Schematic of a longline operation from U.S. patent application 2009/0038205 A1 by Eric Matthew Stroud. (view on Google Patents)

For a shark, a supremely evolved hunter that roams the vastness of the open ocean, hundreds of fish dangling in the water might look like an easy meal. But they might actually be the shark’s last meal, because those fish aren’t there through some natural process, but are bait set out by a fishing vessel.

The fishing method called “longlining” uses vast lengths of baited hooks that often stretch for miles to catch fish like tuna and swordfish.  Although the fishing crew tries to set the lines in an area with a high population of the target fish, the hooks on the longlines are indiscriminate, and will grab any species that takes a bite.

Longlines are a major hazard for sharks (and also sea turtles and other creatures). The Pelagic Shark Research Foundation notes that shark “bycatch” could be as much as 50% of the reported catch (bycatch is a term used to describe non-targeted animals that are caught in fishing operations) .  The Monterey Bay Aquarium Seafood Watch report on sharks (PDF) observes that “it is entirely possible to fish at maximum sustainable yield for the fast growing species such as tuna and swordfish while depleting the slower-growing species such as sharks” and that bycatch is generally unreported and unmanaged.

For the longliners, bycatch isn’t only an ecological black eye — there are some financial implications too.  For example, sharks can damage the fishing gear with their powerful jaws, a captured shark can be a hazard to the
crew on deck, each captured shark is one less hook for target fish, and requires time to
remove them from the line.

A repulsive solution
An accidental discovery from a decade ago could help reduce shark bycatch.

A piece by Ari Daniel Shapiro at the NOVA website has the story:  in the early 2000s, Eric Stroud was doing some research on shark repellents — in a kiddie pool in his basement in New Jersey, of all places — and discovered that his sharks responded dramatically when a magnet accidentally fell into the pool:  the shark immediately changed direction and swam the other way.

A NOVA special called Hunting the Elements also has coverage of the subject. As part of the chapter on rare earth elements (the lanthanides, scandium and yttrium), guest host David Pogue visits Patrick Brice in Florida to see some live demonstrations of the effect (starting at about 1:32:25).  The results are stunning, with sharks drastically influenced by rare earth elements — in both magnetic and non-magnetic forms (e.g., a piece of samarium) — even when the magnet is outside of the tank.  There are probably two effects.  With magnets, an electric field is created in the sea water, which irritates the shark (magnetic fields create electric fields, and vice versa).  With non-magnetic samples, the rare-earth metals lose atoms in sea water, which then shed electrons, creating positive ions.  Shark skin has a slight negative charge, so an electric current is created between the two surfaces. (The video has a good demonstration of this.)

A 2008 press release from NOAA’s Northeast Fisheries Science Center (via Science Daily) includes two photos from laboratory work at the Virginia Institute of Marine Science using juvenile sandbar sharks.  The left-hand image below shows the swim tracks for sharks in a tank that has lead weights dangling in the water:  the sharks swim throughout the tanks, not leaving any area unexplored. The right-hand image shows what happens when the experimenters hang three bars of palladium neodymium in the tank in the position marked by the black circle: the sharks avoid the area. Commenting on the results, Richard Brill, a research scientist at
NOAA, said

“Our results were very promising but need further study…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.”

Left: three lead weights at approximately the 5 o’clock position. Right : three bars of palladium neodymium in the same place.  (Photos by Leonie Smith, Bangor University, Wales, copied from a U.S. government website)

And so, it follows that if the magnets could be integrated into longline hooks, perhaps sharks would be repelled from the bait that would make them bycatch.  Way back in 2006, WWF gave an  International Fishing Gear Award (press release) to Michael M. Herrmann for his magnet plus hook design.

(Source: Patent app. 2009/0038205 A1)

Will the idea attract attention?
It’s unclear if these hooks are being used at sea in any significant numbers — neither the NOVA article, television program, or other sources mentioned above hint at any wide use. In addition, a search of Monterey Bay Aquarium’s website for “rare earth” comes up empty* (MBA sponsors Seafood Watch).

If a magnet or hunk of rare earth metal on a longline rig actually repels sharks, how can we get them into wider use? Two ideas come to mind:  labeling and certification.

You’ve probably seen or heard of “dolphin safe” tuna, a certification given to tuna fishing operations that avoid capturing dolphins in their nets (the effectiveness of some of the programs, however, have been called into question by Earth Island Institute). You might have also heard of “turtle safe” shrimp, shrimp caught in trawls that have escape hatches for sea turtles.  So wouldn’t it also make sense to have “shark safe” fish from longline operations**?

Certification agencies, like the Marine Stewardship Council (MSC) could also play a role by requiring that use of shark-repelling gear become a prerequisite for certifications of longline operations (e.g., the North West Atlantic Canada longline swordfish fishery).  Principle 2 of the MSC certification requirements is “Minimising environmental impact”, which requires that “Fishing operations should be managed to maintain the structure, productivity, function and diversity of the ecosystem on which the fishery depends.”  Quite a few pages in the document address bycatch (in rather technical language).

With the oceans under great stress, it’s well past time to start trying new ideas in fishing fleets (and in our personal shopping and eating habits, too). Might the rare-earth enhanced hook be one of these new ideas?

* Somewhere in the Seafood Watch area, I found this success story about reducing bird kills by longline operations:
“Seabirds often flock around longline vessels, and can become snared and drown as they try to feed on baited hooks thrown into the ocean. ‘Streamer lines’ have proven to be a cost-effective solution that has dramatically reduced seabird deaths in several longline fisheries. Brightly colored streamer lines made of polyester rope are positioned on each side of the longline. The colors and the flapping of the lines scare seabirds away from the baited hooks. From 1993 to 2001, roughly 16,000 seabirds died each year in Alaskan groundfish longline fisheries. In 2002, streamer lines became required gear; since then, the number of seabird deaths has decreased by approximately 70 percent.”
** Note, however, that most sustainable seafood guides give lower ratings to fish from longline operations than from rod-and-reel operations, mainly because of the bycatch problem.