February 2012 Expedition - Day 11 - Victory Bank
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, 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 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 to about 35% closer than even in other marine protected areas.
The dive 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 a normal internet link.
The BRUVS work is going very well and Jessica takes on the story from here.
Victory Bank – a small submerged atoll rising from 100’s of metres to 5 m. 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 on the 21st of February. 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, 25th of February, 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, and 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.
We promise to make clips of the BRUV videos available on the website at a future date!
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 still a heart stopping sight. Again, the curse of the working marine biologist had Charles and Anne with heads down recording the coral cover and missing it swimming over their 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.