The potential of Donegal Bay as
an SAC for Bottlenose Dolphins
Simon Berrow
Irish Whale and Dolphin Group, Merchants Quay, Kilrush, County Clare
Report to the National Parks and Wildlife Service
January 2009
The potential of Donegal Bay as an SAC for Bottlenose Dolphins
Summary
The occurrence of bottlenose dolphins in Donegal Bay was reviewed and its suitability as a Special Area of
Conservation for bottlenose dolphins assessed.
A total of 147 sightings of bottlenose dolphins in Donegal Bay were collected by the IWDG between 1994
and 2008. Most sightings were in McSwynes Bay or on the south side of St Johns Point. Another cluster of
sightings occurred off Mullách mór in north Co Sligo, however sightings were also well spread out in the
inner bay, east of a line from Mullách mór to Drumanoo Head. There were very few sightings to the west
of this line with just six sightings off Slieve League. Sightings have been received regularly by the IWDG
since 1994, but the number received each year has increased since 2001. Sightings were received in every
month but with a peak from June to October.
Eight dedicated boat-based surveys were carried out in Donegal Bay between July and September 2008. A
total of 637km were surveyed. Over 90% of the entire survey time was carried out in sea-state ≤2.
Bottlenose dolphins were recorded during three visits to this site. A total of five groups were recorded. All
sightings were in the inner bay and none to the west of St Johns Point despite a large amount of survey
effort. All groups observed were traveling fast with no foraging, socializing or other behaviour recorded.
Calves were reported in at least four of the five groups observed.
Images of bottlenose dolphins were obtained on three occasions with a total of 44 individually recognized.
Two individual dolphins were seen on all three trips with dolphins, seven dolphins (15%) were seen on two
occasions with the remaining 35 seen on only one occasion. When all individually recognizable dolphins
are taken into account then images of both left and right fins were obtained from a total of 20 dolphins, left
side of the dorsal fin only for 14 and right side only for 10 dolphins. There were not enough data to derive
an abundance estimate using mark-recapture analysis. Two dolphins identified on 23 July 2008 were
matched to a group photographed in Galway Bay on 26 March 2007, a distance of 300km and a gap of 483
days. There was also very strong evidence to link one of these dolphins to the Moray Firth, northeast
Scotland, however this potential match has not yet been confirmed.
Encounter rates with groups of bottlenose dolphins were lower in Donegal Bay compared to the Lower
River Shannon cSAC, however mean group size was much greater giving a similar dolphin encounter rate.
Smaller group sizes are typical of resident populations, which are described as having a fission-fusion
social structure with individuals leaving and joining different groups regularly. The larger group size in
Donegal Bay may reflect the different use of the bay by transient bottlenose dolphins, which enter the bay
for short periods before ranging further afield.
Donegal Bay is considered a good candidate for designation as an SAC for bottlenose dolphins, as dolphins
regularly use the site in good numbers and there was evidence of site fidelity. We recommend further work
is carried out to determine how bottlenose dolphins use the bay, especially regarding the regular presence
of the same individuals. This should involve the collection of more photo-identification data to enable a
better understanding of their site fidelity, ranging patterns and enable an abundance estimate to be derived
using mark-recapture analysis.
Citation: Berrow, S.D. (2008) The potential of Donegal Bay as an SAC for Bottlenose Dolphins. Report
to the National Parks and Wildlife Service. Irish Whale and Dolphin Group. pp.
Cover image: Bottlenose dolphin in Donegal bay © Simon Berrow/NPWS
2
Introduction
Under the EU Habitats Directive, Member States are required to provide strict protection to all species of
cetacean (all on Annex IV) within the Irish EEZ. For species on Annex II, Member States are also required
to designate Special Areas of Conservation (SAC). This includes the harbour porpoise (Phocoena
phocoena) and bottlenose dolphin (Tursiops truncatus). To date, two sites (Blasket Islands cSAC and
Roaringwater Bay cSAC) have been designated for harbour porpoise and one site (Lower River Shannon
cSAC) for bottlenose dolphin. The National Parks and Wildlife Service (NPWS) seek information on a
number of other sites to assess their potential to be designated as SACs.
