Marine Mammal Monitoring in Broadhaven Bay SAC, 2008
Final project report to RSK Environment Ltd.
COASTAL AND MARINE RESOURCES CENTRE ENVIRONMENTAL RESEARCH INSTITUTE UNIVERSITY COLLEGE CORK IRELAND
Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Marine Mammal Monitoring in Broadhaven Bay SAC, 2008
Mary Coleman, Evelyn Philpott, Mairéad O’ Donovan, Hannah Denniston, Laura Walshe, Margaret Haberlin, Anneli Englund
COASTAL AND MARINE RESOURCES CENTRE ENVIRONMENTAL RESEARCH INSTITUTE UNIVERSITY COLLEGE CORK IRELAND
Citation: Coleman, M., Philpott, E., O’Donovan, M., Denniston, H., Walshe, L., Haberlin, M. and Englund, A. 2009. Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project report to RSK Environment Ltd. Coastal and Marine Resources Centre, University College Cork. 68pp. Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
CONTENTS Page Number SUMMARY 1
1. INTRODUCTION
1.1 Study background 3 1.2 Marine mammals in Irish waters 3 1.3 Broadhaven Bay SAC 4 1.4 Marine mammals in Broadhaven Bay 5 1.5 Corrib Gas project 6 1.6 Potential impact on marine mammals 1.6.1 Direct impact 6 1.6.2 Mitigation for direct impacts 7 1.6.3 Indirect impact 8 1.6.4 Mitigation for indirect impacts 8 1.6.5 Long-term impacts 8 1.7 Research objectives 8
2. VISUAL MONITORING FOR MARINE SPECIES
2.1 Introduction 9 2.2 Methodology 2.2.1 Cliff-based visual survey 2.2.1.1 Study area and observation sites 10 2.2.1.2 Data collection 12 2.2.2 Boat-based survey methods 14
2.2.3 Analyses of visual survey data 15 2.3 Results & discussion 2.3.1 Visual survey effort 16 2.3.2 Marine mammal sightings 2008 16 2.3.3 Comparative Analysis 20 2.3.4 Cetaceans in Broadhaven Bay 24 2.3.5 Seals in Broadhaven Bay 36
2.3.6 Other species of interest 38
Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
3. ACOUSTIC MONITORING FOR SMALL CETACEANS
3.1 Introduction 41 3.2 Methods 41 3.2.1 Data analysis 42 3.3 Results 3.3.1 Survey effort 43 3.3.2 Acoustic detections 44 3.3.3 Porpoise detection 46 3.3.4 Dolphin detection 47 3.3.5 Comparison with all previous years of acoustic monitoring 48 3.4 Discussion 3.4.1 Acoustic coverage of Rossport Bay 49 3.4.2 Cetacean detections 2008 49 3.4.3 Comparison with visual data 51
4. PHOTO-IDENTIFICATION OF BOTTLENOSE DOLPHINS
4.1 Introduction 52 4.2 Methods 4.2.1 Photo-identification field methods 54 4.2.2 Image analysis 54 4.3 Results & discussion 56 4.3.1 Group composition 58 4.3.2 Group size 58 4.3.3 Site-fidelity 60 4.4 Conclusions of photo-identification 61
5. CONCLUSIONS AND RECOMMENDATIONS 62 6. ACKNOWLEDGEMENTS AND PHOTOGRAPHIC CREDITS 64
7. REFERENCES 65
Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
SUMMARY A marine mammal monitoring programme commenced in May 2008 in Broadhaven Bay Special Area of Conservation (SAC) prior to and in concurrence with the inshore construction phase of the Corrib Gas underwater pipeline. The Coastal and Marine Resources Centre (CMRC) of University College Cork (UCC) conducted similar monitoring of the area in 2001-2002 (providing for baseline monitoring) and again in 2005. This report summarises visual results from May to October and acoustic results from June to December 2008 and briefly compares sightings data from 2002, 2005 and 2008 field seasons.
The present monitoring programme provides an assessment of marine mammal occurrence and distribution in the waters of Broadhaven Bay SAC during 2008 by means of visual, acoustic and photo-identification research with the following objectives:
To collaborate with the National Parks and Wildlife Service (NPWS) of the Department of the Environment, Heritage and Local Government (DoEHLG) and with RSK Environment Ltd to monitor any potential impacts on animals due to construction activities within Broadhaven Bay.
To collate the findings of the most recent survey period with those of previous years’ studies to develop an overall understanding of Broadhaven Bay’s significance for marine mammals and to allow for comparative analysis of marine mammal presence and distribution in the area between years.
To further contribute to the international knowledge-base of marine mammals on the Irish west coast.
Visual monitoring for marine mammals
A total of 336.4 hours of dedicated monitoring (cliff and boat-based) were carried out on 44 separate days from May to October 2008.
For comparative analysis, data from June to September was extracted from each of the three survey periods and compared between years, resulting in a total of 248 hours from 2002, 281 hours from 2005 and 247 hours from 2008. Monitoring included 8.48 hours of boat-based effort in 2008 and 54.5 hours in 2002. No dedicated boat-based effort was completed in 2005.
A total of 93 distinct marine mammal sightings were recorded (71 cetaceans and 22 seals) between 15th May and 14th October 2008.
1 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
The total number of distinct marine mammal sightings recorded between June and September 2008 were lower than in previous survey years. In 2002 there were a total of 143 distinct marine mammal sightings (52 cetaceans and 91 seals), compared to 64 distinct sightings (30 cetaceans and 34 seals) in 2005 and 59 distinct sightings (40 cetaceans and 19 seals) in 2008.
Acoustic monitoring for small cetaceans
Acoustic equipment was deployed in Rossport Bay between June and December 2008 for a total of 161 days. Three listening stations were working effectively for 106 of those days. Acoustic monitoring was reduced to two listening stations for 55 days due to removal of a mooring and the anticipated arrival of the pipe-laying ship delaying redeployment.
A total of 4,677.5 hours of data was collected in 2008 compared to 6,590.8 hours in 2002 and 6,350.5 hours in 2005.
Both dolphin and porpoise detections were successfully logged in 2008. Detections were made during day and night and in all tidal states.
Extended acoustic monitoring continuing into the autumn and winter of 2008 indicated a seasonal pattern to dolphin and porpoise distribution in Rossport Bay. Dolphin echolocation activity peaked in early summer while porpoise echolocation activity peaked in late autumn.
Continued acoustic monitoring in Rossport Bay is considered essential during any future construction work. The difficulties in the observation of harbour porpoises in particular highlight the importance of such monitoring.
Photo-identification of bottlenose dolphins
A minimum of 16 and a maximum of 17 naturally marked bottlenose dolphins were identified in Broadhaven Bay in 2008. No matches were confirmed with the 25 to 39 individuals identified in 2002.
The presence of neonate bottlenose dolphins calves was recorded during photo-identification completed in 2008.
2 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
1. INTRODUCTION
1.1 Study background A marine mammal monitoring programme commenced in May 2008 in Broadhaven Bay, Co. Mayo, conducted by researchers from the Coastal and Marine Resources Centre (CMRC) of University College Cork. The CMRC completed similar monitoring programmes during 2001 to 2002 (Ó Cadhla et al., 2003) and in 2005 (Englund et al., 2006). The 2001-2002 monitoring programme represented a baseline study of marine mammal occurrence and habitat use in the area prior to pipeline development with particular consideration given to the evaluation of how potential construction impacts on animals might be minimised. This study identified the waters of Broadhaven Bay SAC and the northwest Mayo area as representing “a significant habitat for marine mammals and other biota” and, in accordance with the recommendations of the 2003 report, similar monitoring recommenced in 2005 when pipeline construction was initiated but subsequently postponed prior to completion. The results of research conducted during 2005 therefore served to extend and complement the preceding baseline study. Specific recommendations in the report for the 2005 study period re-iterated the need to initiate marine mammal monitoring prior to commencement of any construction and highlighted the need to include boat- based surveys and photo-identification as part of future survey effort along with continued visual and acoustic monitoring. It was also advised that construction noise levels be monitored in order that these could be compared with animal occurrence and movement patterns to address the impact of construction noise on animals (Englund et al., 2006).
