Pinnipeds: Airgun Effects On Arctic Seals: Auditory Detection, Masking And TTS In Pinnipeds

Arctic environments are changing rapidly as a result of ice retreat and industrialisation. Subsequently, increased human noise in the Arctic, absence of data on hearing in Arctic seals, and the recent listing of some Arctic species as threatened have increased the need for data on hearing in Arctic pinnipeds. Assessing the risk of hearing effects from shipping and E&P sound and developing appropriate mitigation measures depend on acquiring good baseline hearing data.

Results of hearing tests indicated that spotted (Phoca largha) and ringed (Pusa hispida) seals possess amphibious sound reception capabilities better than those previously described for ice seals, and more similar to those reported for harbor seals (Phoca vitulina). Trained spotted and ringed seals did not exhibit temporary threshold shifts (TTS) when exposed to air gun sounds. The masking component of this work showed that seals could detect signals when exposed to air gun sound signals, but that the ability to detect a signal in the presence of a masking sound depended on the characteristics of the masker. If the masking sound is variable like intermittent air gun signals, the probability of detection increases.

This ongoing collaborative project between the University of California Santa Cruz and SEA Inc. will provide information on the auditory capabilities of three species of Arctic seals.

Objectives and methods

• Captive ringed, spotted and bearded seals were trained for voluntary participation in behavioural hearing tests
• Hearing thresholds were measured under different conditions to assess auditory performance in:
  • 1) the absence of noise both on-land and in-water,
  • 2) the presence of simultaneous (masking) noise, in order to determine critical ratios, and;
  • 3) before and after exposure to impulsive sound (single air gun shots), in order to examine the sound levels that cause a temporary shift in hearing threshold.

Importance

This research describes the auditory capabilities of Arctic seals which improves our ability to predict the effects of sound exposure on these species. The results provide the first description of the auditory biology of spotted seals. Pinniped hearing information from this work fills critical data gaps for some Arctic pinnipeds and progresses best available science informing regulatory decisions related to the impacts of sound on marine life.

Links to Other Research

1. TTS In Odontocetes in Response to Multiple Airgun Impulses.
2. TTS growth and recovery in harbor porpoises exposed to intermittent and continuous signals

Institutions / PIs

University of California Santa Cruz, Long Marine Laboratory (Colleen Reichmuth, Jillian Sills)

SEA Inc. (Brandon Southall)