Photo ID provides clues to Irish humpbacks life-cycle...Update18th Sep 2013
Photo ID provides important clues to Irish humpback whale life-cycle...Update.
Report 11, 16th Sept. 2013
A highly rewarding research trip west of the Blaskets produced a tally of six humpback whales from the rib Míol Mór on 14 September 2013. This large aggregation represents a quarter of the Irish humpback catalogue in the area. Photo ID images were obtained of the following individuals HBIRL: 6, 8, 17, 23, 24 and also the distinctive blunt dorsal of what is a new addition for Irish waters, #HBIRL25. (see image below)
It’s proving to be a bountiful season for humpback whales off the Blasket Islands this year, with no less than seven animals identified so far. With every sighting comes a better understanding of their movements around the Blasket islands. The area is effectively in a blind spot from the shore, as it is in the shadow of the islands, and so is difficult to monitor. This particular feeding frenzy, west of the Foze Rocks, was in the vicinity of where the Celtic Mist picked up two humpbacks, including HBIRL23, on her return from the continental shelf edge last week. Significantly the IWDG have documented HBIRL23 off the Blaskets four times now over the last eight weeks.
The pair HBIRL17 & 24 were again seen together in very tight formation, re-affirming the adult- calf theory; their location at any given time was quite apparent just from their simultaneous little and large blows. Some of the other animals were also forming pairings whilst co-operatively bubble-net feeding; circling a bait-ball at speed in a blur of white pectoral fins before lunging with mouth agape.
Ed note...it is noteworthy that during this current episode of humpback whale activity, IWDG have received no humpback sightings from any other south coast sites. It is entirely plausible that at time of writing, the known Irish humpback whale population is currently held within the Dingle Bay/Blaskets area.
Another important entry in the Irish humpback whale catalogue was added this week following a research trip around the Blasket Islands, Co. Kerry. Two humpbacks were spotted west of An Tearaght, one an obviously large adult identified as HBIRL17 and the other much smaller 7 metre animal, the newly designated HBIRL24. The pair were travelling together, surfacing synchronously and with the size difference and behaviour observed, gave the impression of an adult and calf/juvenile pair. This new edition comes exactly one month after the last new humpback #HBIRL23 was added to the catalogue. HBIRL23 was seen within 10 miles of the latest sightings, highlighting the importance of the Blasket area as humpback habitat; so far this season four humpbacks have been identified here, HB’s 15, 17, 23 and 24.
The initial sighting came from a speculative watch by local IWDG personnel Nick Massett, Stephen Comerford and Vera O’Donovan. Sightings had been sparse in the area recently and the team wanted to confirm whether this was also the case further offshore beyond the islands. So with a good forecast an expedition was planned for an effort watch from Inisvickillane on 28 August.
Common dolphins and minke whales were soon spotted on the watch from the island vantage but it was an hour before the first blows were seen. The initial impressions were confusing as it appeared to be a humpback with a double blow, one small, one large! But more observation revealed two animals surfacing together at close quarters in perfect synchronicity. With a spotter left on the island to keep track of the whales and direct operations, the RIB Míol Mór was able to pick up the humpbacks some five miles west of the islands. The RIB crew spent enough time with the animals to observe their behaviour and get positive photo ID on both. There was also a fin whale feeding in the area along with groups of common dolphins.
Whether this actually was a mother & calf pairing is the subject of some speculation. The general impression, size differences and behaviour suggested it was, however adult humpbacks will often be seen to be travelling in unison with synchronous dive sequences. But what we do know from a previous biopsy sample obtained by Dr Conor Ryan of the IWDG is that HBIRL17 is female. We also have an image of her breaching a year previously, on Sept 7th 2012, in which the seems to have an obviously rotund belly, suggesting she may be pregnant (image below). The gestation period for humpbacks is around 11-12 months, and as we have a further sighting (with images) of her back in July 2011 in the same Blasket area, this surely raises some interesting "life-history" questions. Have we captured three life stages of HBIRL24….its conception, gestation and first year?
Despite considerable IWDG research in the Cape Verdes and genetic studies attempting to link Irish humpbacks to a breeding population, nothing has been proven. Is it possible HBIRL24 could have been born in Irish waters? When fundamental questions such as these concerning humpback ecology are raised, we generally defer to the likes of humpback expert Phil Clapham of NOAA, USA. Phil was the key note speaker at the IWDG’s 1st International Whale conference in Roscarbery, Co. Cork in 2004. His impression however from the information presented to him was that there was insufficient evidence to confirm that HBIRL17 was pregnant in Sept 2012 or that HBIRL24 was her calf. Only a biopsy of HBIRL24 could really ascertain whether it is in fact a calf of #17. So unfortunately no eureka moment yet, but it does point out the importance of maintaining photo ID effort on species like the humpback whale, that are returning to Irish waters year-on-year in increasing numbers.
What we can say is that it is a fascinating time to be studying humpbacks in Irish waters. We have a growing humpback population that has yet to be linked to any other through either genetics or photo ID. The ongoing research efforts of the IWDG is asking questions and contributing key data to the unfolding story of humpback whales and further demonstrates the importance of the Irish sanctuary to their life history.
Ed note….We have just received a comprehensive reply from Dr Peter Stevick, College of the Atlantic who curate the North Atlantic Humpback whale Catalogue. He writes:
“However, let's consider the most probable conception dates for this scenario. The size of the calf in the most recent picture (Aug 2013) is about what we would expect for a calf of the year at that point in the season, so the expectation is that it would have been born in January-March of 2013. This is consistent with the mother being well advanced in pregnancy in September of 2012, but the most probable date of conception is still early in 2012.
Occam's Razor suggests that by far the most likely scenario is that this whale after it was photographed in Irish waters in July of 2011, mated somewhere in tropics, sometime during the following winter, was back in Irish waters, pregnant, late summer 2012, and again with a calf in late summer of 2013”
We’ve come a long way!
Article by Nick Massett and Stephen Comerford
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