The Irish Whale and Dolphin Group (IWDG) have identified Donegal Bay as a potential site for both
harbour porpoise and bottlenose dolphin. This is based on sighting records submitted to the IWDG.
Dedicated survey work in Donegal Bay was limited to three surveys around McSwynes Bay and St Johns
Point carried out by Ingram et al. (2001) in August 2001. They encountered only one group of bottlenose
dolphins during these transects and obtained images of 30 individual dolphins. None of these dolphins were
matched to any other site surveyed in Ireland.
During 2008, the IWDG carried out three surveys of small cetaceans (mainly harbour porpoises and
bottlenose dolphins) in the inner part of Donegal Bay on behalf of the NPWS (Berrow et al., 2008). This
involved carrying out boat-based line-transects each month during July to September and estimating
densities using distance analysis. An overall density of 0.88 harbour porpoise per km2 was estimated which
provided an abundance (±SE) of 249±111.5 (95% Confidence Interval =106-586). Four bottlenose dolphin
sightings were also recorded but no abundance estimate using distance or mark-recapture analysis was
possible.
The IWDG have carried out additional work in Donegal Bay, including a review of sightings data in order
to make a more detailed assessment of the site for bottlenose dolphins. The IWDG funded five additional
visits to the site during 2008 in order to try and obtain enough images of individual dolphins to carry out an
abundance estimate using mark-recapture. The results of this assessment are presented in this report.
Objectives
The objectives of the present survey were to:
1.
2.
3.
4.
review sightings of bottlenose dolphins in Donegal Bay
carry out additional surveys for bottlenose dolphins in Donegal Bay
assess the abundance of bottlenose dolphins in Donegal Bay, using mark-recapture
make recommendations as to the suitability of Donegal Bay as a potential SAC
Methods
Review of Sightings data
The IWDG co-ordinates two sighting schemes; a casual sighting scheme, which collect sightings made
opportunistically while carrying out another activity (e.g. sailing, fishing, walking) and an effort related
scheme, where the effort spent watching for cetaceans or traveling at sea is also recorded. Effort related
sightings provide better data on the seasonal distribution and relative abundance of cetaceans in a given
area. Even when observers record no cetaceans, this scheme still provides useful data as the watching
effort has been quantified.
Sightings from both schemes are recorded in a standardized format. The sightings form prompts the
observer for information on size, blow, fin and head shape, behaviour and high-low-best estimate of
numbers present. It also provides space to report environmental data, the most important of which is seastate. Sightings of cetaceans may be made by a wide range of people, engaged in a wide range of activities.
Sightings data may be submitted to the IWDG through a number of channels including: submitting a
3
sighting form, reporting on-line through the IWDG website (www.iwdg.ie) or directly by phoning in
records on the IWDG phone line.
In order to ensure the quality of the data maintained on the database, it is essential to have a system of
validating records and data control. Each sighting record is assessed to determine whether the basic
information on the sightings form is complete e.g. date, location and contact information of the observer.
All records are then assessed by IWDG using their experience in “field identification” of cetaceans and
knowledge of the observer to determine whether the species reported is accurate based on the description of
each sighting. Increasingly, records are being submitted with photographs or video to verify the record. If
the record is submitted verbally the observer is asked to describe what was seen by prompting for
information without giving hints as to what the characteristic should look like. Other factors such as
weather conditions especially sea-state, observer experience and confidence level are also factors used in
assessing records. If insufficient information is provided to verify the sighting record then the species
identification is downgraded to a level which the information provides warrants.
For this study sighting searches were restricted to bottlenose dolphins only (no downgrades used) and
within an area between 54 .35º to 54.66ºN and 8.70 º to 8.08 º W.
Survey sites
The survey site is shown in Figure 1. The boundaries were extended from those used by Berrow et al.
(2008) to Inishmurray Island to the west and Slieve League to the north. This increased the area of the site
from 281 km2 in to 565 km2. This area could be surveyed thoroughly in one day from a half-decker or RIB.
Survey vessels
Three vessels were chartered during this survey (Table 1) in addition to the IWDG Rigid Inflatable Boat
(RIB). MV Smoothound was initially chartered for this survey, however the vessel sank in July and
additional vessels had to be chartered. These vessels operated from Mullách Mór in north Co Sligo.
Table 1. List of vessels used to survey bottlenose dolphins in Donegal Bay during 2008.
