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Funding :

July 2013

Research project PRISTINE

Tonga

Project leaders

Laurent Vigliola (IRD COREUS Nouméa) & David Mouillot (UM2 ECOSYM Montpellier)

Objective

Redefine the baseline for coral reef ecosystem in the South Pacific by comparing potentially pristine reefs (remote and uninhabited islands) with marine protected areas and fished sites.

Date et destination

Uninhabited South Minerva, North Minerva, and Ata island, Tonga, 02-15 July 2013.

Scientific team:

Laurent Vigliola (IRD), Gérard Mou-Tham (IRD), Stéphanie d’Agata (IRD/ UM2), Jean-Baptiste Juhel (IRD/UNC), Philippe Frolla (EGLE), Sione Mailau (Tonga Fisheries)

Crew of IRD RV Alis Barazer Jean-François, Loic Le Goff, Ludovic Ramet, Eric Saraullo, Pierrick Prigent, Steeve Taalo, Simon Godard, Jean Lamata, Nicolas Josse, Victor Bole, Jacques Qenejoj, Jean-François Trives

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July 1st. Arrival at Tongatapu

New-Caledonia and Tonga are fairly close countries. A direct flight would have taken 2-3 hours. However, two days were necessary to travel from Noumea to Tongatapu via Auckland in New Zealand; a very long journey.

© IRD/L. Vigliola

© IRD/L. Vigliola

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July 2nd. Meeting with officials

The whole team is welcomed at the Tonga Fisheries Department by Mr Viliami Moale, Principal Fisheries Officer, for an official presentation of the project. At the back of the building, ornamental fish and giant clams are reared in experimental basins.

© IRD/L. Vigliola

© EGLE/P. Frolla

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July 3-4. Travel to South Minerva (Tele-Ki-Tonga in Tongan)

South Minerva Reef is a small uninhabited atoll at two days navigation from Tongatapu. Two days and two nights aboard an oceanographic vessel cruising in rough seas is very long and uncomfortable. However, Philippe is having lot of fun trying the safety suit.

© IRD / L. Vigliola

© Google map © EGLE / P. Frolla

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July 5th. Diving South Minerva

After 5 days of travel, we arrive at South Minerva. Everybody is tired but very excited to reach this mythical reef in the middle of the seas. We performed 4 dives on the outer slope and one in the lagoon. Nice dives but not quite what we expected: herbivores strongly dominate the fish assemblage. The predators are almost absent.

© IRD/L. Vigliola

© EGLE / P. Frolla

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July 6th. Diving South Minerva

We enter the closed lagoon at the South of the atoll. It is beautiful. Underwater, however, there are not many fish and we find clear evidence of fishing.

© IRD/L. Vigliola

© IRD/L. Vigliola

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July 7th. Diving South Minerva

Our team also surveys giant clams, trochus and sea cucumbers. The lagoon of South Minerva is a cemetery for giant clams. Most large specimens have been fished, only empty shells remain. Small giant clam species (Tridacnia maxima) show very large abundance. We haven’t seen any trochus; sea cucumbers show very little numbers.

© IRD/L. Vigliola

© IRD/L. Vigliola

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July 8th. Diving South Minerva

Last day in South Minerva. This atoll has been heavily fished for both finfish and invertebrates. However, there is hope. Young giant clams are growing near the empty shells of their ancestors, predators are in very low numbers, but still there, and the atoll is now under a specially managed area status. At least ten years will be necessary to recover if protection is enforced. Hopefully we can come back in a decade and record the recovery of South Minerva reef.

© IRD/L. Vigliola

© IRD/L. Vigliola

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July 9th. Diving North Minerva (Tele_Ki_Tokelau in Tongan)

North Minerva is a small uninhabited atoll at about 4 hours navigation from South Minerva. We performed 5 dives today but the highlight comes from the stereo benthic videos. The system allows measuring the diversity of predators, their ecology and their size. Here, records from left and right stereo cameras allow measuring a 3.35 m female tiger shark at 11 m deep in the lagoon.

