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Commercial Fisheries News
Volume 35 Number 9
May 2008
Mischmetal not feasible as dogfish deterrent
BIDDEFORD, ME – Mischmetal, a mixed metal alloy that initially appeared to hold promise as a dogfish deterrent when attached in small triangular slices to longline gear, failed to produce any significant results during sea trials last September.
“It didn’t work, but now we know it didn’t work,” said Shelly Tallack of the Gulf of Maine Research Institute, who headed up the research.
The real focus of the study was longline gear, though Tallack’s team also attached mischmetal to rod-and-reel gear on selected occasions and to two lines of lobster traps, which didn’t produce any significant results either.
Tallack reported these findings to roughly four-dozen commercial and recreational fishermen at a March 29 dogfish forum here at the University of New England.
It was clear that numerous audience members had been aware of the project and were eager to hear the results. Some asked pointed questions, looking for positive news in the findings.
But even the most hopeful hold-outs were convinced that mischmetal simply wasn’t the answer after Tallack showed a segment of underwater video footage shot off the Isles of Shoals at the University of New Hampshire’s (UNH) aquaculture demonstration site.
There, adjacent to the university’s submerged cod cages, dogfish voraciously attacked bait – completely unintimidated by the mischmetal triangles attached to the gear. A few dogfish even attacked the mischmetal itself after the bait was gone.
“Look at that,” murmured several in the crowd. “They’ll eat anything.”
The amazing feeding frenzy was captured with video equipment aboard UNH’s aquaculture vessel, operated by the university’s Atlantic Marine Aquaculture Center.
Electroreception
In theory, everything about mischmetal’s potential use as a dogfish deterrent made sense.
Dogfish, like many other shark species, possess small pores around their heads – collectively called the “ampullae of Lorenzini” – that detect electric fields at short ranges and help them locate prey.
When submerged in water, mischmetal gives off a gas. Tallack and other elasmobranch (shark, skate, ray) researchers hypothesized this gas might interfere with the electroreception abilities of dogfish and prevent them from going after baited hooks.
Tallack initially proposed to test magnets as a dogfish deterrent. She had heard about the successful use of magnets in the Bahamas to reduce the bycatch of lemon sharks on hooks. The lemon shark magnet research won the World Wildlife Foundation’s Smart Gear Competition in 2006.
But then Tallack learned about other research on the West Coast showing that spiny dogfish in the Pacific seemed to be more averse to mischmetal than magnets.
So Tallack redesigned the project, which was funded by the Northeast Consortium, to test mischmetal instead – a far more attractive proposition than testing magnets with hook gear, which was bound to lead to some nasty magnetic snarls.
Gear trials
Tallack first obtained large triangular blocks of mischmetal, which had to be imported from China via Canada and were “fairly expensive,” she said.
Her first challenge was finding someone to cut the mischmetal into the needed slices for attachment to the hook gear. Mischmetal is “highly flammable,” and very few people were equipped to cut it, said Tallack. In fact, the most common use of mischmetal is for flint-ignition devices found in lighters.
Next came the sea trials. Using the Portland-based fishing vessel Survivor as a work platform and with the help of Capt. Christopher Andrews and crewman Eric Tomazin, Tallack and the team rigged longline gear with 100 hooks – 50 with mischmetal and 50 without, changing between the two configurations every 10 hooks. They set four longlines each day for the first three days, but then one line was lost, reducing the gear complement to three lines.
The team intended to make seven trips but ended up completing six. On two trips, they couldn’t find dogfish, at least not in large amounts as desired for the study. On the sixth trip, the gear became badly snarled and, at that point, the mischmetal was so disintegrated it wasn’t worth using on a seventh trip.
After reviewing the collected data and taking a close look at the hooks with mischmetal and the ones without, Tallack said, “There was no obvious difference except for maybe trip number six.”
But Tallack didn’t trust the results from that trip. Since the mischmetal was disintegrating and the hooks were tangled together, she concluded, “This caused confusion in the data.”
Tallack also provided a quick overview of work being conducted at the New England Aquarium by John Mandelman and colleagues where spiny dogfish videotaped in captivity showed a very mild aversion to mischmetal. Smooth dogfish, on the other hand, showed a mild aversion to magnets.
However, all that changed when the dogfish were deprived of food for two-to-four days, and then the mischmetal and magnets had little to no affect.
“Selectivity declined as hunger increased,” said Tallack.
This is how it goes with science. Experiments sometimes fail. But negative results can be just as important as positive ones, and researchers now know that mischmetal, which in theory seemed promising, just doesn’t work in practice.
Tallack said in conclusion, “The point is that it did not work in the wild. It may have shown mild impacts in the lab, but overall, mischmetal is unlikely to be a feasible solution as a dogfish deterrent.”
Janice M. Plante
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