Effects of the SMART™ (Selective Magnetic and Repellent-Treated) hook on spiny dogfish catch in a longline experiment in the Gulf of Maine

The spiny dogfish, Squalus acanthias, is viewed as a nuisance species due to their high abundance in the western Atlantic, in addition to their seemingly overwhelming presence on a variety of commercial fishing gears. In the present study, we incorporated two types of potential elasmobranch repellents, an (1) electropositive metal and (2) magnetism, which were combined on a fishing hook – the SMART (Selective Magnetic and Repellent-Treated) hook and tested on S. acanthias in the Gulf of Maine. Results obtained after 26 days of longline gear deployment demonstrated that SMART hooks decreased S. acanthias capture by 28.2%; however, SMART hooks had no observed influence on thorny skate (Amblyraja radiata), barndoor skate (Dipturus laevis), and teleost capture. Of the S. acanthias captured, a total of 120 were kept for dissection and S. acanthias captured on controls were found to have significantly higher levels of satiation compared to sharks captured on treatments. Lastly, laboratory analyses demonstrated that SMART hooks produced a mean voltage of 1.05 eV for a duration of 5 days, which thereafter the metal quickly dissolved and the voltage dissipated. In conclusion, the use of the SMART hook may not be economically feasible in this fishery, as the relative target catch (e.g. teleosts) did not offset the cost of the hooks; however, this study suggests SMART hooks as a potentially promising means to increase selectivity of hook gear and reduce S. acanthias capture and therefore future research in other fisheries is warranted.