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Between the 25th and 27th of October 2005, 145 long-finned pilot whales stranded and died in a series of three stranding events in the Marion Bay region in the Southeast of Tasmania. 19 whales were successfully returned to the sea. Mass strandings of this species in this area are not uncommon, occurring seven times over the previous 50 years, most recently in 1998. At the time of this latest stranding event, two Royal Australian Navy mine-hunting vessels were conducting a search in the Marion Bay region using high-frequency sonar in an attempt to locate an historic anchor.

High-power, mid-frequency active sonar has been associated internationally with some stranding events. The high-frequency sonar used by the Navy on this occasion was of an entirely different type that has not previously been implicated in a stranding event. This sonar operates at frequencies from 30-500 kHz and has similar frequencies and power output to those used in some commercial applications such as echo-sounders, fish-finding sonar and hydrographic survey.

The Australian Government Department of the Environment and Heritage (DEH) convened a Stranding Incident Review Panel to examine the circumstances of this stranding event and determine what effect, if any, the presence of two Royal Australian Navy ships had on the event. The panel membership included whale and acoustic experts, non-government conservation groups, the Tasmanian Environment Department and the Australian Government Department of Defence.

The terms of reference for the panel were:

1. Examine the likelihood, nature and extent of any interaction that may have occurred between the stranding events on 25-27 October 2005 at Marion Bay, Tasmania and the Naval activities in the area and document any findings on the likely cause or factors contributing to the events at the time.
2. Make recommendations, if considered appropriate and necessary, on ways of improving communication and coordination between state and Commonwealth agencies and maritime industries/operations that may be associated in time and location with a stranding event.

The panel met in Hobart on 23 November 2005 and examined the available information relevant to the stranding and the presence of the Navy Ships. After reviewing this information, the Panel made the following conclusions and recommendations:

• The strandings occurred in three events over a two day period, being first reported at 1030h on the 25th of October 2005.
• The first event occurred at least six hours prior to the ships arriving and commencing the sonar search of the seabed. This initial stranding was therefore unrelated to either the presence or activities of the Navy ships.
• Sonar transmissions commenced from one ship, HMAS Diamantina at 1722h on 25th October 2005 and continued until 0230h on the 26th. Transmissions recommenced from HMAS Huon at 0600h on 26th and from HMAS Diamantina at 0800h. Both ships ceased transmission at 1200h.
• The second stranding event was observed to have commenced at about 1830h on 25th October and continued overnight. A group of live pilot whales was seen in Marion Bay prior to this second stranding event.
• The panel noted that there is considerable uncertainty about the levels and other characteristics of noise that may injure or cause behavioural responses in whales and this limits the current capacity to make definitive conclusions about the effect that the use of this type of sonar might have had on the whales that stranded after 1830h on 25th October.
• Two possible effects of the sonar considered by the panel were direct physical trauma resulting from the sound source, or behavioural responses by the whales to their detection of audible sounds.
• Given the likely characteristics of the sonar and some preliminary modelling of environmental conditions and sound propagation, the group concluded that direct physical trauma caused by the sonar was highly unlikely. 
• Biological samples including heads were collected and will be carefully analysed for signs of trauma and other pathology that may assist in understanding why these whales stranded.
• Behavioural responses of the whales to the sonar transmissions were not discounted by the panel because of the coincidence in time and space of the sonar transmissions and the second and possibly third stranding events.
• It is not possible to conclude whether or not the sonar transmissions had an influence on the second and third stranding events, as the level at which the whales perceived the sonar transmissions and their behavioural responses to those sounds, especially under stranding conditions, are unknown.
• Pilot whales in the vicinity of the stranding site were likely to be in a stressed and disoriented state and may possibly have been more vulnerable to acoustic or other disturbance. While it is possible that the sonar transmissions influenced the behaviour of the whales, it is also possible that they had no effect at all.
• The panel recognised the importance of effective and timely communication between state and commonwealth agencies and maritime operators to ensure appropriate operational responses in the vicinity of stranding events are triggered. Appropriate responses are necessary in order to minimise any potential impacts that may exacerbate the stranding event. The panel identified that DEH was the appropriate body to coordinate and facilitate such communications mechanisms and the development of protocols establishing appropriate responses by maritime operators when notified of a stranding incident in their vicinity.
• The Panel recognised the value of convening a ‘Stranding Incident Review Panel’ and recommended that similar panels be established ad hoc to evaluate unusual marine mammal stranding events in the future.