On our way to the Three Brothers (the islands on the Great Chagos Bank where we will be working next) we returned and spent the day on Victory Bank, a dish-shaped atoll submerged to at least 5 metres depth at its shallowest, where the BRUVers needed to do some more sampling. The divers who wanted to had an early dive to do their work, in order to be out of the water before the BRUVs were deployed and attracted their large toothed clients.
The rest of us used the day to catch up with data entry and some preliminary analyses. These analyses show that the coral continues to recover, particularly in deeper water where it had lagged behind the shallower depths. Also, the surgeonfish and parrotfish habituation studies (which are looking at responses to diver approach in fished, lightly fished and marine protected areas throughout the Indo-Pacific region), show that in Chagos, divers can approach about 60-85% closer to these species than even in other marine protected areas.
The diving was spectacular, very good visibility, schools of huge fish and a very large nurse shark which almost swam into the divers – resulting in a superb photo by David which will be posted as soon as we get back to Diego Garcia and have a normal internet link.
Jessica Meeuwig, one of our “BRUVers,” takes on the story from here:
Victory Bank: a small submerged atoll rising from 100s of metres to 5 metres . It measures approximately 6 km x 4 km, a perfect oval of coral surrounding a lagoon with reported depths of 33m. Last surveyed in 1837 when its depths were plumbed by leadline, Victory Bank’s most recent research consisted of several exploratory dives by the intrepid Professor Sheppard in 1979.
As part of this expedition, the Pacific Marlin’s Captain Neil Sandes carefully navigated the entrance to the lagoon. We think the Marlin is probably the first ship to ever anchor inside the lagoon! We then dropped our baited remote underwater video systems (BRUVS) at eight locations distributed around the submerged rim of the atoll. On retrieval, we found several of our bait bags shredded. A quick review of the footage found that a beautiful young tiger shark, stripes blazing, and a rather large nurse shark were the culprits.
Crystal clear water and shoaling fish had us determined to return. So on the divers’ rest day a few days later, we anchored on Victory Bank at 07:30. A morning shallow dive provided us with a fish-eye view of the seascape as a whole. The coral studded rim dropping off precipitously into the deep blue, with the shoulders of the atoll home not only to corals but large school of snapper and fusiliers, silvertip and grey reef sharks, but also a very curious nurse shark. We then spent the rest of the day dropping BRUVS in the lagoon of the atoll down to 40m and repeating samples on the rim.
Combined, this footage will provide us with a quantitative understanding of the fish assemblages of this very isolated and pristine submerged atoll. To learn what constitutes unexploited fish communities in both the shallow and deep areas of these atolls provides us with an essential reference point to understand the impacts of human activities on coral reef ecosystems ... and is why it is so important that the Chagos has been protected as a no-take marine reserve.
Charles Sheppard wraps up the day’s activities:
Team members Nick, Pascaline and Bob had an encounter which made everyone extremely envious; they saw the first whale shark observed underwater in Chagos. According to Nick, it was only a small one, but at about five metres long, it was still a heart-stopping sight. Again, the curse of the working marine biologist had myself and Anne with heads down recording the coral cover and missing it swimming over our heads.
Late afternoon we had a fairly bumpy journey over to the Three Brothers. The anchorage here is fairly exposed to the wind and sea so we hope it will settle soon.
Previously in this series:
About the Authors: Professor Jessica Meeuwig, Scientist
Professor Jessica Meeuwig is the Director of the Centre for Marine Futures at the University of Western Australia. Her main expertise is marine and fisheries conservation, and quantitative modelling. Her research group works across a range of taxa, from humpback whales to sharks to bony fish and includes some benthic ecology with key questions centring on how animals use habitat and the impacts of human activities on their ecology, population biology, energetics etc. Her group also has a strong interest in the development of video and image based sampling methods and maximising the power of information obtained from these methods. Jessica has worked as a marine ecologist in a wide range of temperate and tropical ecosystems and is a keen science communicator.