Small cetaceans are susceptible to incidental mortality in the various forms of gillnet fisheries throughout their range. Research conducted since 1994 has shown that acoustic alarms (pingers) emitting high-frequency pulsed sounds effectively reduce the number of harbor porpoise Phocoena phocoena casualties in sink gillnets. However, the mechanisms behind the effects of pingers were still not understood. Until now, advantages and risks associated with their widespread use could not be evaluated. Here we present the results of 2 field experiments: (1) theodolite-tracking of harbor porpoises exposed to a single PICE-pinger in Clayoquot Sound, Vancouver Island, Canada and (2) herring Clupea harengus capture rates in surface gillnets equipped with and without acoustic alarms (Dukane Netmark 1000, Lien, PICE) in the Baltic Sea herring fishery at Rügen Island, Germany. Our results show that harbor porpoises do not seem to react to an experimental net in their foraging area (n = 172 groups, median group size = 2 porpoises). Porpoise distance from the mid-point of the net was distributed around a median of only 150 m (range 4 to 987 m). A net equipped with an acoustic alarm, however, was avoided (n = 44 groups) within audible range (distance distribution median = 530 m, range 130 to 1140 m). The porpoises were thus effectively excluded from the ensonified area. Herring, one of the main prey species of harbor porpoises, were not affected by the acoustic alarms tested (n = 25 407 fish captured). The advantages and risks of using acoustic alarms to mitigate by-catch are discussed.KEY WORDS: Harbor porpoise · By-catch · Mortality · Theodolite-tracking · Acoustic alarms · Pinger · Gillnets · NoiseResale or republication not permitted without written consent of the publisher

Operational underwater noise emitted at 8 m s -1 by a 550 kW WindWorld wind-turbine was recorded from the sea and modified to simulate a 2 MW wind-turbine. The sound was replayed from an audio CD through a car CD-player and a J-13 transducer. The maximum sound energy was emitted between 30 and 800 Hz with peak source levels of 128 dB (re 1 µPa 2 Hz -1 at 1 m) at 80 and 160 Hz (1/3-octave centre frequencies). This simulated 2 MW wind-turbine noise was played back on calm days (<1 Beaufort) to free-ranging harbour porpoises Phocoena phocoena and harbour seals Phoca vitulina in Fortune Channel, Vancouver Island, Canada. Swimming tracks of porpoises and surfacings of seals were recorded with an electronic theodolite situated on a clifftop 14 m above sea level. Echolocation activity of harbour porpoises close to the sound source was recorded simultaneously via an electronic click detector placed below the transducer. In total we tracked 375 porpoise groups and 157 seals during play-back experiments, and 380 porpoise groups and 141 surfacing seals during controls. Both species showed a distinct reaction to wind-turbine noise. Surfacings in harbour seals were recorded at larger distances from the sound source (median = 284 vs 239 m during controls; p = 0.008, Kolmogorov-Smirnov test) and closest approaches increased from a median of 120 to 182 m (p < 0.001) in harbour porpoises. Furthermore, the number of time intervals during which porpoise echolocation clicks were detected increased by a factor of 2 when the sound source was active (19.6% of all 1 min intervals as opposed to 8.4% of all intervals during controls; p < 0.001).These results show that harbour porpoises and harbour seals are able to detect the low-frequency sound generated by offshore wind-turbines. Controlled exposure experiments such as the one described here are a first step to assess the impact on marine mammals of the new offshore wind-turbine industry.

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Field tests suggest that high-density nets can reduce harbor porpoise Phocoena phocoena by-catch in demersal gillnet fisheries. However, it is not clear whether acoustic reflectivity or twine stiffness are responsible for this. We conducted sonar tests in a tank in the frequency range of 110 to 190 kHz and found that the target strength of the high-density BaSO 4 net was 7.2 dB higher at 150 kHz than that of the standard nylon net. In a fjord on Vancouver Island, Canada, we investigated porpoise surfacing and echolocation behavior as they encountered 2 surface gillnets (45 × 9 m, 165 mm mesh size) made of (1) standard 100% nylon and (2) a mix of BaSO 4 and nylon. The distribution of click intervals shifted to longer intervals when the BaSO 4 net was used (median = 51 ms vs. 45.2 ms for the standard net; Kolmogorov-Smirnov test, p < 0.001), indicating a greater target distance. We estimated that porpoises are able to detect BaSO 4 nets 4.4 m in advance of standard nylon nets. However, an unexpected low percentage of echolocating porpoise groups within 50 m of the center of nets (standard 30.6%, BaSO 4 19.3%) indicates that additional measures may be necessary to reduce by-catch. A subsequent experiment showed that transmission of 2.5 kHz tones as a warning sound increased biosonar use by a factor of 4 compared to controls (16.7% for controls vs. 71.4% for groups during ensonification; chi 2 -test, p < 0.001). The combination of reflective nets and warning sounds may be a promising mitigative tool. KEY WORDS: Harbor porpoise · Phocoena phocoena · Barium sulfate · Reflective gillnet · By-catch mitigation Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 313: [285][286][287][288][289][290][291][292][293][294] 2006 effective (e.g. Koschinski & Culik 1997, Kraus et al. 1997, Trippel et al. 1999, Culik et al. 2001, pinger deployment has a number of disadvantages. Harbor porpoises may habituate to the sound (cf. Cox et al. 2001) or the sound may be so aversive that they are excluded from parts of their habitat (cf. Culik et al. 2001). Also, users may fail to replace batteries in time, resulting in 'black holes' in the nets (cf. Berggren et al. 2002). Such non-ensonified spaces may suggest a safe escape to the porpoises and result in even more bycatch. Further, non-compliance with pinger deployment has been observed in restricted areas in the Gulf of Maine in recent years (D. Palka, pers. comm.).Another possible way in which to mitigate by-catch is to improve the acoustic reflectivity of nets to increase detectability by the porpoises' biosonar. During 2 yr of a field trial in the Bay of Fundy (Canada), no porpoises were caught in 231 strings (300 × 4 m) of high-density BaSO 4 nets, while 12 individuals became entangled in nets comprised of 467 strings of standard nylon (Trippel et al. 2003). Larsen et al. (2002a) achieved a similar by-catch reduction using nets with iron-oxideenriched twine in the Danish cod fishery: 8 porpoises were caught in standard nylon ne...

Erbe et al. Antarctic Underwater Noise score was a refinement of noise exposure criteria. Environmental evaluations are a requirement before conducting activities in the Antarctic. Because of a lack of scientific data on impacts, requirements and noise thresholds often vary between countries that conduct these evaluations, leading to different standards across countries. Addressing the identified research needs will help to implement informed and reasonable thresholds for noise production in the Antarctic and help to protect the Antarctic environment.