Attack on Harbour Porpoise (Phocoena phocoena (L. 1758)) by Bottle-nosed Dolphins (Tursiopstruncatus (Montagu 1821))Author(s): Conor RyanSource: The Irish Naturalists' Journal, Vol. 29, Part 2 (December 2008), p. 130Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/20764469 .

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Cetacean Notes

strandings of other ziphiid species in recent years (O'Connell and Berrow 2007 op.cit.), which

were not commercially hunted. This family of whales are known to have been involved in mass

strandings which have been attributed to anthro

pogenic noise pollution such as active sonar

(Zimmer, W.M.X. and Tyack, P.L. 2007 Marine Mammal Science 23(4): 888-925). This could

point towards acoustic disturbance being a factor in pushing more Northern Bottlenose Whales inshore, as observed in recent years in Ireland.

We would like to thank P?draig WTiooley and Mick O'Connell for assistance in the field and Simon Berrow and Jim Wilson for improving earlier drafts of this note. Conor Ryan 3 WTiitepoint Drive, Cobh, Co. Cork Patrick Lyne Disert, Castletownbere, Beara, Co. Cork

dorsal surfaces. The porpoise's body was limp and it did not appear to be moving under its own

strength and was therefore probably dead. The

porpoise was no longer visible after 110 min, when the dolphins' surfacing pattern became less active with longer dives. They then left the area where the attack occurred and entered Cork Harbour. The porpoise could not be seen despite several scans of the area with binoculars.

Critically, the dolphins were not seen to eat the porpoise and nearby seabirds were not

following the animals, suggesting that feeding did not occur. Patterson I.A.P., Reid R.J., Wilson

B., Grellier K., Ross H.M. and Thompson P.M.

(1999 Proceedings of the Royal Society of London. Series B 265: 1167-1170) were first to observe infanticidal behaviour in cetaceans in resident

Bottle-nosed Dolphins in Moray Firth, Scotland.

They proposed that Bottle-nosed Dolphins use

porpoises to practice their infanticide, given porpoises' similar dimensions to Bottle-nosed

Dolphin calves. Alternative explanations for this behaviour are that play, interspecific competition or sexual frustration could lead to such violent interactions (Ross, H.M. and Wilson, B. 1996

Proceedings of the Royal Society of London. Series B

263(1368): 283-286; Baird, R.W. 1998 Mammalia 62(1): 129-134). Conor Ryan 3 Whitepoint Drive, Cobh, Co. Cork

Attack on Harbour Porpoise {Phocoena phocoena (L. 1758)) by Bottle-nosed Dolphins (Tursiops

truncatus (Montagu 1821)) On 22 December 2007, a pod of six Bottle-nosed

Dolphins was observed from Roches Point, Co. Cork with binoculars (20x100). They were c.2 km south of Roches Point and were visible with the naked eye. It is believed that this was the

pod that had been resident in the area since

February 2005.

They were displaying active behaviour such as

breaching and rushing at the surface. Then a Harbour Porpoise, estimated to be about half of their length, was noticed surfacing rapidly amongst the dolphins. The dolphins appeared to be chasing it and butting it with their beaks. On two occasions, as the porpoise attempted to flee, it was seen to be pursued rapidly by the dolphins and receive blows as it surfaced. The dolphins undertook a cyclic swimming pattern: approach ing the porpoise from behind in a V-formation,

corralling it, and then breaching on to it, sub

merging the animal. The porpoise was not seen

to take any further breaths after 40 minutes of this behaviour. On two occasions it was accom

panied by a breaching dolphin as it was flung into the air and somersaulted tail-first, suggesting a high velocity impact. The dolphins then were seen to push the porpoise out of the way of an

oncoming ship by carrying it on their anterior

Pygmy Sperm Whale (Kogia brevi

ceps (de Blainville)) in Co. Kerry A small whale was found washed up at Bally heigue, Co. Kerry (Q7526) on 22 November 2005 and was photographed on 23 November. The images were passed on to the Irish Whale and Dolphin Group on 28 November and the

species was identified by SB as a Pygmy Sperm Whale (Kogia breviceps) due to its square head; small under slung lower jaw; thin, sharp and

backwardly pointed teeth; and small dorsal fin situated at least two-thirds along the length of its back. The whale was buried by Kerry County Council and attempts to recover the carcass were

unsuccessful. However, on 3 December it was

found on the beach within 100 m of where it had been buried. A large hole below the eye in the left side of its head, gave confirmation that this was the same animal.

Pygmy Sperm Whale is rare, this being only the sixth stranding record for Ireland. All

130 Irish Naturalists' Journal 29 No. 2 2008

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