Vessel
MV Smoothhound
MV Assaroe Star
MV Kiwi Girl
RIB Muc Mhara
Port
Donegal, Co Donegal
Mullách Mór, Co Sligo
Mullách Mór, Co Sligo
Mullách Mór, Co Sligo
Type
Vigalente
Aquastar
Kingfisher Fastcatch Sporthunter
XS RIB with 115 Mercury outboard
Length
(m)
Platform height
(m)
11
10
10
6
3.0
2.5
2.8
<0.5
Survey methodology
Conventional single platform line-transect surveys were carried out within the boundaries of Donegal Bay
along pre-determined routes. Transect lines were chosen to cross depth gradients and provide as close to
equal coverage probability as possible following the recommendations of Dawson et al. (2008) who
suggested systematic line spacing resulted in better precision than randomized line spacing. The lines were
changed for each survey to try and get full coverage of the site over the study period to ensure no
potentially important habitats were overlooked.
Each survey vessel travelled at a speed of 12-20 km hr-1 (7-12 knts), which was twice the typical average
speed of the target animal as recommended by Dawson et al. (2008). During each transect the position of
the survey vessel was tracked continuously either through a GPS receiver fed directly into a laptop, or in
the case of the RIB, into a hand-held GPS. Survey effort, including environmental conditions (sea-state,
4
wind strength and direction, glare etc.) were recorded directly onto LOGGER software (IFAW) every 15
minutes when on a hard boat or recorded verbally onto a dictaphone on the RIB.
Two primary observers were positioned on the flying bridge of MV Smoothhound, MV Assaroe Star and
MV Kiwi Girl, which provided an eye-height above sea-level of between 4-6m depending on the height of
the platform (Table 1) and each individual observer. Primary observers watched with naked eye from dead
ahead to 90º to port or starboard depending on which side of the vessel they were stationed. Three primary
observers (Simon Berrow, Conor Ryan and Ronan Hickey) were used throughout this survey. Two-three
crew surveyors were used on the RIB, surveying 90º to port and starboard. Once a sighting of bottlenose
dolphins was made, the track was broken and the dolphins approached in order to obtain images suitable
for photo-identification
Photo-identification
The use of photo-identification for estimating the abundance of coastal populations of cetaceans is
becoming more widespread (Evans and Hammond, 2004). This approach can provide accurate estimates
with a measure of precision. Bottlenose dolphins lend themselves to this technique as they often have
unique and permanent marks that can be easily photographed. Photo-identification of bottlenose dolphins
has been used extensively in the Shannon Estuary (Ingram, 2000; Ingram and Rogan, 2003; Englund et al.,
2007) and elsewhere in Irish coastal waters (Ingram et al., 2001; Ingram and Rogan, 2003; O’Brien et al.,
2008).
Images of bottlenose dolphins are examined for photographic quality and the severity of marks and lesions
on individual dolphins (see Ingram (2000) for detailed methodology). Only individuals with permanent
marks (Grade 1) are used for mark-recapture abundance estimates to minimise the possibility of false
negatives (i.e. not recapturing a marked animal).
Table 2. Categories for quality of images and marks used in this study (after Ingram, 2000).
Images
1
2
3
Marks
Well lit and focused taken perpendicular
to the dorsal fin at close range
More distant, less well lit or slightly
angled shots of dorsal fins
Poorly lit or out of focus shots taken at
acute angles to the dorsal fin
1
2
Significant fin damage or deep scarring
that were considered permanent
Deep tooth rakes and lesions
3
Superficial rakes and lesions
During this survey high quality digital cameras with f2.8 70-200 mm lense (including x2 converters) were
carried on all surveys. At least two such cameras were available on each survey. If bottlenose dolphins
were encountered the track-line was broken and the dolphins were photographed until images of all
individuals present in the group were obtained or dolphins were showing signs of disturbance by the
presence of the vessel. We conformed to the Marine Notice 15 of 2005 whenever possible.
Results
Analysis of sightings data
A total of 147 sightings of bottlenose dolphins in Donegal Bay were collected by the IWDG between 1994
and 2008. Only ten of these sightings were during effort watches so all data have been displayed together
(Figure 1). Most sightings were in McSwynes Bay or on the south side of St Johns Point. Another cluster of
sightings occurred off Mullách mór in north Co Sligo, however sightings were also well spread out in the
5
inner bay, east of a line from Mullách mór to Drumanoo Head. There were very few sightings to the west
of this line with just six sightings off Slieve League.