1.2 Marine mammals in Irish waters To date, 24 species of cetacean have been recorded in Ireland and the country’s waters are recognised as providing some of Europe’s most important habitats for cetaceans (Berrow et al., 2002). Irish waters are thought to represent breeding grounds for up to 11 of these species (Berrow, 2001). In addition to cetaceans, two seal species (Order Pinnipedia) are native to Ireland.
In terms of the conservation status of marine mammals, large whale species have been afforded protection in Irish waters since the Whale Fisheries Act (1937) restricted their commercial exploitation. Protection from hunting was extended to all cetacean species under the Wildlife Act (1976 amended in 2000) and a 1982
3 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. amendment to the Whale Fisheries Act (Gordon et al., 1999). Ireland’s territorial waters were declared a whale and dolphin sanctuary in 1991, a status that encompasses the state’s Exclusive Economic Zone - up to 200 miles offshore (Rogan & Berrow, 1995).
The EU Habitats Directive (92/43/EEC) provides for the protection of all cetaceans due to their designation as Annex IV species (species of community interest in need of strict protection). In accordance with the Habitats Directive, Ireland also has a total of 25 species that merit Annex II status. Annex II applies to species “of community interest whose conservation requires the designation of SACs”. Of these 25 species four are marine mammals, namely: bottlenose dolphin (Tursiops truncatus); harbour porpoise (Phocoena phocoena); grey seal (Halichoerus grypus); harbour/common seal (Phoca vitulina vitulina). The European otter (Lutra lutra) accounts for another of the 25 Annex II species. Significantly, the four species of marine mammal listed in Annex II along with the European otter, are among the species known to utilise Broadhaven Bay (see Section 1.4 below for detail).
1.3 Broadhaven Bay SAC Broadhaven Bay was designated by the National Parks and Wildlife Services (NPWS) of the Department of the Environment, Heritage and Local Government (DoEHLG) as a candidate Special Area of Conservation (SAC) in 2000. The selection of the bay is due to a combination of notable features present in the bay (www.npws.ie/en/ProtectedSites):
The presence of four key marine/coastal habitat types that merit Annex I protection under the EU Habitats Directive. These include: Atlantic salt marsh; tidal mudflats; reefs; large shallow bays.
The presence of a number of unusual marine communities and species, with notably high species richness (up to 72 species).
The importance of the area to wintering wildfowl and breeding terns (Sterna spp.). The occurrence of nationally and internationally important numbers of Brent Geese (Branta bernicla - Annex II (EU Birds Directive)) furthermore warranted the designation of an inner section (Rossport Bay) of the more extensive bay area as a Special Protection Area (SPA). Together with the nearby Glenamoy Bog complex SAC, Rossport SPA represents an important habitat for wintering wildfowl species.
4 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
1.4 Marine mammals in Broadhaven Bay Dedicated research into the distribution and abundance of marine mammals in coastal and offshore Irish waters (e.g. Cronin et al., 2004; Gordon, et al., 1999; Kiely & Myers, 1998; Ó Cadhla et al., 2004, Ó Cadhla et al., 2007; Pollock et al., 1997), together with historical data (Fairley, 1981), incidental sighting records compiled by the Irish Whale and Dolphin Group (Berrow et al., 2002) and stranding records (e.g. Berrow & Rogan, 1997) have highlighted the potential importance of the waters off northwest Mayo for cetaceans (whales, dolphins and porpoises) and seals.
Although the presence of marine mammal species of conservation importance in the Broadhaven Bay SAC is not specifically mentioned under the NPWS’s SAC site synopsis, previous studies indicate the importance of the bay to such species. In addition to the four species of marine mammal listed in Annex II (see Section 1.2 above) six further species of marine mammal and other species such as basking shark, sunfish and the European otter (also Annex II) have been recorded within Broadhaven Bay and its adjacent waters. Furthermore, records of strandings and accounts of historical whaling activities in the region suggest the importance of these coastal waters to a considerable diversity of marine mammal species (Table 1.1). Table 1.1. Marine mammals sighted in Broadhaven bay or stranded* on the adjacent coastline Common name Scientific name Reference Grey seal Halichoerus grypus Harbour seal Phoca vitulina vitulina
Bottlenose dolphin Tursiops truncatus Ó Cadhla et al., 2003 and Harbour porpoise Phocoena phocoena Englund et al., 2006 Minke whale Balaenoptera acutorostrata Common dolphin Delphinus delphis Risso’s dolphin Grampus griseus Atlantic white-sided dolphin Lagenorhynchus acutus Ó Cadhla et al., 2003
White beaked dolphin Lagenorhynchus albirostris Ó Cadhla et al., 2003 Killer whale Orcinus orca Englund et al., 2006 Striped dolphin* (Elly bay – Stenella coeruleoalba Live stranding – CMRC, July 2005) 2005 (pers. comm.) Sperm whale* (Elly beach – Physeter macrocephalus Sweeney, 2009 (pers. August, 1989) comm.)
5 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
The occurrence of such high marine mammal species diversity in an inshore area does not appear to be typical of Ireland’s west coast. Comparable studies at other locations (e.g. Berrow et al., 1996; Ingram, 2000; Ingram et al., 2005b; Rogan et al., 2000; Ingram & Rogan, 2002; Ingram et al., 2003; Ingram et al., 2005a) have not yet identified areas with species diversities as high as observed in and around Broadhaven Bay.
These studies may not necessarily cover as extensive time periods as the monitoring in Broadhaven Bay but are still comparable on a yearly basis. For example, a study by UCC researchers in the waters of Connemara, Co. Galway combined cliff watches, acoustic surveillance and boat surveys over a period of four months (July to October, 2003). A total of 163 hours of effort was achieved during 57 days and resulted in sightings of 30 bottlenose dolphin schools, one school of common dolphins and a small number of harbour porpoises (Ingram et al., 2003). It was also found that bottlenose dolphins showed a degree of site-fidelity to the area, with re- sightings of a number of encountered individuals between years. Another example is a study that took place in north Kerry during four months (July to October) in 2005. In this study, shore-based observation was possible on 21 days, resulting in 120 hours of effort from six different observations sites. Only four species were recorded, bottlenose dolphin (n=6), Risso’s dolphin (n=3), Killer whale (n=1) and grey seal (n=2) (Ingram et al., 2005a).
1.5 Corrib Gas project The Corrib Gas project involves the laying of an 84km underwater pipeline planned to come ashore at the eastern side of Broadhaven Bay with a landfall site located at Glengad. Within Broadhaven Bay, pipeline construction involved the excavation of sediment to create a 3 x 3 metre trench in which the gas pipeline and its associated umbilical and water discharge pipelines will be laid.
1.6 Potential impact on marine mammals
1.6.1 Direct impact
Construction work in Broadhaven Bay has the potential to have a direct negative impact on the bay’s marine mammal population in the event of direct collision with a vessel or construction equipment. The likelihood and potential gravity of such an incident however must be considered in the context of the marine environment of the
6 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. area in general, where animals encounter boat traffic (albeit at lower frequencies) due to the utilisation of the area by fishing and recreational vessels.
The effects of noise from anthropogenic sound sources may vary depending on the source type. In the case of construction work where the main sound sources of concern are from vessels and dredging the impacts include: masking (of animals’ own acoustical communication); habitat displacement, behavioural change and behaviourally-mediated effects (Boyd, 2008). The use of sonar is associated additionally with the potential occurrence of physical trauma and hearing loss (depending on frequency and intensity) (Boyd, 2008).
