The Silky Shark (Carcharhinus falciformis)
Photo Credit: Alex Chernikh
(CC BY-SA 4.0)
Scientific Frontline: "At a Glance" Summary
- Main Discovery: Silky sharks predominantly migrate west and northwest from the Galápagos Marine Reserve into unprotected high-seas corridors, exposing them to industrial fishing fleets despite the existence of nearby Marine Protected Areas.
- Methodology: Researchers deployed fin-mounted satellite tags on 40 adult silky sharks (33 females and 7 males) off Wolf and Darwin Islands, tracking their movements and residence times within protected versus unprotected zones for up to 1.75 years.
- Key Data: The tagged sharks spent more than 50% of the study duration outside Marine Protected Areas, with one individual traveling a record 27,666 kilometers; global populations of the species have declined by 47% to 54% in the last 40 years.
- Significance: The study reveals a critical misalignment between current conservation boundaries and shark behavior, as the animals rarely use the recently established eastern protected areas, preferring instead to travel into high-risk fishing zones.
- Future Application: Conservation planners can utilize this migration data to shift or expand Marine Protected Areas toward the west and northwest to cover the actual pelagic pathways used by the species.
- Branch of Science: Marine Ecology and Conservation Biology
- Additional Detail: Silky sharks are the second-most common species found in the international fin trade, driving their classification as vulnerable with a high risk of extinction.
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| Image Credit: The Save Our Seas Foundation Shark Research Center |
A new satellite-tracking study led by Nova Southeastern University (NSU) has found that the silky shark (Carcharhinus falciformis)—a major victim of the international shark fin trade—spends most of the time outside the relative safety and limited range of Marine Protected Areas (MPAs), migrating long distances through regions where they are highly impacted by commercial fisheries. This new data is critical to informing international planning for protected areas and conservation to support species survival.
In the first assessment of its kind, the study “Pelagic sharks in parks: Marine protected areas in the Eastern Tropical Pacific provide limited protection to silky sharks tracked from the Galápagos Marine Reserve,” published recently in the journal Biological Conservation, found that while the species spent less than half their time within the 133,000 square kilometer Galápagos Marine Reserve (GMR), they were tracked outside the relative safety of the MPAs for over half of the study period.
Listed as vulnerable with a high risk of extinction on the International Union of Conservation of Nature Red List of Threatened Species, global data has shown that overfishing has caused silky shark populations to decline by 47 to 54 percent in the past 30 to 40 years. Meanwhile, fins from silky sharks made up the second-highest proportion, by species, impacted by the international fin trade.
As top-level predators, silky sharks regulate fish populations, specifically schooling fish, such as tuna and mackerel, ensuring that no single species dominates the ecosystem.
As part of the international collaborative study carried out by the Guy Harvey Research Institute, Save Our Seas Foundation Shark Research Center, Charles Darwin Foundation, and the Galápagos National Park Directorate, a total of 40 silky sharks were tagged and their movements tracked by satellite tag technology for up to 1.75 years.
“The study demonstrates that, upon leaving the MPAs, silky sharks run the gauntlet of a range of threats, including longline and purse-seine fisheries,” said Jeremy Vaudo, Ph.D., of the Guy Harvey Research Institute and Save our Seas Foundation Shark Research Center at NSU, lead author of the study. “They are among the most heavily fished shark species in the Eastern Tropical Pacific (ETP) ecoregion and, indeed, the world, and not only are they a major victim of the global fin trade, but their tendency to spend time on the high seas outside the Eastern Tropical Pacific MPAs also puts them at risk of being incidentally taken as bycatch by industrial fishing fleets.”
For the study, 40 adult silky sharks, (33 females and seven males), which can grow up to 3.5m in length, were tagged with fin-mounted satellite tags off Wolf and Darwin Islands in the northern Galápagos. On average, the sharks spent nearly 47 percent of their time in the region’s collective MPAs, but most of this time was focused within the GMR, with comparatively little time spent in the region’s other, recently established, MPAs to the east.
Silky sharks are a nomadic species known to travel vast distances in the high seas. In one instance, a record-breaking silky shark, tagged at Wolf Island in 2021, recorded 27,666 kilometers (17,190 miles) of ocean travel in less than two years.
NSU Professor Mahmood Shivji, co-author of the study and director of the Guy Harvey Research Institute and the Save our Seas Foundation Shark Research Center, says the study reveals both positive, but also concerning discoveries regarding the effectiveness of the current MPAs in the region, many of which are situated to the east of the GMR.
“The good news is that the silky sharks spent a substantial amount of time within the GMR, largely safeguarded from industrial fishing during this period,” he said. “However, the discovery that the sharks, when deciding to migrate, preferentially traveled to the west and northwest rather than east of the GMR, shows them spending a lot of time in unprotected waters, which is concerning given the huge amount of industrial fishing occurring there.”
Studies like this provide essential data to help international collaborators make educated decisions on where to designate areas of protection.
Reference material: Silky Shark (Carcharhinus falciformis): The Metazoa Explorer
Research material:
Published in journal: Biological Conservation
Authors: Jeremy J. Vaudo, Pelayo Salinas-de-León, Ryan K. Logan, Jenifer Suarez-Moncada, Bradley M. Wetherbee, and Mahmood S. Shivji
Source/Credit: Nova Southeastern University
Reference Number: mb012726_01