The year 2015 ended on a high for the Small Cetacean Project. Five of our international bunch of students finished their dissertation projects providing fascinating insights into the ecology of Chilean dolphins. Annie (from Australia) and Julia (from the UK), both Masters students at the University of St Andrews, showed off their results in a joint poster presentation at the biggest biennial gathering of marine mammal scientists, held in San Francisco (USA) in December 2015. Diego and Fran (both Chilean) defended their undergraduate theses at the Universidad Austral de Chile. Lea had already defended her thesis at the University of Konstanz (Germany), and then gave a short talk about her project at the UK student marine mammal conference in January 2016.
Annie and Julie at the Biennial.
So wat have we learned? Well, our difficult to observe Chilean dolphins use the same core habitat in southern Chiloé year-round. We’ve studied them intensely every southern summer since 2001, but doing the same dedicated sighting surveys in the wet and windy winter of southern Chile is not feasible (or fun). So instead of looking we listened for them by placing autonomous hydrophones (underwater microphones) at sites of importance to Chilean dolphins - this technique is called passive acoustic monitoring (PAM). The instruments (CPODs) worked in all seasons and during day and night recording the characteristic echolocation clicks of passing dolphins. Dolphins use echolocation for almost everything they do: to navigate, locate food, investigate objects or interact with each other.
Diego found that Chilean dolphins are present in the bays and channels of Yaldad, Coldita and San Pedro year round. The dolphins are also very active at night when we can’t observe them, and they often use certain areas preferably at night. We discovered a particularly striking pattern of nightly activity near a salmon farm in Canal San Pedro where the dolphins seem to be feeding near (but not at) the salmon cages, possibly exploiting the rich pickings of wild fish that associate with fish farms to feed on all the surplus food dropping from the cages. Two new students from St Andrews, James and Joanna, are now looking at the PAM data in more detail and over a longer period. We are also preparing to install the CPODs in new locations in Chiloé where we might focus on Peale’s dolphins who produce sounds similar to Chilean dolphins.
Lea found that Chilean dolphins in San Pedro and Yaldad don’t often mix, but instead form two distinct communities with mostly varying associations between individuals (so called fission fusion patterns typical for most coastal dolphin societies). Occasionally, some dolphins move a bit further and might mix with other groups, but for most of the 13 years of photo-identification data that Lea analysed, individual dolphins were highly faithful to particular bays and channels where they seem to be able to fulfil all of their biological needs.
Fran tracked the Yaldad dolphins from land with a theodolite (surveyor’s instrument). She saw the dolphins travelling into Yaldad bay regularly from the east, and once in the bay, they changed behaviour, most likely looking for food in a narrow corridor between the tide line and the first lines of mussel farms. During our boat-based surveys we noticed that the dolphins also use areas in the centre of the bay where mussel lines have been removed, but they tend to be reluctant to enter into densely stacked patches of mussel farms. The mussel lines essentially form a dense curtain underwater, so might form a barrier to movement. At the same time, mussel lines also harbour a lot of other marine organisms and might shelter small fish that are of interest to the dolphins.
We have long documented the co-occurrence of Chilean dolphins with mussel farms, but we think that dolphins and mussel farms like the same productive bays, so their distribution overlaps substantially around Chiloé, where most if not all bays are taken up by intense aquaculture operations. This is still somewhat different (luckily) at the continental side of the Ecoregion Chiloensis, an area that Annie and Julia focussed on for their dissertations (and we’ve started more work as well)… but that’s a new story….