A few weeks ago, some friends in my grad program and I were working on various research proposals for a class. One of my friends happened across a paper discussing blue whales and discovered the word “Stenophagous”: feeding on a limited variety of foods. This word stuck with me, because it really described my eating habits too, and since it was such a cool-sounding word, I wrote a post about it. The challenge at the bottom of the post was to guess the animal.
There were a number of really good guesses – snail, plankton, wood warblers, dinosaurs (stenophagosaurus – new species!), koalas, Evergaldes Kite, sea snails, parasitoid insects, Cownose Ray, Fiddler crab, mussels, and sulfur-eating bacteria. But the closest guess goes to Jessymum, who speculated “What about the Whales – don’t a lot of them feed JUST on plankton??” She’s mostly right, so we’ll give her the prize. (Congratulations!! Now what was the prize? Bragging rights, I do believe ;)) Great job to everyone, though! Everyone who played learned about an organism that could be considered stenophagous, and that’s half the fun. I will also tell you that this is NOT what my field of research is about, but I do like whales quite a bit, so it was really fun to write this.
The Blue Whale is the largest organism that has ever lived. It’s even bigger than the biggest dinosaurs. As an adult, it can reach sizes of upwards of 30 meters (100 feet) in length! It can also produce incredibly loud sounds at very low frequencies – it might be the loudest animal on the planet, too. It is part of the “Balaenopteridae” family, and considered a “Rorqual Whale”, which basically just means it is a baleen whale and has a series of skin folds running along their necks that allow for expansion after the intake of big gulps of water. They can way nearly 200 tons (or about 400,000 pounds!) and in general, males are a little bit shorter than females. The scientific name, “Balaenoptera musculus” was given to this majestic creature by none other than Linnaeus, himself (the person who basically invented the taxonomic classification and naming system we use today). The genus means “winged whale”, and the species name “musculus” is either “muscular” or “mouse” – it’s possible that the name was partially a joke.
The blue whale is found mostly all over the world, except in the Arctic Ocean. It’s thought that they might be different populations or subspecies in different regions, however that’s still at least somewhat up in the air. They were heavily hunted during the commercial whaling period, due to their large size, however as they are fast swimmers and live offshore, they weren’t hunted until technology became more advanced and people were able to keep up with them and hunt offshore. Due to their large size, and slow reproduction, they were quickly hunted to very low levels, and are now protected by international law.
Despite being the largest organism on the planet, the blue whale eats some of the smallest: it feeds exclusively on krill (euphasiids), a plankton group (living up in the water column) closely related to lobsters and shrimp.
Krill are pretty small, usually never more than a couple centimeters long, and are really interesting creatures. They are quite often found in large aggregations, or swarms. And this is where the blue whales come in.
Blue whales are huge animals, and they require a large amount of food to sustain their large size. Consequently, they eat organisms much lower on the trophic pyramid – that’s where more energy is, so its better for the whales to eat them, as opposed to say, tuna or other larger fish – there’s more of them, and they’re easier to catch. You’d think, with their size, that blue whales couldn’t afford to be picky, but picky they are. Because its so much work to open their large jaws, they don’t bother to take a bite until there’s enough krill to make it worth it. When they do, they open their mouths and engulf an entire swarm of them. But they only eat krill. And so, the world’s largest animnal is considered a stenophagous feeder. Bon Appetite!
(Image from http://review.ucsc.edu/summer-02/wind2whales.html Photo by Doc White/Seapics.com )
Reeves, Randall R., Brent S. Stewart, Phillip J. Clapham, James A. Powell. National Audubon Society Guide to Marine Mammals of the World. Chanticleer Press, Inc., New York, NY. 2002.