Giants of the Celtic Sea

Lenny Antonelli reports on the many questions that surround the behaviour and migration of fin whales in the Celtic Sea Published in Science Spin magazine, November 2007. This is my edit, not the magazine's. With thanks to the Irish Whale & Dolphin Group.

Right at the southern edge of Ireland, in the open expanses of the Celtic Sea, lives the second largest animal that ever existed on our planet. Here the fin whale (Balaeonoptera physalus) thrives, feeding on herring and sprat among other species. It grows to about 20m in length, weighs between 50 and 70 tons, and its blow can extend over six metres into the air. Only the blue whale is larger.

But it is only very recently that we have become fully aware of the presence of these giants off our south coast. The reason we’ve only heard about them recently, however, is quite simple - the experts have only really become aware of their presence recently too. It was in 1999 that Padraig Whooley, a cetacean enthusiast and currently sightings co-ordinator for the Irish Whale & Dolphin Group, moved to west Cork and began to look for whales from the Old Head of Kinsale. He soon realised that west Cork is, as he describes it, a “mecca for whalewatching”.

Zoologist Dr Simon Berrow, the IWDG’s founder and current co-ordinator, explains: “After Padraig started doing the whale-watches we realised that a pattern was emerging and that the fin whales were coming back year after year. We realised that this was a regular thing and not just a once-off.”

West Cork quickly gained prominence among cetacean (whale and dolphin) enthusiasts, with common and bottlenose dolphins, minke, humpback, and fin whales all to be seen regularly. It wasn’t long, though, before it became apparent that fin whales weren’t just confined to the waters of west Cork. “Our original thinking was that they were just off Cork, then it became the whole south coast, and then it became the south west too,” says Berrow.

Indeed, a quick glance at ISCOPE, a powerful digital tool on the IWDG’s website that allows users to generate maps of species sightings off the Irish coast over any time frame, brings up a huge cluster for fin whales over west Cork, with smaller clusters over east Cork and Waterford, and some scattered dots around Kerry.

Padraig Whooley laughs at his own explanation for the distribution of sightings: “I think it's very much the case that the distribution of sightings reflects the distribution of whalewatchers.” Whooley has spent many days at sea off west Cork recently, camera in hand, as he attempts to photographically catalogue the fin whale population. To date, 29 individuals have been identified, using natural physical markings such as patches of discolouration, nicks on their fins, or scars. “We’ve only touched the surface. There are lots more out there that we haven’t photographed,” he says.

Fin whales – close relatives of other giants such as blue and sei whales - are distributed worldwide, but tend to be less common in polar and tropical waters. They can be spotted off our south coast for almost ten months of the year, generally occurring in small feeding groups of three to eight. They are usually first seen in the waters of the south west in late May or June, persisting right through until February, with their distribution seeming to move eastwards towards Waterford and Wexford when they leave west Cork in December. “When we stop seeing them in west Cork, they start picking them off Ardmore head in Waterford,” Whooley says.

According to Berrow, the explanation for this is simple – they are following their food. “We're pretty confident that the individuals we see in west Cork are the same individuals that are seen further east in Waterford and Wexford. This pretty much mirrors what we know about herring, which spawn in the west earlier and in the east later. And as the herring spawning progresses east, the whales seem to move east too.”

Fin whales usually disappear from our coastal waters early in spring, prompting what remains the most enduring question surrounding their behaviour in Irish waters: Where exactly do they go? The truth is nobody really knows.

The migration of fin whales is generally quite poorly understood. Some textbooks will tell you that they make annual migrations from warm, low latitude breeding and calving grounds to colder, higher latitude feeding waters, as is conventional for many large cetaceans. If this is the rule, however, the Celtic Sea population could be the exception.

Berrow elaborates: “There are only two to three months of the year that they're not in Irish coastal waters. In fact, I'd be surprised if they went all the way out of Irish waters at all, given the time frame. Historically a lot were caught off Spain, so they could be going there to calve, but we haven't seen many fins with calves in Irish waters. One suggestion is that these could be immature individuals just hanging around for a few years before they go off to mate, but some of them are very, very big, and don’t look immature. We’re really not sure.”

To answer the questions that surround the movement and migration of fin whales in the Celtic Sea, the IWDG hopes to tag individuals for satellite tracking. “We want to tag five or six because some tags might fail to transmit. The tags work for about 100 days. I think they’ll show the whales following the fish eastwards along the south coast, and then we’ll get to see where they go when they move offshore,” Berrow explains.

Apart from their migration, there is another major question mark surrounding these animals – just why did it take us so long to realise they were here? Even though concerted whalewatching efforts only began in 1999, surely fishermen, yachtsmen, and seaside locals would have noticed these 20m titans and their giant blows sooner? Dr Berrow thinks that they might actually be relatively new arrivals to our south coast. “We've spoken to fishermen and farmers in the area, and I get the impression that maybe they (fin whales) weren't around so much in the past. Maybe it's because they were hunted so intensely, and what we're seeing now is an increase in population after protection was introduced,” he says.

