A humpback whale that spent more than two weeks in a crocodile-inhabited river in Kakadu in September has returned to the same tropical waterway, baffling scientists as to why it is not heading towards the icy waters of Antarctica.
The creature made international headlines when it was spotted 20 kilometres upstream in the East Alligator River two months ago, in what was believed to be the first recorded humpback in that location.
After 17 days, the whale — dubbed "Humpy" — eventually headed out into the open waters off the Top End coast.
But NT Government scientist Carol Palmer has confirmed it has since been spotted several times near the mouth of the East Alligator, including earlier this week.
"We had a [recreational] fisher on the 12th of October with his phone take some images and some video footage, and then that kickstarted the whole thing again," Dr Palmer said.
"We know it's the same one because we do photo identification of dorsal fins."
'There could be something wrong'
Dr Palmer said her team has been in contact with other Australian and international whale experts to help determine why the large marine mammal is hanging around, but there was still no clear answer.
"By now all of them are heading to Antarctica to feed," she said.
"So the fact that this guy's still in tropical waters — it's really hot up here — it makes us all feel that there could be something wrong.
"We've never ever recorded this kind of thing before."
Dr Palmer said researchers were conducting helicopter and boat surveys from a distance to better understand the whale's behaviour.
"They're such a huge animal and we wouldn't want them to get nervous and knock the boat by accident," she said.
"It's always important for everyone that's out on the water whenever you see a whale, always keep your distance."
Plan to analyse the whale's poo
Dr Palmer said they are hoping the whale will leave the river before the wet season kicks in, when rainwater washes into the Territory's many tidal rivers.
"There's a decrease in salinity and that change in the water can impact on their skin quality, which can have a health impact," she said.
Over the next few days, the researchers plan to gather samples of the whale's poo for analysis.
"They'll be able to tell if it's been eating, and that will be really good information to know if he's actually foraging up here," she said.
"That just gives us a little bit more information we don't have at the moment.
"So, yes, we'd like him to do a poo, please."
