Category: Habituation

Highlight

The ambient noise in aquat6ic habitats is characterized by a large variety of noise levels and spectral profiles due to various abiotic and biotic factors such as running water, wind, tides, and vocalizing animals.

Abstract

We describe an experiment conducted to assess the impact of the sound generated by an acoustic harassment device (AHD) on the relative abundance and distribution of harbor porpoises (Phocoena phocoena) in Retreat Passage, British Columbia. During control periods when the AHD was inactive, the mean number of porpoises observed in the study area was 0.39 for broad area scans conducted with the naked eye and 0.48 for narrow sector scans conducted with binoculars. Abundance declined precipitously when the AHD was activated, to 0.007 porpoises per broad area scan and 0.018 per narrow sector scan. The mean number of porpoise resightings while tracking their movements also declined from 12.2 to 13.6 per sighting during control periods to 1.1–1.9 per sighting when the AHD was activated, which suggested that the few porpoises that ventured into the study area spent less time within it when the AHD was activated. The effect of the AHD diminished with distance. No porpoises were observed within 200 m of the AHD when it was activated. The number of sightings and resightings observed when it was activated was less than 0.2% of the number expected had there been no AHD effect at a range of 200–399 m, 1.4% the number expected at a range of 400–599 m, varied between 2.5% and 3.3% of the number expected at a range of 600–2,499 m, and was 8.1% the number expected at a range of 2,500–3,500 m, which suggested that the impact of the AHD extended beyond our maximum sighting range of 3.5 km.

Abstract

Acoustic Deterrent Devices (ADDs) are often used on aquaculture sites to reduce predation of seals on fish stocks using acoustic emissions. These acoustic emissions may also have secondary effects on marine mammals (including non-target species) ranging from physical injury, behavioural response and reduced sensory capability. The project investigated the effects of water depth, seabed sediment type and bathymetry on the sound propagation and received levels of ADDs. A generalised propagation model was developed to allow the prediction of received levels, and ranges where given SEL (Sound exposure level) thresholds were exceeded for various ADD models. Variant parameters included number of devices, duty cycle and the influencing factors of local environments, sediment types, the functional hearing capabilities of seals and cetaceans and simplistic assumptions about animal movements. The research highlighted a number of knowledge gaps and caveats associated with the models produced and interpretation of outputs.

Abstract

Whale displacement by acoustic “pollution” has been difficult to document, even in cases where it is strongly suspected, because noise effects can rarely be separated from other stimuli. Two independent studies on the natural history of killer whales ( Orcinus orca ) monitored frequency of whale occurrence from January 1985 through December 2000 in two adjacent areas: Johnstone Strait and the Broughton Archipelago. Four high-amplitude, acoustic harassment devices (AHDs) were installed throughout 1993 on already existing salmon farms in the Broughton Archipelago, in attempts to deter predation on fish pens by harbour seals ( Phoca vitulina Linnaeus). While whale occurrence was relatively stable in both areas until 1993, it then increased slightly in the Johnstone Strait area and declined significantly in the Broughton Archipelago while AHDs were in use. Both mammal-eating and fish-eating killer whales were similarly impacted. Acoustic harassment ended in the Broughton Archipelago in May 1999 and whale occurrence re-established to baseline levels. This study concludes that whale displacement resulted from the deliberate introduction of noise into their environment.

Abstract

Acoustic harassment devices (AHD) or ‘seal scarers’ are used extensively, not only to deter seals from fisheries, but also as mitigation tools to deter marine mammals from potentially harmful sound sources, such as offshore pile driving. To test the effectiveness of AHDs, we conducted two studies with similar experimental set-ups on two key species: harbour porpoises and harbour seals. We exposed animals to 500 ms tone bursts at 12 kHz simulating that of an AHD (Lofitech), but with reduced output levels (source peak-to-peak level of 165 dB re 1 µPa). Animals were localized with a theodolite before, during and after sound exposures. In total, 12 sound exposures were conducted to porpoises and 13 exposures to seals. Porpoises were found to exhibit avoidance reactions out to ranges of 525 m from the sound source. Contrary to this, seal observations increased during sound exposure within 100 m of the loudspeaker. We thereby demonstrate that porpoises and seals respond very differently to AHD sounds. This has important implications for application of AHDs in multi-species habitats, as sound levels required to deter less sensitive species (seals) can lead to excessive and unwanted large deterrence ranges on more sensitive species (porpoises).

Abstract

Many salmon aquaculture sites in the Bay of Fundy employ acoustic harassment devices (AHDs) to deter seals from approaching fish pens. These devices may also exclude harbour porpoises (Phocoena phocoena) from important habitat. To determine the effects of AHDs on harbour porpoises an AHD was deployed experimentally in the Bay of Fundy, Canada. Relative porpoise abundance (visual scans) and porpoise movements (tracked by theodolite) were recorded for separate, daily, 2-h periods in the vicinity of either an active (n=9) or inactive (n=7) AHD. Fewer porpoises were sighted during active periods (0.22±0.44, mean±SD ) than inactive periods (2.91±1.29; P<0.05). The mean closest observed approach of porpoises to the AHD during active periods (991±302 m) was significantly greater than during inactive periods (364±261 m; P<0.01). Porpoise density was therefore reduced in the vicinity of active an AHD. These results should be considered before AHDs are deployed in porpoise habitat.

