Friday, 28 November 2008
Not so long ago this site carried a report titled Yamba - a nice place to live about Yamba being a very friendly place for humans.
Now, Christine Fury, a researcher with Southern Cross University’s Whale Research Centre, has found that Northern Rivers bottlenose dolphins agree - the most popular place for them to live is the Clarence River,which runs through Yamba, Maclean and Grafton.
Ms Fury, who has been studying local estuarine dolphin populations for three years, has uncovered some fascinating facts about our warm-blooded mammalian cousins.
SCU reports that Ms Fury's study provides the first published data on Indo-Pacific bottlenose dolphins in Australian estuaries.
Ms Fury estimates that about 71 dolphins live in and around the Clarence River compared to about 34 dolphins in the Richmond River.
“The Clarence River is the most popular because it is the largest estuarine river system in NSW and therefore has a greater volume of water. It also has less urban and agricultural development. Both these factors mean the water quality is better,” Christine said.
“Dolphins are the top predators in the river systems, so the cleaner the water, the more fish in the river and the better the ability to sustain a bigger dolphin population.”
During her 2,000 hours on the rivers observing dolphins, Christine found that a dolphin’s favourite fish is mullet, or whiting as a second choice.
The mothers teach their calves how to catch fish, but it takes three to four years for the youngsters to become proficient at catching their own dinner and they are supplemented with their mother’s milk until that age.
Once weaned, the juveniles leave their mothers and hang out in mixed-sex pods, learning from each other and spending a lot of time in play.
As the males get a little older, they break off into pods of three or four, working collectively to catch fish and mate with females using an uncommon herding manoeuvre.
Mothers and their calves, and female pods, escape the more aggressive sexual attention of the males by entering the shallower waters of river tributaries, where the males generally do not follow as they prefer to remain in the deeper, main channels, where they can assert their dominance.
Also, the tributaries have smaller fish, which are easier for the calves to catch and eat. Fish are swallowed whole, head first, after first being either stunned by a tail flap or bitten. Dolphins will often flip a fish into the air and then catch it head-first so as to be able to swallow it properly.
Like humans, dolphins have distinct personalities. Research shows the more gregarious, inquisitive and curious dolphins prepared to stray furthest from mum have the best chance of long-term survival.
Diligent and informed management of future increased environmental disturbances will be needed to ensure the long-term survival of these dolphin populations, Christine said.
You can read the full research paper at http://www.publish.csiro.au/nid/126/paper/MF08109.htm