A decade-long study of whale sharks off the Ningaloo coast has found that females grow 5m longer than males.
The research conducted by Australian Institute of Marine Science fish biologist Mark Meekan and AIMS marine scientist Brett Taylor tracked 54 whale sharks from 2009 to 2019.
The study, published last week, found that males grew quickly before plateauing at an average adult length of about 8m.
In contrast, females grew more slowly, eventually reaching an average size of about 14m. Lead author Dr Meekan said it was the first evidence that males and female whale sharks grew differently.
He said one reason the females were probably getting big was the need to carry numerous pups.
“Only one pregnant whale shark had ever been found, and she had 300 young inside her,” he said.
“That’s a remarkable number, most sharks would only have somewhere between two and a dozen.”
Dr Taylor said the team recorded more than 1000 whale shark measurements using stereo-video cameras.
“It’s basically two cameras set up on a frame that you push along when you’re underwater,” he said.
“It works the same way our eyes do, so you can calibrate the two video recordings and get a very accurate measurement of the shark.”
Dr Meekan said the results also explained why gatherings of whale sharks in tropical regions were made up mostly by young males.
“They gather to exploit an abundance of food, so they can maintain their fast growth rates,” he said
Dr Meekan said the discovery had implications for conservation, with whale sharks threatened by targeted fishing and ship strikes.
“If you’re a very slow-growing animal and it takes you 30 years or more to get to maturity, the chances of disaster striking before you get a chance to breed is probably quite high,” he said.