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Summary
Marine mammal acoustic pingers and deterrent devices are commonly deployed during fishing activities in New Zealand to alert marine mammals to the presence of fishing gear, and/or to deter them from areas of risk or potential feeding opportunities. Hector’s and Māui dolphins (Cephalorhynchus hectori and Cephalorhynchus hectori maui, respectively) are of particular concern for the fishing industry due to their small population sizes and ‘endangered’ and ‘critically endangered’ statuses. JASCO Applied Sciences (JASCO) performed a measurement and modelling study of underwater sound levels associated with two devices that are regularly utilised in New Zealand waters: the Netguard Dolphin Pinger (60 – 120 kHz model); and the STM Dolphin Deterrent Device (DDD) (DDD03H model). It is important to determine the accuracy of manufacturer-supplied technical specifications to ensure devices are operating as expected when deployed. Confirming the technical specifications also improves the understanding of the true extent of potential dolphin awareness and potential displacement around commercial fishing activities while using these devices, and aids in
recommending how to deploy the devices most effectively.
Three separate devices of each type were measured underwater at a quiet coastal location in Brisbane, Australia. Sound source characterisation aimed to determine the source level, spectra, output pattern, and directivity pattern of each device by using a purpose-built mounting frame that allowed each device to be pivoted with respect to an associated hydrophone and recording equipment. All acoustic data were processed with JASCOs PAMlab software suite, which performed automated analysis of the data to quantify their active and inactive (silent) periods. Statistical measures of the sound during each active period were exported and back-propagated to obtain the source level measurement for each device.
Once the source levels of the devices were known, underwater noise modelling was undertaken to ascertain the propagation of sound from the devices within typical usage environments (i.e. coastal, shallow-water shelf seas). The modelling study specifically assessed distances from the measured devices where underwater sound levels reached thresholds corresponding to behavioural response,
impairment (temporary reduction in hearing sensitivity or temporary threshold shift (TTS)) and injury (permanent threshold shift or permanent threshold shift (PTS)) for Hector’s and Māui dolphins. The devices considered are generally deployed to trigger behavioural responses in free-ranging animals and are not intended to cause impairment or injury, but nonetheless have the potential to result in
these effects if dolphins are exposed to multiple emissions in relatively close proximity. The devices are considered to be intermittent non-impulsive noise sources, and non-impulsive noise effect criteria have therefore been considered as part of the modelling. Estimated underwater acoustic levels for non-impulsive noise sources are presented as sound pressure levels (SPL, Lp), as appropriate for
assessing behavioural response zones, and as accumulated sound exposure levels (SEL, LE), as appropriate for assessing impairment and injury.
The SPL metric is the root-mean-square pressure level over a stated frequency band over a specified time window; a time window of 1 s was used. To evaluate the potential for accumulated sound exposure levels (SEL), the duration of the SEL accumulation was defined as integrated over a 24-hour period, as per injury and impairment criteria. The SEL24h is a cumulative metric that reflects the
dosimetric impact of noise levels within 24 hours based on the assumption that an animal is consistently exposed to such noise levels at a fixed position. The corresponding SEL24h radii represent an unlikely worst-case scenario. More realistically, marine mammals would not stay in the same location for 24 hours. Therefore, a reported radius for SEL24h criteria does not mean that marine fauna
travelling within this radius of the source will be injured, but rather that an animal could be exposed to the sound level associated with impairment if it remained within the ensonified region for 24 hours.
In addition to the noise effect criteria for behavioural response and hearing impairment/injury, the modelling was also used to consider the maximum distance at which Hector’s and Māui dolphins would be able to hear and distinguish the sound of each device within a typical underwater noise environment. Device detectability is an important factor in determining appropriate spacing of devices
during deployment, particularly for lower-level devices that are only intended to provide dolphins with an awareness that an area contains a high-risk feature (e.g., a set net).
Publication information
Warren, V.E., T.J. Stephen, S. C. Connell, and C.R. McPherson. 2025. Dolphin Acoustic Device Characterisation: Quantifying the Technical Specifications, and Modelling the Usage, of Two Acoustic Devices in New Zealand’s Coastal Waters. Document 03595, Version 2.0. Technical report by JASCO
Applied Sciences for Seafood New Zealand.