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Shark liver and giant squid on seal sea-food-and-eat-it diet

25/07/2016 11:30:00 a.m.


A first of its kind study may make selfie-snapping tourists take a step back from the seemingly indolent New Zealand fur seals scattered around our craggy coastlines.

A study of the DNA in the seals’ faeces is revealing their true identity when they hit the water, from the bottom up — through their diet.

Analysis of the samples collected around New Zealand gives a much more accurate picture of what they eat than before. It includes giant squid and sharks. Big sharks.
 
However these Hannibal Lecters of the ocean are nonchalant about taking on the feared predators: they just eat the nutrient rich livers of the sharks and some stomach.

Their diet also includes commercial fish species, which make up 10 per cent of the species identified.

One of the study’s authors, Lincoln University Associate Professor Adrian Paterson, says up to 46 fish, and 18 squid and octopi, species were taken at any one sample site.

“The major finding was that seals seem to eat pretty much anything that they come across.

“Sharks and other cartilaginous fish seemed to be more important than previously thought to fur seals and there is evidence that they can predate even very large sharks, where they take just the choice parts (livers and stomachs).”

However, the DNA method does not reveal the proportion a species could make up of the diet.

“The commercial species might make up 80 per cent of the numbers consumed or 8 per cent. So there is potential for conflict with human fishers. On the upside, given that the seals appear to be very generalist feeders, it seems unlikely that they would focus on any particular species.”

This study is the first application of a DNA-based methodology to identify prey species of New Zealand fur seals.

It uses a technique called massively parallel sequencing to identify what species have been eaten.

Associate Professor Paterson says the New Zealand fur seal numbers are growing as quickly as it comes back from the edge of extinction that they are coming into conflict with fishers who feel that the increasing populations are competing with them for preferred fish species.

“Here, the emphasis is on colony-level diet reconstruction, which will provide marine ecosystem managers with a level of resolution necessary for most conservation plans.

“Knowledge of fur seal diet is essential to conservation and management strategies,” he says.
 
Access Identifying prey items from New Zealand fur seal (Arctocephalus forsteri) faeces using massive parallel sequencing here: http://link.springer.com/article/10.1007%2Fs12686-016-0560-9
 

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