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Naturalist’s Notebook: May 24 to May 30
This week, as in the past several weeks, a number of different species have been observed from the Dolphin Fleet boats. They include both toothed and baleen whales. I thought it might be a good idea to talk a little bit about the differences.
There are roughly eighty species of whales in the waters of the earth. These eighty species can be divided into two groups based on what they eat and how they eat. The first group of whales are the odonticetes, or toothed whales. These are the vast majority of the whales, comprising about 65 of the 80 species, and include all of the dolphins, the porpoises, belugas, orcas, and sperm whales. These animals have teeth in their mouths and catch their prey items one at a time. The other group of whales, roughly a dozen or so, are the mysticetes, or baleen whales. They include most of the really big animals like humpback whales, blue whales, finback whales, right whales, and minke whales. These animals have baleen in their mouths and catch their prey items in large mouthfuls, rather than one at a time.
Lets start with the odonticetes. These animals all share several, common characteristics. On the tops of their heads, they each have a single nostril, or blowhole. They use something called echolocation to navigate through the waters and to find their prey. Echolocation is fairly similar to the sonar that has been developed by the navy and private enterprise. Simply, you emit a beam of sound into the waters around you. It travels away from you and bounces off objects in your environment and returns to you. Based upon the return you get, you can tell things about your environment. You can tell things like how far away objects are, how large they are, whether or not they are moving, and, most importantly, whether or not those objects are food. It is the toothed whales that spend most of their lives in close, tight-knit social groups called pods. Some live in small pods of just 3 or 4 animals and some live in very large pods of 3 or 4 hundred (or even a thousand) animals. Regardless of the size of the pod, all of the animals in the pod will spend the vast majority of their lives living within the same pod. Some of the members may depart for a while to forage or to mate with members of another pod, but they will return to their pod after a short time. And, of course, what makes these animals toothed whales is the fact that they have teeth in their mouths. Some have just two teeth and some as many as two hundred fifty. Regardless of how many teeth are in the mouth of any one animal, all of the teeth in that mouth have the same shape and same size. In our mouths, our teeth have many different shapes and sizes. In our mouths, all of our different teeth have different jobs. In the mouths of toothed whales, all of the teeth have the same shape and size because they have the same job. That job is to grab prey items out of the water and swallow them hole. There is no chewing going on in the mouths of toothed whales.
The mysticetes also share things in common.. On the tops of their heads, they each have two blowholes rather than one. They do not appear to have the ability to echolocate. That does not mean, however, that they are not viewing the world around them with sound. Light only penetrates about 30 or 40 feet here, meaning that these whales are spending as much as eighty percent of their time, or more, in nearly total darkness. They are viewing the world around them through the sound they receive through their hearing, hearing fairly similar to that of human beings. In fact, the inner ear structure of most cetaceans is fairly similar to that of human beings. Baleen whales do not live in pods, the only long term association between baleen whales is that between a mother and her calf. The mother will spend the best part of the calf’s first year with it, but once it has been weened from its mother’s milk, the two will go their separate ways. Once they do, it is no more likely that you will see them together than you would see either with another member of the population. The female will give its calf just one year of maternal care and, in which, will teach it everything it needs to know to be a whale. So she will try to teach it, in its first year, everything that we try to teach our children in their first fifteen or twenty, or forty, years. (As mammals, they are still social animals. Social interactions are short term things, ranging from a few minutes to a few hours or even months. But even a few months, in the life of an animal that might be over a century, is a short period of time.) And, of course, what it means to be a baleen whale is to have baleen in your mouth instead of teeth.
Baleen grows down from the upper jaw in triangular-shaped plates. The short side is embedded in the gums. The side facing the outside of the mouth is smooth and flat. And the side that faces the tongue is lined with hairs or bristles that range in thickness depending on the prey species the species of whale focuses on. Generally, several hundred plates hang down from the left side of the upper jaw and several hundred hang down from the right side of the upper jaw. When combined, they form a horseshoe-shaped curtain, like your teeth hang down from your upper jaw.
Baleen is a way to separate food from sea water. Fish-feeding baleen whales have a variety of ways to scare their schooling fish in to a tighter ball. Once they have done so, they open their mouths and lunge through the school of fish, taking in as much of the fish and seawater as they can. Large whales can take as much as 15,000 gallons of fish and seawater in one mouthful.
Now, the whale has a mouthful of fish. It does, also, have a mouthful of seawater. Whales are mammals, just like you and I. Just like you and I, whales do not have kidneys that can process large amounts of saltwater. They need to get rid of that water. That is where the baleen comes in. The whale closes its mouth and uses the strong muscles of its throat and tongue to push all of the fish and saltwater against the back or inside edges of its baleen. The water is pushed out between the gaps between the plates and the fish is left trapped by the bristles on the inside edges of the baleen plates (where it crisscrosses over the gaps and creates almost a fishnet to trap the fish). So the whale can now swallow a mouthful of fish that might be as much as a hundred or two-hundred pounds down a throat the size of a basketball.
It’s kind of like when you come down for breakfast in the morning and you fill your bowl with rice krispies (because they talk to you) and milk. Then you decide you only want cereal in your mouthful. So you clench your teeth together and use your tongue to push the cereal and milk against the back edges of your teeth. The milk escapes from your mouth through the gaps between your teeth and the cereal is left behind for you to swallow.