Nav: Home

Travel distances of juvenile fish key to better conservation

May 16, 2017

Marine reserves -- sections of the ocean where fishing is prohibited--promote coral reef sustainability by preventing overfishing and increasing fish abundance and diversity. But to be effective, they need to be sized right, and in a way that accounts for how far juvenile fish travel away from their parents after spawning.

Scientists at the Woods Hole Oceanographic Institution (WHOI), along with researchers from Australia, France, and Saudi Arabia, have successfully measured the dispersal distances of two coral reef fish species across a 3,000 square mile section of the ocean -- an area the size of Yellowstone National Park. The study, published in the May 8, 2017, issue of the journal Nature Ecology & Evolution, marks the largest, most comprehensive study of larval dispersal ever conducted and has important implications for the sizing and spacing of marine reserves.

"How far fish will disperse in their lifetimes is critical when you start thinking about how marine reserves should be designed," said Simon Thorrold, co-author of the study and a senior scientist at WHOI. "This is the first time we've been able to measure dispersal distances on spatial scales that are relevant to marine reserves, which means we can now provide data that informs management on optimal spacing and sizing."

Size matters

Marine reserves come in many shapes and sizes. But if a reserve is too small, it can't accommodate enough larvae to sustain populations. And if it's too big, larvae will simply stay within the confines of the reserve without contributing to surrounding fisheries -- a critical secondary role marine reserves need to play to improve fisheries management.

To get a read on fish dispersal in the past, scientists relied on population genetics approaches that lacked the power to measure dispersal over space and time scales relevant to protected areas of the ocean. More recently, ecologists have turned to computer-generated models of water currents to track particles through virtual oceans. According to Thorrold, this approach also has limitations since there was no way to verify the accuracy of the models. "The software can generate a lot of cool-looking graphs, but it was impossible to test the skill of those models in any real way."

An empirical approach

To overcome these limitations, Thorrold and his colleagues took direct measurements of dispersal distances in the field. They collected DNA samples from thousands of adult and juvenile clownfish and butterflyfish throughout Kimbe Bay, Papua New Guinea, in 2009 and 2011. The entire sampling process occurred underwater, with the 30-person science team spending thousands of man-hours on SCUBA over several weeks in the field each year.

When the scientists returned to the lab, they used DNA parentage analysis, a sequencing technique that allowed them to match the juveniles up with their parents based on the DNA samples and spawning and settlement location data. From that, they were able to determine that most of the juvenile clownfish stayed relatively close to home, settling at mean distances of 10-15 kilometers from their natal reefs. The butterflyfish dispersed further, averaging distances of 43-64 kilometers before settling into their new habitats.

"Since we knew the respective locations of the adults and babies, we were able to come up with the exact linear distances that the larvae had dispersed. We're no longer talking about estimates," said Thorrold.

Benefits beyond design

In addition to helping inform the design of protected areas, the measurements can help to test the ability of reserves to perform key conservation functions. For example, one way a marine reserve network may improve fish population sustainability is through the so-called "rescue effect." In theory, if fish in a reserve suffer catastrophic mortality, the reserve can be repopulated by larvae from other reserves within the network. Thorrold and colleagues were able to track larvae from one reserve to another in the study area, confirming that rescue effect is likely to occur in real-world reserve networks.

The dispersal measurements could also allow fisheries managers to monitor the effectiveness of existing reserves, helping answer the question of whether or not a particular reserve is contributing to fish populations beyond its boundaries. This, according to Thorrold, has been a big unknown.

"If you can trace larvae from one reserve to a place that's fished, you can come up with a direct measure of how many fish the reserve is contributing to exploited populations beyond the reserve," he said. "This helps when trying to convince fishermen that networks of marine reserves are a good management tool."

Future work

According to Thorrold, as coral reef seascapes continue to face pressure from man-made stressors, marine reserves will continue to serve as an important conservation management tool. As such, it will become increasingly important to be able to provide direct measurements of larval dispersal, and find ways to apply the information to other regions of the ocean.

"The next thing we are working on is developing a coupled bio-physical model of the area that will allow us to take the results from this study and generalize them to other coral reef seascapes around the world," he said. "Limited resources for ocean management, particularly in the developing world, means that we need to maximize the chances of successful conservation outcomes from these efforts. These types of scientific insights will be critical for ongoing efforts to promote resilience of coral reef ecosystems in the face of human exploitation and climate change."
-end-
This research was supported by Australian Research Council, the King Abdullah University of Science and Technology, and the National Science Foundation.

The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment. For more information, please visit http://www.whoi.edu.

Woods Hole Oceanographic Institution

Related Protected Areas Articles:

Caribbean sharks in need of large marine protected areas
Governments must provide larger spatial protections in the Greater Caribbean for threatened, highly migratory species such as sharks, is the call from a diverse group of marine scientists including Stony Brook University School of Marine and Atmospheric Sciences (SoMAS) PhD Candidate, Oliver Shipley.
Red coral effectively recovers in Mediterranean protected areas
Protection measures of the Marine Protected Areas have enable red coral colonies (Corallium rubrum) to recover partially in the Mediterranean Sea, reaching health levels similar to those of the 1980s in Catalonia and of the 1960s in the Ligurian Sea (Northwestern Italy).
Mobile protected areas needed to protect biodiversity in the high seas
As the United Nations rewrites the laws of the high seas, the new document should anticipate emerging technologies that allow protected areas to move as animals migrate or adapt to climate change.
Road salt pollutes lake in one of the largest US protected areas, new study shows
New research shows road salt runoff into Mirror Lake in Adirondack Park prevents natural water turnover and therefore poses a risk to the balance of its ecology.
Extent of human encroachment into world's protected areas revealed
Largest study yet to compare protected with 'matched' unprotected land finds 'significantly higher' increases in human pressure -- primarily through agriculture -- in protected areas across the tropics.
Satellite-based estimates of reduced deforestation in protected areas needed
In the context of progressing towards new targets for a post-2020 Global Biodiversity Framework, the debate remains on whether the emphasis should be on protected area coverage or protected area effectiveness.
Do marine protected areas work?
A study describes how to use data collected before and after Marine Protected Areas are created to verify that they work.
Analysis: World's protected areas safeguard only a fraction of wildlife
A new analysis published in the journal Frontiers in Ecology and the Environment shows that the world's protected areas (PAs) are experiencing major shortfalls in staffing and resources and are therefore failing on a massive scale to safeguard wildlife.
How protected areas are losing ground in the United States and Amazonia
Once champions of global conservation, the United States and Brazil are now leading a troubling global trend of large-scale rollbacks in environmental policy, putting hundreds of protected areas at risk, a new study suggests.
Chimpanzees at the crossroads: adapt to living outside protected areas
Chimpanzees at the crossroads: how they adapt to living outside protected areas Research carried out into the impact of changes to chimpanzee habitats found they have adapted to human developments in a number of ways -- including learning how to cross roads safely and the best times to visit human habitats -- but their survival is still threatened.
More Protected Areas News and Protected Areas Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.