1st Sei Whale Sighting Validated by IWDG in Irish Waters

26th Sep 2009 After a flurry of emailing of images among colleagues both at home and overseas, IWDG are delighted to confirm the 1st sei whale sighting (not subsequently stranded) validated by the IWDG in Irish waters.

On Wed. 23rd September 2009 IWDG member, John Brittain based in Clifden was out on one of their angling charters in quite poor sea conditions with a very large swell east of Inisboffin Island, Co. Galway, when they observed a whale of >30ft, with a visible blow and secured images of it.

Eager to establish its species John and Sue forwarded an image to IWDG on returning from the trip. (see left) It was an excellent head shot, which was fortunately taken from the right side, and showed the mouth open, rostrum and dark baleen plates. At a glance we could rule out its being a fin whale, as there was no evidence of the diagnostic white baleen plates found towards the rostrum tip on the right side of a fin whale's head.

Although not a huge whale, this was a large whale, and appeared too large to be a minke whale. That said there are some very large minke whales out there and no doubt a small number of these may be >30ft in length. The curved rostrum was also inconsistent with minke whale, which tends to be flat in profile. The baleen plates on this animal were very dark, which is also in contrast with the minke, whose baleen plates are pale or creamy. So on a number of counts, the minke whale was also removed from further investigation.

Being able to remove both minke and fin whales really only left one real contender, but we still needed to eliminate an outsider, the Bryde's whale. This rorqual has a more warm water distribution and is unique in having a series of three rostral ridges running from the blow hole along the length of the rostrum; in sharp contrast to all other rorquals which have a single ridge. So we could also remove Bryde's whale from our enquires, clearing the way for us to announce with confidence that this is a sei whale Balaenoptera borealis.

Although not previously sighted in inshore Irish waters (apart from one animal which subsequently stranded in Larne in 2006), there are three stranding records of this species; the last of which was a well publicized live stranding in Larne, Co. Antrim in July 2006 which was euthanased. You have to go back a further 92 years to find the next stranding record of this species in 1914, which demonstrates that this species rarely enters Irish inshore waters. There is always the possibility that this species is mis-identified under normal field conditions, as we've almost become conditioned in Ireland to assuming that every large whale with a visible blow is a fin whale. On reflection, this could be a dangerous assumption and a number of sightings of this species were logged by CMRC in 1999-2001 in offshore waters to the southwest of Ireland.

So the presence of sei whales off the Irish west coast is an intriguing development, and places an onus on those of us fortunate enough to observe large whales to re-double our efforts at describing as much possible diagnostic detail as possible …..or alternatively make sure you've a decent camera on board and forward relevant images to IWDG.

IWDG had heard through the grapevine, mention of sei whales in the past few weeks off the Broadhaven area of Co. Mayo. But as of yet we've received no details of these sightings which remain unvalidated. Any further sei whale sightings are crucial in helping us piece together the few scraps of data that exist on this species in Irish waters.

So if you feel you've observed this species or have any images of what you think might be sei whale in recent weeks from the Northwest, we'd love to hear from you, so that we can try to establish a “bigger picture”….if indeed there is a “bigger picture” regarding this species in Irish waters.

A huge thanks to John and Sue Brittain for bea

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