Nav: Home

Study finds preliminary recovery of coastal sharks in southeast US

February 28, 2017

A new analysis of population trends among coastal sharks of the southeast U.S. shows that all but one of the seven species studied are increasing in abundance. The gains follow enactment of fishing regulations in the early 1990s after decades of declining shark numbers.

Scientists estimate that over-fishing of sharks along the southeast U.S. coast--which began in earnest following the release of Jaws in 1975 and continued through the 1980s--had reduced populations by 60-99% compared to un-fished levels. In response, NOAA's National Marine Fishery Service in 1993 enacted a management plan for shark fisheries that limited both commercial and recreational landings.

Now, says lead scientist Cassidy Peterson, a graduate student at William & Mary's Virginia Institute of Marine Science, "We've shown that after over two decades of management measures, coastal shark populations are finally starting to recover and reclaim their position as top predators, or regulators of their ecosystem. Our research suggests we can begin to shift away from the era of 'doom and gloom' regarding shark status in the United States."

Joining Peterson in the study, published in the latest issue of Fish and Fisheries, were VIMS professor Rob Latour, Carolyn Belcher of the Georgia Department of Natural Resources, Dana Bethea and William Driggers III of NOAA's Southeast Fisheries Science Center, and Bryan Frazier of the South Carolina Department of Natural Resources.

The researchers say their study--based on modeling of combined data from six different scientific surveys conducted along the US East Coast and in the Gulf of Mexico between 1975 and 2014--provides a more accurate and optimistic outlook than previous studies based on commercial fishery landings or surveys in a single location.

"Data from shark long-lining operations or shark bycatch can be suspect," says Peterson, "because what looks like a change in abundance might instead be due to changes in fishing gear, target species, market forces, or other factors."

Research surveys are scientifically designed to remove these biases. Survey crews purposefully sample a random grid rather than visiting known shark hot spots, and strive to use the exact same gear and methods year after year to ensure consistency in their results.

But even with these safeguards, data from a single survey often aren't enough to capture population trends for an entire shark species, whose members may occupy diverse habitats and migrate to different and far-flung areas depending on age and sex.

"Because many shark species undergo vast migrations and have complex life cycles," says Peterson, "it's not uncommon for results from different surveys to conflict. Producing an estimate of total abundance requires combining data from different surveys--sometimes from several states or even countries--and applying intricate stock-assessment models."

For the current study, the scientists combined data from six different shark surveys: the VIMS Longline Survey, the SouthEast Area Monitoring and Assessment Program's South Atlantic Coastal Trawl Survey, the South Carolina Coastal Longline Survey, the Georgia Red Drum Longline Survey, the Southeast Fisheries Science Center's Longline Survey, and the Gulf of Mexico Shark Pupping and Nursery Area Gillnet Survey.

"Our study represents the most comprehensive analysis of patterns in abundance ever conducted for shark species common to our area and the Southeast coast," says Latour, who directs the longline survey at VIMS. Established in 1973, it is the world's longest running fishery independent monitoring program for sharks, skates, and rays.

By pooling and modeling data from all six surveys, the researchers were able to estimate population trends for seven of the region's most common coastal species: the large-bodied sandbar, blacktip, spinner, and tiger sharks, and the smaller Atlantic sharpnose, blacknose, and bonnethead sharks.

The results of the analysis were clear, says Peterson. "All the large-bodied sharks showed similar population trends, with decreasing abundance from the mid-1970s to the early 1990s, then a multi-year period of low abundance, and recent indications of recovery from past exploitation."

All but one population of small coastal sharks also increased in abundance. The exception was blacknose sharks in the Gulf of Mexico, which decreased from the onset of records in 1989 until the study's end in 2014. This species is known to be susceptible to by-catch within the trawl fishery for Gulf shrimp. The blacknose population along the Atlantic coast of the southeast U.S. actually increased during the same period.

The overall population trends make biological sense, says Latour. "The large-bodied species saw the greatest initial declines, both because they were highly sought by anglers, and because they mature late and produce relatively few pups. Their slow growth rate also helps explain the pause in their recovery following the onset of fishing regulations in the early 1990s." The smaller shark species, whose higher growth rates make them less susceptible to fishing pressure, saw lesser declines and more rapid recoveries.

The team also found a correlation between shark numbers and both fishing pressure and large-scale climatic patterns.
-end-
Funding for the study was provided by NOAA Fisheries, the NMFS Highly Migratory Species Office, the Atlantic States Marine Fisheries Commission, the South Carolina Saltwater Recreational Fishing License Funds, and the Federal Assistance for Interjurisdictional Fisheries Program.

Virginia Institute of Marine Science

Related Fisheries Articles:

Meeting the challenges facing fisheries climate risk insurance
Insurance schemes with the potential to improve the resilience of global fisheries face a host of future challenges, researchers say.
Healthy mangroves help coral reef fisheries under climate stress
Healthy mangroves can help fight the consequences of climate change on coral reef fisheries, according to a University of Queensland-led study.
Study champions inland fisheries as rural nutrition hero
Researchers from MSU and the FAO synthesize new data and assessment methods to show how freshwater fish feed poor rural populations in many areas of the world.
For global fisheries, it's a small world after all
Even though many nations manage their fish stocks as if they were local resources, marine fisheries and fish populations are a single, highly interconnected and globally shared resource, a new study emphasizes.
New study maps how ocean currents connect the world's fisheries
It's a small world after all -- especially when it comes to marine fisheries, with a new study revealing they form a single network, with over $10 billion worth of fish each year being caught in a country other than the one in which it spawned.
Federal subsidies for US commercial fisheries should be rejected
A pending rule change proposed by the US National Marine Fisheries Service would allow the use of public funds to underwrite low-interest loans for the construction of new commercial fishing vessels.
Sustainable fisheries and conservation policy
There are roughly five times as many recreational fishers as commercial fishers throughout the world.
For the fisheries of the future, some species are in hot water
Some fisheries may falter while others could become more productive as the world's waters continue to warm, according to a new study, which looks to the productivity of fisheries in the past to help predict the impact of climate change on future fisheries.
'Dead zone' volume more important than area to fish, fisheries
A new study suggests that measuring the volume rather than the area of the Gulf of Mexico's dead zone is more appropriate for monitoring its effects on marine organisms.
Study: Aquaculture does little, if anything, to conserve wild fisheries
New research finds that aquaculture, or fish farming, does not help conserve wild fisheries.
More Fisheries News and Fisheries Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Accessing Better Health
Essential health care is a right, not a privilege ... or is it? This hour, TED speakers explore how we can give everyone access to a healthier way of life, despite who you are or where you live. Guests include physician Raj Panjabi, former NYC health commissioner Mary Bassett, researcher Michael Hendryx, and neuroscientist Rachel Wurzman.
Now Playing: Science for the People

#544 Prosperity Without Growth
The societies we live in are organised around growth, objects, and driving forward a constantly expanding economy as benchmarks of success and prosperity. But this growing consumption at all costs is at odds with our understanding of what our planet can support. How do we lower the environmental impact of economic activity? How do we redefine success and prosperity separate from GDP, which politicians and governments have focused on for decades? We speak with ecological economist Tim Jackson, Professor of Sustainable Development at the University of Surrey, Director of the Centre for the Understanding of Sustainable Propserity, and author of...
Now Playing: Radiolab

An Announcement from Radiolab