Now we know where sharks go in the winter months

ANOTHER LIFE:Arriving once, in innocence and at the wrong or right time (depending on one's sensibilities) at the cliffs above Achill's Keem Bay, I found myself watching the execution of a large basking shark trapped in nets in the water below. As a lance was thrust from the crowding currachs, the scene had little in common with bold battles in wild seas re-enacted for Flaherty's famous "documentary" Man of Aran. Blood trailed briefly through the limpid water as the beast was towed ashore for the great oily liver that made, perhaps, one third of its weight.

Forty years on from the peak of the Achill enterprise that killed 12,342 of the world’s second largest fish, Irish marine researchers have had an amazing summer. In forays off Inishowen in Co Donegal and around the Blasket Islands off Kerry, they caught up with no fewer than 101 of the sharks swimming at the surface and reached out from their rib with extendable painter’s poles to plant colour-coded tags in the dorsal fins.

Off Slea Head, they used satellite tags that will track two sharks for the next six months. And in a painless, biopsy-free innovation in DNA sampling, they scraped thin, black slime from the skin of each fish with a scouring pad tied around a mop handle.

Even a decade ago, remarkably little was known about the comings and goings of Cetorhinus maximus.What had been sorted out was its maximum size (rarely more than 10 metres) and phenomenal, open-mouthed throughput of ocean (nearly 1,500 cubic metres every hour) to gulp the pink-centred zooplankton, Calanus, that fills its stomach with something like tomato ketchup.

The big mystery was where the animals went in winter. Until quite recently, it was theorised that the sharks hibernated in the ocean depths, taking nourishment from the squalene oil in the liver. In fact, this low-density hydrocarbon gives the shark its buoyancy, needing the slightest tilt of the big pectoral fins to lift it from the seabed or hold it at the surface.

The sharks congregate in areas, often off headlands, where currents bring plankton to surface and gather it offshore. In Donegal’s Trawbreaga Bay, in the first of days of June, Simon Berrow and Emmett Johnston estimated about 135 of the fish were cruising there, similar to the assemblies that sometimes bring crowds to the cliffs of bays in Cornwall.

Dr Berrow’s name is familiar as leading founder of the Irish Whale and Dolphin Group and guardian of the Shannon bottlenose dolphins. But having worked successfully to secure protection for cetaceans in Irish waters, he has gone on to study the basking sharks, which still lack the Republic’s commitment to conservation. Emmett Johnston is the National Parks and Wildlife Service’s conservation ranger in Inishowen and fascinated with the sharks on his doorstep. He is organising a seminar in the National Fisheries College at Greencastle, Co Donegal, on October 30th and 31st with the aim of setting up an Irish Basking Shark Study Group (more on all this at baskingshark.ie, which also has a startling photograph of a shark breaching from the sea like a dolphin).

The IWDG has been logging records of the sharks since 1992, but there has been a rapid increase in reports since 2004 that cannot be explained entirely by more whale-watching effort or recording. Climate change has produced some big changes in the patterns of plankton “fronts” in the Atlantic and something like this, rather than overfishing, probably accounted for the eventual decline at Achill Head.

But it is the global decline in the species, part of the general overfishing of sharks for meat and shark’s fin soup, especially on the high seas, that has put them on the international Red List of endangerment and led to last year’s moratorium on their fishing in European waters. In Irish seas, the ban on salmon drift-nets has reduced the risk of accidental catching, but bottom-set gill nets are still a threat.

Meanwhile, satellite tagging has started to solve the mystery of sharks’ apparent disappearance from continental shelf waters in winter. It has shown that the fish remain active and embark on long migrations through deep water: in 2008, a female basking shark tagged off the Isle of Man released its tag off Newfoundland, Canada, having travelled for 9,589 km and reached a record depth of 1,264 metres.

On the west side of the Atlantic, this summer, satellite tags were placed on 25 basking sharks off Massachusetts. To the researchers’ great surprise, the big fish headed south, 18 of their tags popping up as far south as Brazil. It was the first time they had been recorded moving into tropical waters.

The apparently different winter habits of the sharks between the west and east Atlantic is another puzzle about the species. But their international travels prompt researchers on both shores to urge global protection for these inoffensive giants of the fish world.

Eye On Nature

A greeny-brown stuff that looks like seaweed appears in patches all over our yard after those very heavy downpours of rain. It can appear on gravel, on sand and on clay. It looks like it's fallen from the sky.Anne Ryan, Enniscorthy, Co Wexford.

Professor Michael Guiry, algae expert from NUIG, tells me that it is a blue-green alga called Nostoc commune. It is normally not noticeable on the ground but after rain swells up into a jelly-like mass which people thought had fallen from the sky, hence the name star jelly.

Among a flock of starlings I saw one that was pure white on the head, neck and part of the breast.Sadie McClintock, Dunkineely, Co Donegal

It was a leucistic or partially albino starling, a condition that occurs occasionally.

We saw a red squirrel on the Crossmolina/Ballina road at Ardagh crossroads. Some years ago red squirrels were released in Beleek Castle Woods in Ballina, could this one be an escapee?John Cosgrove, Crossmolina, Co Mayo

In a recent squirrel survey, that area and some areas in the southeast were the only ones in Mayo in which red squirrels were found.

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo. E-mail : viney@anu.ie Include a postal address