Pinger use on gillnets instruction and background information
Published:
19991.0 Acoustic pingers
Acoustic pingers are now used in many places around the world for the purpose of reducing bycatch of porpoises and dolphins in gillnets. The pingers either deter the animals from the nets or alert them to the nets. In either case, the pingers have been shown to reduce entanglement and death of several dolphin and porpoise species.
There are various types of pingers in use today. Each has specific acoustic characteristics. Based on New Zealand Department of Conservation (DOC) Conservation Services Levy research by Stone et al. in 1999, the Dukane Manufacturing company in the United States custom designed a pinger for use with Hector’s dolphins. It is known as model Netmark 1050. This pinger, as well as others, can be obtained directly from Dukane or through New Zealand distributors.
2.0 Pinger structure and assembly
The pinger has a simple screw top. Inside is a battery cartridge that holds four AA alkaline batteries. A rubber O-ring in the threads of the the cap prevents leakage.
Place four batteries in the battery cartridge and secure with a heavy duty rubber band. This holds the package together, even if the cartridge itself gets broken or jarred loose during net set out.
Place the end cap on top, be sure the O-ring is in place and hand tighten. You should hear a quick high-pitched ping when the battery cartridge is in the correct position.
Don't over-tighten the top-cap – "hand tight" is good enough. If a top-cap refuses to release, use a screw-driver placed through the holes in the top cap to loosen it.
3.0 Pinger attachment to gillnet
In general, pingers should be located AT LEAST every 100 meters along a net. The bridle is a good place to place them, at the top near the float line. There are two ways to attach the pingers to the net: 1) Inside a bait bag or 2) Direct attachment.
3.1 Inside a bait bag
It is a good idea to have an extra piece of twine to doubly secure the pinger within the bait bag as a fail-safe should the bait bag break open (which they occasionally do). Simply thread the twine through the holes at the end of the pinger, pass it through the bait bag mesh and tie the pinger itself to the net-frame in addition to the bait bag attachments. Attach the bait bag to the net frame in two places - either tied with nylon wire-ties or other secure attachment technique.
3.2 Direct attachment
Another common practice is to thread a piece of line through the hole at the end of the pinger and knot it -- the body end of the pinger can then spin freely for battery change. The attachment line is then woven into the lay of the rope of the float line -- it doesn't take much as there isn't a lot of tension on it. In this sort of rig the pinger is free to flop around too much for some people's handling techniques. In such a case, duct-tape the body of the pinger to the float line, taking care to leave the screw area free for battery changes.
4.0 Maintenance and troubleshooting
Gillnets are hauled in a variety of ways. Whatever the setting and haul-back techniques, a lot of pinger breakage or failure seems to occur due to stresses from being wound tightly during hauling -- if they don't break like an egg, the stress distorts the O-ring seal and the pinger subsequently leaks. To prevent this, the ends of the pinger can't be tightly secured to the net-frame -- there has to be some "give" there.
Pingers themselves withstand hard impacts incurred during the "set-out" procedure. Nets with pingers can be set-out at full speed over the stern or side of the fishing vessel. However, the battery cartridges will often break or distort inside the pinger due to the pounding (on the ends), and the batteries jar loose. To avoid these problems, the pingers can be placed on the net as it is set. In this way the pingers are stored off the net in between sets, allowing easy battery changes and maintenance.
Pingers should be checked regularly for sound output. Some will leak -- it causes an ugly black sludge in the pinger cavity. Rinse the pingers in warm soapy water and use a small soft-bristled tooth brush to clean around the contacts. This can rehabilitate about 50% of problematic pingers.
Silicone grease should be applied to the O-rings periodically to maintain their performance.
Expect attrition. Buy more pingers than you need.
5.0 Batteries
Batteries should be changed every four weeks or less. Alkaline batteries work well. Buy twice as many battery cartridges as needed so that when it comes time to change batteries you can bring a fresh set of full cartridges, rather than trying to put new batteries into the cartridges at sea. Colour-code the fresh cartridges -- it’s too easy to mix them up when changing them during the haul-back. Try to minimise the time that the pinger insides are exposed to the elements.
