Swimming downwards, the whale pelts head-first towards a large group of sea lions. After it opens its mouth and takes a huge gulp of fish, a sea lion darts across its back in hot pursuit of an anchovy that got away.
This is a glimpse of some of the footage captured when marine researchers in Monterey Bay, California, put video tags on humpback whales and watched them lunge feeding on bait balls.
Lunge feeding is when the whales herd fish into a tight group then propel themselves towards them, taking a massive mouthful and filtering water out through their baleen plates.
The footage is part of a new study published in Philosophical Transactions of the Royal Society B: Biological Sciences that revealed humpbacks fed more often when California sea lions were also foraging with them.
The whales seemed to feed faster and had shorter breaks between lunges when sea lions were around, according to the study. “Across 1,808 lunge-feeding events, whales foraging with sea lions exhibited a 23% higher feeding rate and a 16% shorter inter-lunge interval,” write the authors in the paper.
Whether or not sea lions were there didn’t change the whales’ speed, acceleration or manoeuvring capabilities. This suggests their presence doesn’t affect how much energy the whales use for each lunge.
And the humpbacks foraged for the same length of time whether sea lions were present or not.
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The researchers suggest the whales gained more energy when their foraging buddies were hunting nearby, probably because the sea lions help to bundle the fish into more concentrated bait balls. This allows the whales to find and capture food more quickly.
The scientists also think that both the whales and the sea lions may benefit from foraging together. The humpbacks have an advantage because the anchovies are crammed together in denser groups while the sea lions can pick off fish that are stunned or knocked away from the safety of the group by the whale’s attack.
“We observed sea lions foraging on individual, slow-moving anchovies separated from the school by humpback whale lunges,” write the authors.
Their different modes of hunting may also reduce competition between each other. Humpback whales try to eat as many fish as possible in one giant gulp while sea lions go after one fish at a time.
“If this association were more competitive, we would expect to see increased manoeuvring expenditure of humpback whales when sea lions are present, as they work to avoid or outmanoeuvre the other species,” write the authors.
By feeding together, both species enjoy more success. But are they choosing to work together or have they just both been tempted in by the same prey?
The experts aren’t sure, writing: “whether whales actively track sea lion activity or both predators simply converge on anchovy schools remains uncertain.”
Video and image credit: videos taken under NMFS permit #26602
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