Avoidance of possible collision events and noise is likely to represent the most probable impact of construction on animals. Avoidance would signify a behavioural response to the presence of construction vessels and their associated noise. Changes in behaviour of marine mammals in response to the presence of boats has been the subject of much investigation (e.g. bottlenose dolphins in New Zealand, (Lusseau, 2003); bottlenose dolphins in Scotland (Lütkebohle, 1995); killer whales in Canada (Erbe, 2001); bottlenose dolphins in Florida (Nowacek et al., 2001)). The concern associated with a behavioural response as such would relate to the resultant changes in behavioural budget and the consequent effect on an animal’s energetic budget (Lusseau, 2003) in response to increased vessel presence in the bay. The threat in the long-term might be displacement of animals to avoid the energetic costs of boat impact (Lusseau, 2003). The complexity of quantifying such an impact is considerable and therefore prevention as far as possible obviously represents the best option particularly given the 24-hour nature of construction work, which offers no respite from disturbance.
1.6.2 Mitigation for direct impacts
Mitigation aiming to ensure marine mammal protection is provided for via a “Code of Conduct for vessels and personnel operating within Broadhaven Bay SAC” and the NPWS requirement that “coastal works” be carried out according to guidelines based on a variation of the “Code of Practice for the Protection of Marine Mammals during Acoustic Seafloor Surveys in Irish Waters” (NPWS, 2007) (where “coastal works” are defined as “any operations outside of acoustic seafloor surveys where mitigation for potential impacts of marine noise are required for marine mammals e.g. dredging, pile-driving etc” (npws.ie)).
7 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
1.6.3 Indirect impact
Degradation of marine mammal habitat in the Broadhaven Bay area would correspond to an indirect impact of construction work on marine mammals. Such an impact is probable on a temporary basis due to the effect of construction on water quality (e.g. sedimentation), which may affect prey species and their availability, thereby altering foraging opportunities for marine mammals. The duration of such habitat degradation is likely to be short-term
1.6.4 Mitigation for indirect impacts
Alleviation of such an indirect impact may be achieved to some extent through application of best practice methods for construction to minimise environmental impacts and through adequate habitat reinstatement post-construction.
1.6.5 Long-term impacts
More permanent habitat degradation potentially induced by pipeline installation and the cumulative effects of construction impacts overall remain difficult to pre-empt. While a certain degree of temporary displacement and an impact on behaviour is inevitable the potential for permanent displacement remains a threat. Long-term monitoring of marine mammals to evaluate the magnitude of such impacts would be beneficial as marine mammals (in their role as top predators) represent potential indicators of overall ecosystem integrity (e.g. Mössner & Ballschmiter, 2008).
1.7 Research objectives
The main objective of the study was to implement a marine mammal monitoring programme in Broadhaven Bay to coincide with pipeline installation works in the area. The objectives and approach to the study were the outcome of consultation between the CMRC and RSK Environment Ltd (Watson, 2008) and can be summarised as follows: To collaborate with the National Parks and Wildlife Service (NPWS) of the Department of the Environment, Heritage and Local Government and with RSK Environment Ltd to monitor the impact, if any, on animals due to construction activities within Broadhaven Bay;
To collate the findings of the most recent survey period with those of previous years’ studies to develop an overall understanding of Broadhaven Bay’s significance for marine mammals and to allow for comparative analysis; and
To further contribute to the international knowledge-base of marine mammals on the Irish west coast.
8 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
2. Visual monitoring for marine species
2.1 Introduction
The visual monitoring component of the study incorporated both land- and boat- based survey methods. The surface behaviour of marine mammals lends itself to the effectiveness of visual observation, as it is possible to locate, identify and follow many species using telescopes and other optical equipment.
Visual observation from fixed positions on land is commonly used for monitoring of marine mammals in inshore waters (e.g. Janik & Thompson, 1996; Lütkebohle, 1995; Williams et al., 2002). This method represents a relatively low-cost method of collecting data that is non-invasive and does not impact on the behaviour of animals being observed. The use of fixed observation sites on land confers advantages such as: the ability to standardise data (Evans & Hammond, 2004); the facilitation of methods such as theodolite-tracking; and, where vantage points at relatively high altitudes are available, a large study area can be surveyed effectively. Drawbacks of this type of surveying include the restriction of data collection within the relatively confined area and species identification issues when animals are observed a distance from the site.
For in-shore study areas land-based surveying is ideally complemented by employing boat-based methods. A boat-based platform allows for observation of animals at closer range providing more accuracy in terms of species identification (especially, for example, where mixed-species groups occur) and definition of behaviour, group cohesion and composition (e.g. juvenile/calf presence). Juveniles were here defined as subadults (<2/3 the size of adults), calves (<1 year) and neonates (<1 month old) and were recognised due to their smaller size, the presence of foetal folds or lines and their close association with a larger animal assumed to be the mother. The use of boat-based line-transect sampling also provides a means of estimating animal density within the study area based on extrapolation of animal density within surveyed strips of defined area (Evans & Hammond, 2004). Data collection by means of boat-based surveying is however exposed to potential bias due to the possible movement and/or change in animal behaviour in response to the survey vessel. An additional constraint associated with boat-based methods is their notable sensitivity to prevailing weather conditions.
9 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
A considerable limitation of visual surveying of marine mammals in general is the inter-species variability of detection probability. This depends on a species’ size and aspects of a species’ typical behaviour e.g. dive sequence and frequency. For example, the harbour porpoise is notoriously difficult to detect owing to the animals’ relatively small size, tendency to avoid boats and characteristically short periods spent surfacing, during which only a small portion of the body tends to be visible (Evans & Hammond, 2004, Leopold et al., 1992, Rogan & Berrow, 1996). Interpretation of results therefore requires consideration of the potential bias towards species that are more disposed to detection. Confounding this issue is the effect of weather conditions (in particular sea state) on the quality of data attainable, which varies depending on species. The ability to detect minke whales has been shown to notably decline in sea states greater than Beaufort force 2 (Leaper et al., 1997 in Gordon et al., 1999); similarly, sea states of Beaufort force 3 or greater markedly affect the ability to detect harbour porpoises (Hammond et al., 1995). Ideally visual surveys should not be conducted in sea states above Beaufort force 2 (Evans & Hammond, 2004) although the general upper limit for inclusion of data in estimating relative abundance is a sea state of Beaufort force 3 (e.g. Wall et al., 2006; Ó Cadhla et al., 2004).
2.2 Methodology
2.2.1 Cliff-based visual survey
2.2.1.1 Study area and observation sites
Broadhaven Bay is situated on the north-west coast of county Mayo. The bay has a north-westerly aspect, with the mouth of the bay extending c.8.6 km from Erris Head on the western side to Kid Island at its eastern limit. As in the previous studies of 2001-2002 and 2005, the present study incorporates the waters of Broadhaven Bay and the waters outside of the bay to a distance of about 10 km off the coast (i.e. those within the visual range of observers). A number of suitable sites were selected for land-based observations during the baseline study of 2001-2002 and used again in 2005 (Ó Cadhla et al., 2003, Englund et al., 2006). These were selected based on their suitability for cliff-based observation, with a particular emphasis on height above sea level and the field of view offered over the survey area. In order to ensure comparability of data, the same observation sites were used during the 2008 study (Fig. 2.1).
10 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 2.1. Map of the Broadhaven Bay study area illustrating sites used for shore-based and acoustic (T-POD) monitoring components of the study along with routes of boat survey line-transects.
