Why sharks and other wide-ranging ocean species need more than protected areas
Whale sharks are the largest living fish. The best available evidence suggests that populations have been cut in half over the past 50 years. What’s known about the highly mobile species is based on sporadic and unpredictable encounters. Photo by Sam Farkas/NOAA
Marine protected areas are meant to support vulnerable ocean life, but many species are too mobile to gain meaningful benefit, new research shows.
In a study out today, researchers gathered a massive set of data tracking the movements of sharks, seabirds, turtles, whales and other highly migratory marine animals. It showed that less than 8% of the area used by tracked individuals overlaps with designated marine protected areas.
The findings make clear that area-based conservation is not sufficient to protect the ocean’s most mobile species, according to Arizona State University’s Leah Gerber, who co-authored a commentary on the research in the journal Science.
Gerber is a professor of conservation science in the School of Life Sciences and founding director of the Center for Biodiversity Outcomes at ASU. She spoke with ASU News about the research and what it means for protecting migratory marine animals.
Question: Hundreds of researchers were involved in this study. They gathered tracking data from 15,845 individual animals and 121 different species to get a global picture of their wide-ranging lifeways. Why is this kind of data so important for conservation?
Answer: To conserve these animals, we need to know what habitats they use. But the oceans are so vast, and migratory species are difficult to track. Without knowing where they are, it's hard to prioritize where we should establish conservation areas or take other protective measures.
Status of migratory marine animals
Sharks and rays: Global abundance has fallen by 71% since 1970; three-quarters of species are now threatened with extinction.
Seabirds: 31% of species are threatened; 47% are declining in population.
Whales, dolphins and porpoises: 26% of species were in threatened status in 2021, up from 15% in 1991.
Sea turtles: Populations are rebounding worldwide; over 40% of marine turtle populations are now considered low risk/low threat, up from 23% in 2011.
Q: How would you describe or put in context the status of these migratory marine animals? What’s the threat level?
A: For a lot of these species, we simply don't have enough data to understand how they are faring. We do know that the status of different populations is quite variable. For large whales, most populations have recovered substantially and are doing well since International Whaling Commission put an end to commercial whaling in 1940s. There are of course exceptions where whaling continues, and there are other threats to whales, such as ship strikes.
In contrast, sharks are not doing well. (See sidebar.)
Q: How can these kinds of data be used to make conservation planning more effective?
A: These aggregated data allow us to see where animals are moving over time, but also how much time they spend traveling or staying put in different locations. To understand what type of conservation measures are most important, we need to know where the species are in space and time.
To be effective, conservation measures have to account for the times, the places and types of interactions between marine animals and threats such as fishing gear, ship strikes, ocean noise, plastic pollution and whaling. These threats are often managed separately in ways that don’t account for the cumulative impact they have on wide-ranging species.
Q: So these new data provide a good foundation. What are the highest-priority gaps that need to be addressed now?
A: Everyone who contributed data to this global repository originally had another purpose for doing their individual research projects. And so, in a sense, the dataset is incidental to the initial purpose. In general, when developing conservation strategies for marine megafauna, or frankly any species, given the urgency of the challenges and how sparse the resources, we really need to think strategically about what data we collect and how we're aligning those data with necessary interventions and decisions.
So often in conservation, people become really interested in a scientific question and invest significant effort collecting data that may have no relevance to decision-making. Now, this gets into a debate about the value of basic versus applied science, and I think there is a value for basic science; sometimes when you're collecting long-term monitoring data, you can uncover something unanticipated, and this can be important. But in the case of conservation, especially for marine megafauna, I think we need to be strategic in aligning the collection of data with what decisions we need to be making for conservation.
Q: You’ve noted that focusing on marine protected areas can unintentionally oversimplify the range of threats. Can you explain a little bit more about that?
A: I'm a strong advocate, of course, for any protective measures. But we need to synthesize what we understand about which interventions work under different contexts. There are really good data showing that marine protected areas are effective for some marine species, particularly marine fishes and invertebrates that are not as wide-ranging.
But for wide-ranging species, it’s less clear. I've done a lot of population modeling to explore this issue for the International Whaling Commission. We showed that, when a whale is migratory, more than 50% of the time, a protected area is not going to be effective compared with a quota-based system that manages harmful interactions, such as limiting bycatch in fisheries. So there is not one Band-Aid for all problems. We’ve developed a whole toolbox for conservation actions, and we should be thinking about which tools work under different conditions.
Q: What work are you pursuing now?
A: My co-author, Katrina Davis at the University of Oxford, and her team got so excited about the direction of this research that we're initiating research examining how life history traits relate to how a given species responds to different conservation measures. For example, do top predators have certain responses that are different from animals lower on the food web? We're going to dig deeper into the data.
We're also going to be looking at the cost of conservation intervention. We want to be efficient in conservation because there's limited funding. We need to consider not only the benefits of the intervention, but also the cost, the return on investment.
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