12:00am Tuesday 25 February 2020

You are what you eat: variety in diet good for Aussie fur seal survival

Deakin PhD candidate Laetitia Kernaleguen used the camera footage to gain insight into the seals’ individual dietary preferences, which could be affected by the impact climate change has on population levels of fish.

Ms Kernaleguen, from Deakin’s Centre for Integrative Ecology, within the School of Life and Environmental Sciences, found the survival prognosis looks good for the species, which is still recovering from the commercial sealing era of the 18th and 19th centuries.

The Australian fur seals (Arctocephalus pusillus doriferus) are found only in south eastern Australia and most prolifically in Bass Strait. The Deakin team attached cameras to 16 female fur seals off Kanowna Island, Wilsons Promontory National Park in northern Bass Strait.

Ms Kernaleguen investigated the seals’ seals by analysing video from National Geographic crittercams attached to their backs.  She then analysed blood and whisker samples, to gauge the chemical composition, providing a longer-term analysis of what nutrients they were digesting and, therefore, what sea life they were consuming.

“We wanted to see if the crittercam evidence of a short-term period matched the longer-term diets,” Ms Kernaleguen said.

“Understanding what the Australian fur seals eat is important because it has implications for conservation management, both for them and for what they are eating.

“For example, if they were all eating the same types of fish then this would mean competition for that species would be high, placing not only the food source in danger but also impacting on the survival of those fur seals who missed out on their meals.

“The Australian fur seal represents the greatest marine predator biomass in south eastern Australia, but its population is increasing at just 2 per cent a year and still sits at levels below 60 per cent of what they were before the commercial sealing era.

“Climate change is also affecting the population levels of fish so it’s essential that we can understand what is happening to our ocean populations under the sea.

“We were pleased when we saw the crittercam footage that the fur seals appeared to have a diverse diet, primarily based on fish and octopus, with the occasional stingray thrown in.”

The research project supervisor, Deakin University Associate Professor John Arnould, said the blood and whisker samples confirmed the diversity in their diet was consistent over a longer period.

“This really does show that you are what you eat – because we use our food to synthetise our own body, its chemical composition provides indirect information on our diet,” Associate Professor Arnould said.

“In this case the whiskers revealed the stable isotopes of carbon and nitrogen. Seals’ whiskers are a keratinous tissue, like hair, that grows continuously and we cut each whisker into three millimetre long sections and analysed each one.

“This allowed us to go back in time for several years and confirmed the fact that not all fur seals adopt the same foraging strategy.

“So the Australian fur seal has a much stronger chance of survival because of their varied diet.”

The research is detailed in the journal article, From video recordings to whisker stable isotopes: a critical evaluation of timescale in assessing individual foraging specialisation in Australian fur seals, published in a recent edition of Oecologia.

The project also involved researchers from the University of Tasmania’s Institute for Marine and Antarctic Studies, National Geographic and France’s Centre d’Etudes Biologiques de Chizé at Université de La Rochelle.

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