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Professor David Raubenheimer dissecting snapper at Massey’s Marine Pathology Unit at the Albany campus

 

Study gets to the guts of snapper diet



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Snapper, or ‘tamure’ in Māori.

Snapper is a favourite fish dish of many New Zealanders, but new research will find out what these fish themselves eat, and why.

Massey University nutritional ecologist Professor David Raubenheimer says his research could not only provide vital knowledge for conserving the species to ensure it remains in abundance in our waters and on our menu, but could challenge existing theories on predator foraging.

“Ecologists hold a long-standing belief that the goal of a foraging predator is to maximise energy gain, but recent studies suggest this may not be the case,” he says.

The study is the reason Professor Raubenheimer will be putting a ‘Gone Fishing’ sign on his office door in the coming months. He and postdoctoral researcher Dr Alice Tait plan to catch hundreds of snapper from several regions around New Zealand, then analyse their gut contents.

They will compare the diets of snapper in the Hauraki Gulf, the east coast of Northland around the Kerikeri peninsula, and the west coast of the North Island in different seasons to determine whether differences in food sources provide the same nutrient mix.

The researchers will relate variations in nutrients they find in these populations to differences in growth rates, age, reproductive health and body composition. Snapper survive on shellfish, sea eggs (kina), crabs, worms, molluscs, crustaceans and plankton, jellyfish, and small fish species such as anchovies, pilchards and sprats.

But the ultimate aim of the study is to find out if snapper select food that gives them a balanced nutritional diet relevant to their needs, or if they simply eat whatever comes their way for instant energy. This knowledge is critical for understanding potential impacts on snapper of changes to their environment and food sources, and how this might be managed from a conservation perspective in the future, says Professor Raubenheimer, at the Institute of Natural Sciences, Albany.

“Predators in laboratory setting can distinguish between the energetic macronutrients protein, carbohydrates and fats, and prioritise gaining these in balanced proportions,” he says. “We aim to perform the first ever test of whether this balancing of nutrient intake drives foraging behaviour in wild predators, using New Zealand snapper as a model.”

Previous studies he and other researchers have done of herbivores such as gorillas and spider monkeys, and omnivores such as rats, cockroaches and humans, have shown they do select food in order to have a nutritionally balanced diet.  

He says the findings could provide “an entirely new perspective for understanding the dynamics of food webs” – a point he argues in his new book with co-author Steve Simpson, due to be published by the Princeton University in 2012.

The study will also compare dietary differences between snapper in marine reserves, such as the Hauraki Gulf, and those outside. Professor Raubenheimer says such information will be useful for the Department of Conservation, which has partly funded the study, for species management.

Snapper belong to the sea bream family and in New Zealand grow to over 80cm in length. They are the most commercially caught species in New Zealand.


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