1. Community monitoring of nesting sea turtles at D’Arros Island and St Joseph Atoll
The D’Arros and St Joseph nesting sea turtle monitoring programme is the longest-running sea turtle monitoring programme in the Amirantes Islands. Initiated in November 2004, it has now spanned nine nesting seasons without interruption. It is a ‘community monitoring programme’, for which data are collected predominantly by interested members of the Seychellois community living on D’Arros Island. The programme focuses on four islands: D’Arros, St Joseph, Banc Coco and Île Ressource. Project protocol is for beach patrols to be conducted daily at D’Arros Island, where the human population lives, and weekly at St Joseph Atoll. However, for logistical reasons St Joseph tends to be monitored less frequently and as a result more extrapolation is needed to calculate levels of nesting activity at St Joseph Atoll than at D’Arros.
2. Growth rates, movement and population size of resident juvenile hawksbill and green turtles at D’Arros Island and St Joseph Atoll
The objective of this study is to gain a better understanding of population numbers, demographics, growth rates and movements of juvenile turtles foraging at D’Arros and St Joseph. Both hawksbill and green turtles recruit into the neritic environment when they attain approximately 35 centimetres in carapace length and will remain there for up to 10 years or more. Efforts to conserve foraging hawksbill populations are hindered by a lack of basic demographic and ecological information. Although an increasing number of foraging population studies are being carried out in the Atlantic Ocean, fundamental data such as population demographics, habitat requirements, home range and movements of foraging hawksbills are largely lacking for the Western Indian Ocean. The high density of juvenile hawksbill and green turtles foraging at D’Arros and St Joseph provides a unique opportunity to study and monitor the populations of these endangered species.
Even though hawksbills are less common in the area, the study so far has focused more on this species as it has suffered global declines in excess of 90% and is considered critically endangered – and at the same time is data deficient.
Reef mantas occur year-round at D’Arros Island and are mostly observed feeding on near-shore plankton accumulations. Baseline research conducted between 2009 and 2012 revealed the year-round presence of mantas of both sexes and all age groups at the islands and that the population appears to number in excess of a hundred.
Increasing demands for manta products on the Asian market has recently resulted in drastic population declines and it is therefore vital that the planning of the proposed D’Arros and St Joseph Marine Protected Area take the reef manta into account. Considering the proven link between healthy terrestrial ecosystems and marine productivity in adjacent waters, D’Arros may experience an influx of mantas as the ambitious vegetation rehabilitation programme on the islands advances. A better understanding of the population structure and behaviour of mantas may shed light on the role that these islands play in the ecology and continued protection of this vulnerable species.
Opportunistic photo identification excursions have been ongoing since 2009. In November 2012 a formal monitoring programme was implemented and was refined in April 2013 with the valuable input of Guy Stevens, founder of the Manta Trust.
The fundamental aim of the coral reef monitoring programme is to assess trends in the structure and health of coral reef communities at D’Arros and St Joseph. The purpose of this is to:
Our protocol employs standardised methods and sampling strategies and includes the monitoring of ambient environmental parameters; benthic cover and composition; coral recruitment; coral bleaching; the survival and growth of coral recruits; and reef fish and mobile invertebrates. For the most part, prescribed monitoring techniques are employed and it normally takes three experienced data-recorders about two months out of every year to fulfil all field-work requirements, except coral bleaching surveys. Bleaching surveys will be conducted only when required and additional field workers will be brought in to maximise sampling effort in years when bleaching is expected (via NOAA Coral Reef Watch website). Extensive use is made of photo and video sampling since this significantly reduces field work and provides permanent records that can be analysed in greater detail.
Climate is scrutinised very carefully at D’Arros and St Joseph as it exerts an overriding influence on all ecological processes. Weather conditions are monitored by means of a meteorological station that measures variables such as temperature, humidity, rainfall, solar radiation, UV intensity and wind speed and direction. Sea surface temperature is checked at 101 locations in and around the atoll, D’Arros and the greater Amirantes bank. Tidal height, light intensity and current flow are also monitored using sophisticated underwater loggers.