The seas around Macquarie Island support a huge number of small animals that feed directly on photosynthetic microorganisms in the top layers of the ocean. These small animals are eaten by larger animals and one way or another end up as food for birds and mammals which breed on Macquarie Island. The limited terrestrial habitat in the southern ocean makes the island a breeding site for large numbers of penguins, flying seabirds like albatross and petrels; and also for many seals. These predators potentially feed on diverse range of smaller animals like fish, squid, salps, jellyfish and a diversity of crustaceans such as krill, amphipods, copepods, mysids and ostracods. So, studying the diet of birds and mammals that breed on Macquarie Island is a very useful way to find out what smaller animals are present in the ocean for a couple of hundred kilometres around the island.
Determining the diet of wild animals has been a difficult problem for scientists because animals rarely eat their food where they can be easily seen and food species are inevitably damaged when they are consumed and digested, so it isn’t easy to see what food species are eaten when this happens, or to identify their remains in stomach contents or scats. For this reason, a range of chemical diet analysis methods have been developed such as looking at the chemical composition of fat deposits, or the ratios of isotopes of carbon or nitrogen that are incorporated into other tissues. These chemical methods give some information, but usually only in very general terms. The Ecological Genetics group at the Australian Antarctic Division has spent about ten years developing the analysis of food DNA in animal scats to estimate animal diet. We originally developed these methods to study whale diet, but have since applied this technique to many other marine mammals and marine birds as well other animals like krill, squid and crayfish. Scat collection allows rapid sampling of large numbers of diet samples without causing significant disturbance to the animals being studied. Most bird species are sensitive to being disturbed when they are breeding as a natural response to predation, but we can sample scats without having to enter the breeding area or handle the birds at all.
Bruce Deagle and Simon Jarman have been collecting scats from penguin and seal species. Anna and Jaime from the Tasmanian Government Department of Primary Industries, Parks, Wildlife and Environment have been helping them by collecting scats from albatross species that they are already studying for population assessment purposes. Overall about 850 scats were collected for this study during the 2012/2013 season and a further 1250 were collected in 2009/2010. These samples will have the food DNA in them analysed in the next year and this will tell us the proportions of diet items present in each scat. Combining the scats from each species in a given location at a particular phase of the predator’s breeding cycle will give a population diet estimate, so for example, we will estimate the diet of royal penguins during the chick creche phase of the breeding cycle from the approximately 50 scats we collected there. We know from tracking studies that penguins and other marine predators alter their foraging trips durations and locations with different breeding cycle phases, so we treat each phase of their breeding cycle as a different estimate of diet. The idea of sampling in different years is to get an initial idea of how much variability there might be in the availability of food species in different years. This study will give us comparisons of the diet of king, royal, gentoo and rockhopper penguins, light-mantled sooty and grey-headed albatross, fur seals, kelp gulls and Macquarie Island shags, all compared with the same DNA based methods. This will tell us about competition among these species and how they divide up the available food in the ocean among the species. It will also tell us what food is available to these predators overall.
We have had two very successful sampling seasons for this project with the help of TasPAWS, DPIPWE and AAD staff. The facilities for living at Macquarie Island and conducting our scientific work there are excellent and the station staff have done a great job making our work successful and fun. We are hoping to publish the major results from this work later in 2013. This will be the largest DNA-based diet survey ever conducted and the first major cross-species one. We hope that it will be a example for future non-invasive studies of animal populations in other areas as well as telling us a lot more about the marine life in the Macquarie Island region.
Dr Simon Jarman — Senior Research Scientist (Simon and Bruce are now back in Australia)
This week is a special time for the IHAT team - annual pit digging time! It is an opportunity for the team to come together, dig big holes, sample the soil profile at depth and then fill the holes in again. A lot of holes have been dug, a lot of shovels have been lent on and even some friendly stranded biologists have kindly pitched in. The annual pit digging will continue for a little while longer, hopefully providing encouraging results for the remediation project and a good source of invertebrate/contamination interaction data. Corrine is currently out in the field collecting seeds for future germination tests but is looking forward to joining the hole digging effort upon her return.
Josie Van Dorst