Large Marine Protected Areas Can Benefit Migratory Species—But Design and Management Are Key

Marine protected areas (MPAs) are designed to conserve critical marine habitats, localized fauna, and highly migratory species such as turtles, whales, and sharks. However, although some MPAs cover more than 1 million square kilometers, some scientists question how well these areas safeguard ocean megafauna with large geographic ranges. The Pew Bertarelli Ocean Legacy project advocates for interconnected networks of MPAs, linked by protected biological corridors and underpinned by sustainable financing, shared regional governance and effective monitoring and enforcement. As part of such networks, it is important to assess the efficacy of large MPAs.

For some answers, we sat down with Melinda Conners, Ph.D., senior postdoctoral associate at Stony Brook University in New York and co-author of a study published this week in the peer-reviewed journal Frontiers in Marine Science. The authors overlaid the tracks of 36 species of ocean megafauna with existing marine protected areas and concluded that MPAs are more likely to provide crucial protections for highly migratory megafauna if decision-makers carefully consider the location, size, and dynamic management of MPAs, i.e., designing MPAs that have boundaries that shift through time to match the movement of key species. This interview has been edited for clarity and length.

Q: What are marine megafauna?

Courtesy of Melinda Conners

A: Marine megafauna are large-bodied marine animals, typically vertebrates, such as sharks, whales, turtles, and seabirds. Most are highly mobile, meaning they regularly traverse hundreds to tens of thousands of kilometers each year—distances that vary by species. In their lifetime, a small seabird may cover a couple hundred square kilometers, while leatherback sea turtles often travel more than 15,000 kilometers per year across the Pacific Ocean. These distances can be covered quickly; for example, the Laysan albatross, a large seabird of the North Pacific, will often travel from its breeding colony in Hawaii to foraging grounds thousands of kilometers away in a matter of days before returning to its nest. Many species of marine megafauna are vulnerable to exploitation or disturbances, and they can be challenging to protect given their highly mobile natures that can quickly take them in and out of a protected area.

Q: How does the size of MPAs affect mobile marine megafauna?

A: Most protected areas are small and coastal; however large MPAs that encompass open ocean are becoming increasingly common. Larger MPAs are being designated to protect large-scale marine ecosystems, including critical habitats of marine megafauna. But how big is “big enough” for MPAs to protect the migratory ranges of megafauna? To answer this, we examined tracking data from almost 2,000 animals representing 36 species of marine birds, turtles, cetaceans, and elasmobranchs (sharks and rays) across the world’s oceans. In general, we found that many MPAs are large enough to encompass habitats of localized and intermediate-ranged species, like manta rays and sea lions. But for larger, vast-ranged species, such as leatherback sea turtles and albatross, the bigger the MPA was in size, the better. Of course, an MPA can’t cover the entire ocean so we should focus protection on regions and times of the year when species are aggregated.

Q: What constitutes a “large” MPA, and what’s the difference between those and smaller ones?

A: A large MPA is one designed to be big enough to protect entire ecosystems and ecological processes—typically over 100,000 square kilometers (just over 62,000 square miles). Currently there are 35 large MPAs ranging from 110,000 square kilometers—Australia’s Lord Howe Commonwealth Marine Reserve, which is about the size of Cuba—to the Southern Ocean’s 1.5 million-square-kilometer Ross Sea Region MPA, which is roughly the size of Mongolia. While small MPAs are no less important than large MPAs, they typically have more specific conservation goals, such as protecting important habitat features like seamounts or fish nursery grounds. Large MPAs, on the other hand, are designed to increase biodiversity and resilience within a region by encompassing multiple habitat types that support communities of species. For example, the Ross Sea MPA includes the continental shelf, seamounts, sea ice, and open ocean that supports an ecologically diverse region encompassing critical habitat for mobile megafauna such as penguins, killer whales, and Weddell seals. It also serves as a breeding ground for Antarctic toothfish, a commercially important species, and is home to unique assemblages of plants and invertebrates.

Q: What percentage of a species’ migratory range needs to be protected for it to thrive?

A: It really depends on the species. Mobile species are particularly vulnerable to habitat degradation and threats that occur in any part of the annual cycle can impact the population. To protect them, we need to start by identifying core areas that are important for a large proportion of the population, such as breeding and molting grounds and migratory corridors. By targeting these regions where individuals aggregate, and especially where these regions overlap with threats, conservation action would have a disproportionate influence on population dynamics and species persistence. This means that you don’t need to protect the entire range of a species to have conservation impact, but you do need to consider marine megafauna and the threats they encounter during the planning and design phase of MPAs.

Q: What happens when animals migrate outside the borders of protection?

A: Because mobile marine megafauna can navigate huge swaths of ocean across their annual cycles, comprehensive protection for many species may take the form of other conservation strategies beyond spatial protection from MPAs. For example, when Laysan albatrosses are foraging at sea to bring food back to chicks, their ranges are small and fall partially within the boundaries of the Papahānaumokuākea Marine National Monument. However, for the remainder of their annual cycle, albatross are predominately found in pelagic waters—far beyond boundaries of protection—where they interact with fisheries operations and are susceptible to mortality from bycatch. To address this threat when birds are moving at scales too large for traditional, static MPAs to protect, additional conservation strategies are necessary—such as bycatch reduction measures or seasonal fishing closures—as part of interconnected regional conservation networks. While there is great value in MPAs to sustain and recover marine megafauna populations, ultimately the most effective conservation strategies for these highly mobile species will need to be multifaceted, including static MPAs as well as dynamic spatial management tools and sustainable fisheries management.

The ocean is a large space but migratory routes are overrun with human activity that threatens highly migratory species’ ability to sustain healthy populations. They need refugia, and we need large MPAs that consider the needs of these important species.