SharkDefense scientists discovered and performed the initial tests of the world’s first two selective shark repellent materials that are capable of deployment as terminal tackle and are non-polluting. These technologies do not require batteries and add only nominal cost-per-hook, which is offset by increased target catch. This grant-winning research has been commercialized as electropositive metal weights for bottom longlines, and a first-generation SMART Hook, licensed to RepelSharks for sale. New research is being pursued to greatly improve the characteristics of the SMART Hook, making it suitable for use in all fisheries.
Pelagic longlining is an open-sea fishing technique that employs a long main line from which individual hooks are suspended at intervals of 250 to 350 feet (ref: National Oceanographic and Atmospheric Administration). The hooks are attached to the main line by monofilament branch lines called gangions or “snoods”. Floats attached to branch lines are spaced along the main line to keep it elevated horizontally in the water, and the gangions hang vertically from it. A variety of bait is used, with whole smaller fish, such as Atlantic mackerel and squid. Luminescent light sticks are often fastened to the gangions near the baited hooks, making them more attractive to the targeted species and also attracting smaller species on which targeted species feed. The longlines used by the United States domestic pelagic longline fleet range from 20 to 40 miles in length. The depth at which the hooks are set is controlled by the length of the lines attaching the main line to the floats, by the length of the gangions, and by the speed at which the longline gear is set. After a variable “soak time,” the gear is retrieved, and the catch is brought on board for cleaning and icing down in the hold. This “one at a time” processing and handling gives longline products a high quality distinction in the marketplace.
Pelagic shark species such as the blue shark ( Prionace glauca) are often attracted to miles of attractive stimuli resulting from the longlines. Shark interactions on pelagic longlines result in substantial inconveniences and adverse economic effects (ref: Gilman, Clarke, Brothers, Alfaro-Shigueto, Mandelman, Mangel, Petersen, Piovano, Thomson, Dalzell, Donoso, Goren, Werner, 2007). In fisheries with restrictions on shark-finning, a lack of market for shark meat, or a per-trip limit on shark retention, shark interactions cause:
Damage and loss of gear: Sharks bite off terminal tackle (e.g., baited hook, leader, weighted swivel, and line) from branch lines, stretch and chafe branch lines, break the main line, and some shark species will pull the gear down causing branch lines to become entangled;
Reduced catch of marketable species: When baited hooks are unintendedly occupied (referred to as “bycatch”) or removed by sharks, there are fewer hooks available to catch non-shark marketable species;
Risk of injury: It is dangerous for crew to handle caught sharks and there is a risk of being hit by weights when branch lines containing sharks break during gear retrieval; and,
Expenditure of time. A majority of fishers consider the time required to remove sharks from gear, retrieve terminal tackle and repair and replace gear as a central concern resulting from shark interactions.