery of some species of conservation concern, including olive Ridley sea turtles and oceanic whitetip sharks, had been higher in the Monument than the rest of fishing grounds. However, bycatch rates of other at-risk species, including albatrosses and shortfin mako sharks, had been lower in the Monument.
Mean trophic level of the longline fishery catch (the average position in the food chain from which catch are taken, ranging from primary producers at the bottom of the chain, to apex predators at the top) was significantly higher around the Monument, likely due to the aggregating effect of shallow features and there having been light fishing pressure within the Monument before it was established. This means that a larger proportion of the pelagic community in the Monument is made up of top predators than in open ocean areas, and suggests that the Monument contains a relatively undisturbed pelagic community structure, which are important ecological attributes.
The MPA did not achieve some ecological objectives, including changes in species diversity, size of the catch and the local abundance of some assessed species. This may have been because the MPA is young and too small to affect highly migratory species, it did not contain habitat critical for certain life-history stages, or that it had only been lightly exploited before eliminating fishing, or experienced fishing along the MPA’s boundary.
By removing fishing grounds near shallow atolls and reefs where pelagic predators aggregate, the MPA decreased local catch rates of bigeye tuna by 84%, reducing the economic viability of fishing for the U.S. vessels that periodically fish at these distant grounds.

The study evaluated an extensive, but not exhaustive, range of ecological attributes. Exploring an even wider range of attributes is a priority to support evidence-based evaluation of this unique blue water MPA, which includes endemic species not found anywhere else in the world, and rare and endangered species, such as the Hawaiian monk seal.

In general, the larger individual and networked spatially-managed areas are, the more likely they are to achieve certain ecological objectives such as representativeness, replication, ecological connectivity and refugia, including resilience to ocean warming and other outcomes of climate change. Tools to identify and manage dynamic blue-water spatially managed areas, including mobile MPAs, are not as well developed as those for terrestrial and coastal areas. This is a priority for pelagic ecosystems. Findings augment a small body of evidence of ecological consequences of pelagic MPAs, in particular from studies that provide a strong basis for causal inference, improving the knowledge of optimal designs for pelagic MPAs to achieve ecological objectives. More studies like this one are needed to improve our understanding of which ecological objectives large blue water MPAs are likely able to achieve, and how to design MPAs to optimize the likelihood of success. These findings contribute to the understanding of how very large MPAs and other area-based management tools can contribute to achieving ecological objectives of managing pelagic, blue water fisheries.

For More Information - study co-leads:

Dr. Eric Gilman, Pelagic Ecosystems Research Group, FisheriesResearchGroup@gmail.com

Dr. Milani Chaloupka, Ecological Modelling Services Pty Ltd & Marine Spatial Ecology Lab, University of Queensland, m.chaloupka@uq.edu.au