fishydreams

A couple of summers ago, before I began to write this blog, I joined a group of bird watchers on a trip into the Straits of Gibraltar in order to see what we might find by way of birds and cetaceans. We left Tarifa by yacht and spent some time in the straits, crossing to within spitting distance of the Morroccan coast. It was during the homeward leg of this trip that I was lucky enough to see a whale spout and when we approached, we chanced upon a sperm whale at the surface and had the rare privilege of taking a close look at it before it sounded and returned to the cold depths where it spends most of its life.

I do not know if I will ever again be fortunate enough see such an enigmatic giant but if I wanted to have a chance to make another sighting, this particular stretch of water, the meeting point of the Eastern Atlantic and the Mediterranean is an ideal place. The Straits of Gibraltar is considered the fourth best place in the world for dophin and whale watching. In addition to the sperm whales, there are pilot whales, fin whales and orcas as well as three species of dolphin; the striped, common and bottlenose.

Sperm whales can be found in every ocean and at every latitude making them, with ourselves, one of the most widely dispersed of all mammals. Surveys from planes and ships produce an estimated global population of some 360,000 and even though this appears an enormous number, it is only a quarter of the population prior to the use of the iron harpoon.

The sperm whale was given its binomial, Physeter macrocephalus (big-headed blower) by Linneaus in 1758 and it is outstanding in so many respects that it seems almost unreal.  For a start, it is the largest predator in the world. It has the largest brain of any animal. It has, reputedly, the most complex social interactions of any species apart from us. It produces such violently loud sounds underwater that it may use these to stun or even kill its prey. It has the lowest reproductive rate of any mammal (one calf per females every 4 to 6 years) and is very long lived. A 45 year old would be middle aged. Then, in taxonomic terms, it is unique in being the only member of its family.

Sometimes at school, if we happen to be discussing such things, a kid might ask about why these things are called sperm whales. This can be a bit of an awkward question but the answer is that the fluid, called spermaceti, which comes from the dead whale´s head reminded the early whalers of sperm. Sometimes I answer this question, sometimes I don´t!

The whale we saw was a big solitary bull. These old boys grow much bigger than the females and can reach 20 metres or so and 50 tons. It was brown in the bright sunlight and, if its jet of its exhaled breath had not shot into the air it would have been all but invisible because almost nothing of this giant clears the surface of the sea.

Curiously, the eyes of sperm whales are so situated on the sides of its wedge shaped head that it cannot see in front of it although it does have stereoscopic vision of the water below. If the whale wants to take a look above it, it may turn upside down to do so. Much has been written of the deep diving ability of these whales. One had the misfortune to become trapped by an undersea cable and drown at a depth of 1134 metres. Another, caught off South Africa, had in its stomach two bottom living symodon sharks which are found at a depth of 3000m.

Being air breathing mammals ourselves, it is tempting to imagine the sperm whale as a surface-breathing animal which feeds at great depths, but it is perhaps more accurate to suggest, though less intuitively easy to visualise, that this whale is truely a creature of the black depths (it normally feeds at depths between 300 and 800 metres) but which periodically rises to the surface to breathe. It is superbly adapted to swimming and feeding at depths which are pitch black even during daylight hours and, it seems to me, that its need to breathe at the surface, a legacy of its evolutionary history (its closest land living relative is the hippopotamus) is the only reason we see them at all.

It seems strange that these great lumps which, on the face of it, seem to possess the hydrodynamic grace of a double decker bus, should be such effective hunters. But they are. In addition to the squid of which they can consume between 300 and 700 per day they have been found to have consumed barracuda, tuna and sharks as much as 30 feet long and the combined annual consumption of these whales adds up to a staggering 100 million metric tons, fully the equivalent of the entire human annual catch of marine fishes.

Our own whale remained on the surface for around 10 minutes or so where it would have taken between 60 and 70 breaths. When it sounded its enormous tail was lifted completely clear of the water (this is a characteristic of sperm whales) before it sank out of sight into the water which, the skipper informed us, was 700 metres deep. If its dive was typical it would follow a U shaped trajectory in which the horizontal leg might be as much as 2 or 3 kilometres and it is interesting to think that it might well take its next breaths some two hours later after we had tied up again in Tarifa.

People often suggest, when they look at the night sky, that the stars and galaxies can give us a sense of how little our lives are, and how our survival is the result of a unique and fortunate set of happy accidents. And vast space seems hostile and a little frightening to us.You can get a perspective like this in the black ocean depths too where the sperm whale is at home.

This is a National Geographic picture. What a beast!

If you are interested in whales you might like to read this book. It is “mighty” as we Paddies like to say.