Sharks dine out on fast food

James Cook University’s Dr Adam Barnett said scientists evaluated the eating habits of broadnose sevengill sharks at Norfolk Bay in Tasmania, Australia.

The scientists used a bioenergetics model, which works out the energy expenditure of a school of predators and how much of a target species they need to eat to supply that energy.

Dr Barnett said that predators play crucial roles in the structure and function of ecosystems and mortality amongst prey species they eat can exceed that from fishing.

“But quantifying how much predators actually eat is difficult, and limits our understanding of the roles they play. This new paper integrates multiple types of information from a comprehensive suite of studies on sevengill sharks, and provides one of the first quantified estimates of predation rates for an apex predator shark species.”

The main prey consumed by sevengill sharks in Norfolk Bay is the gummy shark, also known as flake and widely used as the ‘fish’ ingredient in the fast food fish-and-chips meal.

Using three different models, each with two different estimates of the numbers of sevengill sharks present, researchers found the predators ate a minimum of more than 2200 gummy sharks and a maximum of more than 11,000 over a 36-week time period.

“Based on the average weight of gummy sharks in Norfolk Bay, that means sevengill sharks eat between 4 and 21 tonnes there annually.

“It looks likely they play an important role in ecosystem dynamics and this study shows how the integration of ecology and fisheries science can be used to provide data that benefit both,” he said.

Images available here – Please credit Morne Hardenberg and sharkexplorers.com

Link to paper here.