When I was a kid there was a small convenience store located about a mile from my family home. Whenever I had gotten a hold of some money, I would walk there and spend it on candy, carefully doing the math to get the most “bang for the buck.” Sometimes my mom would send me to get an item that we had run out of, but the family shopping was done by car in a larger store. We all know that buying in bulk is cheaper and to do so it takes some more powerful means of transportation to haul the bounty back.
The same principal can be applied to feeding strategies in the ocean. There, we have particle feeders and filter feeders. A sea lion for example is a particle feeder, eating his daily share one fish at a time. This means that the sea lion needs to find the fish, focus in on an individual, chase and catch it, then eat it and do it all over until the belly is full. Baleen whales employ a different strategy; they find a school of small fish or a swarm of krill and lounge into it with mouths wide open. Special grooves on their throat expand to make room for all the water that gushes into their mouths, then a powerful tongue pushes the water through a curtain of hard bristles called baleen, in which the fish or krill get trapped. If the school of fish or the swarm of krill is dense, this method of feeding is highly effective, allowing for the consumption of huge amounts of calories all in one big bite. Right whales use a different method of filtering; they just swim along slowly with their mouths open and let the krill and copepods get trapped in their fine, long baleen. Gray whales turn sideways and use their jaws like a plow, filtering the mud rather than just water; you might say they are gold panning.
It is easy to find lists of what these whales eat, since that information can be gleaned from observation, but it is more difficult to estimate how much they eat. Blue whales, the biggest whales in the ocean, eat mostly krill. Krill are planktonic crustaceans that occur in large swarms. They live in all the world’s oceans but are most abundant in upwelling regions and in the cold polar regions. In the Antarctic, krill grow to finger length and build huge swarms that feed on ice algae. In our part of the world krill are also an important player in the ocean food web, but they are only half the size of their Antarctic cousins. Nonetheless, krill are an important item in the baleen whales’ diet because they contain about 50% fat and 25% protein, which makes them incredibly nutritious. In comparison, feeder fish like herring and sand lance, which are also in the food spectrum of humpback and fin whales contain about 5-8% fat and 15-20% protein. In terms of energy efficiency, it makes sense for the whales to seek out krill.
Bigger whales need more calories, so they go where the krill are most abundant. In fact, when reading about whale evolution I recently learned that baleen whales evolved as filter feeders long before some of them started to grow to giant sizes. It is theorized that the distribution of krill may be to blame for the large size of some whales! The patchy distribution of krill has to do with the icy polar caps of the planet. In the ocean, a general rule is that cold water is more productive in terms of biomass, while warmer water has more species, which are more specialized. On the other hand, a warm-blooded animal living in the cold has to spend a lot more energy staying warm (we can relate this winter in Kodiak!). One solution for the smaller filter feeding whales was to follow their favorite prey, krill. However, during the winter months reduced numbers of krill no longer make up for the increased energy loss. The whales went back to where the water is warmer and they need less food. Hence, whales evolved big bodies that are better adapted to long migrations, the ability to store large amounts of energy in the form of fat and to live from that for many months, and the ability to eat and store huge amounts of food in a very short time.
About 3 million years ago began the glaciation of the planet’s poles and with that upwelling regions in the world oceans and a growing patchiness in the distribution of whale food. The planet went through a major climate change event; only it was the opposite of what we are now experiencing. Then, the world was cooling while now it is warming. There are good and bad news in this story: the good news is that whales have been around for so long and have survived through so many changes, that it is unlikely that they will all disappear on our watch. On the other hand, the large whales evolved to deal with the world oceans patchy resources, and if there are no longer predictable large biomasses of krill in the northern seas, that life model may no longer be suitable for the new, warmer ocean.
You may have noticed that I have been writing about whales a lot this winter. There is a reason for that: I am involved in a group of energetic people who are working on organizing events for a celebration of whales in general, and in particular the annual migration of the gray whales past Kodiak. may be smaller than it was in the past, but we are bringing whale fest back to Kodiak in 2020! The time is the month of April and a schedule will be distributed in March. If you are interested in helping the efforts, please join our meetings posted on the Kodiak Whale Fest Facebook page (https://www.facebook.com/groups/Whalefestkodiak/). Hope to see you at the events to celebrate the amazing creatures we have the pleasure to share our world with!