7.2 Acoustic devices and marine mammal conflicts in fisheries
In the “Pinger Use on Gillnets Instruction & Background Information”
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).