Figure 1. IWDG Sightings of bottlenose dolphins in Donegal Bay.
There was one sighting of seven bottlenose dolphins in August during 21 effort watches off Mullách mór in
Co Sligo, seven sightings, all in July, during 19 watches off St Johns Point and two sightings during 43
watches off Tawney near Kilcar in Co Donegal.
Number of sightings
Sightings have been received regularly by the IWDG since 1994, but the number received each year has
increased since 2001, which probably reflects greater recording effort (Fig. 2). The highest number of
sightings was received in 2001, with 25 sightings.
40
35
30
25
20
15
10
5
0
1994
1996
1998
2000
2002
2004
2006
2008
Year
Figure 2. Annual distribution of bottlenose dolphin sightings in Donegal Bay submitted to the IWDG
The monthly distribution of sightings is shown in Table 3. Sightings were received in every month but with
a peak from June to October. Peak in the number of individuals occurred earlier from April to October but
this is inflated by one sighting on the 7 April 2007 of between 150 and 200 dolphins between Mullách mór
and Bundoran. This sighting was validated through video footage and was an exceptionally large group of
bottlenose dolphins for Irish waters. If we remove this exceptional sighting, then the mean group size varies
between two and 26 individuals, with an increase between September and December (Table 3).
6
Table 3. Number of bottlenose dolphin sightings, individuals and mean group size per month in Donegal Bay.
Month
Sightings
January
February
March
April
May
June
July
August
September
October
November
December
TOTAL
Individuals
Mean group size
1
1
2
4
9
11
45
41
16
12
3
2
2
2
38
190
147
175
632
804
386
314
67
55
2
2
19
47
16
16
14
20
24
26
22
27
147
2812
19
Site surveys
Eight surveys were carried out in Donegal Bay between July and September 2008 (Table 4). Over 90% of
the entire survey time was carried out in sea-state ≤2. Six surveys were carried out in sea-state ≤2 for the
majority of the survey, with only two days (24 July and 20 August) experiencing significant proportion of
survey effort in sea-state ≥2. No dolphins were observed on these latter two days.
Bottlenose dolphins were recorded during three visits to this site (Table 4). Two groups were observed on
two occasions but the second group on 23 July could not be approached for photo-identification. No
dolphins were observed on two days (31 August and 23 September) despite excellent sea conditions.
Table 4. Date, distance traveled, sea-state and number of sightings of bottlenose dolphins in Donegal Bay during 2008.
Sample
Date
1
2
3
4
5
6
7
8
23 July
24 July
08 Aug
15 Aug
20 Aug
30 Aug
31 Aug
23 Sept
Total
Vessel
MV Smoothhound
MV Smoothhound
MV Assaroe Star
RIB Muc Mhara
MV Kiwi Girl
MV Kiwi Girl
RIB Muc Mhara
MV Kiwi Girl
Total distance
(km)
104
73
85
92
96
63
61
63
637
Sea-state
(% of total survey time)
0
1
2
3
87
0
15
38
0
7
68
60
13
16
62
31
28
33
24
35
0
38
23
22
40
52
8
5
0
46
0
9
32
8
0
0
Total
sightings
Total
dolphins
2
0
1
2
0
0
0
0
26
0
40
55
0
0
0
0
5
121
7
The track-lines and sightings are shown in Figure 3. All sightings were in the inner bay and none to the
west of St Johns Point despite a large amount of survey effort (Figure 3).
Figure 3. Map showing location of all track lines surveyed and all bottlenose dolphins observed.
Details of each sighting are shown in Table 5. All groups observed were traveling fast with no foraging,
socializing or other behaviour recorded. Calves were reported in four of the five groups observed. The
second group on 23 July was observed from a great distance and the presence of calves could not be
determined. The proportion of calves varied from 10% to 15% and was 11% overall.
Table 5. Sightings of bottlenose dolphins in Donegal Bay during the present survey.
Date
Number of
individuals
(calves)
Number of
identifiable
dolphins
Location
Latitude
Longitude
Behaviour
23 July
23 July
20 (3)
6 (?)