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As illustrated by the map above the primary site at Doonanierin Point, situated close to Rossport Bay, provides an excellent view over the eastern bay area and over the location of the pipeline’s landfall site, i.e. the main area of inshore construction work. The other primary observation site used (Gubastuckaun) is located approximately 1.2km south east of the tip of Erris Head providing an ideal vantage point for monitoring marine mammals entering or leaving the bay. Brandy Point is a secondary shore-based site located adjacent to the relatively sheltered inner section of Broadhaven Bay, thereby providing a potential alternative observation site for inshore observations when conditions at Doonanierin may be unfavourable for effective monitoring. Although a considerably lower vantage point, Brandy Point provides a good view of Rossport Bay, close to which aspects of construction work were concentrated.
2.2.1.2 Data collection
Effective observation was facilitated using a tripod-mounted telescope (Kowa) equipped with a 32x magnification wide-angle eyepiece and a pair of 7x50 binoculars (Talamax). A digital surveyor’s theodolite (Sokkia) was used to record accurate angles (vertical and horizontal) to sighted animals to enable calculation of their positions and to track their movements within the study area. Data collection was essentially obtained using two sampling methods as described below.
Scan sampling consisted of repeated systematic scans of the bay, the duration of which was typically 60 minutes with variations depending on prevailing weather conditions and on the frequency of sightings during any given scan. To maximise the efficacy of scanning effort successive sample periods were divided by a 30 minute “rest” interval during which environmental data could be recorded and equipment checks made. Watches were continued in this way for as long as daylight and weather conditions permitted. Weather conditions were monitored and recorded along with details of sightings when they occurred.
Theodolite tracking involved the use of a surveyor’s theodolite to track animal movements within the study area or at least to get an accurate position of the initial sighting. As in previous years a theodolite was utilised at the Doonanierin site owing to this observation site’s proximity to the location of construction activities within the bay. The 2008 survey season presented an opportunity to introduce the use of a second theodolite at the Gubastuckaun site (Plate 2.1) allowing for improved
12 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. accuracy in determining the positions of animal sightings. The second theodolite was on-site from July. Prior to this, positions of animals were specified according to the compass bearing to the animal and a distance estimate (acquired with the aid of reticle binoculars or a distance measuring stick when possible or by the use of known reference landmarks within the study area).
Plate 2.1. Visual survey set-up at Gubastuckaun, with the Stags of Broadhaven in the background showing a telescope and a surveyor’s theodolite used for positioning of sighted animals.
Once a sighting was confirmed and appropriately recorded, scan sampling recommenced. The availability of two observers on-site allowed for scan sampling and theodolite tracking to be carried on simultaneously thereby maximising the data acquired from a single sighting.
Communication between observers on either observation site was maintained via walkie-talkies in order to co-ordinate and thereby optimise data collection in the field. This allowed for sightings to be identified as duplicate or non-duplicate (see Section 2.2.3 below for an explanation of “duplicate”) so that sampling effort could be efficiently allocated.
Off-effort sightings were also recorded, i.e. animals seen by CMRC observers outside dedicated scan sampling periods. Such off-effort sightings were excluded from analysis of sighting rates and associated graph compilation.
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2.2.2 Boat-based survey methods
Boat-based surveys were conducted aboard a 40-foot sea angling boat, An Gearóidín. This vessel provided an observation platform offering an eye-height of c.3 m above sea-level. The method consisted of line-transect surveys conducted in accordance with the method employed during previous boat surveys in the bay in 2002 (Ó Cadhla et al., 2003), as summarised below:
Adequate conditions for this survey method necessitated a combination of light wind (≤ Beaufort force 3), little or no swell (maximum swell = 0.5m) and calm sea conditions (≤ Beaufort sea state 3). Relatively high cloud cover was another favourable factor as it minimised the occurrence of glare on the sea surface.
The line transect survey route developed for Broadhaven bay during the 2002 survey period (Ó Cadhla et al., 2003) was followed during the 2008 boat surveys. This consisted of nine parallel transect lines spaced approximately 1 km apart. Eight of the lines were within the SAC, with the ninth approximately 500 m beyond its boundary (Fig. 2.1). Ideally, line transects were conducted simultaneously to cliff- based monitoring, allowing for co-ordination of survey effort by means of communication between observers.
A dual observer approach was implemented to cover a 180° arc (i.e. 90° either side of the bow). Observers scanned with the naked eye and each was equipped with a pair of 7x50 binoculars (Talamax) to assist with marine mammal identification. All data parameters recorded during cliff-based monitoring (i.e. active scanning effort, environmental conditions, species, group size and composition, location etc.) were also collected during line transects. Boat speed during transects was maintained at 10 knots with completion of a survey taking a minimum of five to six hours. An allowance was made to diverge from the transect line if animals were seen and needed to be approached for identification purposes or, in the case of bottlenose dolphins, for photo-identification (see Section 4 below). In such instances the behaviour of animals was taken into account, for example a feeding group would not be approached, as disturbance of foraging was undesirable. After completion of identification or photo-identification of a particular individual or group the line transect was resumed from the point of interception.
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Casual boat-based surveys were conducted opportunistically when the Rigid Inflatable Boat (RIB) was mobilised for deployment and collection of T-PODs on six occasions between June 12th and November 1st. Surveillance was conducted with the naked eye. A pair of 7x50 binoculars (Talamax) was used for species identification if necessary and a camera was also available if an opportunity arose to undertake photo-identification (see Section 4 below).
2.2.3 Analyses of visual survey data
Visual survey data (i.e. sighting, effort and weather information) were compiled into a Microsoft Access database and analysed using Microsoft Excel. Duplicate sightings (i.e. any subsequent sighting of an individual or group seen from the same or any other observation site) were excluded from all analysis and results so that sighting rates, graphs, tables and maps refer only to “distinct sightings”. Off-effort or incidental sightings recorded outside of dedicated scanning times were excluded from analysis and results presentations that relate sightings to effort. Only sightings recorded in sea states of less than force 4 were included in the analysis of sightings relative to effort in order to ensure truly representative sighting rates per unit effort. For analysis per species only species identifications that were classified as “definite” were included. Analysis of sighting rates relative to tidal state took into account sampling effort per tidal state and applied where possible to the time of the initial sighting of an individual or group.
Irish National Grid (ING) co-ordinates were derived for sightings using theodolite angles recorded. Where theodolite angles could not be obtained in the field co- ordinates were derived from compass bearings and distance estimates. The co- ordinates of the observation sites were the same as those used in previous studies (acquired using a Differential GPS (Ó Cadhla et al., 2003)). The introduction of theodolite tracking from the Gubastuckaun site necessitated the location of the theodolite in a suitable position, the co-ordinates of which were attained using a handheld GPS (Garmin). Derivation of ING co-ordinates of sighting positions took into account theodolite eye height above sea level, which was related to the tide height at the time of the sighting. Distinct sightings were mapped using GIS software ArcGIS ArcMap Version 9.2 © ESRI Inc.
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2.3 Results & discussion
2.3.1 Visual survey effort
Shore-based monitoring began on 15th May 2008 and will continue throughout the winter months in 2009 when weather permits. For the purpose of this report data up to and including October is presented (thus correlating to the period of construction work taking place in the area). Monitoring effort was conducted on 44 days during this period including a total of 82 distinct watches, allowing for a total of 336.4 hours actively scanning the bay. A total of 326.9 hours of this active scan time was conducted in sea state (SS) ≤ 3 and was therefore deemed “effective”. The greatest proportions of effective scanning effort were achieved in July (26%) and May (24%), followed by June (21%), with less effort in September (14%) and August (13%) and considerably less in October (2.7%) (see Figure 2.2 below).
90
80
70
60
50
Hours 40
30
20
10
0 May June July August September October
Figure 2.2. Graph illustrating total hours of observation effort per month, including 15th May to 14 th October 2008. Data includes 8.48 hours of boat-based effort in July and September.
