Sharks come in all sizes, from the dwarf lantern shark (Etmopterus perryi) to the massive great white(Fig. 1)。他们是一种很有意思的生物,必须继续ally move to stay alive as movement is the only way to move water through their gills to provide them with oxygen. Sharks are critical to the ocean ecology, but, as with many marine lifeforms, they’re being stressed by pollution, global warming, and man.
While most sharks are small or inoffensive, larger critters can cause harm to people. The movieJawstakes things to extremes, but people have been killed by sharks. Such attacks have become more frequent as oceans adjust to global warming and people become more numerous in areas where sharks have been living for millennia, like the east coast of Australia.
Shark Beach with Chris Hemsworthis a newNational Geographicfilm about sharks hosted by actor Chris Hemsworth, of course(Fig. 2)。Chris is an avid surfer and is interested in shark ecology. I enjoyed watching the film and picked up on a few technology-related items that I will mention here.
A significant portion of the film relates to larger sharks like the great white and the danger they pose to people, as well as the issues related to the sharks themselves. For example, massive shark nets have been deployed along the coast near beaches frequented by people, and there’s a lot of them. Unfortunately, these shark nets aren’t that effective—sharks can swim around or under them and the nets also snag other marine life that will not attack man. Eventually, these animals succumb once trapped in the nets.
Another tactic is called a drumline. These are buoys with a hook, line, and sinker tipped with a fish that the shark would eat, causing them to become hooked. The shark dies horribly, but it prevents that shark from coming close to a person. In most cases this would not happen anyway, though thousands die to prevent one human catastrophe.
The Smart Drumline Program uses the same approach. However, instead of letting the shark die, the buoy contains a radio transmitter—it alerts a nearby boat that can then catch, tag, and release the shark(Fig. 3)。They can also notify any nearby surfers and beachgoers, which is typical when a shark is sited by other means. Tagging also provides information about shark movements, enhancing our understanding of these creatures.
Personal shark protection is something a number of companies and organizations are involved with, and it’s examined within the movie. Professor Huveneers leads the Southern Shark Ecology Group within the Marine & Coastal Research Consortium atFlinders Universityin Adelaide, South Australia. They are evaluating various techniques and products that repel sharks. Most center around electrical fields(Fig. 4)。
For more on this research, check out theThe Technology Behind Shark Beachvideo interview I did with Professor Huveneers discussing the technology and movie.
Essentially, sharks have a very sensitive front end. This generally turns out to be a big advantage for the shark, unless a human has a device that can generate a field affecting that sensitivity. The approach is not 100% effective but significant enough that it could greatly reduce bad shark/person interactions.
Some products are commercially available and used in devices, such asOcean Guardian’ssurfboards(Fig. 5)。Furthermore, systems are being worked on that can be used to deter sharks from large areas, such as around ships or beaches.