6.0 Pinger manufacturer contact information
Dukane Corporation
Seacom Division
2900 Dukane Drive
St. Charles, Illinois 60174
USA
Ph: (630) 584-2300
Fax: (630) 584-5154
7.0 Additional background on acoustic deterrents for marine mammals
Large increases in fishing during the latter half of the 20th century brought total world fisheries production from 20 million mt in 1950 to over 100 million mt in the 1990s (Hilborn 1990, FAO 1993, FAO 1995, Safina 1995). Wild caught marine fish account for approximately 85% of this production (Mace 1997). These impressive increases were possible because of growth in world population, more fishing vessels, and the development of technologies that enabled more fish to be caught per unit of effort. Many of these technologies grew out of developments from WWII such as electronic navigation which enabled boats to return to good fishing locations time after time, hydraulic winches for hauling nets and traps with fewer people, sonar for finding fish schools underwater, and new types of nets and hooks that proved more efficient and durable.
A deleterious aspect of this massive global fishing industry is bycatch: the unintentional catching and killing of birds, non-target fish species, marine turtles, and marine mammals during the course of normal fishing operations (Mooney-Seus 1999). The problem lies in the fact that ocean ecosystems are composed of multi-species complexes. Most fishing operations are non-discriminatory, and usually catch other animals in the course of harvesting the target species. These incidentally caught animals are the bycatch. While there is variation in bycatch rates between fisheries world wide, it is estimated that on average the total bycatch or discard is approximately 20%; that is for every five kilograms of a target species caught there is one kilogram of bycatch thrown overboard, usually dead (Alverson et al. 1994).
All major stakeholders (scientists, environmentalists, and the fishing industry) are concerned about this problem. There are now world-wide efforts to try and reduce bycatch. In many cases, the fishing industry is leading in the development of technologies to mitigate bycatch (Mooney-Seus 1999).
7.1 Gillnet fishing and marine mammals
Gillnet fishing is only one of many different types of fisheries that have by-catch. Gillnets are made of either multi-filament twine or monofilament nylon, woven into netting designed to lock behind the gills of fish. Gillnets come in all sizes and range from the large pelagic driftnets that can reach lengths of 50-60km down to small coastal nets less than 30m (Northridge 1991, Richards 1994). However, regardless of size, gillnets sometimes catch animals that were not the target species of the fishery including other fish, turtles, birds, and marine mammals.
Marine mammals, especially dolphins and porpoises, are particularly susceptible to being caught in gillnets. When the flippers, dorsal fins, tails, or heads of these animals become entangled underwater in the webbing of a gillnet, the animal will soon drown because they cannot swim backwards to dislodge from the net. It is estimated that many tens of thousands of marine mammals, most of them dolphins and porpoises, are caught and killed in passive fishing gear (e.g. gillnets and fish traps) world-wide (Northridge 1991, Perrin et al. 1994).
7.2 Acoustic devices and marine mammal conflicts in fisheries
Marine mammals have excellent hearing and use sound in various ways in the ocean to navigate and communicate (Thomas et al. 1992). It is therefore not surprising that efforts to introduce sound into the ocean to solve marine mammal related problems date back to the 1980s.
Sound generators were used in an effort to keep pinnipeds away from aquaculture operations in the Pacific Northwest and the North Atlantic (Mate and Harvey 1987, Wickens et al. 1992, Mate 1993, Wickens 1995, Johnston and Woodly 1998). These "Acoustic Harassment Devices" (AHDs) emit pulsed frequency sweeps in the 11 to 17-kHz range at source levels of ~187-195dB. Initially there was a substantial deterrent effectiveness, but it declined slowly over time. It was reported that some individuals became habituated and were actually attracted to the sound, and the term "dinner-bell" effect was introduced to describe this phenomenon (Mate 1993). Small explosive charges (seal bombs), other pyrotechnics, and gunshots have also been used to deter pinnipeds from aquaculture operations with varying degrees of success (Rueggeberg and Booth 1989, Morris 1996).
Wooldridge and Belton (1980) reported on electronically produced "roar" sounds to deter polar bears (Ursus maritimus, Gervais, 1855) in the 100-600 Hz range, which showed some deterrent effect on the animals. Davis et al. (1987) reported that sea otters were not deterred by an airborne warble sound near 1 kHz or by air horns at 0.5 to 20 kHz underwater.
Lien et al. 1992, Lien 1994, experimented and showed some success with low frequency sounds to keep humpback whales out of cod traps in coastal Newfoundland (Canada) fisheries. Up to six alarms with peak frequencies around 5 kHz were installed in each net 2 m below the surface. The sample consisted of 2,223 days of fishing without alarms and 2,392 days with alarms. There were a total of 129 collisions between whales and traps that did not have alarms and 37 collisions with nets that did have alarms.
