For the oceans’ largest and most mobile animals, the size of the area they call home can be unimaginably vast. As the world’s biggest vertebrate, the blue whale moves across a home range of nearly 2 million square kilometres (772,200 square miles). Fast-moving mako and blue sharks range across an area double that, covering more than 4 million square kilometres (1,544,400 square miles) of ocean. For a multitude of species, from the Laysan albatross to the northern elephant seal and the leatherback turtle, the ocean is as borderless as they choose and they travel incredible distances across its extent.
But historically it was the large animals that were exploited first and many marine megafauna now face the threat of extinction. Protecting these animals wherever they roam is a challenge not always easily solved by delineating borders around their preferred habitat. However, as our footprint of marine protected areas grows, we must think critically about what strategies work best to protect different animals with a diversity of life histories.
The paper ‘Mismatches in scale between highly mobile marine megafauna and marine protected areas’, published in Frontiers in Marine Science last month, highlights that our existing global marine protected areas may be too small to protect the widest-ranging species in the ocean, since less than 1% of them encompass the home ranges and core-use areas of the most mobile ocean nomads. In fact, marine protected areas in general protected less than 5% of the core home range areas of all the species the researchers assessed. This finding shows that most large, mobile animals are not protected in the hotspots they visit the most.
The researchers, led by Melinda Conners with a host of co-authors, analysed satellite tracking data from 36 tagged species from five groups of animals: seabirds, cetaceans (whales and dolphins), pinnipeds (seals and sea lions), sea turtles and elasmobranchs (sharks and rays). Their results show that while very few marine protected areas overlap with the home ranges of far-roaming or highly mobile species such as basking sharks, certain humpback whale populations, gentoo penguins and green turtles, 40% of them did actually encompass the localised home ranges of some of the smallest-ranging megafauna, such as Weddell seals, Franciscana dolphins and certain populations of brown, masked and red-footed boobies (seabirds).
Far from decrying the value of protected areas, the researchers instead wanted to understand and assess the alignment of large home ranges with large marine protected areas. Their reasoning? Protected area thinking has, to date, encouraged the idea in some settings that the larger the marine protected area, the more likely it is to also protect wide-ranging animals. Hawaii’s Papahānaumokuākea Marine National Monument (PMNM), for instance, adequately protects three seabird species with intermediate ranges. However, even this (relatively) gargantuan marine protected area with its footprint of more than 1.5 million square kilometres (579,150 square miles) is insufficient to protect the home range and core-use areas of two albatross species that breed in it but range over a much larger area. This is despite the explicit goal stated in Papahānaumokuākea’s objectives to protect the habitat of these birds.
The answer, the researchers urge, is not to discourage marine protected areas and their designation, but to think more critically about how they might work in a global network, or in concert with other measures, to protect our largest and most charismatic ocean dwellers.
Location, location, location! Where a marine protected area is located makes all the difference. The researchers cite the protection of humpback whales within the US National Marine Sanctuaries as an example. This west coast network encompasses nearly 30% of this species’ home range. However, even where a network of marine protected areas seems well placed to safeguard members of one species as they swim from one protected area into the next, it does not necessarily work the same way for another roaming species. Blue whale tracks showed that this species’ core area does not overlap with the series of protected areas that these whales swim past parallel to the US coastline. The take-home idea? Critical areas need to be identified according to life stage and behaviour.
For instance, we know that many animals aggregate at certain times of the year to feed or breed. Marine protected areas can work for ‘central location foragers’ (species that return reliably to the same place to feed). Or they can protect groups like sea turtles that, despite ranging far and wide during most of their life, have a strong instinct to return each season to specific nesting beaches to lay their eggs. The researchers found that more than 50% of the core area of olive ridley turtles overlaps with marine protected areas in Gabon, probably because of this very behaviour and the fact that their home ranges are smaller during this particular life stage.
Understanding how different sexes and different age groups use ocean space will also help to design more nuanced and effective conservation measures. For example, male northern elephant seals hug ocean territories closer to the coast than their female counterparts do. This behaviour makes them more suitable candidates for place-based conservation measures, like marine protected areas, than the females of the same species. And whereas juvenile short-tailed albatrosses literally spread their wings across the entire North Pacific ocean basin, adults of the same species form dense groupings around the continental shelf. This makes the adults the more suitable candidates for spatial protection.