2.3.2 Marine mammal sightings 2008 After deduction of duplicate sightings (i.e. any subsequent sighting of the same individual or group observed from the same or any other observation location (boat or cliff)) from the 2008 dataset, a total of 93 distinct marine mammal sightings were identified, including 71 cetacean and 22 seal sightings recorded over the survey period (Table 2.1). A total of seven marine mammal species were recorded during the 2008 survey period. Six of these were cetacean species and one seal species, the grey seal. The majority of marine mammal sightings recorded in 2008 occurred within the boundaries of the SAC (Fig. 2.3) with a pattern of distribution comparable to previous study years. Species recorded during the 2008 survey period were in-
16 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. keeping with the findings of Ó Cadhla et al. (2003) and Englund et al. (2006), confirming the recurrent use of the bay by these species.
It is notable that, when compared with other similar well-studied areas along the Irish coast, Broadhaven Bay has a relatively high diversity of marine mammal species frequently occurring in the area. Comparable study areas in Ireland include: the Shannon Estuary, where long-term study of a resident bottlenose dolphin population has been ongoing since 1996 (e.g. Rogan et al., 2000; Englund et al., 2007; Englund et al., 2008); Bantry Bay (Roycroft et al., 2007); Tralee Bay (Ingram et al., 2005a); North Kerry (Ingram et al., 2005b) and Connemara (Ingram et al., 2003). For these study areas the marine mammal species diversity documented or anecdotally reported is markedly lower than that confirmed to recur in the Broadhaven Bay area.
The most frequently sighted species in Broadhaven Bay during 2008 was the harbour porpoise with 13 distinct sightings, followed by ten sightings of common dolphins, nine sightings of bottlenose dolphins and seven Risso’s dolphin sightings. The species observed in the highest numbers was the common dolphin, with 310 animals in total across ten distinct sightings. Killer whales were the least frequently observed species with only one sighting of three animals (see Table 2.1 below for details of all species observed).
Analysis of the overall (i.e. all species combined) sighting rate in relation to the sampling effort at different tidal states (low, flooding, high and ebbing) suggests a higher sighting rate per hour of effort during high tide (where high tide was defined as one hour either side of high water) (Fig. 2.4 below). Correlation between bottlenose dolphin utilisation of certain areas with particular tidal states has been documented in other research areas (Ingram & Rogan, 2002; Lütkebohle, 1995). The implication of a pattern of marine mammal occurrence relative to the tidal state for this study area cannot be conclusively established without comparative analysis of previous year’s data. Furthermore, inter-species variability may confound results and therefore the identification of any actual patterns requires more intensive examination per species.
17 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Table 2.1. All marine mammal sightings recorded by CMRC observers in Broadhaven Bay between 15th May and 14th
October 2008.
Number of Number of Species sightings animals 2008 2008 Cetaceans Minke whale (MI) 6 6 Unidentified whale (UW) 2 3 Killer whale (KW) 1 3 Risso’s dolphin (RD) 7 38 Bottlenose dolphin (BND) 9 77 Common dolphin (CD) 10 310 Harbour porpoise (HP) 13 26 Unidentified dolphin (UD) 20 128 Unidentified cetacean (UC) 3 12 Cetaceans total 71 603 Seals Grey seal (GS) 10 16 Unidentified seal (S) 12 13
Seals total 22 29 Total marine mammals 93 632
18 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 2.3. Map showing distribution of distinct sightings between 15th May & 14th October
2008. Cetaceans are represented by triangles; circles denote seals; squares represent basking sharks (red), sunfish (green) and otter (blue). Positions were derived from theodolite readings where possible and otherwise via estimated distance and compass bearing.
0.6
0.5
0.4
0.3
0.2
0.1 Sighting rate per hour of effort of hour per Sighting rate
0 High Ebbing Low Flooding
Figure 2.4. Graph illustrating sighting rate relative to observation effort (per tidal state) for distinct sightings recorded between 15th May and 14th October 2008.
19 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
2.3.3 Comparative analysis For comparative analysis over the three survey periods (2002, 2005 and 2008) only sightings from the months common to all years (June to September) have been included. Notably, over half (55%) of all sightings of bottlenose dolphin, 69% of all harbour porpoise sightings and 60% of common dolphin sightings for 2008 occurred in May and are therefore excluded from analyses incorporating the 2002 and 2005 study periods. Continued monitoring over the winter and spring period of 2009 will provide valuable data for months that were not covered sufficiently in previous years of survey.
The graph in Figure 2.5 below compares hours of survey effort for 2002, 2005 and 2008 over the summer months. During June 2008 the total observation effort achieved was greater than in previous years but poor weather conditions during August 2008 in particular led to fewer hours of observation effort compared to 2002 and 2005.
A similar diversity of species was recorded in 2008 relative to the same period in 2002 and 2005, as displayed in Table 2.2. In 2008 there were also two sightings of unidentified large whales (possibly fin or sei whales), representing the first instance where a whale of this size was observed in the bay by UCC observers. Although, due to the distance between the observer and animals, identification to species level could not be confirmed, this sighting probably represents a new (i.e. previously unrecorded) species in the area, implying even higher species diversity than documented to date.
Killer whales were seen in 2005 but not in 2002, and were recorded again in 2008, with one sighting of three animals. White-sided and white beaked dolphins, both relatively small dolphin species, were recorded in 2002 but not observed in either 2005 or 2008. In 2002 these species were generally encountered during boat surveys, occurring in mixed species groups with common dolphins (a species from which they are difficult to tell apart unless observed at close distance). The lower level or lack of boat effort may account for these species not being identified during 2005 or 2008 survey periods. On two occasions in 2008 “unidentified dolphin” sightings were deemed to be “possible” white-sided dolphins but the distance of animals from the observation site prevented confirmation of a “definite” species identification.
20 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Group sizes recorded in 2008 were similar for most species when compared to those recorded during previous surveys (Table 2.3). The maximum group size recorded in 2008 for Risso’s dolphins (n=10) was notably greater than observed in 2002 (n=3) or 2005 (n=5). The group size range recorded for common dolphins varied between the three survey periods with the largest group recorded in 2005 (n=250).
When compared with previous survey years, sighting rates showed some variation (Fig. 2.6). The overall sighting rate in 2008 was similar to that of 2005 but both of these years had overall sighting rates less than half of the 2002 equivalent. Closer examination reveals that the difference can be largely attributed to a lower sighting rate of seal species, which was notably lower in 2005 and 2008 compared to 2002. This difference may in part be a consequence of the relatively higher boat-based effort achieved in 2002 (54.5 hours) compared to 2005 (0 hours) and 2008 (8.48 hours), which may have incurred a particular advantage for the observation and identification of seals. It is also possible that, due to increased vessel activity in the bay owing to construction, seals may have been displaced. The sighting rate for cetaceans was similar across the three survey periods – the highest cetacean sighting rate was observed in 2002, with the lowest recorded for 2005.
100 2002 2005 2008 90 80 70 60 50
Hours 40 30 20 10 0 June July August September
Figure 2.5. Graph illustrating hours of observation effort for June to September in 2002, 2005 and 2008.
21 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Table 2.2. All sightings from June to September in 2002, 2005 & 2008 (i.e. the comparable field survey
period across the three years) excluding any duplicate sightings. Data from 2002 includes 54.5 hours of
boat-based observation effort during July and August and data from 2008 includes 8.48 hours of boat- based effort in July and September. There was no boat-based effort in 2005.