Past locations of whaling stations and old sighting records don’t point to a long established Celtic Sea population. “The old whaling stations in Ireland were along the west coast. The one in Mayo was located there, for example, because it's the closest point to the shelf edge, which we know oceanic Atlantic fin whales migrate along.  The odd fin whale was caught in the 1700s, but mainly around Donegal, but there are no historical records of them off the south coast. So this habitat could be relatively recent,” Berrow explains.

In the past, fins were a major target for whalers. Initially, they were simply too fast for fishermen, as despite their massive size, they are among the ocean’s fastest swimmers, and can travel at speeds of up to 22 knots (40km per hour). But in the nineteenth century the invention of the steamship and explosive harpoon made them easier prey. Fin whales catches increased through the nineteenth and early twentieth century, and by the 1950s and 1960s around 30,000 were being caught annually, most in the southern hemisphere. Around 600 were landed at the Norwegian whaling station at Inishkea, Co. Mayo. Padraig Whooley thinks fins were “probably the mainstay” of the whaling industry off the west coast.

But if their appearance in the Celtic Sea is part of a global ‘bounce’ in their numbers, just how many were in the north Atlantic before whaling began? There is considerable debate over the figures.  Estimates based on ships’ logbooks have put the number at between 30,000 and 50,000, about the size of the current population. A recent estimate based on new genetic methods, however, suggests the figure could be far higher.

Researchers in the US examined samples of mitochondrial DNA from north Atlantic fin whales and humpback whales, and compared the genetic “distance” between these two species of the same family. Then, they measured the genetic diversity within the fin whale population. By doing so, they were able to calculate how many breeding females would have been required to account for the genetic variation they found, and thus they could estimate population size. They concluded that there were once a staggering 350,000 fin whales in the north Atlantic.

Critics of this study have pointed out that this could have been the maximum size of the population at any point in history, and that the reduction to their current numbers might have been caused by natural factors over hundreds of thousands of years, long before whaling began.

Nonetheless, fin whale populations do appear to be recovering towards pre-whaling numbers, and Dr Simon Berrow believes the Celtic Sea would present an ideal habitat for recovering populations to colonise.  “They could be colonising a new habitat here along the south coast. The waters there are very different to what they used to be. There is massive productivity down there now that’s associated with the changing climate, with massive blooms of phytoplankton. It could be these oceanographic factors that have brought them here now,” Berrow says.

As news of the Celtic Sea’s fin whale population has spread, a fledgling whalewatching industry has sprung up in recent years. Currently, there are two operators running whalewatching tours from west Cork, with more expected to join them soon.  Whalewatching has the potential to be of massive benefit to local communities, and can provide a viable and sustainable alternative to fishing, but Whooley stresses the need for it to be done the right way.

“Here in West Cork the whalewatching industry is gaining momentum, but we need to try and avoid a situation which has too many operators working in the same waters, as concentrations of tourist boats may well have a detrimental impact.”

He continues: “Apart from the demise of salmon stocks, the second biggest threat to killer whales near Victoria (British Colombia, Canada) is commercial whalewatching. Research has shown that killer whales spend less time in the areas where commercial whalewatching boats operate, and that they also dive more and dive deeper and longer here. I don't think we're anywhere near that stage yet, but it does seem that whales have a preference for water where is no pressure. Of course if a fin whale doesn't want you around it will lose you remarkably quickly. It can dive for fifteen to twenty minutes and resurface a mile away. But that said, fin whales shouldn't have to go out of their way to avoid whalewatching boats.”

A policy document produced by the IWDG providing guidelines to marine wildlife tour operators has since been given legal status by the National Parks & Wildlife Service and the Marine Safety Directorate. The document sets out a variety of regulations, such as the speed whalewatching boats can travel at, how close they can approach whales and how long they can spend with them.

Simon Berrow believes there is “huge potential” for marine wildlife tourism in Ireland, citing Scotland as an example of a country that has successfully developed such an industry. Berrow would like to see a whole ecosystem approach taken in the management of the whales in Irish waters: “I spent a few years working in the Antarctic, and there, when they’re setting quotas for the krill catch, they don t just take into account the sustainability of the krill population, but also the amount of krill needed by predators. This isn't really in the mindset in the North Atlantic. The whole push should be on ecosystem management.”

West Cork and the south coast is now quickly gaining a reputation as one of the premier whalewatching spots not just in Europe, but in the world. Whooley recalls a recent day at sea when he encountered harbour porpoises, common dolphins, minke and fin whales. “You could have whale-watched anywhere in the world on the same day and you wouldn't have seen the same diversity,” he says. And if this is a haven for cetaceans, fin whales are certainly the jewel in its crown. But with pressure on these behemoths likely to grow as the area becomes more popular with tourists and enthusiasts alike, Whooley stresses the importance of ensuring adequate protection is in place. Especially when, as he says “so little is known about the ecology or behaviour of these fin whales in Irish waters.”

The website of the Irish Whale & Dolphin Group provides up-to-date news and records of whale and dolphin sightings and strandings, as well as information on whalewatching, IWDG events and courses, and species profiles. It can be found at

Channel 4 produced an excellent documentary about the fin whale that beached at Courtmacherry, Co Cork in 2009. Watch it here.