As the ornithologist on the expedition my primary role is to record seabirds at sea. To achieve this I spend the best part of the daylight hours on my “perch” on the bridge wing, scanning the ocean, logging all the bird activity I see. The reason for this research and why it is so important is that globally there is a huge gap in the knowledge of where seabirds go when not tied to the land for breeding and in particular, how they use the different marine habitats, such as sea mounts, banks and trenches. This statement holds true in the Chagos Marine Protected Area (MPA).
Throughout the world many seabird populations are in serious decline. The reason for these declines are many but, generally, involve some form of disturbance on their breeding grounds (e.g. predation by introduced animals) or, a decline in prey availability (e.g. through overfishing) or, something directly impacting the birds themselves (e.g. being caught and drowned on long-lines). Worse, many species are affected by two or all three of the above. All of the above impacts can have their root-cause traced back to man.
The Chagos MPA provides an opportunity to study seabirds free from many of the anthropomorphic pressures felt elsewhere around the world’s oceans. I say this because within the MPA it is known which islands have introduced predators on (mainly rats) and which do not. (Steps are being taken to remove rats from the islands of the northern atolls, with Vache Marine in Peros Banhos being cleared in August 2014). Further, the MPA is a no-take zone. Therefore, there are no commercial long-liners operating in the area and, greater global events permitting, the availability of prey to seabirds should not be a constraint on their populations. So, with the parameters outlined above, it could greatly benefit seabird populations elsewhere, if we understood how seabirds function ecologically in a healthy, protected area.
This trip has been fascinating! Besides having the opportunity to continue studying seabirds in a part of the Indian Ocean where little research has taken place, some of the information we are gleaning is “filling in the Chagos MPA jigsaw.” For example, surveying the same sites, using the same survey method but at different times of the year is revealing there is seasonality in the use of marine habitats by seabirds. In November 2012 when we first surveyed a prominent seamount we recorded 12 species of seabirds feeding and foraging above it and Bottlenose Dolphins were noted daily. Repeating the survey in January 2015 found only four species, less than a quarter of the total abundance of seabirds and no dolphins. Some of this variability can be explained by the migratory nature of seabirds. Wilson’s Storm-petrel that was regularly recorded in November but not seen on this trip will have returned to its southern ocean breeding grounds; Matsudaira’s Storm-petrel, the commonest tubenose over the feature in November 2012 and again not recorded on this trip, will have headed east back to breeding islands south of Japan. Why resident seabird numbers decline with seasonality (and the absence of dolphins) remains to be explained.
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