10
0
54.56124
54.55597
-8.45098
-8.31041
Traveling
Leap/Splashing
8 August
40 (4)
20
54.58727
-8.38197
Traveling
20 (2)
30-40 (4)
9
15
54.52700
54.49617
-8.27799
-8.37649
Traveling
Traveling
15 August
15 August
Images of bottlenose dolphins were obtained on three occasions. A group of about 20 dolphins were
photographed on 23 July, which included three calves, was observed off St John’s Point heading west along
the south side of the headland. These dolphins rounded the Point and headed into McSwynes Bay. From
this group, 10 individuals were individually recognizable using photo-identification. A second group of six
8
individuals were seen at a long distance heading east towards Bundoran along the south shore of Donegal
Bay. No images were taken of the second group as they were observed from a distance and were travelling
fast.
Table 6. Quality of marks and lesions of bottlenose dolphins from
Donegal Bay on 23 July 2008.
Photo Grade
L
R
Marks Grade
L
R
both
1
2
3
9
1
0
0
0
0
1
2
3
6
3
1
0
0
0
0
0
0
Total
10
0
10
0
0
Total
10
One group of around 40 dolphins, with four calves, were observed on 8 August heading east along the
southern side of St John’s Point. These dolphins passed the fish-farm at the mouth of Inver Bay but did not
enter the bay. From these, 20 individual dolphins could be recognized of which only two had been recorded
previously on 23 July.
Table 7. Quality of marks and lesions of bottlenose dolphins from
Donegal Bay on 8 August 2008.
Photo Grade
L
R
Marks Grade
L
R
both
1
2
3
6
7
0
12
3
0
1
2
3
13
3
1
11
2
1
8
1
1
Total
13
15
16
14
10
Total
20
Two groups of bottlenose dolphins were observed on 15 August. The first group of around 20 dolphins was
observed off Kildoney Point, east of Bundoran on the south shore of Donegal bay. They were spread out
and traveling fast. From these, images of eight individual dolphins were obtained of which of four had also
been recorded on the 23 July, three on 8 August and one on both days.
The second group of 30-40 dolphins were observed in the center of the inner bay northeast of Mullách mór.
This group of 30-40 dolphins included 4 calves and were heading east. A total of fifteen individual
dolphins could be recognized of which none had been recorded previously.
This suggests that the first group observed on 15 August had a higher fidelity to Donegal Bay as some of
these dolphins had been recorded previously (23 July). The second group may have been a transient group
which had entered the bay. However these data are too few to support this suggestion but demonstrates the
potential complexity in group composition.
A log of the individual dolphins recorded is shown in Table 7. Of the 44 individually recognized dolphins,
two were seen on all three trips with dolphins, seven (15%) were seen on two occasions with the remaining
35 seen on only one occasion.
9
Table 8. Quality of marks and lesions of bottlenose dolphins from
Donegal Bay on 15 August 2008.
Photo Grade
L
R
Marks Grade
L
R
both
1
2
3
5
8
0
5
7
0
1
2
3
15
1
0
17
1
0
9
1
0
Total
13
12
16
18
10
Total
24
When all individually recognizable dolphins are taken into account then images of both left and right fins
were obtained from a total of 20 dolphins, left side of the dorsal fin only for 14 and right side only for 10
dolphins (Table 9). There were not enough data to derive an abundance estimate using mark-recapture
analysis.
Table 9. Number of bottlenose dolphins recognized from left, right and
both sides of the dorsal fin.
Marks Grade
L
R
Both
Total
14
10
20
44
Two dolphins identified on 23 July 2008 (DB04 and DB07) were matched to a group photographed in
Galway Bay on 26 March 2007, a distance of 300km and a gap of 483 days (see O’Brien et al., 2008). Five
of the dolphins identified on 23 July were matched to a survey day funded by the IWDG in Donegal Bay on
15 August 2008.
There is also very strong evidence to link one of these dolphins (DB04) to the Moray Firth, northeast
Scotland as it matches dolphin number CRRU233 recorded by the Cetacean Research and Rescue Unit,
however this potential match has not yet been confirmed (Joanne O’Brien, pers. comm.).
