In the first, 14 actively feeding juvenile sandbar sharks were present in the holding tank and 14 trials (seven with the electropositive metal and seven with the stainless steel bolt) were conducted every other day over a 14-d period.
Bottom longline fishing gear was used to test the ability of electropositive metal to influence shark catch rates in the field.
Small pieces (approximately 30-70g initial weight) of electropositive metal comprising lanthanum (28%), cerium (53%), neodymium (15%), and praseodymium (4%) were attached to the dropper lines approximately 10 cm from the hook by using plastic zip ties.
In contrast, sharks generally avoided approaching electropositive metal bars, which precluded them from passing between the electropositive metal bars and the tank wall.
The frequency distributions of positions in relation to the lead fishing weights or electropositive metal bars demonstrate avoidance of the latter by the sharks (Fig.
There appeared to be a tendency for swimming speeds to be greater in proximity to the electropositive metal bars than under the other circumstances.
In contrast, sharks did not attack baits located in proximity of an electropositive metal bar within three minutes, at least during the initial trials.
Because it was impossible to identify individuals, it is unknown if only one or a few sharks overcame the deterrent effect of electropositive metal.
During the second set of experiments with fewer sharks in the tank (seven animals versus 14), the deterrent effect of electropositive metal was apparent until day 8 and it did not completely disappear until day 12 (Fig.
The ratio of sharks caught on hooks near plastic to sharks caught on hooks near electropositive metal (2.
In contrast, juvenile sandbar sharks generally avoided approaching the electropositive metal bars presumably because they produce mild irritation.
Because of the limited range of deterrence, electropositive metal would have to be placed near every hook in pelagic longline gear, although it appears that it could be placed at distances that are unlikely to interfere with capture of the targeted fishes.