Research Shows Shortfin Mako Shark Fishing Mortality Rate Is Much Higher Than Previously Thought
FORT LAUDERDALE/DAVIE, Fla. – More bad news for sharks.
A new study using satellite tracking by researchers from Nova Southeastern University’s Guy Harvey Research Institute (GHRI), the University of Rhode Island and other colleagues shows that the fishing mortality rate of the shortfin mako in the western North Atlantic is considerably higher than previously estimated from catches reported by fishermen. These data suggest that this major ocean apex predator is experiencing overfishing, raising serious concerns about whether the current levels of fishery catches in the North Atlantic are sustainable.
The new study has been published in the Journal Proceedings of the Royal Society B.
“Traditionally, the data obtained to determine the rate of fishing mortality, a key parameter used to help gauge the health of shark stocks, has depended largely on fishermen self-reporting any mako sharks they may have caught,” said Mahmood Shivji, Ph.D., senior author of the study and director of the NSU’s GHRI. “The challenge is that not all fishermen report the same way or some may underreport or even not report their mako shark captures at all, so the these catch data are known to be of questionable reliability.”
Shivji said that near real-time tracking of mako sharks using satellite tags and directly seeing how many were captured allowed researchers to bypass the dependency on self-reporting by fishermen.
“Using satellite tags for makos and possibly other fished species can be a time-efficient way and a fisheries-independent tool for gathering useful fisheries-interaction data, including answering fundamental questions about the levels of fishing survival and mortality,” said Michael Byrne, Ph.D., the paper’s lead author and postdoctoral fellow at NSU’s GHRI when the study was done. “The tracking data also showed these mako sharks entered the management zones of 19 countries, underscoring how critical it is for countries to work together closely to manage and conserve these long-distance oceanic travelers.”
When the researchers began to gather, compile, disaggregate and review the data, the results were startling.
An unexpectedly high proportion, 30% of the 40 satellite tagged sharks, were captured in fisheries. After modelling the probability that a mako shark would survive a year without being captured (a 72% chance) and calculating the fishing mortality rates, researchers determined that the rate at which shortfin makos were being killed in fisheries was actually 10 times higher than previously believed.
“From a conservation and protection point of view, this is huge,” said Bradley Wetherbee, Ph.D., a research scientist from the University of Rhode Island’s Department of Biological Sciences and a member of NSU’s GHRI. “It’s vital that we have the most accurate data possible to aid decision-makers in managing marine life populations sustainably. If they have inaccurate information, it’s much more difficult to make the correct decisions for properly managing populations. Everyone wants the populations managed in a sustainable way.”
The tracks of the tagged mako sharks, including the ones captured, can be viewed online on NSU’s GHRI shark tracking website (nova.edu/sharktracking).
Globally, many shark species have seen significant declines in their numbers, with fisheries overexploitation cited as a major cause. This can happen in many ways – some shark species are specifically targeted while others are captured by accident (called bycatch.) No matter how sharks are taken from the world’s oceans, the fact remains that the current levels of removal for many species are unsustainable.
The researchers stress that the work they are doing has the goal of providing the most accurate information possible to those in positions to take action to manage mako and other shark species. They both say that the goal is create successful fisheries management and conservation – to avoid declining populations, and to do that, we must have as much accurate data as possible.
“We have to have sustainable approaches to fishing,” Dr. Shivji said. “Sharks might get a bit of a bad rap in the media, but these apex predators are vital to the overall health of our oceans. You remove them from the equation and, quite honestly, we don’t know how far those ripples will be felt. One thing we do know is it won’t be inconsequential.”
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About Nova Southeastern University (NSU): Located in beautiful Fort Lauderdale, Florida, Nova Southeastern University (NSU) is a dynamic research institution dedicated to providing high-quality educational programs at the undergraduate, graduate, and first-professional degree levels. A private, not-for-profit institution, NSU has campuses in Fort Lauderdale, Fort Myers, Jacksonville, Miami, Miramar, Orlando, Palm Beach, and Tampa, Florida, as well as San Juan, Puerto Rico, while maintaining a presence online globally. For more than 50 years, NSU has been awarding degrees in a wide range of fields, while fostering groundbreaking research and an impactful commitment to community. Classified as a research university with “high research activity” by the Carnegie Foundation for the Advancement of Teaching, NSU is 1 of only 50 universities nationwide to also be awarded Carnegie’s Community Engagement Classification, and is also the largest private, not-for-profit institution in the United States that meets the U.S. Department of Education's criteria as a Hispanic-serving Institution. Please visit www.nova.edu for more information about NSU and realizingpotential.nova.edu for more information on the largest fundraising campaign in NSU history.
About NSU’s Guy Harvey Research Institute: Established in 1999, the Guy Harvey Research Institute (GHRI) is a collaboration between the renowned marine artist, scientist and explorer, Dr. Guy Harvey, and Nova Southeastern University’s Oceanographic Center. The mission of the GHRI is to provide the scientific information necessary to understand, conserve, and effectively manage the world’s marine fishes and their ecosystems. The GHRI is one of only a handful of private organizations dedicated exclusively to the science-based conservation of marine fish populations and biodiversity. The research, education and outreach activities of the GHRI are supported by the Guy Harvey Ocean Foundation, AFTCO Inc., extramural research grants, philanthropic donations by private businesses and individuals, and NSU. Please visit nova.edu/ocean/ghri/index.html for more information.
About NSU’s Halmos College of Natural Sciences and Oceanography: The college provides high-quality undergraduate (bachelor’s degree) and graduate (master’s and doctoral degrees and certificates) education programs in a broad range of disciplines, including marine sciences, mathematics, biophysics, and chemistry. Researchers carry out innovative basic and applied research programs in coral reef biology, ecology, and geology; fish biology, ecology, and conservation; shark and billfish ecology; fisheries science; deep-sea organismal biology and ecology; invertebrate and vertebrate genomics, genetics, molecular ecology, and evolution; microbiology; biodiversity; observation and modeling of large-scale ocean circulation, coastal dynamics, and ocean atmosphere coupling; benthic habitat mapping; biodiversity; histology; and calcification. The college’s newest building is the state-of-the-art Guy Harvey Oceanographic Center, an 86,000-square-foot structure filled with laboratories; offices; seminar rooms; an auditorium; and indoor and outdoor running sea water facilities. Please visit cnso.nova.edu for more information.