Sightings Sightings Sightings Animals Animals Animals Species 2002 2005 2008 2002 2005 2008
Cetaceans Minke whale (MI) 4 1 6 4 1 6 Unidentified whale 0 0 1 0 0 3 (UW) Killer whale (KW) 0 2 1 0 6 3 Risso’s dolphin (RD) 6 4 7 19 11 38 Bottlenose dolphin 14 8 3 152 81 27 (BND) Common dolphin 3* 5 4 49 307 192 (CD) White sided dolphin 3* 0 0 91 0 0 (WSD) White beaked 2* 0 0 8 0 0 dolphin (WBD) Harbour porpoise 16 3 4 34 3 7 (HP) Unidentified dolphin 4 7 12 9 75 72 (UD) Unidentified 0 0 2 0 0 2 cetacean (UC) Cetaceans total 52 30 40 366 484 350
Seals Grey seal (GS) 58 22 8 63 24 13 Harbour seal (HS) 31 10 0 83 10 0 Unidentified seal (S) 2 2 11 8 2 12 Seals total 91 34 19 154 36 25
TOTAL 143 66 59 520 520 375
Note * indicate instances of mixed groups of animals observed in 2002. Two of these groups consisted of common dolphins and white-sided dolphins. One of these groups also included a third species; white beaked dolphins.
22 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. Table 2.3. Summary of group size range for species encountered in Broadhaven Bay during June to September 2002, 2005 and 2008.
Group size Group size Group size Species range 2002 range 2005 range 2008 Cetaceans Minke whale (MI) 1 1 1 Killer whale (KW) - 2 – 4 3 Rissos dolphin (RD) 1 – 3 1 – 5 1-10 Bottlenose dolphin (BND) 1 – 18 4 – 20 1-17 Common dolphin (CD) 1 – 49 5 – 250 1-125* White sided dolphin (WSD) 4 – 25 - 0 White beaked dolphin (WBD) 3 – 4 - 0 Harbour porpoise (HP) 1 – 4 1 1-4
Seals Grey seal (GS) 1 – 7 1 – 2 1-4 Harbour seal (HS) 1 – 11 1 0 Unidentified seal (S) 1 1 1-2 Note* Best estimate for maximum group size of common dolphins (Oudejans, 2008).
0.7 2002 2005 2008 0.6
0.5
0.4
0.3
0.2
0.1
Sighting rate per hour of effort of hour per Sighting rate 0 All Sightings Cetaceans Seals
Figure 2.6. Sighting rate per hour of effort for all marine mammal sightings from June to September in 2002, 2005 & 2008 recorded in favourable monitoring conditions (SS ≤ 3).
23 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
2.3.4 Cetaceans in Broadhaven Bay There were a total of 71 distinct cetacean sightings recorded over the 2008 survey period (15th May to 14th October) as summarised in Table 2.1, with 40 distinct cetacean sightings occurring in the months of June to September (Table 2.2).
Both Risso’s dolphin and minke whales were found to have slightly higher sighting rates in 2008 compared to both 2002 and 2005 (Fig. 2.7). The 2008 sighting rate of harbour porpoises was slightly higher than in 2005 but lower than in 2002. Notably, 69% of all harbour porpoise sightings for 2008 occurred in May and are therefore not included in this comparative figure. The sighting rate for bottlenose dolphins was considerably lower for 2008 relative to both previous survey periods.
As in both previous survey periods a range of behaviours were recorded for cetaceans in the bay. These included travelling, foraging, socialising and milling. All three dolphin species recorded (bottlenose, common and Risso’s) were observed foraging and on some occasions this behaviour was associated with the presence of seabirds, often diving gannets. Juvenile animals were observed with killer whale, Risso’s, bottlenose and common dolphins while young calves were present with one group of bottlenose dolphins and sighted with Risso’s dolphins on two separate occasions. In 2002 calves were observed in groups of common and white-sided dolphins and in 2005 in groups of common and bottlenose dolphins. The presence of calves within groups of dolphins suggests that the area may be of significance as breeding or nursing ground for these species.
24 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
0.07 2002 2005 2008
0.06
0.05
0.04
0.03
0.02
0.01 Sighting rate per hour of effort of hour per Sighting rate
0 MI KW RD BND CD WBD WSD HP UD UC UW
Figure 2.7. Sighting rates per species per hour of total effort (SS ≤ 3) for 2002, 2005 and 2008 between June and September (MI = minke whale, KW = killer whale, RD = Risso’s dolphin, BND = bottlenose dolphin, CD = common dolphin, WBD = white beaked dolphin, WSD = white sided dolphin, HP = harbour porpoise, UD = unidentified dolphin or porpoise, UC = unidentified cetacean, UW = unidentified whale).
BALEEN WHALES (Mysticeti)
Historically, large baleen whales were relatively abundant in Irish waters with fin whales, blue whales, sei whales and sperm whales frequently taken in commercial whaling (Fairley, 1981) until the Whale Fisheries Act in 1937 restricted commercial exploitation of the larger whale species. Large whales are still considered relatively rare on these former whaling grounds (Gordon et al. 1999). Blue, fin, sei, humpback and sperm whales are all occasionally observed off Irish coasts with fin and humpback whales now seen regularly off the south coast (these species are thought to migrate seasonally along the continental shelf edge to the west of Ireland (Fairley, 1981)). Although there were no sightings of large whales confirmed to species level in 2008, two sightings of unidentified whales are thought to represent possible fin or sei whale sightings.
Atlantic minke whale (Balaenoptera acutorostrata) The only baleen whale previously observed in Broadhaven Bay by the CMRC, the minke whale, was identified again in 2008 from cliff-top observation sites. There were six distinct minke whale sightings in 2008, four of which were inside the SAC boundary of Broadhaven Bay. Three sightings occurred in July, two in September and one in August. There was one off-effort sighting of an adult minke whale
25 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. approximately 1km from the eastern observation site at Doonanierin. Other sightings were also relatively close to the shore (see map in Figure 2.8). This pattern of animals occurring in the waters close to the coastline is in accordance with a survey of cetaceans off the Mullet Peninsula, (Gordon et al., 1999) which found all minke whale sightings to be within 5km of the coast.
All minke whale sightings consisted of a single adult-sized individual and occurred during the months June to September, corresponding to the pattern of all preceding sightings of this species recorded by Ó Cadhla et al. (2003) and Englund et al. (2006).
Plate 2.2. Minke whale (Balaenoptera acutorostrata) surfacing.
26 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 2.8. Map illustrating the distribution of all distinct minke whale sightings in the study th th area between 15 May and 14 October 2008.
TOOTHED WHALES, DOLPHINS AND PORPOISES (Odontoceti) Five species of toothed cetacean were positively identified in the survey area during the 2008 survey period. These were the same five species identified in the 2005 survey period. Two species of small dolphin (white-sided and white beaked dolphins) that were recorded in 2001-2002 were not recorded in the 2005 or 2008 surveys.
Killer whale (Orcinus orca) There was one sighting of three killer whales travelling west beyond Erris Head on the evening of 12th July 2008 (Figure 2.9). This was thought to be a family group with one male, one female and one juvenile. Three killer whales were reported south of Annagh Head (approximately 15 km south west of Broadhaven Bay) by a local fisherman on the same morning and in the same week there were local reports of this species observed close to the Céide Fields visitor centre in Ballycastle, Co. Mayo (approximately 30 km east of Broadhaven Bay) (Oudejans, pers. comm.).
27 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Englund et al. (2006) also recorded two killer whale sightings in early July 2005. Although this species was not recorded by the CMRC during the initial base-line study, local fishermen did report their presence in August 2002 just off Achill Head close to the study area (Ó Cadhla et al., 2003).
Plate 2.3. A male killer whale (Orcinus orca) with its
distinctive tall dorsal fin.
Figure 2.9. Map showing the track of killer whales observed on 12th July 2008 between 19:33 and 20:20. Position co-ordinates calculated using approximated distance and compass bearing.
28 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Risso’s dolphin (Grampus griseus) This species was sighted on several occasions between June and August 2005 (Englund et al., 2006) and a distinct peak in Risso’s dolphin sightings per unit effort was recorded in July 2002 by Ó Cadhla et al., (2003). There were seven distinct sightings of Risso’s dolphins in Broadhaven Bay during 2008 between July and August illustrating a similar temporal pattern to previous years.
