Spinner dolphins have a predictable daily cycle of resting in shallow coral reef systems or bays during the day and then moving offshore to forage on mesopelagic fish and squid in the evening. From our research to date WDCS has confirmed that our study site, Moon Reef (Fiji) as one of these day-time resting habitats for a small, resident pod of spinner dolphins. However, there are many other coral reefs nearby this reef so this begs the question: What’s so special about Moon Reef? There are two particular reasons we’re interested in this question. Firstly, we know that the day-time resting activity that we’ve observed at Moon Reef is critical for their survival. Therefore, we consider Moon Reef an important resting habitat for this population. Secondly, through our own observations and many discussions with local villagers and fishermen we know that Moon Reef is used on a very regular and frequent basis, whereas the surrounding reefs are not. Therefore, we want to know why this reef is being chosen and not others.
In partnership with Flinders University (http://www.flinders.edu.au/science_engineering/biology) we began an environmental characterization of both Moon Reef and nearby Horseshoe Reef (which we chose for comparison purposes) last year. Using a CTD (Conductivity, temperature and depth) sensor we were able to get measurement profiles (taken every ½ metre from the surface to the seafloor) of temperature, chlorophyll-a, turbidity and salinity both inside and outside of each reef. After finding some initial differences we decided to repeat these surveys last month but this time using a sampling scheme on a much finer scale. In addition, we organized for staff from the Institute of Marine Resources from the University of the South Pacific (http://www.usp.ac.fj/index.php?id=imr) to undertake some biological diversity surveys on fish, invertebrates, and coral species in the two reefs also.
We are now in the process of putting all this data together as we try and describe the important resting habitat of spinner dolphins in Moon Reef. That said, we are also not discounting that there may be other factors at play here such as the social culture of the dolphins or perhaps predator avoidance.
We will keep you updated.