Researchers who tracked movements of sharks and longline fishing vessels in North Atlantic found significant overlap driving shark declines.

MIAMI, Fla. (January 25, 2016)—A new study from an international team of scientists found commercial fishing vessels target shark hotspots, areas where sharks tend to congregate, in the North Atlantic. The researchers suggest that sharks are at risk of being overfished in these oceanic hotspots.

Neil Hammerschlag, research assistant professor at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science and Abess Center for Ecosystem Science and Policy, was part of the scientific team that published its findings in the January 25 issue of the journal Proceedings of the National Academy of Sciences. The authors report in the study that catch quotas for sharks by commercial fishers might be necessary to protect oceanic sharks.

“Our research clearly demonstrates the importance of satellite tagging data for conservation,” said Hammerschlag, director of the UM Shark Research and Conservation Program who conducted the satellite tagging and tracking of several shark species in the northwestern Atlantic for the study. “The findings both identify the problem as well as provide a path for protecting oceanic sharks.”

During a four-year period from 2005 to 2009, the researchers tracked more than 100 sharks equipped with satellite tags from six different species in the North Atlantic while concurrently tracking 186 Spanish and Portuguese GPS-equipped longline fishing vessels. They found that the fishing vessels and sharks occurred in ocean fronts characterized by warm water temperature and high productivity, including the Gulf Stream and the North Atlantic Current/Labrador Current Convergence Zone near Newfoundland.

“Many studies have tracked sharks, and many studies have tracked fishing vessels, but fine-scale tracking of sharks and fishing vessels together is lacking, even though this should better inform how shark fisheries should be regulated,” said David Sims of the Marine Biological Association, and the senior author of the study.

According to the researchers, about 80 percent of the range for two of the most heavily fished species tracked—the blue and mako sharks—overlapped with the fishing vessels’ range, with some individual sharks remaining near longlines for over 60 percent of the time they were tracked. Blue sharks were estimated to be vulnerable to potential capture 20 days per month, while the mako sharks’ potential risk was 12 days per month.

“Although we suspected overlap might be high, we had no idea it would be this high. Space-use overlap on this scale potentially increases shark susceptibility to fishing exploitation, which has unknown consequences for populations,” said Nuno Queiroz of the University of Porto, Portugal, the lead author of the study.

Tens of millions of ocean-dwelling sharks are caught by commercial fishing operations each year. The researchers suggest that a lack of data on where sharks are likely to encounter fishing vessels has hampered current shark conservation efforts.

The researchers propose that because current hotspots of shark activity are at particularly high risk of overfishing, the introduction of conservation measures, such as catch quotas or size limits, will be necessary to protect oceanic sharks that are commercially important to fleets worldwide at the present time.

In addition to Queiroz and Hammerschlag, co-authors of the study, titled “Ocean-wide tracking of pelagic sharks reveals extent of overlap with longline fishing hotspots,” include Nicolas E. Humphries, Gonzalo Mucientes, Fernando P. Lima, Kylie L. Scales, Peter I. Miller, Lara L. Sousa, Rui Seabra, and David W. Sims. Instituations contributing to the research were the Marine Biological Association of the United Kingdom, Universidade da Porto in Portugal, National Oceanography Centre Southampton, University of Southampton, Fundación CETMAR, University of Miami, Plymouth Marine Laboratory, University of California Santa Cruz, National Oceanic and Atmospheric Administration, and Faculdade de Ciências da Universidade do Porto.

Hammerschlag’s work was supported by the Disney Worldwide Conservation Fund, Batchelor Foundation, and West Coast Inland Navigation District in Florida. The research study was part of the European Tracking of Predators in the Atlantic (EUTOPIA) initiative.

Special to UM News

MIAMI, Fla. (July 23, 2015)–Scientists at the Rosenstiel School of Marine and Atmospheric Science and the Abess Center for Ecosystem Science and Policy who examined predator-prey interactions between tiger sharks and sea turtles in the northwestern Atlantic Ocean found that tiger sharks alter their movements to take advantage of nesting turtles.