10
Table 10. Log of individual dolphins recorded in Donegal Bay during 2008. Number
shows the quality of marks photographed on the left or right of the dorsal fin.
Catalogue
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
TOTAL
CUMULATIVE
TOTAL
25 Jul
1*
Date
L*R
8 Aug
Total
days sighted
15 Aug
-*1
1*1
1*
1*
1*
2*
1*
2*
2*
3*
1*
10
10
1*-
1*1
1*-
1*1
1*1
-*1
1*1
1*1
-*1
-*2
3*3
2*2
2*1*1
1*1
1*1*1
1*1
2*1*1*
1*-*1
-*1
20
27
1*1
1*1*-
1*-
1*1*1*1
*1
-*1
1*1
-*1
1*1
1*1
1*1
2*2
-*1
-*1
-*1
1*1
24
44
2
1
2
1
1
1
2
1
3
1
2
1
2
1
1
1
1
1
1
3
2
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
11
Discussion
Bottlenose dolphins have been recorded regularly in Donegal Bay since 1994, when records began. They
have been recorded in all months with a peak during the summer. This summer peak may represent
observer effort and not the seasonal distribution of dolphins.
During eight transects in Donegal Bay during 2008, bottlenose dolphins were observed on three days. The
ability to detect small cetaceans visually at sea is extremely dependent on sea-state. During the present
study, six of the eight transects were carried out in sea-state 2 or less for 90% of the survey. On six of the
eight survey days, sea conditions were excellent for observing dolphins, however dolphins were only
observed on three of these days suggesting dolphins do not always occur within the site but are transient.
If we compare the encounter rate with the Lower River Shannon cSAC then encounters rates were lower in
Donegal Bay compared to the Shannon Estuary. For example Ingram (2000) encounter 162 dolphin groups
during 45 boat-based surveys, which is 3.6 groups per transect. Ingram and Rogan (2003) encountered 66
groups during 14 surveys an encounter rate of 4.7 groups per survey and Englund et al. (2007) encountered
3.1 groups per survey. During this survey the encounter rate was 0.6 groups per transect. However the
mean group size in the Shannon Estuary is 5-6 compared to around 25 in Donegal Bay and the number of
dolphins encountered, when dolphin were observed on a transect, were similar.
Ingram et al. (2001) carried out three surveys in Donegal Bay between 3-10 August 2001 and encountered
only one group in total, a rate of 0.3. This group was also large with an estimated 30 in the group including
four calves. However they report a total of 35 identifications in this group so presumably the columns in the
table are the wrong way around and the group size was estimated at 35.
Smaller group sizes are typical of resident populations, which are described as having a fission-fusion
social structure with individuals leaving and joining different groups regularly. The larger group size in
Donegal Bay may reflect the different use of the bay by transient bottlenose dolphins, which enter the bay
for short periods before ranging further afield.
One objective of the present survey was to assess the abundance of small cetaceans within these sites. For
bottlenose dolphins the preferred method for assessing abundance is using mark-recapture data from
individually recognizable dolphins. During the eight surveys carried out five sightings of bottlenose
dolphins were recorded and images obtained from four of these groups. The total of 44 individually
recognizable dolphins of which nine (20%) were recaptured between transects was not enough to enable
abundance estimates using mark-recapture analysis.
Englund et al. (2007) recommended a minimum of 12 surveys, assuming a mean individual capture
frequency of circa. 2, would be necessary in the Shannon Estuary to obtain an abundance estimate with a
Coefficient of Variation of approximately 0.12. The encounter rate of bottlenose dolphins in Donegal Bay
was less than the Shannon Estuary, thus to obtain a similar capture frequency it is likely that more than 12
surveys would need to be carried out.
Ranging patterns of bottlenose dolphins
The data from the present study was also used by O’Brien et al. (2008) who analysed bottlenose dolphin
photo-id catalogues from all around the Irish coast. From a total of 114 individually recognizable dolphins
they recorded 16 matches, which was a re-sighting rate of 14%. Re-sightings ranged over distances of
between c130km and c650km and 26 to 760 days. Seven of the dolphins from Donegal Bay matched to
Galway Bay and one each to Co Antrim and Cork Harbour.
