MALE dolphins in the Swan River are forming “alliances”, teaming up with fellow fellas to woo potential mates.
Murdoch University marine biologist Delphine Chabanne led the recently published study based on hundreds of sightings in the Swan Canning Riverpark since 2011.
By closely examining photos to match up dolphins’ unique spots, scars or other markings, the researchers have identified individual Indo-Pacific bottlenose dolphins and tracked their socialising.
Early on it became clear from how often some dolphins were sighted together that some males were pairing up.
That kind of social bond has been seen before in larger dolphin populations in Shark Bay, but this latest study in the journal Mammalian Biology is the first to analyse male alliances here in the river where there’s a small, isolated, urbanised population.
Among the eight males studied, the closest alliance was a triad of three dolphins named Arrow, Hii, and Bottomslice. The bonds didn’t seem to be because they were related or happened to hang out in the same areas, “but by differences in gregariousness”, the study says.
The pairs and the trio all seemed to be teaming up to increase their chances with females. When the lads were together they would often then interact with female potential mates, herding females to their favoured waters or performing a “rooster strut” display to try to impress female dolphins.
“Our work revealed strong social bonds and long-term, non-random associations among individual males,” Dr Chabanne said in a media release about the study.
“Behavioural observations of alliances interacting with potentially receptive adult females, and exhibiting sexual display behaviours near females, suggest that these alliances occur in a reproductive context.”
It also seems dolphins in our river are closer than their seagoing counterparts.
“Dolphins in the [riverpark] appear to have stronger and more enduring associations with their peers than do dolphins in coastal habitats,” the study says, as the sheltered estuary and year-round food sources mean they don’t have to migrate huge distances so can get to know each other better.
by DAVID BELL