The research team used long-term satellite tagging data from large tiger sharks and adult female loggerhead sea turtles—common prey of tiger sharks—to examine their movement patterns and evaluate if turtles modify their behaviors to reduce their chances of a shark attack when turtle and shark home ranges overlapped.

The study revealed that tiger sharks undergo seasonal movements to take advantage of the turtles nesting off the Carolinas during the summer. Tiger sharks are ambush predators, primarily attacking surfacing turtles from below. In theory, loggerhead turtles should reduce their exposure at the surface in regions of high habitat overlap with tiger sharks. However, surprisingly, the researchers found that when shark-turtle overlap in the study region was high, turtles did not alter surfacing behavior to reduce the risk. But sharks did exhibit modified surfacing behavior believed to enhance predation opportunity.

“We suggest that sharks may not be an important factor influencing the movements of turtles,” said Neil Hammerschlag, research assistant professor at the Rosenstiel School and Abess Center. “In fact, it is possible that fishing of tiger sharks in our study area has reduced their populations to levels that no longer pose a significant threat to turtles at the individual level, with other factors becoming more important for turtles, such as the need to avoid boat strikes, which is a huge threat to turtle survival.”

The study is one of the first to test if the “landscape of fear” model, a scientific theory used to explain how animals move and interact with the environment based on their fear of being attacked by their predators, is applicable to large open marine systems involving wide-ranging species, like sharks and turtles.

“This is one of the first studies to compare the large-scale, long-term movements of sea turtles with their natural predators, tiger sharks,” said study co-author Lucy Hawkes of the University of Exeter’s Centre for Ecology and Conservation.

“These data are essential for setting and prioritizing marine protection for these species, which are both of conservation concern,” said another co-author, Matthew Witt of the University of Exeter’s Environment and Sustainability Unit.

The study, titled “Evaluating the landscape of fear between apex predatory sharks and mobile sea turtles across a large dynamic seascape,” was published in the July 23 online edition of the journal Ecology. Other co-authors include Kyra Hartog and Emily Rose Nelson of the University of Miami; Annette C. Broderick and Brendan J. Godley of the University of Exeter; John W. Coker, DuBose B. Griffin, Sally R. Murphy, and Thomas M. Murphy of the South Carolina Department of Natural Resources; Michael S. Coyne of SeaTurtle.org; Mark Dodd of the Georgia Department of Natural Resources; Michael G. Frick of the University of Florida’s Archie Carr Center for Sea Turtle Research; Kristina L. Williams of the Savannah Science Museum’s Caretta Research Project; and Matthew H. Godfrey of the North Carolina Wildlife Resources Commission.

Special to UM News

MIAMI, Fla. (July 22, 2014)—A new study that examined the survival rates of 12 different shark species captured as unintentional bycatch in commercial longline fishing operations found large differences across the 12 species, with bigeye thresher, dusky, and scalloped hammerhead being the most vulnerable. Led by researchers at the Rosenstiel School of Marine and Atmospheric Science and the Abess Center for Ecosystem Science and Policy, the study provides new information to consider for future shark conservation measures in the northwest Atlantic. The unintentional capture of one fish species when targeting another, known as bycatch, is one of the largest threats facing many marine fish populations.

Researchers from the University of Miami and the National Marine Fisheries Service analyzed over 10 years of shark bycatch data from western Atlantic Ocean and Gulf of Mexico tuna and swordfish longline fisheries to examine how survival rates of sharks were affected by fishing duration, hook depth, sea temperature, animal size, and the target fish. Some species, such as tiger sharks, had bycatch survival rates that exceeded 95 percent, while other species, such as night sharks and scalloped hammerheads, had significantly lower survival rates— in the 20 to 40 percent range.

“Our study found that the differences in how longline fishing is actually conducted, such as the depth, duration, and time of day that the longlines are fished, can be a major driver of shark survival, depending on the species,” said Austin Gallagher, a Rosenstiel School Ph.D. student and lead author of the study. “At-vessel mortality is a crucial piece of the puzzle in terms of assessing the vulnerability of these open-ocean populations, some of which are highly threatened.”