It may well be that 40% of localised species with the smallest home ranges overlap with marine protected areas and 12% of these areas provide adequate protection for species with intermediate-sized home ranges. Yet for species operating at scales greater than 10,000 square kilometres (3,860 square miles), marine protected areas appear to be less effective – and possibly not suitable at all. To protect these largest and most mobile of animals, combining different strategies might be the answer. Certainly, marine protected areas may provide some protection, but ensuring that there are bycatch limits to avoid overexploitation or that shipping routes can be changed to avoid ship strikes may also help to safeguard these species when they are ranging away from their critical habitats or during periods when they are not aggregating or staying in an area.
The idea, assert the researchers, is that simply being large does not necessarily make a marine protected area effective. Rather, they reiterate that the resolution and extent of the information we now have about where animals move, and what they do wherever they go, is improving. They are not saying that marine protected areas do not work; rather, that they can work more effectively when all the information available is used to make decisions. Obviously, we don’t know everything about the oceans yet – far from it! So it is impossible to go into designing marine protected areas with all the information needed to make decisions. But our knowledge is improving year by year and as we learn more we can adapt our plans. We should draw on collaborative efforts – across disciplines and political borders – to design an effective network of global marine protected areas.
Thanks to technology like satellite and acoustic tracking, we now know more than ever about how animals live. We also happen to be at a point of no return for the responsibility that we carry for their lives. Scientists from across the planet are working together on processes like the Important Shark and Ray Areas (ISRAs) and other important area assessments for marine mammals (IMMAs), marine turtles (IMTAs) and birds (IBAs). The aim of these important area processes is to gather the best and latest information about critical areas of the ocean used by each of these different animal groups.
Through a series of workshops, researchers hope to create maps of habitat ‘hotspots’: a visual representation of the most important areas that these animals use for different events (feeding) and stages of their lives (courtship, mating, pupping). If we cannot protect marine megafauna everywhere, we should be prioritising protection for the areas most needed by these animals. The ISRAs and other important area processes will guide us to the key places we should be protecting – where we can get the biggest bang for our conservation buck.
At the same time, countries are chasing their commitment to achieving 30% protection of their national waters by 2030. This target was set by the Convention on Biological Diversity (CBD), an international forum that outlines commitments for conserving biodiversity. Now a window of opportunity is opening, as technology, mapping processes and protection goals come together. If we are to avert a conservation crisis and make the most of this final push for 30% ocean protection by 2030, we will do well to use the growing bank of satellite data at hand and think critically about the best strategy (or combination of tools) to protect marine megafauna.
You can read the paper by Melinda Conners and her colleagues here.
**Reference: Conners MG, Sisson NB, Agamboue PD, Atkinson PW, Baylis AMM, Benson SR, Block BA, Bograd SJ, Bordino P, Bowen WD, Brickle P, Bruno IM, González Carman V, Champagne CD, Crocker DE, Costa DP, Dawson TM, Deguchi T, Dewar H, Doherty PD, Eguchi T, Formia A, Godley BJ, Graham RT, Gredzens C, Hart KM, Hawkes LA, Henderson S, Henry RW III, Hückstädt LA, Irvine LM, Kienle SS, Kuhn CE, Lidgard D, Loredo SA, Mate BR, Metcalfe K, Nzegoue J, Kouerey Oliwina CK, Orben RA, Ozaki K, Parnell R, Pike EP, Robinson PW, Rosenbaum HC, Sato F, Shaffer SA, Shaver DJ, Simmons SE, Smith BJ, Sounguet G-P, Suryan RM, Thompson DR, Tierney M, Tilley D, Young HS, Warwick-Evans V, Weise MJ, Wells RS, Wilkinson BP, Witt MJ and Maxwell SM. 2022. Mismatches in scale between highly mobile marine megafauna and marine protected areas. Front. Mar. Sci. 9:897104.10.3389/fmars.2022.897104
Frontiers in Marine Science