Sunday, 4 June 2017

Giant bumphead parrotfish begin mating in their hundreds

2 June 2017
By Sandrine Ceurstemont

It was a sight to behold. A group of about 1200 giant bumphead parrotfish have been caught in the act of mating off Palau in Micronesia, turning the water cloudy with their sperm. It’s the first time the species has been seen doing so in such large numbers.

George Roff from the University of Queensland in St Lucia, Australia, witnessed the behaviour while diving. “I’ve only ever encountered schools of 30 to 40 individuals before,” he says. Mass spawning events among the fish were first observed in 2011, but never previously involving more than 100 individuals.

During the latest event, the fish tended to mate in groups of up to 10 individuals, comprising several males fighting over one or a few females.

The activity is usually far more sedate, involving just one member of each sex. “It’s a sharp contrast to the frenzied spawning rushes in the Palau aggregation,” says Roff.

Giant bumphead parrotfish (Bolbometopon muricatum), which can grow to a metre or more in length and weigh up to 46 kilograms, play a unique role in their ecosystem. They use their large jaws to graze on reefs, making space for new corals to settle.

But in recent decades, overfishing led to the Palau population shrinking. This was particularly visible in terms of a dramatic drop in individuals landed by fishing vessels, down from more than 1000 most years in the 1990s to less than 100 in 2006.

This prompted the government to issue a total ban on fishing the species in 2006. And the strategy seems to be helping the population to recover. “This large spawning aggregation is evidence that it is having a positive effect,” says Alan Friedlander from the University of Hawaii at Manoa, who filmed the event.


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