The researchers also generated overall vulnerability rankings of species, taking into account not only their survival, but also reproductive potential. They found that species most at risk were those with both very slow reproductive potential and unusual body features, such as hammerheads and thresher sharks. The study authors suggest that bycatch likely played an important role in the decline of scalloped hammerhead species in the northwest Atlantic, which has been considered for increased international and national protections, such as the U.S. Endangered Species List.

The researchers suggest that high at-vessel mortality, slow maturity, and specialized body structures combine for the perfect mixture to become extinction-prone.

“Our results suggest that some shark species are being fished beyond their ability to replace themselves,” said Neil Hammerschlag, research assistant professor. “Certain sharks, such as bigeye threshers and scalloped hammerheads, are prone to rapidly dying on the line once caught, and techniques that reduce their interactions with fishing gear in the first place may be the best strategy for conserving these species.”

The study, titled “Vulnerability of oceanic sharks as pelagic longline bycatch,” was published online in the open-access journal Global Ecology and Conservation.

In addition to Gallagher and Hammerschlag, from UM’s R.J. Dunlap Marine Conservation Program, coauthors included Joseph Serafy and Eric Orbesen from the National Oceanic and Atmospheric Administration’s Southeast Fisheries Science Center.

UM researchers hoist a tiger shark aboard the boat platform to begin their sampling.

By Annie Reisewitz
Special to UM News

MIAMI, Fla. (January 29, 2014) – A new study led by scientists at the University of Miami Abess Center for Ecosystem Science and Policy and the Rosenstiel School of Marine and Atmospheric Science investigated how several species of coastal sharks respond to stress from catch-and-release fishing. The results revealed that each of the shark species responded differently, with hammerhead sharks by far the most vulnerable to the adverse effects of fighting on a fishing line.

The UM scientists experimentally simulated catch-and-release fishing on five shark species—hammerhead, blacktip, bull, lemon, and tiger sharks—in South Florida and Bahamian waters. Researchers took blood samples to examine stress, including pH, carbon dioxide and lactate levels, conducted reflex tests, as well as used satellite tags to look at the sharks’ post-release survival. Similar to what happens to humans during intense or exhaustive physical exercise, fighting on a fishing line significantly affected the blood lactate levels of sharks, which has been linked to mortality in many species of fish.

The study revealed that even with minimal degrees of fighting on a fishing line, hammerhead exhibited the highest levels of lactic acid buildup of all species studied, followed by blacktip, bull, lemon and tiger sharks. Tagging results also suggested that, after release, hammerheads were also prone to delayed mortality.

The Abess Center’s Austin Gallagher takes samples from a shark for the study.

“Our results show that while some species, like tiger sharks, can sustain and even recover from minimal catch-and-release fishing, other sharks, such as hammerheads, are more sensitive,” said lead author and Abess Center Ph.D. candidate Austin Gallagher. “Our study also revealed that just because a shark swims away after it is released, doesn’t mean that it will survive the encounter. This has serious conservation implications because those fragile species might need to be managed separately, especially if we are striving for sustainability in catch-and-release fishing and even in bycatch scenarios.”

Study co-author Neil Hammerschlag, research assistant professor at UM, adds, “Many shark populations globally are declining due to overfishing. Shark anglers are some of the biggest advocates for shark conservation. Most have been making the switch from catch and kill to all catch and release. Our study helps concerned fishermen make informed decisions on which sharks make good candidates for catch-and-release fishing, and which do not, such as hammerheads.”

The study, titled “Physiological stress response, reflex impairment and survival of five sympatric shark species following experimental capture and release,” was published in the special theme issue “Tracking fitness in marine vertebrates” in the journal Marine Ecology Progress. In addition to Gallagher and Hammerschlag, the study co-authors include Joseph E. Serafy of the National Marine Fisheries Service in Miami, and Steven J. Cooke of the Ottawa-Carleton Institute of Biology and Institute of Environmental Science in Ontario, Canada.