Our understanding of odontocetes sound production and use of sound has been facilitated by dolphins, which are relatively easy to keep in captivity and study when compared to large whales. Dolphins use sound for communication and for echolocation (Au 1993). There have also been studies and observations of odontocetes related to sound, echolocation, and net entanglement (Jefferson and Curry 1994, Reeves et al. 1996). Reports included: watching the behavioural effects on wild animals to banging pipes underwater (Kasuya 1985, Akamatsu et al. 1993); studying the echolocation and reaction of captive animals to the presence of nets and pingers (Hatakeyama and Soeda 1990, Akamatsu et al. 1994, Kastelein et al. 1995, Kastelein and Rippe 2000); and actual trials of acoustic pingers in gillnet fisheries (Gearin et al. 1996, Kraus et al. 1997). In the eastern North Pacific (Gearin et al. 1996), and in the eastern and western North Atlantic (Kraus et al. 1997, Trippel et al. 1999) significant decreases were noted in the rates of harbour porpoise (Phoceana phoceana) entanglement in gillnets.
There are also now numerous uses of pingers throughout the world, but few controlled experiments like those described above. In those field trials some nets were left as controls with no pingers, while a comparable number were equipped with pingers. The observed catch rates of these two experimental conditions were then used as a basis to show the effectiveness of pingers. Finally, The International Whaling Commission’s small cetacean committee held a special meeting in the April, 1999 to further address the topic of acoustic alarms on fishing nets (IWC in press).
8.0 Data keeping - what to do if you catch a dolphin
Should there be an entanglement, it is vital that you keep careful records of fishing locations and pinger use. Even if the dolphin is alive and returned to the water, please follow these instructions. All of your observations will be valuable.
In the event of ANY dolphin entanglements please:
- Remove the pinger from the net
- Turn the battery pack upside down in the pinger so as not to deplete the remaining power
- Seal the entire pinger unit inside a plastic bag with the corresponding bycatch number enclosed.
- On return to land, please ring the Department of Conservation Field Office in Akaroa to arrange collection of the animal and the pinger: 03-304-1000 or 025 324 744.
Please provide information about the deployment of the pinger as follows:
Date deployed:
__________________________________________
Time Net Set:
__________________________________________
Time Net Hauled:
__________________________________________
Place deployed:
Lat: _________ Long:_________ Depth:__________
Method of deployment:
__________________________________________
Sea conditions:
__________________________________________
General weather (sunny, windy, cloud cover):
__________________________________________
__________________________________________
Entanglement distance from pinger: ______________
Specifics of entanglement (caught in top of net, caught by tail, caught in buoy line, released alive, completely wrapped up in net etc.):
__________________________________________
__________________________________________
Please also note any evidence of predation of carcass by sharks, pingers chewed, and anything out of the ordinary. Brief description of situation such as the number of dolphins present \lobster krill present\ type of fish caught in net, etc.;
__________________________________________
__________________________________________
Skipper’s comments as to what he thinks could have contributed to the bycatch. Please make note of anything you observe: __________________________________________
__________________________________________
__________________________________________
__________________________________________
References
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Akamatsu, T., Hatakeyama, Y., Kojima, T., Soeda, H. 1994. Echolocation rates of two harbor porpoises (Phocoena phocoena). Marine Mammal Science 10(4):401-411.
Alverson, D., Freeberg, M.H., Murawski, S.A., Pope, J.G. 1994. Global assessment of fisheries bycatch and discards. Technical Paper 339. Food and Agriculture Organisation of the United Nations (FAO).
Au, W.W.L. 1993. The sonar of dolphins. Springer-Verlag, New York.
Davis, R.W., Awbrey, F.W., Williams, T.M. 1987. Using sounds to control the movements of sea otters. Journal of the Acoustical Society of America 82(Suppl. 1):S99.
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Acknowledgements
Funding provided by the New Zealand Department of Conservation Services Levy program and the Pew Fellowship in Marine Conservation and the Environment. We thank Scott Kraus, John Williamson and Christine Courtney for assistance with this manual.
Manual produced by the New England Aquarium Conservation Department for and in collaboration with the New Zealand Department of Conservation.