Quality, not quantity, important in whale food

During the FV Margiris Abel Tasman supertrawler fiasco, one issue that worried people was the impact of overfishing on marine ecosystems. But recent research suggests that, at least for some whales and dolphins, getting the right food is more important than getting enough food.

This study looked at the diets of 11 species of cetaceans (whales and dolphins) in the North Atlantic and found a close correlation with their ‘cost of living’, i.e. those species whose muscles burn more energy tended to seek out higher calorie food (Spitz J, Trites AW, Becquet V, Brind’Amour A, Cherel Y, Galois R & Ridoux V 2012, “Cost of living dictates what whales, dolphins and porpoises eat: the importance of prey quality on predator foraging strategies”, PLoS ONE, vol. 7, no. 11, e50096, doi:10.1371/journal.pone.0050096).

A sperm whale eating a fish on the ocean surface near Kaikoura, New Zealand (click to embiggen)
A sperm whale, Physeter macrocephalus, eating a fish on the ocean surface near Kaikoura, New Zealand. Sperm whales normally feed in the ocean depths rather than the surface, but this one was clearly being opportunistic – and in fact they were one of the species found to get by on low quality, don’t-care-what-they-eat-as-long-as-there’s-enough food. The classic ‘see food’ diet, if you will. (Photo by Richard Giddins, via Wikimedia Commons)
This was independent of body size, as some similar species – such as the Common and Striped Dolphins – had very different feeding patterns.

The researchers put this down to evolution, in that high-energy prey moves faster, so their predators need to burn more energy to catch them – which means that in turn the prey needs to move even faster to escape, and so on.

The implications for conservation are that some whales and dolphins need the right kinds of high quality food to survive, so we can’t just assume that large amounts of low quality ‘junk food’ will be good enough.

(This story aired on 6 December 2012 – you can listen to the podcast.)

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