Contrasting group composition and size was recorded in 2008 compared to that of previous CMRC studies. In 2008 group size ranged between one and ten animals while in previous research years the largest group size recorded was five animals (Table 2.3). Two juveniles were recorded by Englund et al. (2006) in late July 2005. Prior to the study in 2005 all groups recorded consisted of between one and three adults (Ó Cadhla et al., 2003). Risso’s dolphin juveniles were recorded in early August from both primary observation sites in 2008. Calves were seen for the first time by CMRC observers and recorded from the western observation site in late July and again in early August.
Plate 2.4. Risso’s dolphins (Grampus griseus) photographed off Erris Head in
2008.
During the 2001-2002 and 2005 studies, the spatial distribution of sightings for this species appeared to be relatively concentrated close to the observation site at Gubastuckaun and off Erris Head. In 2008 some sightings were again made close to Gubastuckaun and just off Erris Head but animals were also recorded further into the middle of the bay and closer to the eastern observation site (Fig. 2.10).
29 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 2.10. Map showing distribution of all distinct Risso’s dolphin sightings in the study
area between 15th May and 14th October 2008.
Bottlenose dolphin (Tursiops truncatus) There was a total of nine distinct bottlenose dolphin sightings over the whole survey period in 2008, with five sightings in May and one sighting per month in June, July, September and October. Group size (Table 2.3) ranged from a minimum of a single individual up to a maximum of 17 animals, a similar range to other survey years (1-18 in 2002 (Ó Cadhla et al., 2003) and 4-20 in 2005 (Englund et al., 2006)).
There was one occasion in September 2008 when bottlenose dolphin calves (see Plate 2.5) were seen within a group from the Doonanierin observation site. The same group were the subject of a photo-identification survey on that day (see Section 4 below). Calves were recorded by the CMRC for the first time in Broadhaven Bay in 2005. There were reliable reports of bottlenose dolphin calves occurring in 2001- 2002 (Ó Cadhla et al., 2003) but researchers did not record any observations to confirm this.
Sighting rates for bottlenose dolphins (Fig. 2.7) between June and September were found to be lower in 2008 compared to the same sampling period in 2005 (Englund et
30 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. al., 2006), which in turn were lower than for the same period in 2002 (Ó Cadhla et al., 2003).
Bottlenose dolphins displayed the widest spatial use of Broadhaven Bay among species recorded by Ó Cadhla et al. (2003) and Englund et al. (2006). All bottlenose dolphins sighted in 2008 were inside the SAC boundary, with groups distributed widely across the bay including some recorded in the very inner parts of Broadhaven Bay close to Rossport Bay and Glengad, where nearshore and intertidal construction works were concentrated. In addition to those sightings mapped in Figure 2.11 there were several reliable reports of bottlenose dolphins in and around Ballyglass during the 2008 survey period. A number of reliable reports were also made of this species close to the shore at Ballyglass, Glengad and Rossport during the summer months of 2002 (Ó Cadhla et al., 2003).
In addition to sightings displayed in Table 2.1 there were three off-effort sightings of bottlenose dolphins in 2008. In May a group of three adults were observed inside Ballyglass harbour. These animals stayed in close proximity to the pier for several hours. A second off-effort sighting on the 29th of July (observed from the survey vessel) comprised of three adults travelling and then bow-riding another boat, the Noreen Bán, in the direction of Ballyglass. Photo-identification could not be performed on this occasion as light conditions were inadequate. The third off-effort sighting was on the evening of September 25th from Doonanierin when a group of six adults appeared to be travelling northward.
Plate 2.5. Bottlenose dolphins (Tursiops truncatus) surfacing in Broadhaven
Bay.
31 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 2.11. Map showing distribution of distinct bottlenose dolphin sightings in the study
area between 15th May and 14th October 2008. Note: red arrow indicates the initial position
of the bottlenose dolphin group that was the subject of photo-identification.
Common dolphin (Delphinus delphis) Common dolphins were recorded in the bay on ten different occasions between 15th May and 14th October 2008. Four of these sightings were recorded between June and September. Common dolphins were seen in relatively large groups compared to other species, consistent with the observations of 2002 and 2005. A total of 310 individuals were recorded during 10 distinct sightings. The best estimate for the largest group seen was 125 (Oudejans, 2008). There was only one sighting of a single individual (during October). More typically, group sizes were between 20 and 40 animals. Behaviours most commonly observed for this species were travelling and feeding and groups were often associated with foraging seabirds. As in 2005, this species was commonly recorded further inside the bay (see map in Fig. 2.12). In contrast, 2002 sightings of this species generally occurred in the outer parts of the bay near to the SAC boundary. In 2002 also common dolphins were occasionally observed with groups of white-sided and white beaked dolphins. Although no mixed groups were identified in 2008 such mixed species groups are more easily identifiable from the survey vessel, which was mobilised more frequently in 2002 compared to 2008.
32 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Plate 2.5. Bottlenose dolphins (Tursiops truncatus) surfacing
in Broadhaven Bay.
In addition to the ten common dolphin sightings recorded during dedicated survey time an off-effort sighting was recorded on 14th June 2008. This active foraging group consisted of approximately 20 individuals and was associated with diving gannets.
Figure 2.12. Map showing distribution of distinct common dolphin sightings in the study area between 15th May and 14th October 2008.
33 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Harbour porpoise (Phocoena phocoena) There were 13 distinct harbour porpoise sightings over the 2008 survey period with groups ranging in size between one and four animals. Nine of these sightings were recorded in May, three in July and one in August. One off-effort sighting of three adult harbour porpoises was made from Doonanierin.
All sightings of animals were inside the SAC and often occurred relatively close to the Doonanierin observation site (see map in Fig. 2.13). This spatial distribution was different to previous studies – 2002 harbour porpoise sighting distribution was more uniformly distributed throughout the bay area, while 2005 sightings (numbering just three) were predominantly in inner parts of the bay. No harbour porpoises were visually recorded in the immediate vicinity of the listening stations (refer to map in Figure 2.1) deployed by the CMRC in 2008.
Harbour porpoises are Ireland’s smallest cetacean species and are notoriously difficult to detect (Rogan & Berrow, 1996) owing to their size and elusive behaviour. As a result, sighting rates recorded for this species are likely to represent an underestimation of harbour porpoise occurrence and therefore acoustic techniques provide a valuable accompaniment to visual observation (see Section 3).
Plate 2.7. Harbour porpoise (Phocoena phocoena) photographed in Connemara waters in September 2008.
34 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 2.13. Map showing distribution of all distinct harbour porpoise sightings in the study area between 15th May and 14th October 2008.
Unidentified cetaceans Where animals could not be definitely identified to species level they were classified as ‘unidentified’. Such instances where species could not be confirmed were due to a variety of factors including distance, weather conditions and behaviour of the animals.
35 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 2.14. Map illustrating distribution of all distinct unidentifiable cetacean sightings in the th th study area between 15 May and 14 October 2008. Black circles represent unidentified whales; green squares signify unidentified cetaceans and grey triangles denote unidentified dolphins.
2.3.5 Seals in Broadhaven Bay There were 22 distinct sightings of seals in 2008, primarily single animal sightings but some were observed in pairs, threes and one group of four, giving a total of 29 animals recorded (Table 2.1). Most were adult seals but two juvenile grey seals were recorded in July. Grey seals are known to breed on islands along the coast close to the survey area (Ó Cadhla et al., 2005).
