Malnutrition behind whale strandings
Malnourished whale mothers giving birth to calves are believed to be the cause of an increased number of stranded whales on West Australian beaches.
A rise in the number of humpback whales beaching themselves along the WA coast led a group of veterinary researchers, working in collaboration with the Department of Parks and Wildlife, to investigate why this was occurring.
Carly Holyoake from Murdoch University said that an unprecedented number of humpback whales, predominantly calves and juveniles, had stranded on the west coast of Australia since 2008.
"Between 1989 and 2007 the mean number of humpback whales ashore was between two and three," she said.
"In 2008 there were 13 strandings, followed by 46 in 2009 and 16 in 2010.
"In 2011 there were 17 strandings consisting of 14 calves and three juveniles, representing a rise in the number of young whales perishing than in previous years.
"The aim of our project was to find out why this was happening through post-mortem examination."
All the strandings occurred between Exmouth and Stokes Inlet, east of Esperance, so the calves would have been born at least 1000 kilometres south of the regular breeding grounds in the Kimberley region.
"Post mortem examination and analysis of the fat content of blubber samples revealed most calves were in an extremely malnourished state," Holyoake said.
"Most had very low blubber fat, which is required for energy, thermoregulation and for buoyancy.
"One individual also had pneumonia which would have made it difficult to breathe and may have contributed to its death."
A number of theories were proposed for why there had been such high numbers of whales beaching themselves in the area, these included that the incidents were reflective of an increased population size and inherent high mortality rate in humpback calves and that mothers were giving birth in unsuitable areas due to environmental conditions.
The researchers concluded that the most likely cause of the humpback calf strandings was due to mothers in poor nutritional states were giving birth to malnourished calves.
"It's also significant that the calves were born several thousands of kilometres south of the known breeding grounds," Holyoake said.
She said the mother whales may have spent more time in the Antarctic trying to feed for longer, keeping them further south at the time they were ready to give birth than they would usually be.
"Humpback whales feed almost exclusively on krill in the Antarctic and it's unknown what effect an expanding krill fishery in conjunction with climate warming might be having on the abundance of krill," Holyoake said.
She said there is an active krill industry in the waters that the whales feed in and while little research in these areas was currently undertaken, it was important to have a good "grasp" on krill populations.
Holyoake will discuss the matter in a presentation at the Australian Veterinary Association's Annual conference on its fourth day in Perth today.