Stranded Killer Whale was a Pregnant Female

11th Oct 2010 A Killer Whale was reported stranded at Doohoma in Tullaghan Bay, Co. Mayo by James Kilroy (NPWS), Patrick Cusack on 04 October 2010. This was only the 15th stranding recorded of this species in Ireland since records began and this was the 7th in 40 years.

Conor Ryan (IWDG & GMIT) and Alessandro Pierini (GMIT) carried out a post mortem examination on the carcass on 10 October. Skin, blubber and muscle samples were taken for genetic, pollutants and stable isotope analyses. Given that the carcass was not badly decomposed, the decision was made to examine the stomach contents - a rare opportunity to take a look at the diet of a killer whale from these waters. There were fish remains and unidentified bones in the stomach and no plastic or litter.

When the abdominal cavity was opened, we found a large, near-term foetus of 2.09m (newborn calves are believed to be 2.5m long). It was a female, and was fully formed with large teeth and visible white eye-patches. The dorsal fin and tail flukes were soft, to aid in delivery and usually stiffen soon after birth. Samples were taken from this specimen also which will be particularly useful to geneticists, as mother-calf samples are very used to test the accuracy of parentage assignment techniques using DNA.

It is a pity to find a double mortality of this kind, given that calves have not been recorded alive in Irish waters in recent times and there is much concern over the health of this population. Of the seven most recent Killer Whale strandings, three have been of neonate calves or pregnant females. The cause of death of this animal was not obvious. The the orientation of the calf in the birth sac was atypical - it would have been delivered head-first which is very rare in cetaceans and can be fatal given their need to breath air immediately after birth.

Unfortunately, the skull and jaw bones were defaced by someone using an electric saw. This meant that the skull or complete skeleton could not be prepared for display purposes (which can be a nice tourist attraction). As such, a pectoral fin was removed for display in the Natural History Museum in Dublin.

Conor Ryan & Alessandro Pierini

Irish Whale and Dolphin Group & Galway-Mayo Institute of Technology