© IRD-UNC/J.B. Juhel

© IRD-UNC/J.B. Juhel

© IRD-UNC/J.B. Juhel

© google map

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July 10 th. Diving North Minerva

More dives in North Minerva confirm the presence of many fish and fair abundance of large predators. The site is not pristine but in a much better state than South Minerva. Today was perfect for a walk on sand banks at low tide in between dives.

© EGLE / P. Frolla

© EGLE / P. Frolla

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July 11 th. Diving North Minerva

Today we report the first record of Chromis pamae in Tonga. We also report the presence of three boats in the atoll. Minerva North is shelter to fishing charters, yachts and sailing boats cruising across the Pacific. Protecting the reef will not be an easy task.

© Egle / P. Frolla

© IRD / L. Vigliola

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July 12 th. Travel to Ata island

French oceanographic research vessel ALIS was built in 1986. This 28.40 m old lady is well equipped and perfectly suited to survey the waters of Pacific Islands Countries. Minerva reefs and Ata Island have been mapped using our multibeam sounder.

© IRD/L. Vigliola

© IRD/ ALIS

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July 13 th. Dive Ata island

Ata is a very scenic island with huge cliffs falling in the ocean. Underwater, we observe hundreds of surgeonfish (Acanthurus leucopareius), drummers (Kyphosus vaigiensis), many bluefin and black trevallies and a few humphead wrasses. Above the water, whales and marlins are jumping not so far away from our boat.

© IRD/L. Vigliola

© IRD/L. Vigliola

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July 14 th. Dive Ata island

Today is national celebration in France. Here, this is our last working day. More dives in Ata confirm the presence of many fish, mostly herbivores grazing algae on rocks. The sea is rough and special attention is required when deploying our pelagic and benthic stereo-video systems. These baited stereo cameras allow surveying oceanic and reef predators such as sharks, groupers, marlins or dolphin fish and complement well our dive data on fish diversity, invertebrate abundance and habitat quality.

© IRD / G. Moutham

© IRD / G. Moutham

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July 15,16 & 17th. Return to Tongatapu and presentation of results

After a night of travel, the team is back to Tongatapu. However, the work isn’t finished. We clean up and store the equipment, put together the first datasets, present our first results to the Chief Executive Officer for Fisheries and Agriculture, the Director of the Fisheries, some Staff of the Fisheries of Tonga, and provide our trip report. An interesting discussion follows. The team is exhausted but happy of the work achieved.

© EGLE / P. Frolla

© EGLE / P. Frolla

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Achievements

Habitat quality, structure of fish assemblages and abundance of some invertebrates have been recorded on 38 underwater transects, each 50 m long. This represents about 45 hours work per diver and a hundred hours of underwater observations in 9 days. This information will be compared to our regional database which includes 1700 transects in 17 countries of the tropical Pacific.

Thirty nine reef and forty five mid-water baited stereo-video stations have been recorded on reefs and offshore the three explored islands. This is the first deployment in Tonga. This data make a focus on population of endangered large predators and will be compared to other sites of the Indo-Pacific where our group is collecting information.

Several hours of video and hundreds of photos have been recorded to archive the state of visited reefs, for documentaries and for expositions to the general public.

Visited islands have been mapped using our multibeam sounder. These maps will be very useful for the fisheries department of Tonga.

First results

Presence of sharks has been recorded in 17% of the 1700 dives performed by our group in 68 sites from 17 countries of the Pacific. At a given site, the largest percentage was 68%. This project revealed presence of sharks in large abundance in over 90% of dives at remote, uninhabited islands of New Caledonia and French Polynesia. Here, we report low abundance of shark in 65% of the dive performed in Ata and Minerva reefs. Our survey is the first baseline survey of Minerva reefs.

NEXT

The team will explore some pristine sites of New Caledonia as part of a National Geographic TV documentary in November 2013.

© EGLE / P. Frolla