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As one of many prime predators roaming Antarctica, the sizeable southern elephant seal has its honest collection of the menu. But it surely seems they do not simply need to eat something and every thing.
In response to new analysis led by UNSW Sydney, male southern elephant seals have their very own favorite meals, they usually like to stay with them. In different phrases, they’re very fussy eaters.
“They might have the choose of the buffet, and but every male southern elephant seal eats plenty of the identical meals, which is only a fraction of what is on provide,” says Andrea Cormack, lead creator of the examine and a PhD candidate at UNSW Science. “So, they’re extraordinarily choosy eaters, every with their very own distinctive favorite meals they go after, whether or not or not it’s fish, squid species, crustaceans or octopus.”
The analysis, printed within the journal Marine Ecology Progress Collection, is without doubt one of the first research to analyse the food regimen of grownup male southern elephant seals, who, regardless of their spectacular dimension, are comparatively understudied in comparison with females.
“We did not particularly evaluate males to females on this examine,” Ms Cormack says. “However females are identified to take care of a reasonably specialised food regimen between each other, simply nowhere close to as excessive as what we discovered with the males in our analysis.”
Unlocking chemical clues from whiskers
Getting shut sufficient to review the food regimen of male elephant seals within the wild might be difficult, given their highly effective stature and aggressive temperament — they will weigh as much as 4 tonnes, dwarfing their extra placid, smaller feminine counterparts. As an alternative, researchers analyse the composition of smaller exhausting tissues again within the lab that preserve extra detailed data of the animal’s exercise.
For the examine, the scientists inferred the consuming habits of 31 male southern elephant seals from the Western Antarctic Peninsula by analysing a whisker pattern from every seal that holds steady isotopes — chemical clues concerning the meals they’ve eaten up to now. Every whisker analysed within the examine contained as much as a yr’s price of information about every seal’s culinary preferences, permitting the staff to assemble essentially the most in depth image of the male southern elephant seal food regimen so far.
“These guys are out within the water foraging for months, after which fasting for 2 to a few months on land throughout breeding season, so it is exhausting to collect plenty of details about their food regimen by means of examine strategies like abdomen evaluation,” Ms Cormack says. “However by analysing exhausting tissues that retailer an inert chemical file of what they’ve eaten, we will begin placing collectively the items about their consuming habits.”
The researchers discovered almost all male southern elephant seals are specialists, with people constantly consuming the identical meals gadgets over time with little variation in food regimen. Most of these might be thought-about excessive specialists, feeding on lower than 20 per cent of their inhabitants’s vary of meals sorts. In the meantime, just one seal within the pattern was a generalist and selected to eat a broad food regimen of assorted meals sources.
“The Antarctic ecosystem has plenty of selection, however male southern elephant seals don’t love to combine it up,” says Professor Tracey Rogers, a marine ecologist at UNSW Science and senior creator of the examine. “They every have their very own favorite meals, they usually stick with them regardless of all of the choices obtainable.”
Hypothesis over specialisation
The examine discovered variation between people strongly correlated with their physique dimension. The heaviest seals ate additional up the trophic scale, or meals chain. In different phrases, they ate bigger energy-dense prey, resembling huge squid, main as much as the breeding season.
But it surely wasn’t the dimensions of the seal that decided specialisation. Even seals on the smaller finish that fed additional down the trophic scale on smaller fish had been excessive specialists from early grownup life.
“They had been all constantly choosy on their meals sort no matter dimension,” Ms Cormack says. “For these guys, who can lose as much as 50 per cent of their physique weight in the course of the breeding season once they’re fasting on land, what you select to eat might be crucial.”
The researchers do not know the precise reason behind the male’s choosy consuming habits however suspect it might be for a lot of causes together with gape dimension, which can dictate superb prey dimension and feeding approach, to fluctuations in seasonal and yearly meals availability.
Specialisation may even have a number of ramifications. Concentrating on totally different, however very specific meals sorts — even a subpar option- may assist enhance foraging success charges between male seals and permit them to realize the dimensions wanted to compete with different males for breeding rights.
“We all know from earlier research that people will typically return annually to the identical feeding grounds searching for their favorite meals,” Ms Cormack says. “However we want extra research to be assured about precisely what’s driving specialisation and the way it impacts breeding success.”
The looming local weather change menace
Because of conservation efforts, the southern elephant seal inhabitants has bounced again after being hunted to close extinction and is not thought-about endangered. Nevertheless, the danger of a brand new decline looms from the affect of local weather change.
For instance, climate-driven shifts within the Southern Ocean can change krill availability, which impacts the seal’s means to feed on its favorite meals additional up the meals chain. Moreover, rising pathogens like lethal avian flu strains additionally threaten to wipe out populations.
“The Western Antarctic Peninsula, the place these unimaginable animals dwell, is without doubt one of the areas experiencing the best modifications from ocean warming,” Prof. Rogers says. “The ice cliffs are virtually fully gone, and the intervals the place new ice types are getting shorter, altering the entire ecosystem. This might be problematic, with local weather change affecting meals useful resource availability throughout the Southern Ocean, which is why we want extra analysis.”
Future work would additionally profit from growing the pattern dimension to make the evaluation extra strong, taking a look at teams of male southern elephant seals from different colonies across the Southern Ocean, and extra satellite tv for pc monitoring to enhance our understanding of the seal’s dietary specialisation.
“We have established a strong basis of proof about how the person diets of male southern elephant seals range,” Ms Cormack says. “It will be nice to do extra longitudinal-type research to proceed constructing our data of male southern elephant seal specialisation and its impacts.”
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