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Operational underwater noise emitted at 8 m s–1by 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 μPa² Hz–1at 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 porpoisesPhocoena phocoenaand harbour sealsPhoca vitulinain 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.

As one of the elements for a model on the food requirements of Humboldt penguinsSpheniscus humboldtiwe determined, via gas respirometry, metabolic rates while swimming and resting in water. During rest in water at 19°C Humboldt penguins (mean body mass 3.6 kg) required 5.95 W kg–1. This corresponds to a thermal conductance in water of 0.2975 W (kg °C)–1(atTₐ 19°C and assuming aT bof 39°C). When swimming in a 20 m long channel, metabolism rose from 8 W kg–1at a speed of 0.6 ms–1to 23.1 W kg–1at 2.2 m s–1. Transport costs (the cost to move 1 kg of body mass over a distance of 1 m) reached a minimum at 1.4 ms–1with 8.1 J (kg m)–1, which corresponds to 0.89 J (Nm)–1. We corrected for acceleration and deceleration in the channel to determine transport costs of free-ranging Humboldt penguins travelling at sea, which were calculated as 7 J (kg m)–1(0.71 J [Nm]–1), at 1.7 m s–1. Birds feeding chicks need to balance the costs of either (1) returning to the breeding island for the night and travelling back to the feeding grounds in the morning or (2) incurring increased thermoregulatory costs associated with resting at sea overnight. Simple calculations show that at water temperatures of 19°C we expect Humboldt penguins to show a tendency to remain at sea overnight if foraging areas are >4 km from their island. In colder waters (12°C), this distance increases to >9 km. Using previously published data on at-sea activity of Humboldt penguins, we found that foraging costs during chick rearing amount to 340 g anchovies d–1. Finally, we present a general model to convert Humboldt penguin activity data at sea to food requirements.

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 Ruegen 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 = 25407 fish captured). The advantages and risks of using acoustic alarms to mitigate by-catch are discussed.

Field tests suggest that high-density nets can reduce harbor porpoisePhocoena phocoenaby-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 BaSO₄ 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 BaSO₄ and nylon. The distribution of click intervals shifted to longer intervals when the BaSO₄ 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 BaSO₄ 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%, BaSO₄ 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; chi²-test, p < 0.001). The combination of reflective nets and warning sounds may be a promising mitigative tool.

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 sub(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 x 9 m, 165 mm mesh size) made of (1) standard 100% nylon and (2) a mix of BaSO sub(4) and nylon. The distribution of click intervals shifted to longer intervals when the BaSO sub(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 sub(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 sub(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 super(2)-test, p < 0.001). The combination of reflective nets and warning sounds may be a promising mitigative tool.

Diel vertical migration by zooplankton is thought to allow marine animals to exploit the more abundant food resources in the upper water strata at night while minimizing predation from optically orientating predators. Contrary to this, consistantly shallower dives at night made by marine reptiles, mammals, and birds have been attributed to enhanced feeding conditions as predators exploit prey that have become accessible near the surface. We found foraging success in penguins reduced at night and dive depth limited exclusively by ambient light levels. Consideration of foraging strategies adopted by air-breathing predators may explain typical vertical migration patterns of prey, as well as departures from them.

Energy requirements of beavers(Castor canadensis)swimming voluntarily underwater were investigated in Neumünster Zoo (Germany) in a covered, still‐water swim channel with oxygen and carbon dioxide respirometry. During the experiments, all activities of the beavers were monitored and recorded. While at rest within their thermoneutral zone on land (17°C), beavers had a respiratory quotient of 0.95 and a resting metabolic rate of 1.58 W kg−1. When resting in water, energy requirements rose to 2.31 W kg−1. When swimming underwater in the channel, beavers preferred a mean speed of 0.64 m s−1, and their energy requirements rose to 2.64 W kg−1. Cost of transport, however, was minimal at 0.9 m s−1and amounted to 0.36 J NT1m−1. Although beavers must compromise form and function to operate on water and on land, their energy requirements while diving amount to only 1.65 times the resting metabolic rate and compare well with those of accomplished swimmers such as aquatic mammals and birds.

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 porpoisePhocoena phocoenacasualties 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) herringClupea harenguscapture 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.