underwater

The Atlantic humpback dolphin Sousa teuszii is endemic to the west coast of Africa and is poorly studied. During January 2008, 2.7 hr of acoustic recordings were made during 11 S. teuszii encounters in the Namibe province of Angola. Echolocation click trains were audible in most recordings. A total of 298 individual dolphin whistles were recorded, of which 86 were of sufficient signal to noise ratio for the measurement of 10 fundamental frequency variables. Sousa teuszii whistles occurred in the 2.5 to 23.4 kHz fundamental frequency range and were relatively simple in structure, with 85% having a single inflection point. The fundamental frequency was relatively low, with mean minimum and maximum frequencies of 4.8 and 8.2 kHz respectively. Harmonics occurred in 92% of whistles, sometimes extending beyond the 44 kHz recording range. The most frequently recorded contour categories were convex and concave, and very few whistles exhibited complex modulation. The whistles produced by S. teuszii are broadly comparable with those published for the Indo-Pacific humpback dolphin S. chinensis. Future studies should consider context-specific use of whistle types, and should include comparisons with S. teuszii groups in other geographic locations to ensure the full species’ whistle repertoire is adequately characterised

The pulsed calls of Long-finned Pilot Whales Globicephala melas have received little study, and their structure and function remain unclear. We examined the pulsed calls of Pilot Whales off Nova Scotia by taking multiple measures of 419 spectrograms from recordings made over a span of eight years. The results offer a quantitative description of pulsed call structure necessary for subsequent analysis of signal functionality and social relevance. Pilot Whale pulsed calls were found to be physically complex, with multiple, independently modulated components that are likely rich in information and difficult for eavesdroppers to imitate. The production of such structurally complicated signals suggests they play an important role in Pilot Whale communication. The pulsed calls appear to form two main call types: those with a maximum visible sideband above 18 kHz and those with a maximum visible sideband below 15 kHz. However, there is no indication of further discrete categories despite a large amount of variation between calls within those two broad categories. The high variation in call structures may indicate communicative plasticity, allowing the whales to communicate state, such as level of arousal, and to compensate or variable background noise levels. The structural similarity of Pilot Whale and Killer Whale Orcinus orca pulsed calls raises the question of whether the distantly related whale species, with a shared but rare social structure, have evolved similar call structures to solve similar communication challenges.

Probably all odontocetes use echolocation for spatial orientation and detection of prey. We used a four hydrophone “Y'' array to record the high frequency clicks from free-ranging White-beaked Dolphins Lagenorhynchus albirostris and captive Harbour Porpoises Phocoena phocoena. From the recordings we calculated distances to the animals and source levels of the clicks. The recordings from White-beaked Dolphins were made in Iceland and those from Harbour Porpoises at Fjord & Bælt, Kerteminde, Denmark during prey capture. We used stringent criteria to determine which clicks could be defined as being on the acoustic axis. Two dolphin and nine porpoise click series could be used to track individual animals, which presumably focused on the array hydrophones or a fish right in front of the array. The apparent source levels of clicks in the individual tracks increased with range. One individual White-beaked Dolphin and three Harbour Porpoises regulate their output signal level to nearly compensate for one-way transmission loss while approaching a target. The other dolphin regulated the output differently. For most of the recordings the sound level at the target remains nearly constant and the echo level at the animal increases as it closes on the target.

Several studies on fishes have shown that behaviour and auditory sensitivity are often affected by underwater noise. The current investigation concentrates on noise encountered by fish kept for leisure in aquaria and ponds. Noise spectra showed that all aquarium filters measured created a high amount of low-frequency noise, while the water outflow above the surface created additional high-frequency noise components. Audiograms of the Goldfish Carassius auratus, a species possessing hearing specializations, were determined between 0.1 and 4kHz using the noninvasive
auditory evoked potential (AEP) recording technique. The amount of masking was determined in the presence of four different noise-types: aquaria with external filter with outflow above the water surface (119dB re 1 µPa), external filter with outflow below the water surface (115dB), internal filter with outflow below the water surface (114dB broadband LLeq, 1min), and an unfiltered pond (95dB). The goldfish’s hearing was masked by all filter noise types and most affected at 0.1 and 0.3kHz by the external filter noise (threshold shifts of 15-19dB). Pond noise had no effect on the hearing threshold. The results indicate that fish with hearing specializations are considerably masked under common holding conditions found in aquaria but probably not in ponds. Thus, using a quieter filter setup with a quiet outflow might help to improve holding conditions in aquaria without compromising aeration of the water.

Sound plays an important role for toothed whales in foraging and communication. However, little is known about acoustic communication in the toothed whale species that only produce narrow band high frequency (NBHF) clicks, such as the harbour porpoise Phocoena phocoena. To study acoustic behaviour and to quantify the source parameters of porpoise communication signals, the acoustic and swimming behaviour of three adults and one calf were recorded using an array of hydrophones, acoustic tags and an overhead video camera. We tested the hypothesis that different behavioural interactions between porpoises involve specific click patterns for communication and measured the source characteristics of these click patterns to estimate the active space of porpoise click communication. Our results provide strong evidence that porpoises communicate acoustically using specific patterns of clicks with source properties comparable to normal echolocation clicks, and that they employ stereotyped aggressive click patterns, exposing conspecifics to received levels of up to 180 dB re 1 µPa (pp). The measured source properties render estimated active spaces of less than 1000 meters for porpoises' communication sounds. Compared to other cetaceans, porpoises must therefore remain much closer to be able to communicate acoustically.