Fishing Technique Modifications


Modifications to fishing gear can significantly mitigate bycatch without reducing a fishermen’s target catch.  To read about more examples of gear modifications search the Bycatch Reduction Technique Database.  The Consortium works with scientists and fishermen to test gear modifications that have the potential to reduce bycatch, while maintaining target catch, minimizing cost, and preserving fishermen’s safety.  

Acoustic Pingers

171 Acoustic Pinger. Photo: WaplesPingers are small devices that emit sounds (“pings”) underwater at various intervals.  The alarms alert certain dolphin and porpoise species to the presence of fishing gear and thus decrease the probability of entanglement.  In 1994, the New England Aquarium led the first study to evaluate the potential for these devices, and showed that pingers nearly eliminated bycatch of harbor porpoise (Phocoena phocoena) in gillnets deployed in the Gulf of Maine.  As a result, pingers were adopted by New England’s gillnet fishermen. 

Elsewhere, including in Europe and off the Pacific coast of the US, other tests of pingers demonstrated their utility in deterring bycatch of small cetaceans, and their use is now mandated within these regions.  Argentina, Australia, and New Zealand are among the other countries that have evaluated the efficacy of pingers with promising results.  The research and development of this bycatch reduction method is still an active area of research, contributing important refinements and discoveries in acoustic deterrents for mitigating bycatch.

"Whale-Safe" Hooks

In the Atlantic pelagic longline fishery, pilot whales (Globicephala spp.) and Risso's dolphins (Grampus griseus) commonly interact with fishery operations, and in the Pacific, false-killer whales (Pseudorca crassidens) interact with the Hawaii-based pelagic longline fishery. Interactions between the odotocetes and longlines occur because the animals are attacted to the bait, the catch, and/or the discard. 

These odotocetes can become hooked at the mouth or entangled in the line, and the former tends to result in more serious injuries. The goal of this research is to determine whether a "whale-safe" circle hook could be used as a gear modification to reduce bycatch and serious injury, while retaining target catch. A "whale-safe" hook is a weaker hook that a large mammal could pull, bend,and straighten, allowing it to escape possible entanglement - but the hook is still strong enough to retain the smaller fish that are targeted.

Hook Designs and Strengths

The University of North Carolina Wilmington conducted tests on common commercially available longline hooks to measure the force required to pull the hooks through the soft and hard tissues of short-finned pilot whales, Risso's dolphins, and false killer whales. The researchers found that the different materials the hooks were made of influenced how they bent or broke when pulled through the odontocete tissue. 

196 Lip tissue of a short-finned pilot whale with a Korean Carbon 16 hook. Photo: UNCW

Field Trials


187 Whale depredation on tuna. Photo credit: Sohail Khamesi
Field research testing "whale-safe" fishing hooks in the North Carolina-based and Hawaii-based pelagic longline fisheries is ongoing. During the studies, one pilot whale and one false killer whale were observed caught and subsequently released when the hooks straightened out after a few minutes. There was also no significant decrease in the catch of any target species.

Read the report on target catch rates using variable strength circle hooks in the Hawaii based tuna longline fishery.

Metallic Repellents

38 Photo Credit: John MandelmanMany species of elasmobranchs (sharks and rays) make up a large portion of pelagic longline bycatch. Sometimes shark bycatch even exceeds the percentage of target catch, such as tuna.

Through an array of recent studies, some species of sharks have been documented to show an aversion response to certain electrogenic metals, alloys and strong magnets. This is a presumed result of an overstimulation of the sensitive electroreceptors in elasmobranchs.  Past and present studies sponsored by the Consortium have investigated several different metallic elements to evaluate their potential as reliable (i.e. consistent, practical) shark repellent devices for fishing gear.

Previous studies have examined the reactions of captive spiny piked dogfish (Squalus acanthias) and dusky smoothhound (aka smooth dogfish) (Mustelus canis) sharks to two metals - a lanthanide/cerium alloy (mischmetal) and a rare-earth magnet (neodymium-iron-boride).

The data collected suggest that the repellent effects of each metal vary from one shark species to another. The spiny dogfish were more averse to the mischmetal, while the smooth dogfish were more deterred by the magnet. However, both species are more likely to ignore the repellents if they were hungry. Overall, it was determined that electrogenic mischmetal would not be an effective and/or practical deterrent to interactions between fishing gears and both the spiny dogfish and dusky smoothhound.

Researchers at Florida Atlantic University (FAU) tested the efficacy of various lanthanide elements and their alloys as potential shark repellents. The various metals were examined for output voltage (uVolts/gram), dissolution rate, machinability, and cost to determine which to use for further testing. Based on those criteria, the lanthanide element, neodymium (Nd) was selected for use in subsequent behavioral trials with sharks.

Behavioral trials by FAU and the NEAq were then conducted at the FAU marine lab on lemon sharks (Negaprion brevirostris) and bonnethead sharks (Sphyrna tiburo), which represent two families (Carcharhinidae and Sphyrnidae, respectively). Trials were also conducted at the Marine Biological Laboratory in Woods Hole, again on the spiny dogfish (Squalus acanthias) and the dusky smoothhound (Mustelus canis). Preliminary results suggest that neodymium is effective for deterring individual bonnethead and dusky smoothhound sharks and groups of spiny dogfish. However, it was an ineffective deterrent when presented to groups of lemon sharks, bonnethead sharks, or dusky smoothhound sharks. 

See the results of this research here and here
Also read about how understanding elasmobranch sensory biology may help find new ways to reduce their bycatch. 

Ropes

Ropes in the water column pose an entanglement risk to whales, other cetaceans, and marine turtles.  The Consortium is working with scientists and fishermen to evaluate the efficacy of alternative ropes for reducing bycatch while retaining target catch and maintaining fishability.  Examples of the types of ropes already tested or undergoing evaluation by the Consortium include: 

Stiff Rope

The Consortium is testing whether ropes that have greater stiffness or fish under greater tension may be effective for reducing entanglements.  The stiffness or tension would reduce the ability of the rope to bend, allowing animals to slide off any rope encountered.  The Consortium is measuring rope tension under different environmental conditions and studying the fisheries that use tense rope to determine how effective it may be to reduce bycatch.    

Sinking Groundline

Sinking groundlines are now mandatory in the Gulf of Maine pot fishery for lobster in order to avoid bycatch of the North Atlantic right whale, humpback whale, minke whale, and fin whale. The Consortium is working with fishermen to determine sinking groundlines’ wear and tear to avoid contributing to lost gear.  

Glow Rope37 Photo Credit: Tim Werner

The rope is chemically treated to give it a glowing property that increases its visibility to whales.  It could potentially be used in the Gulf of Maine pot fishery for lobster and in gillnet fisheries for multiple species to avoid entanglements.

Weak Rope

Polypropylene rope is infused with barium sulfate manufactured in such a way that they
are made strong enough for fishing but that break under the pull of an entangled whale.  Maine lobstermen worked with the Consortium to test various ropes that were designed to break under impact with a whale, but maintain sufficient strength for fishing.