Sharks in captivity avoid metals that react with seawater to produce an electric field, a behavior that may help fishery biologists develop a strategy to reduce the bycatch of sharks in longline gear.
"Individual sandbar sharks would generally not approach the metal ingots closer than about 24 inches, nor attack pieces of cut bait suspended within approximately 12 inches,” said Richard Brill, a research scientist at NOAA’s Northeast Fisheries Science Center and head of the Cooperative Marine Education and Research (CMER) Program at the Virginia Institute of Marine Science. “This study clearly shows the alloy has the potential to repel sharks from pelagic longline fishing gear so they are not caught as bycatch, but the optimal size and shape of the alloy and other factors needs to be determined. This is a promising step.”
Up to now, electronic devices capable of repelling sharks have been large and not practical for use on longline fishing gear. The current project was undertaken to determine if small ingots of a relatively inexpensive electropositive alloy were repulsive to sharks under controlled laboratory conditions. If repulsion occurs consistently in the lab, the next step would be to conduct field trials.
Brill says juvenile sandbar sharks were used in the study because they are readily available in the estuaries along Virginia’s coast, do well in captivity, feed easily, and their constant forward motion makes it easy to measure changes in their swimming patterns. “They are good models for the species of sharks that are a significant problem in pelagic or open ocean longline fisheries worldwide.”
An estimated 11 to 13 million sharks are caught worldwide as bycatch each year, sometimes more than the targeted fish species. Sharks, part of the taxonomic group known as elasmobranchs which also includes skates and rays, generally have slow growth and reproductive rates and late sexual maturity. These factors result in an inability of shark populations to support high rates of fishing mortality, or slow population recovery. There is concern among scientists and fishery resource managers that severe reductions in elasmobranch populations could restructure marine ecosystems.
The sandbar shark, Carcharhinus plumbeus, is one of the largest coastal sharks in the world and can reach lengths of eight feet and weigh as much as 200 pounds. Sandbar sharks are usually found in shallow coastal waters including bays and estuaries in tropical and temperate waters around the world. In the western Atlantic Ocean they range from Massachusetts to Brazil, with the waters of the lower Chesapeake Bay considered a major nursery ground. Humans are their main predator.
“Our results were very promising but need further study,” Brill said. “The alloy we used, palladium neodymium, appears to be a good alternative to more expensive metals. It is also machinable and is reasonably resistant to corrosion in seawater. How long the metal will last before corroding and how long it will repel sharks in the field, however, needs to be determined.”
The lab experiments were conducted at the Virginia Institute of Marine Science using juvenile sand sharks up to five years old caught in surrounding waters and brought to an outdoor holding tank.
In addition to Brill, the study included scientists and students from Indiana University, Bangor University in Wales, Hampton University in Virginia, the University of Hawaii, and the research firm Shark Defense LLC of Oak Ridge, NJ, which develops shark repellents. Principal funding was provided by the Pacific Islands Fisheries Science Center of NOAA’s National Marine Fisheries Service in Honolulu, with logistical support from the VIMS Eastern Shore Laboratory.
This study by Brill and colleagues is among the first to rigorously test the use of rare earth materials on repelling elasmobranchs, and supports a recent study using metal alloys to repel spiny dogfish conducted by NOAA researchers in Oregon.
Results of the sandbar shark study were presented at a NOAA-sponsored shark deterrent workshop in Boston earlier this month.
Shelley Dawicki | EurekAlert!
When corals eat plastics
24.05.2018 | Justus-Liebig-Universität Gießen
Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences