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seasonal trends were consistent between years. Also, there
was no significant variation in this seasonal abundance within
sites, suggesting that these seasonal trends were also
consistent at all sites within a region.
Cetacean numbers have varied over time, with the greatest
numbers observed in 1999 and the fewest in 1993 and 2001.
However, the total number of watches prior to 2005 was
generally low, so the data must be treated with caution. In the
years since 2002 the mean sighting rate of cetaceans has
been relatively consistent, irrespective of the increase in overall
effort. This suggests that present watch effort is sufficient to
establish overall trends in cetacean abundance in Irish coastal
waters and is actually greater than required.
Sightings in 2001 were poor despite similar, albeit low, overall
sightings effort to 1999 and 2000. Sighting rates from 2002 to
2009 were quite consistent, with peaks in 2003 and 2007.
These peaks suggest that cetacean abundance was greater
inshore during these years.
Site summaries
Sighting rate increased along the south and southwest coasts
before declining in the northwest and increasing slightly along
the north coast. A similar trend occurred with the number of
animals per hour watched. However, both sighting rate and
animal abundance were less than expected off Castle Point,
which probably reflected that this site looks into a bay
(Roaringwater Bay cSAC) rather than looking into the open
ocean. Relative abundance off Ramore Head, Co Antrim, was
also slightly less than might be expected from adjacent sites.
Howth Head, Co Dublin
Howth Head is a headland northeast of Dublin city. Originally
an island, it is connected to the mainland via a narrow strip of
land and forms the northern boundary of Dublin Bay, roughly
corresponding to Killiney Head in the south of the bay. At the
watch site, water depth off the headland drops rapidly to 35m.
The first watch from this site was carried out in June 1994.
Since then, a total of 134 watches have been completed up
to 2009 with 187.1 hours of watch effort. Sightings were made
on 79 watches (59%) and 79 sightings were made in total. All
(a)
2
1.5
1
0.5
Sightings per hour
0
Howth Head
Hook Head
Ram Head
Galley Head
Castlepoint
Slea Head
Loop Head
Black Head
Downpatrick
Malin Beg
Dunree Head
Ramore Head
Portmuck
Bloody Bridge
(b)
16
12
Animals per hour
8
4
0
Howth Head
Hook Head
Ram Head
Galley Head
Castlepoint
Slea Head
Loop Head
Black Head
Downpatrick
Malin Beg
Dunree Head
Ramore Head
Portmuck
Bloody Bridge
Figure 97. Cetacean sighting rate per hour (a) and relative abundance (b) for all species in all sea conditions combined.
46
Irish Cetacean Review 2000-2009