These results suggest there is large-scale movement of transient dolphins along the western seaboard of
Ireland, which includes Donegal Bay and between the south, north and east coasts. This has implications
for the conservation of this species, including site designation as a network of SACs might be necessary if
sites can be identified that have a “regular presence” of the same individual bottlenose dolphins.
12
Figure 4. Photo-identification matches of bottlenose dolphins from around the Irish coast
(from O’Brien et al., 2008)
Criteria recommended for selection of sites as potential SACs
The Habitats Directive states a site, which “corresponds to the ecological requirements of the species” may
be designated as a SAC. The Directive states that the selection of sites eligible for identification as of
Community importance are those “for aquatic species which range over wide areas, such sites shall be
proposed only where there is a clearly identifiable area representing the physical and biological factors
essential to their life and reproduction”. It has proved difficult for Member States to identify sites based on
these criteria due to insufficient knowledge of species distribution and abundance and life-history.
To assist with identifying SACs an ad hoc meeting was convened by the Commission and concluded that
“it was possible to identify areas representing crucial factors for the life cycle on the basis of i) the regular
or continuous presence of the species, ii) good population density (in relation to neighbouring areas) and
iii) high ratio of young to adults during certain periods of the year”.
A summary of the criteria that should be considered when selecting sites as potential SACs is shown in
Table 8 and an attempt to relate the present results to these criteria has been made.
13
Table 8. Summary of criteria recommended by the European Commission for SAC site selection
Criteria
1. Size and density of population on site in relation to
population present in national territory
2. Degree of conservation features of the habitat
which are important for the species concerned
3. Degree of isolation of the population present on
the site
4. Global assessment of the value of the site for the
conservation of the species concerned
5. Resident (to be found throughout the year on the
site)
6. Uses the site to raise young
Information
Available
Comment
Some
Using abundance data for all Irish
waters data from SCANS-II (2008)
Habitat
requirements
not
fully
understood
No
Yes
No
Yes
Yes
Proportion of dependent young
Each criteria is discussed in relation to the present survey below:
1.
Abundance estimates carried out by SCANS-II (2008) suggested that around 6,500 bottlenose
dolphins occurred all Irish waters, which was around 50% of the total abundance estimates for
northeast Atlantic continental shelf waters. No population estimate is available for Donegal Bay
however we suggest that the proportion of the population that occurs within the site is between
2%-0% (Category C).
2.
Degree of conservation features of the habitat, which are important for the species concerned:
Bottlenose dolphins occur regularly in Donegal Bay and they have frequently been observed with
calves. It is not known if the calves were born within the site but certainly the site has importance
for the rearing of these calves. The site cannot be considered “essential to the life and
reproduction of the relevant species” but could be considered important to the life and
reproduction of the relevant species.
3.
Degree of isolation of the population present on the site: The population structure of bottlenose
dolphins in the northeast Atlantic is not known however it is likely that Donegal Bay is Grade C
i.e. not isolated within extended distribution range.
4.
Global assessment of the value of the site for the conservation of the species concerned: No
assessment is possible but the site is small relative to the range of bottlenose dolphins and as thus
cannot be considered of global significance.
5.
Resident (to be found throughout the year on the site): Although bottlenose dolphins have been
recorded throughout the year and it is likely that the same individuals use the site on a regular
basis, however bottlenose dolphins cannot be considered resident in the site.
6.
Uses the site to raise young: Young individuals, still dependent on their mother, were recorded in
Donegal Bay and thus this site is used to raise young.
One of the underlying objectives behind the EU Habitats Directive is to protect representative habitat of
species listed of Annex II of the Directive throughout Member States through designation as SACs.
Bottlenose dolphins occur throughout Irish coastal waters with important concentrations along the western
seaboard. To date only the Lower River Shannon cSAC is designated for bottlenose dolphins, thus if we are
to achieve this objective by protecting habitats representing the range of this species in Ireland then it is
necessary to designate additional SACs for bottlenose dolphins along the western seaboard of Ireland.
14
Donegal Bay is considered a good candidate for designation as an SAC for bottlenose dolphin, however,
we recommend further work is carried out to determine how bottlenose dolphins use the bay, especially
regarding the regular presence of the same individuals. This should involve the collection of more photoidentification data to enable a better understanding of their site fidelity, ranging patterns and enable an
abundance estimate to be derived using mark-recapture analysis.
