Unprecedented (that word again) - humpbacks in the East Alligator River – which really should be named the East Crocodile River
Way up in the warm water of the Northern Territory - an exclusion zone is in place for boats on the East Alligator River. Map supplied: Parks Australia
15 September 20
From the Strange Sea Stories file: A team of whale experts from around Australia are considering how to shepherd two humpback whales out of Kakadu's East Alligator River, as concerns mount over the risk of a possible stranding.
Northern Territory Government scientist Dr Carol Palmer is part of the emergency response to guide the whales out of the river.
In an interview with ABC Radio Darwin, Dr Palmer said a team of experts was looking into the use of whale calls and also underwater noise pollution to encourage the wales back out to sea.
"There have been examples of whale calls being used before to influence where a whale goes. We are also looking at loud sounds to discourage the whale from heading further [upriver]," she said
The NT team will try to tag one of the whales to better monitor its movement in the coming days before deciding on what interventions will be required.
"Then, I think, based on that information, the next step will be to try and see if we can, from a 100 per cent safety perspective, move the whale out into Van Diemen's Gulf," Dr Palmer said.
The humpbacks were first spotted by local marine biologist Jason Fowler on September 2, while he was out fishing with friends on his yacht, the Shaguar.
Mr Fowler said he spent four hours furiously debating with his friends, who are all biologists, on whether they were actually seeing humpbacks.
It is the first time in recorded history that humpbacks have been seen 20 kilometres upriver in Kakadu.
Three humpbacks were initially spotted, but it is believed one has since returned to sea.
An exclusion zone for all boats is in place for 30 kilometres upstream from the river mouth
Dr Vanessa Pirotta is a marine scientist who specialises in whales.
She said the best way of coaxing whales out of a muddy river was "a real puzzler".
"Unlike dolphins, these whales do not have echo location. So they may be navigating using sight and sound, and this makes it difficult for the whale to navigate," she said.
"The team in charge of encouraging the whales out probably will focus on either physical or acoustic deterrence. Either strategy has been shown to work in previous cases.
"Physical deterrence would include banging an object against a ship's hull, such as a metal rod. Acoustics could involve killer whale [orca] calls, which have been shown in some cases to discourage humpbacks," she added.
Growing Australian humpback population could mean more whales in strange places
Dr Pirotta said one reason we could be seeing humpbacks in the East Alligator River was because they were natural explorers.
Their numbers have been growing significantly in recent years, with Australia's two migratory populations, the east and west coast groups, totalling around 70,000 animals.
"Humpbacks are very curious animals. We have seen a spike in their population in recent years. There are probably upwards of 40,000 whales in the west coast population and 35,000 along the east coast," she said.
"These whales would almost definitely be part of the west coast group, who come up to an area off the Kimberley to calve.
"Perhaps they have come into the river out of curiosity and found themselves lost.
"There are instances of humpbacks in Sydney Harbour, and that is not part of their migratory route, so they like to explore."
- AUTHOR: HENRY ZWARTZ
- SOURCE: ABC AUSTRALIA