What began with the intention of a quiet day in the office at the South West Marine Research Program…..
….. rapidly shifted direction during the morning of Monday 23 March 2015. A phone call came in notifying me (Murdoch University’s PhD candidate John Symons) of a stranding of > 20 long-finned pilot whales (Globicephala melas) in Koombana Bay, Bunbury, Western Australia. Department of Parks and Wildlife were already on site with members of Bunbury Port Authority when staff of Dolphin Discovery Centre and myself first reached the site in the morning by boat. At the time, many of the animals were already on the rocks with multiple already deceased with several more in the shallows and approaching the rocks.
Initial efforts focused on keeping those animals not already stranded on the rocks from stranding as animals in a social unit will often follow each other. During this time, assessments of where along the rocks individuals had stranded as well as their condition were being noted and a plan established.
Members of Department of Parks and Wildlife, Bunbury Port Authority, Dolphin Discover Centre, Bunbury Sea Rescue, ORCA, and members of the community assisted with trying to safely get the few living animals off the rocks and over to a nearby beach using slings.
They managed to get five off the rocks alive and onto the beach, where they were monitored and a veterinary inspection conducted. In total, four pilot whales were rescued and released back to sea with efforts focussed on merging them with a group of pilot whales that were around the area. During the initial release, a single member of another dolphin species arrived in the area, a fraser’s dolphin (Lagenodelphis hosei); this animal also nearly stranding, but fortunately, was prevented from doing so and left the area.
In total, 12 individual pilot whales died during the day. A team from Murdoch University Cetacean Research Unit, led by veterinary pathologist Dr Nahiid Stephens and accompanied by research members Fredrik Christiansen and Kate Sprogis, arrived later in the day to examine the deceased individuals. Unfortunately, light was waning and much of the work had to be carried out by torchlight, which restricted capability. The sex and total body length of each of the 12 was recorded to assist with identification of age class. A genetics sample (skin and blubber) was taken from each of the 12. Of the 12 deceased individuals, blood was drawn from a total of nine. A limited post-mortem examination was carried out on five individuals of mixed sexes and age-classes; tissue samples were collected from these five individuals. Dr Stephens reports: “we were presented with the heart-breaking sight of 12 individuals recently deceased on the beach.
The group was comprised of both males and females, as well as mixed age classes – from very young calves through to large adults. All appeared in good body condition; the only external wounds visible were attributable to recent trauma from stranding, although a few individuals sported recent cookie cutter shark bites – these are a common finding in wild cetaceans and an incidental finding. Limited internal post-mortem examinations on five individuals failed to find any signs of disease that could have contributed to the animals stranding. The bloods and tissue samples taken will be screened for the presence of disease, in particular the presence of Cetacean Morbillivirus, a virus related to Measles which only affects cetaceans and was implicated in the deaths of some of the Swan River Indo-Pacific bottlenose dolphins in 2009. Ultimately, it may not be possible to ascertain why these beautiful creatures stranded, however it is important to screen for the presence of disease in the wild population whenever we are presented with an opportunity. An incident such as this is incredibly sad and it is important to maximise what we can learn from it.” The results of testing are expected to take several months, as some samples will need to be sent to interstate and international laboratories.
Facts about long-finned pilot whales:
Long-finned pilot whales (Globicephala melas) are found ranging in the Northern Atlantic and Southern Pacific Oceans. The species is currently listed as Data Deficient by the IUCN due to no reliable estimates of the global population level. They range in size up to 7.6 meters in length and can weigh over 2,000 kg. Males reach sexual maturity between 12-13 years, while females reach maturity at 8 years of age. They form long term social units (typically between 10-20 individuals, though formation of much larger groups does occur) and have been shown to have high relatedness to other individuals in their unit. This suggests a social group’s structure may be based around matrilineal lineages. These close bonds within units are thought to present part of the reason for mass standings occurring. Long-finned pilot whales are capable of making prolonged dives of 10-16 minutes while foraging to depths of around 600 m. Their diet is composed mostly of fish, cephalopods, and crustaceans.
Blog developed by PhD candidate John Symons and Dr. Nahiid Stephens