TO sample plants on a hillside, botanists often stretch a line across the ground and see what is growing at, say, every metre. They call this a transect. I like to think of the tideline as a transect of the ocean, from the sea-bed right up into the sky. But my sample is usually of mortalities, recent and not so recent. Thus, on a gilded, frosty morning last week, my walk began with a bird and ended with a fish - both as it were, belly-up.
The bird was a female merlin, smallest and fastest of Ireland's falcons. Its bright yellow legs were suddenly longer in death, the way a human corpse's bony wrists can seem to stretch out in a coffin. But this is the merlin's true, even disproportionate grasp as it dashes up behind a lark or pipit.
In winter, it moves down to the shore, or out to the islands, to prey on small waders dunlin, sanderling, purple sandpipers. I last watched a merlin hunting on a stormy day on Inishkea and marvelled at its flying control so low above the sand. But sometimes, obviously, a gust is just too powerful, or a wave roars in at the wrong moment.
The fish was Balistes capriscus, the trigger fish, which swims vertically, like a dinner-plate, with undulating fins. The first spine of its dorsal fin is very strong and can be locked upright - hence the name - and the device must have its uses in a life spent largely in rooting around for sea urchins and shellfish in seaweedy holes among the rocks. It has a prissy little mouth but tough, thick lips and sharp teeth - a fish with a bite and a bad temper, as some aquarists have discovered.
The trigger is found most commonly around the Azores and in the Mediterranean. A few decades ago it was quite a rarity in Irish waters, but now an influx in late summer can almost be relied upon. One day last August, a neighbour lifting his pots near Old Head found no fewer than seven triggers in one pot, which must set some sort of record for Ireland.
Scientists have been interested in the changing habits of the trigger fish as a possible way to monitor global warming. But the casting ashore of dead fish in November - a regular occurrence in recent years suggests that the trigger is still a long way from surviving the colder, rougher conditions of our inshore seas in winter.
The recent stranding of many scores of Portuguese men-of-war (or what was left of them, after the storms) on Inch Strand in Dingle Bay could seem a related event.
But while Physalia, with its gas-filled pink-and-blue float, or "sail", is mostly an animal of warmer water, it is very much at the mercy of wind and current. The angled mounting of the sail (as in its more familiar miniature counterpart Velella, or by-the-wind sailor) is thought to be a device to disperse it widely across the ocean.
But just as Velella comes ashore in Ireland by the million, and at every stage of growth (I was picking up its tiny rafts in handfuls earlier this autumn), so Physalia can be herded into fleets in the Gulf Stream and swept ashore at random in Ireland and Britain. The last big Irish stranding on record was at Cape Clear in the early-1960s.
Each of these siphonophores (not jellyfish) is a whole colony of interdependent organisms. The float and its base are thought to bed one individual, each trailing tentacle another individual. The float is not always as big as pictures in books suggest. Kevin Flannery, the Dingle fisheries research scientist who spotted the multitude of Physalia gleaming on the strand at dusk, was disappointed to find their sacs about six inches long instead of the 12 they might have been at full growth.
Kevin is an adviser to Dingle's impressive Oceanworld and a great recruiter of unusual specimens from fish caught live by trawlers. But for a few weeks now the aquarium has also been nursing a small cluster of eggs I salvaged from the Thallabawn tideline, in the hope of hatching them out.
The eggs - grey, rubbery capsules like very small grapes - came ashore stuck in the neck of a plastic cylinder. I opened one and teased apart the jelly within. Under a magnifying-glass, the tiny, half-formed embryo had little shape, but reminded me somewhat of a cuttlefish - not a bad hunch, as things turned out.
Between marine experts in Dublin, Cork and Perpignan, the choice rapidly narrowed down to one of three sepiolid species, compact cephalopods four inches long or less, pink to purple in colour, and sometimes known to fishermen as "Mickey Mouse squids". The drawing shows the favoured candidate, Rossia macrosoma.
Sepiolids are caught accidentally in huge numbers by trawlers fishing for prawns on the Porcupine Bank, and then dumped back for lack of cocktail appeal. But little is actually known about their biology and development - hence the interest of university zoologists
There was a puzzle about the eggs. Sepiolids lay their eggs on the bottom of the ocean: how, then, could these float so gently ashore, like Moses in a basket?
The answer came when, hoping to hatch the last few myself, I launched the plastic container in a bucket of sea-water. It floated with perfect neutral buoyancy, the upper rim just level with the surface. A touch was enough to sink it, or to lift it in the water. Mere chance - nature's favourite device - had raised it from the deep.
