IWDG publish research on humpback whales in Ireland

24th Jan 2015

We still know very little about ‘our’ humpback whales in Ireland, once they leave our coastal waters. Where do they go to breed? Is Ireland their main feeding ground? Do they mix with other populations elsewhere? Answers to all of these questions are needed to inform necessary conservation measures for protecting humpback whales, which continue to recover from decades of persecution in the early 1900s. IWDG has recently tackled some of these questions, using decades of data collected largely through a network of seasoned whale-watchers. Thanks to keen eyes stationed on headlands and boats along southeast and southwest coast, we have been able to gather the necessary data to track the seasonal movements of the humpback whales in Irish waters. What’s more, we have been able to monitor individual animals over many years using photo-identification. Two thirds of these images were submitted by members of the public: citizen science at its best!

IWDG and colleagues based in the USA, Iceland, Norway and The Netherlands have just published a peer-reviewed paper in the Journal Marine Biological Association of the United Kingdom. The study reports on a comparison of the 28 humpback whales photo-identified in Irish waters to a catalogue of over 8000 humpbacks recorded elsewhere throughout the North Atlantic, including the two known breeding grounds of the West Indies and Cape Verde. This labour-intensive (and addictive!) matching process was carried out by Allied Whale personnel at College of the Atlantic in Maine, where IWDG sends copies of all photo-identification images.

Staggeringly no matches were found between whales documented in Ireland and those on the known breeding grounds (West Indies and Cape Verde). The mystery of where they go to give birth still evades us. However, we are delighted to announce that two whales were tracked between Ireland and Arctic feeding grounds. One whale, known as HBIRL25 was photographed by Christian Schmidt in Iceland on 28 July 2013 off Husavik in Iceland before crossing paths with eagle-eye Nick Massett off the Dingle Peninsula just 48 days later (and some 1740 km away). Another whale called ‘Dutchy’ (HBIRL 7) was recorded off Toe Head in West Cork in September 2007. In the paper, we document this whale’s movements from the Netherlands to Ireland and then to Tromso in northern Norway where it is now regularly observed during winter by Fredrik Broms. If you think winter whale-watching in Ireland is tough going, spare a thought for Fredrik who regularly has to break ice his boat out of the ice before braving conditions to photograph whales in the short twilight of mid-winter in the Arctic!

The main stomping ground for humpbacks in Ireland was described by analysing the movements of well-known whales such as ‘Boomerang’, who has been identified 34 times in several locations off the south and southwest coasts. A strong seasonal trend emerged in the analysis of sighting data: humpbacks first appear inshore off Co. Kerry each summer, then they move to West Cork in autumn, and finally they push east to Waterford and Wexford in late winter. This easterly movement mirrors that of spawning sprat and herring. It seems that the fish spawning behaviour (where they gather inshore to lay eggs on certain gravel beds) may entice the whales inshore and then eastwards.

Apart from finding out where our humpbacks go to breed, the next challenge is to look after the whales’ food source and make sure that they are given a large slice of the pie. When deciding on fish quotas, we must realise that the whales cannot make do with the leftovers – there needs to be more fish in the sea than they can eat. In order for bait balls of sprat and herring (which the whales seek out and feed on) to form, the fish need to occur in high densities. It is very worrying that there are still no quotas for sprat catches in the Celtic Sea. The fishery is a free-for-all and has been for many years. Who knows how much longer this can be tolerated by the Celtic Sea ecosystem?

Conor Ryan

Conor Ryan, Pádraig Whooley, Simon D. Berrow, Colin Barnes, Nick Massett, Wouter J. Strietman, Fredrik Broms, Peter T. Stevick, Thomas W. Fernald, JR and Christian Schmidt. 2015. A longitudinal study of humpback whales in Irish waters. Journal of the Marine Biological Association of the United Kingdom, In Press. doi:10.1017/S0025315414002033.

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