Acknowledgements
We would like to thank all the boat operators Declan Kilgannon and Richard Timony for providing vessels
and Ronan Hickey, Eugene McKeown and Conor Ryan for help in the field. Conor Ryan analysed most of
the images and Ian O’Connor of GMIT kindly produced the map of boat transects and sightings in Donegal
Bay from 2008.
References
Berrow, S.D., Hickey, R., O’Brien, J. O’Connor, I. and McGrath, D. (2008) Small Cetacean Investigations
Survey 2008. Report to the National Parks and Wildlife Service. Irish Whale and Dolphin Group. pp
29.
Dawson, S., Wade, P., Slooten, E. and Barlow, J. (2008) Design and field methods for sighting surveys of
cetaceans in coastal and riverine habitats. Mammal Review 38(10), 19-49.
Englund, A., Ingram, S. and Rogan, E. (2007) Population status report for bottlenose dolphins using the
Lower River Shannon SAC, 2006-2007. Final Report to the National Parks and Wildlife Service.
University College, Cork. pp35.
Evans, P.G.H. and Hammond, P.S. (2004) Monitoring cetaceans in European waters. Mammal Review
34(1), 131-156.
Ingram, S. D. (2000) The ecology and conservation of bottlenose dolphins in the Shannon Estuary,
Ireland, University College Cork. PhD thesis, 1-213.
Ingram, S., Englund, A. and Rogan, E. (2001) An extensive survey of bottlenose dolphins (Tursiops
truncatus) on the west coast of Ireland. Final report to the Heritage Council (Ireland) WLD/2001/42,
1-17.
O’Brien, J., Berrow, S.D., Ryan, C., Whooley, P., McGrath, D. and O’Connor, I. (2008) Long-distance
movements of bottlenose dolphins (Tursiops truncatus) around the Irish coast using photoidentification. Report to the National Parks and Wildlife Service.
Reid, J. B., Evans, P.G.H. and Northridge, S.P. (2003) Atlas of Cetacean distribution in north-west
European waters. Joint Nature Conservation Committee, 1-75.
Ross, H. and Wilson, B. (1996) violent interactions between bottlenose dolphins and harbour porpoises.
Proceedings of the Royal Society (London) 263, 283-286.
SCANS-II (2008) Small Cetaceans in the European Atlantic and North Sea. Final Report to the European
Commission under project LIFE04NAT/GB/000245. Available from SMRU, Gatty Marine
Laboratory, University of St Andrews, St Andrews, Fife, KY16 8LB, UK.
15
Appendix I: Individually recognisable bottlenose dolphins from 23 July 2008
DB01_23072008_SB
DB06_23072008_SB
DB03_23072008_SB
DB07_23072008_SB
DB04_23072008_SB
DB08_23072008_SB
DB05_23072008_SB
16
DB09_23072008_SB
DB010_23072008_SB
DB20_23072008_SB
17
Appendix II: Individually recognisable bottlenose dolphins from 8 August 2008
DB02L_08082008_SB
DB11L_08082008_SB
DB12R_08082008_SB
DB14L_08082008_SB
DB02R_08082008_SB
DB11R_08082008_SB
DB13R_08082008_SB
DB16L_08082008_SB
18
DB17L_08082008_SB
DB18L_08082008_SB
DB19L_08082008_SB
DB20L_08082008_SB
DB21L_08082008_SB
DB23L_08082008_SB
DB20R_08082008_SB
DB22L_08082008_SB
DB23R_08082008_SB
19
Appendix III: Individually recognisable bottlenose dolphins from 15 August 2008
DB01L_15082008_SB
DB03R_15082008_SB
DB07L_15082008_SB
DB07R_15082008_SB
DB09L_15082008_SB
DB09R_15082008_CR
DB11R_15082008_SB
DB21L_15082008_SB
20
DB27L_15082008_SB
DB30R_15082008_CR
DB31L_15082008_SB
DB35R_15082008_SB
DB32R_15082008_SB
DB36R_15082008_SB
DB33R_15082008_SB
21
DB35R_15082008_SB
DB37R_15082008_SB
DB39R_15082008_SB
DB36R_15082008_SB
DB38R_15082008_SB
DB40R_15082008_SB
22