Overview

Communication in networks has received considerable research attention over the last few years (Naguib & Todt, 1997; Otter et al., 1999; Peake et al., 2001; Mennill et al., 2002; Ch. 1). This is true for two types of network interaction, one in which several receivers react to the signal of just one individual and a more complex one in which receivers eavesdrop on the signal exchange of two or more individuals and use the information they gained in their own decision making (McGregor & Dabelsteen, 1996; Ch. 2). If we think about communication, the fact that there often is more than just one individual receiving any given signal is not surprising. One reason that many studies on more transient signals concentrated on only one signaller and one receiver was a methodological problem. It is notoriously difficult to sample behaviour from more than one or two individuals at a time, especially if interactions are rapid and involve movements of individuals. Recently, the simultaneous tracking of several individuals in a large group has become feasible. This has led to an increase in studies investigating the effects of signals on several receivers in rapid communication interactions. Many such studies have concentrated on the acoustic domain, a modality that is inherently transient. Signals rarely last more than a few seconds and usually provide a variety of different messages within a single signal.

While there is ample evidence from terrestrial environments that more than one individual can receive and use information from a call or a calling interaction, data on acoustic communication networks in marine environments are sparse.

Abstract

Acoustic harassment devices (AHDs) are used by the Atlantic salmon (Salmo salar) industry to deter harbour seals (Phoca vitulina) from aquaculture cage sites. Two preliminary behavioural studies suggest that many harbour seals in the Bay of Fundy, Canada, have habituated to the sounds of AHDs. Although the sample size was low, no response or change in behaviour of seals in the water occurred when a nearby AHD was activated. Some seals came within 45 m of an active AHD. Seals also passed close by an active AHD when moving to a haulout site. In situ sound pressure level measures were made around the periphery of nine aquaculture cage sites in the Deer Island area of the Bay of Fundy. Sound pressure levels at 1, 5 and 10 m depths within the aquaculture cage sites were generally c162 dB re 1 Pa. The individual pulse lengths of the AHD pulse trains were typically 2 msec. Ambient noise levels at 9–11 kHz did not vary with time of day, but were influenced by weather. The highest sound level recorded at cage sites within 10 m of the surface was 168 dB re 1Pa which is about 80 dB above the seal’s detection threshold for short pulses at these frequencies. On most days, AHD sounds would be clearly audible to harbour seals at ranges of 1.1 to a theoretical maximum of 20.2 km, depending on the ambient noise levels and sound transmission characteristics in the region adjacent to the cage site. Our results suggest that harbour seals in the study area are not frightened away by the sounds of AHDs and that the sound levels throughout most of the cage sites do not reach the likely pain threshold.

ABSTRACT:

Acoustic deterrent devices (ADDs) to prevent pinniped predation on fish farms and fisheries are widely used, but show highly varying success. Recently, ADDs have also been high-lighted as a conservation concern due to their adverse impact on toothed whales. We review the available literature on the efficiency of commercial ADDs, evaluate the unintended impact on behaviour, communication and hearing of marine life, and suggest solutions based on psycho-physiological predictions. The main problems associated with ADDs are a lack of long-term efficiency, introduction of substantial noise pollution to the marine environment and long-term effects on target and non-target species. Odontocetes have more sensitive hearing than pinnipeds at the frequencies where most ADDs operate, which may explain the reported large-scale habitat exclusion of odontocetes when ADDs are used. Furthermore, long-term exposure to ADDs may damage the hearing of marine mammals. Fish and invertebrates have less sensitive hearing than marine mammals and fewer efforts have been made to quantify the effects of noise on these taxa. Solutions can be found by decreasing sound exposure, exploiting neuronal reflex arcs associated with flight behaviour and making use of differences in species’ hearing abilities to increase target specificity. To minimise adverse effects, environmental impact assessments should be carried out before deploying ADDs and only effective and target-specific devices should be used.

Abstract

For marine mammals, auditory perception plays a critical role in a variety of acoustically mediated behaviors, such as communication, foraging, social interactions, and avoidance of predators. Although auditory perception involves many other factors beyond merely hearing or detecting sounds, sound detection is a required element for perception. As with many other processes,sound detection may be adversely affected by the presence of noise. This chapter focuses on two of the most common manifestations of the effects of noise on sound detection: auditory masking and noise-induced threshold shifts. The current state of knowledge regarding auditory masking and noise-induced threshold shifts in marine mammals is reviewed, and perceptual consequences of masking and threshold shifts are discussed.