The unusual fish swimming in our warmer waters

ANOTHER LIFE:WATCHING HAIL squalls greying out the islands, and a chill viridian darkening the sea, it is hard to think of the Atlantic as being in any way warm, or getting warmer. The sea surface is now something over 11 degrees, if I've read Met Éireann's tables right. That's a few notches down from the August high (around 15 degrees this summer) and a fair way to go to the February low, worst off the northeast coast, where the shallow, wintry Irish Sea can dip below seven degrees.

Eleven degrees is warmer than the air as I write, however it would feel to a bare toe. But collected figures do now confirm the warming Irish ocean promised by climate change. The Atlantic was already working to a 50-year cycle, which puts it in a warm phase until about 2020. But temperatures filed away at Malin Head shows the present cycle to be half a degree warmer than the last one. Warming has accelerated since the 1990s, and record highs have been set in three years of this infant century. Along with such omens, the Atlantic is getting saltier, a lot more like the Mediterranean, in fact.

The new studies of marine climate change by scientists in the Marine Institute, NUI Galway and NUI Maynooth began with historic records. They included more than 50 years of data from the State's research station on the Burrishoole river, up the coast in Clew Bay, Co Mayo, measuring the declining fortunes of ocean-going fish, such as salmon, sea trout and eels. The Marine Institute adds its great database, built from annual surveys of stocks of commercial fish at sea.

THE FISH MIGRATING from our rivers could be doubly vulnerable, if climate change threatens their freshwater supplies of food through droughts and catastrophic floods. And salmon, like cod, are coldwater fish, adapted to timely hatches of particular kinds of zooplankton.

As warmer ocean currents flow north, these bring new patterns of plankton food and an abundance of new fish species used to eating it.

The Marine Institute's records show a gradual decline in coldwater species such as cod, "with a rising abundance of warmer water species such as lesser spotted dogfish, poor cod and even boarfish". Poor cod, as you might guess, is a mere hand-sized fish, not any kind of cod (though cod eat them) and caught in bulk for processing as fish meal.

Boarfish, too, is now reckoned an "industrial" species, but the "even" invites a closer look, as it is a distinctly pretty little subtropical fish with a nervous temperament that deserves better than being minced up to feed farmed salmon. It swims like a vertical saucer, some 13cm long, and, like miniature John Dory, it has spiny dorsal fins and a protrusible mouth that shoots out to capture shrimps and copepods. In deep water, as at the edge of Ireland's continental shelf, its huge eye comes into its own.

There it is flushed with deep red, but in shallower water the colour gets pink and stripy and this has been the look of the rare specimen washed up on Ireland's south coast.

The spines put off most predators, but shoals of boarfish are also swiftly mobile and good at swimming backwards. They are on the rise in the northeast Atlantic generally. In the Bay of Biscay, a French scientist, Fabian Blanchard, has described "the exponential abundance increase" that has turned a sub-tropical fish rare in the 1970s to a "dominant" species in 2002. He relates it to warming of the bottom waters during its breeding season, along with "its ability to invade and the absence of predators as well as the absence of fishing".

But the absence of human predation could be changing. Up to a few years ago, the little boarfish was reckoned a prickly nuisance, a discarded by-catch in the nets of pelagic fishermen trawling for herring and mackerel. In the Dutch pelagic freezer fleet, boarfish has been the commonest species in the 30,000 tonnes of fish discarded annually.

But in 2006, as quotas for other pelagic species declined, targeted trawling for boarfish began from Killybegs, Co Donegal: perhaps boarfish, like blue whiting, could repay pursuit for grinding into fishmeal. But there was one snag on return to the quayside. Boarfish was a light but bulky catch, its fins clogging up the chutes and silos, both of trawlers and factories.

Ireland's big crabbers, however, have been happy to take boxes of them as bait for their pots - bait not for crabs or lobsters, but for the conger eels that, extracted and chopped in pieces, make the best crustacean bait of all.

Ireland's Ocean: A Natural History, by Michael and Ethna Viney, has just been published by Collins Press