When you look for stars at dusk, the more you look, the more you see. When you look for the incomprehensibly weird, the same rule applies: at least, it does if you look at the wild world. And perhaps that rule counts double when you look at the sea, when, by necessity, the creatures' lives run wildly counter to our own understandings and expectations.

So I was out with my friends from Marine Discovery, taking one of their trips out to sea from Penzance, and I had an encounter with as weird a thing as I have ever seen. A fin, breaking the surface: but not a shark, no, nor a dolphin. The fin was slightly floppy and translucent, and when we got up close, the whole damn animal just flopped on to its side and lay on the surface of the water as on a fishmonger's slab.

A fish, yes, but what a fish. A fish's head, with a couple of fins stuck behind, pouting at us with a disturbingly sensual mouth. It just lay there, like a large dinner plate, as if floating on its side was the only way for a living fish to behave. It looked in deep trouble: but this is just the way of the sunfish.

It was a couple of feet across, which is nothing for a sunfish. They can get up to 10ft and can weigh a ton, which makes them the largest bony fish in the world. (Sharks and rays can get bigger, but they don't count as bony.) They live mostly in tropical seas and they eat jellyfish, and despite this habit of lying doggo, they can move swiftly enough when they have a mind to. There are stories about them leaping into boats with disastrous consequences for all concerned.

They are seen off the coast of Cornwall in the summer: no one is sure whether the more frequent sightings mean that there are more sunfish or more observers. And no one is entirely sure why they bask on their sides: one suggestion is that they do it to warm up after a spell chasing jellyfish in the deep. Another is that by basking, they make themselves available to creatures who eat their parasites.

There is mystery about sunfish, then, in most aspects of their lives. They look like living heads: I was reminded of the Face of Bo in Doctor Who, a bit of living tissue divorced from anything that looks like sense. And yet this is a fully functional living creature, with an urgent and effective way of life, with every bit as much right to call itself the crown of creation as the humans in the boat who gazed at it with so much astonishment.

Life on the ocean wave

When you make a transition from one place to the next, the birds change. This must be so, if you think about it: different places require different ways of life. If you move from lakeside to wood, the birds change and the music of the place is different: if you move from wood to hilltop, it changes again. Inevitably, that happens when you move from the seashore to the beginnings of the sea itself.

The edges of the land are the domain of what we call seagulls but are really shoregulls. But as you move a mile or more out, you move through some kind of passport control, and find yourself among the true birds of the sea. As we bounced across the waves, the birds we saw most were now gannets: the great spear-beaked fishers that pursue their trade by hurling themselves into the water from impossible heights. They are impressive things: the adults foam-white with ink-black tips to the wings.

Every so often, infinitely more agile, a small group of Manx shearwaters, dark, restless, close to the surface, constantly changing their angle of flight so that they will, indeed, seem to be slicing the water as they go. Unless you visit their nest colonies you will seldom see these from land: they are birds of the sea, and if you want to see them, you must take to the seas yourself.

And that is one of the answers to the great riddles of life: where do all the seabirds go in the winter, all the millions that nest on our shores? The answer is as simple and obvious as the sea itself: out into the frightening and forbidding waters that cover most of our wet and heaving planet.

Salt of the Earth

There are still a few fulmars to be seen on the cliffs: nesting in inaccessible places, with fat chicks almost ready for a winter at sea. Fulmars are only a bit like seagulls: they are actually related to albatrosses, and that makes them supremely talented at the art of vomiting.

They have a curious nasal tube which helps them to regulate the amount of salt in their bodies. When threatened, they will use this item of personal hygiene offensively. Moral: if you want to see something weird, a good way to start is by turning your back to the land.

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