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New study of parrotfish

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Gently does it: scientists at Hungry Bay fitting a Rainbow parrotfish with an acoustic tracker (Photograph supplied)

Bermuda’s healthy population of parrotfish, colourful reef grazers that have all but vanished in many islands, are under new study.

Reefs depend on them for survival: without foraging parrotfish, corals smother under seaweed and sponge.

Thanks to a collaboration between local scientists and the University of the Virgin Islands, Bermuda’s parrotfish are being tracked in greater than ever detail. “We want to learn more about their ecology, since they have been fished out from most of the Caribbean,” explained Rick Nemeth, a research professor of marine biology at the University of the Virgin Islands.

The species in question are the Rainbow, Blue and Midnight parrotfish, which Dr Nemeth is helping to fit with acoustic transmitters.

Sending out a ping each minute, to be picked up by listening devices, the fish are continually followed. Four were tagged in July 2015, and four more this August.

The data give clues to their habits or, in the case of one of last year’s fish, which covered 30km in six days, its possible fate as a shark’s meal.

“We wanted to understand what part of the ecosystem the United States Virgin Islands lost when these large species were fished out,” said Dr Nemeth.

By tracking how much algae parrotfish chew with their powerfully beaked mouths, and the areas covered, scientists underscore their value, and can offer tips to speed up their recovery.

Hungry Bay in Paget, secluded behind a narrow entrance and with abundant mangroves, provided the tagging site — but the fish are also surveyed across the island.

Implanting the transmitter resembles a deft piece of minor surgery, complete with antibiotics to protect the fish from infection. Once released, the tagged fish speeds away into the sea — but shows up, complete with identification, whenever it passes in range of a listening station.

It turns out that Hungry Bay’s parrotfish are swimming inshore from about 7am to 7pm, sticking to the bay 60 to 80 per cent of the time. Once they were spotted leaving each day, however, extra receivers were placed outside.

The Rainbow and Blue varieties were also seen setting out from the bay for about two weeks a month during the winter.

Bermuda boasts a thriving stock of parrotfish, a protected species that Dr Nemeth, a grouper expert, noticed teeming in the shallows of Tobacco Bay during a 2006 visit.

“These species used to be very common in the Virgin Islands, but are now rare due to overfishing,” he said.

The parrotfish project is a collaborative study with other UVI scientists, Tyler Smith and Marilyn Brandt, and will extend to Curacao later this year.

Local scientists include Thad Murdoch, Struan Smith and Gretchen Goodbody-Gringly.

Dr Smith, a curator at the Natural History Museum, pointed to a host of other local studies: Dr Murdock’s ecological monitoring, supported by the Bermuda Zoological Society, examines the entire fish community and the status of corals at more than 40 sites around Bermuda.

Andreas Ratteray, a local student, is another studying local parrotfish, while the black grouper has been tagged for years by Tammy Trott, of the Department of Environmental and Natural Resources.

Tracking ultimately enables better management, Dr Smith said: if the tagged parrotfish stick to the same areas, then surveys elsewhere are likely accurate for a particular reef’s population.

“If we find many parrotfish in an area, and there appear to be increases in their abundance, we can be confident that populations really are growing — and not just the fish moving around a lot.”