Giant of the sea may be making a comeback

IN A WILDLIFE equivalent of the Olympic Games, Irish animals would win gold and silver medals. The gold would go to the blue whale, for being the largest mammal ever to have lived.

This enormous beast used to be fairly common in our waters but is rarely seen nowadays and only just qualifies as an Irish species.

It generally keeps well out to sea and only one was ever stranded here. The record for the biggest blue whale goes to a 190-tonne, 28-metre long female, caught in the Antarctic Ocean in 1947, the largest animal ever recorded anywhere.

The silver medal would go to the basking shark, for being the world’s second largest fish. This is a true Irish resident but the great fish is also found in the Pacific and Indian Oceans. It has favourite haunts, such as Lambay Achill and the Calf of Man, where it congregates in particular seasons.

The shark is in the news just now. Some diving friends of mine encountered one, just off the harbour in Achill last week. There were sightings out at sea later in the day but these might have been of the same fish. According to Simon Berrow on the Mooney Goes Wild radio show, eight basking sharks were observed off the Inishowen peninsula in County Donegal and there have been reports of over 100 off Valentia in County Kerry. Such a large gathering would be unusual but by not means unprecedented. In the summer of 1998, hundreds were observed off the Lizard in Cornwall.

Basking sharks can be up to 10 metres long. Only the whale shark is bigger; one killed off the coast of Pakistan in 1949 was 12.65 metres long and is estimated to have weighed between 15 and 21 tonnes. The two giants have similar lifestyles but the whale shark likes warm tropical waters whereas the basking prefers cooler temperate seas. Both fish are plankton feeders. The basking shark has an enormous gape. With its mouth wide open, it moves through the water, like a giant vacuum cleaner, at speeds of up to 5km per hour. The water entering its mouth exits through five pairs of gill slits. Estimates of the throughput vary from 2,000 to 6,000 litres per hour. The gills act as filters, collecting plankton from the water. Thus, one of the sea’s largest creatures feeds exclusively on some of the smallest. The main items in the diet are copepods, tiny crustaceans. The shark still has teeth, inherited from its voracious ancestors, but these are tiny, rendered redundant through natural selection. This great beast is docile, totally harmless and not too fearful of humans. Divers can even approach and swim with basking sharks.

Michael Viney in his “Ireland, a Smithsonian Natural History” gives an interesting account of the shark’s fortunes in Ireland. It’s not a happy story. At the beginning of the 19th Century, the basking shark was one of the main stays of the Irish sea fishing industry. Only the herring was more important as a prey species. The huge dorsal fin of the shark protrudes from the water and, in calm weather, a fish is easy to spot. Fishermen would approach the shark quietly, in a small boat, and plunge a harpoon, with a rope attached to it, into the fish. It could take several hours for an exhausted shark to be captured. The enormous liver would be removed and boiled in cauldrons to extract oil. This would be sold as fuel to power lamps, streetlights in cities and the lanterns of lighthouses. According to Michael Viney, between 100 and 200 sharks were killed in a single day in May, 1815 off the Sunfish Bank west of Inishbofin, County Galway. Such levels of exploitation could not be sustained and shark numbers declined.

Then a new technique was developed to extract oil from coal. This was a less labour intensive way to produce oil and the shark-fishing industry collapsed. There were attempts to revive it from time to time. Five men drowned when a shark capsized a boat off Inishbofin in 1873 and, thereafter, the hunting of basking sharks virtually ceased. Shark fishing was revived off Achill at the end of World War II, when there was an acute shortage of industrial oils. Up to 1,000 sharks were killed annually, 1,800 being caught during 1952 alone. The Achill fishery closed in the mid 1970s.

Almost all of the sharks caught by fishermen are female. Just why males should be absent is not understood. The life-cycle of the basking shark is a bit of a mystery. Until comparatively recently, it was not even known whether the shark laid eggs or gave birth to live young. Then, in 1936, one caught off Norway gave birth to five young while being towed into port. Male sharks have a pair of copulatory organs, called claspers, and fertilisation is internal. The eggs hatch within the body of the female but the young are not born for about three and a half years. Sharks have no equivalent of a mammal’s placenta, however; the eggs, and the young which hatch from them, are retained only as a protection against predators.

That sharks are being recorded off Ireland in such numbers this year is heartening. Perhaps the great fish is staging a comeback. If so, shark watching could soon become a major Irish tourist attraction.