|Dolphins > Feeding|
The mysticeti are the vacuum cleaners of the marine world, scooping up huge quantities of food, chiefly plankton and krill, both of which are some of the richest sources of protein available. You can try catching this for yourself with a very fine net when you next visit the sea. After dragging it through the water for some minutes, you will find a minute quantity of a jellylike substance in the bottom of the net. This is plankton and on examination with a powerful magnifying glass, is seen to be composed of minute plants and animals. If Jonah found himself in the stomach of a whale it certainly was not one of the group mysticeti, which can only swallow objects of a few centimetres in size. It is interesting to note that Dr. Alan Bombard fed himself mostly on this substance while crossing the Atlantic in the rubber dinghy "Le Herotic", the fresh water in the plankton augmenting his water supply. Krill is composed of larger creatures such as very small shrimps etc.
The odontoceti which include the dolphin species found here in the Bay of Gibraltar, are hunters and take a much wider range of food than the Baleen Whales. On examination, the immediate difference is that they all have teeth. These are not generally used to render the flesh of their prey, but to stop it escaping when caught. An exception is the Orca or Killer Whale who does use his teeth to kill and break apart his prey and is able to take large animals such as seals and dolphins and frequently does so. We were in the Bay of Gibraltar one day amongst a large school of Common Dolphin, who were quietly playing on the surface, when suddenly they exploded into a line abreast high speed dash. On looking around, we suddenly saw a large Orca about 400 yards away. Our little friends had picked him up on their sonar and were leaving at about 40mph! We followed and it was over 4 miles before they stopped and settled down to their previous routine. They obviously were not taking any chances!
Most of the odontoceti seem to hunt in an organised manner. We have seen a large shoal of Garfish corralled into a compact group by about a dozen dolphins, who were taking it in turns to swim through them at high speed and catching several before coming out on the other side. Flying Fish are another favourite food of the dolphin and provide a good example of the contest between creatures that ultimately influences their development. The flying fish has learnt to fly to escape from predators and can travel long distances down wind at high speed. The dolphin however, has learnt to swim even faster and is invariably awaiting the fishes re-entry into the water with the inevitable result. If you want to see a dolphin swimming really fast, then this is the time to do so. It also demonstrates how well they can see out of the water.
Dogs live in a world that is painted in pictures of smell. You only have to see how a dog stops at every lamp post and how they greet each other to realise that this is so. Most of their foraging for food relies on this sense and is most effective when the animal is down wind from its quarry.
The cetacean world however has to be painted in terms of sound, because the medium they live in has poor visibility and total darkness at great depths. Sound has a further advantage that underwater it is not dependent on the direction of currents and carries enormous distances. When used with an extremely well developed sense of hearing, it can provide cetaceans with a great deal of information about their surroundings.
Cetaceans find their food by using sonar in the same way as bats do. They emit a series of high pitched clicks or squeaks and then wait for the echo to return. The direction and time taken for this return supplies them with the information as to the bearing and distance from them. Not only this, but because they can vary the frequency and power of the sound beam, they can receive further information as to size, shape and density of the object being scanned. Consequently, when a Sperm Whale is many thousands of feet below the surface on the sea bed in total darkness, he is still able to find the squid upon which he feeds.
Possibly one of the reasons that a powerful animal like the Orca does not attack humans in the water, even though we might be wearing a black wet suit and look rather similar to a seal, may well be that his sonar informs him that we are a very different air-breathing creature. The air escaping from the relief valve of the scuba gear and the echo from the metal air tanks inform him of this fact. This was confirmed during a conversation we had last year with BBC cameraman Martin Saunders, who had filmed with the Killer Whale in the open sea.
We are now starting to see that the cetaceans are a special and very unusual life form. They may collectively take large quantities of food from the sea but this has not been a problem until recently. Man with modern methods of fishing is now gradually emptying the oceans of their fish stocks. Some countries have misguidedly sought the solution to this problem by trying to eliminate the cetaceans that are to be found in their waters, namely Japan and some of those countries around the edge of the Black Sea. Even if all the cetaceans were eliminated, there would still have to be stringent controls over quotas and stocks, as there would still not be enough to supply world demand. It would appear that a possible solution to this problem could be a much higher emphasis on fish farming, thus helping to preserve the only other creature, apart from man, that has an intelligent consciousness. In the next part of this guide we shall be discussing this intelligence.