Thursday, August 05, 2010
Krill are a small, shrimp like, animal that blue whales feast on all year long. One might think that it must be impossible to get enough energy from eating such small, little animals. Or that they’d have to eat way more krill to get the same energy they’d get from just eating larger fish. As it turns out, its actually much more efficient to eat animals lower in the food chain than higher!
I remember watching a video in my high school science class where the question was posed: Which is better? Eating grain or feeding the grain to the chicken and then eating the chicken? Of course it would seem like feeding the grain to the chicken and then eating the chicken would give us more energy. However, it’s actually more efficient to just directly eat the grain. It’s better to eat the grain because as energy is transferred up the food chain, only 10% is usable. For example, if krill had 100 units of energy and a fish ate the krill, only 10 units of energy would be usable to the fish. If a whale then ate the fish, only 1 unit of energy would usable for the whale. In the case of the blue whale, by eating lower in the food chain, they’re able to obtain more energy per unit of food by skipping the fish and directly eating the krill. If they ate larger fish, they’d have to eat A LOT more fish to get the same amount of usable energy. Pretty much all of the larger animals eat lower in the food chain. Think of the whale shark. They don’t eat large animals like other sharks do…they filter feed on small plankton like the blue whale!
Don’t get my wrong; blue whales eat a lot of food. They can eat up to 40,000,000 krill a day! That is quite a bit of krill to be eating in one day. Luckily, the blue whale is well adapted to eat like that. For example, they have ventral pleats. These are like stretch marks under the chin that allows their throat to expand so they can take in a lot of water…roughly 17,000 gallons in each gulp. This is very useful when you’re filtering out small krill that are less than the size of a penny. Their baleen is also well adapted for catching the krill. Different whales will have different types of baleen. For example, the gray whale has very coarse baleen because they feed in the mud, and the bowhead has very long, thin, baleen because they eat tiny copepods.
Last week we got a good look at some of the krill found off of California. A couple times a year we’ll see large gatherings of the krill off the coast at the surface. Normally the krill lives in much deeper water, but when the currents are just right, it gets pushed to the surface. We were actually able to grab a sample last week and take a really good look at it. It was amazing to see how many of these krill there were! Sometimes when the krill is at the surface like this, we’ll also get to see the blue whales feeding at the surface with their mouth open and ventral pleats expanded. If you’re interested in trying to find blue whales feeding at the surface, join us on our daily whale watching trips!
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