Most seals were observed in the water (see map in Fig. 2.15) but one of the sightings (notably the sighting including the two juveniles) was of animals hauled out on rocks to the north west of Gubastuckaun. The highest sighting rate (i.e. distinct sightings per hour) for seals was in July (0.14), followed by September (0.08) and August (0.07), with fewer sightings per hour of effort in May (0.03) and June (0.02) (Fig. 2.16). Although harbour seals were sighted during both previous survey periods in 2001- 2002 and 2005 and there are known haul out sites in the vicinity of Broadhaven Bay (Cronin et al., 2004) there were no sightings of this species recorded in 2008.
36 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Plate 2.8. A female grey seal (Halichoerus grypus)
photographed in Galway Bay in 2007.
Figure 2.15. Map illustrating all distinct seal sightings between May and October 2008. Grey circles represent grey seal sightings and purple squares denote sightings of unidentified seals.
37 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02 Sighting rate per hour of effort of hour per Sighting rate
0 May June July August September
Figure 2.16. Graph illustrating sighting rate per hour of effort for all seal sightings in the study area between May and September 2008. There were no
seal sightings in October.
2.3.6 Other species of interest Several other species of interest were sighted in 2008 (Table 2.4), all of which were known to occur in the bay and had been observed previously by CMRC observers. There were 11 sightings of basking shark (Cetorhinus maximus) during the 2008 survey period (see Plate 2.11 map in Fig. 2.17). Of the 14 animals that were seen just over 50% were in May. There were four sightings in June and one in July. Although the frequency of sightings was higher than the 2005 study, which had two sightings, the 2008 sighting rate was lower than that of the 2002 study, which had 17 sightings from July to September.
Generally these animals were observed singly but on occasion two individuals were seen together which is similar to group size recorded in previous years. In some cases animals occurred in the inner bay and close to the cliffs at both observation sites (see map in Fig. 2.17). The sighting directly under the cliff at Gubastuckaun was of a juvenile that stayed in the area feeding for several hours and was later joined by a larger animal. As this species only feeds in summer months they must “locate and capture enough patchily distributed plankton within a restricted feeding season in coastal areas” (Sims & Merrett, 1997). The dominant behaviour observed by this species was feeding, implying the significance of Broadhaven Bay as a foraging area for this species.
38 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
There was one off-effort sighting of the European otter (Lutra lutra) in late September 2008. A mother and two young were sighted travelling quickly northward on land close to the Doonanierin observation site (see Plate 2.9 and map in Fig. 2.17). They had apparently recently emerged from the water. This species was not recorded in 2005 but was seen on two separate occasions in 2002 (Ó Cadhla et al., 2003) and is known to occur regularly in the bay according to reliable anecdotal reports.
Plate 2.9. European otter (Lutra lutra)
photographed on the Aran Islands in 2008.
There was a single sighting of a sunfish (Mola mola) (see Plate 2.10 and map in Fig. 2.17) from the Gubastuckaun observation site in October relatively close to the cliff. The species was seen in similar proximity to Gubastuckaun in 2005.
Plate 2.10. Sunfish (Mola mola) photographed Plate 2.11. Basking shark (Cetorhinus maximus), in the Shannon Estuary. the second largest existing fish.
39 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Table 2.4. Other species of interest sighted (including off-effort otter sighting) in
Broadhaven Bay between 15th May and 14th October 2008.
Other species of Number of Number of Group size interest Sightings 2008 animals 2008 range 2008
Basking Shark (BS) 11 14 1-2 Sunfish (SF) 1 1 1 Otter (OT) 1 3 3
Total 13 18
Figure 2.17. Map showing the distribution of distinct sightings of basking shark, sunfish and otter in the study area between May and October 2008. Red squares represent basking sharks, the green square denotes the sunfish and the blue square represents an otter sighting.
40 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
3. ACOUSTIC MONITORING FOR SMALL CETACEANS
3.1 Introduction Passive acoustic monitoring is becoming an increasingly used tool in monitoring marine mammal populations. As cetaceans spend most of their time below the surface of the sea it is often difficult to observe them, especially at night or in rough weather conditions. T-PODs are self-contained electronic devices containing a hydrophone and a hardware data logger. The T-POD does not record sound but rather logs echolocation clicks of cetaceans. These clicks can then be designated as originating from porpoises or dolphins depending on the frequencies detected and the characteristic patterns in which they are emitted.
T-PODs have been successfully used to detect the echolocation of small cetaceans in Ireland, for example in Broadhaven Bay (Ó Cadhla et al., 2003, Englund et al., 2006), the Shannon Estuary (Philpott et al., 2007) and Connemara (Ingram et al., 2003).
The aims of this element of the project were: To conduct continuous acoustic monitoring for dolphins and porpoises in Rossport Bay, throughout all weather conditions and 24 hours a day; To correlate visual with acoustic data; To compare acoustic data collected in 2008 with data collected in 2002 and 2005.
3.2 Methods Three T-PODs were deployed in Rossport Bay in the same general positions as in previous years (2002, 2005) to enable comparison to be carried out between the years (see map in Fig. 3.1). For more detail on methods used please refer to Ó Cadhla et al. (2003) and Englund et al. (2006).
41 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 3.1. Map showing Rossport Bay and the three listening stations (LS 1, LS 2 and LS 3) where acoustic monitoring took place. The grey circles represent a 500m radius around each T-POD (blue dots). The primary observation site at Doonanierin Point and the secondary site at Brandy Point are indicated by red circles.
3.2.1 Data analysis In 2006 new T-POD analysis software was released with an improved train detection algorithm. This algorithm allows automatic detection and classification of click-trains (distinctive sequences of clicks) according to how likely they are to be of cetacean origin. The detection algorithm used is based on a probability model that uses the click rate logged to calculate a probability of the train arising by chance within a comparable cluster of purely random clicks. The raw data from 2005 was reanalysed but the data from 2002, having been collected on the earliest version of T-PODs for which the new train detection algorithm was not suitable, was excluded from re- analysis with the new software algorithm and the original 2002 results were used for comparison. As T-PODs are constantly being developed and improved there are differences in sensitivity between older versions so it was decided to focus re-
42 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. analysis on the data gathered using the most recent versions of T-POD which would have the most accurate information.
The acoustic data from the T-PODs was analysed using Detection Positive Minutes. This is the most commonly used statistic when examining habitat use and refers to the number of minutes in each day containing a cetacean detection. Click trains from dolphins and porpoises were analysed separately.
3.3 Results
3.3.1 Survey effort The first T-POD deployment of 2008 occurred on 12th June when one T-POD was positioned at each of the Listening Stations (LS) used in previous years (see Ó Cadhla et al., 2003, Englund et al., 2006).
Table 3.1. T-POD deployment periods in 2008.
Deployment Listening Listening Listening period Station 1 Station 2 Station 3 1 12th June – 20th Aug 12th June – 20th Aug 12th June – 20th Aug 2 31st Aug – 6th Oct - 31st Aug – 6th Oct 3 14th Oct – 6th Dec 1st Nov – 6th Dec 14th Oct – 6th Dec
Shortly after the first deployment period the north T-POD (LS1) was reportedly struck by a vessel in the area. Unfortunately the centre T-POD at LS 2 could not be re- deployed at the end of August as the mooring had been removed (presumably accidentally due to the intensive boat traffic in the bay during this time). The centre T- POD was not re-deployed at any time during the second listening period as it was in the path of the Solitaire pipe-laying vessel, which was due to begin construction works during this period. As construction of the pipe was postponed, acoustic pre- construction monitoring continued into the winter months for the first time. The three T-PODs will be redeployed on extra strong winter moorings in the next available weather window. Technical difficulties and weather constraints resulted in less hours of acoustic monitoring compared with the summer season in previous years with 4677.5 hours of data collected in 2008 compared with 5003.05 hours in 2002 and 6350.47 hours in 2005 (Fig. 3.1). Total acoustic monitoring to date (including post-
43 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. summer monitoring) in 2008 is 7852.7 hours. Acoustic monitoring covered all tidal states equally due to continuous monitoring effort.
3000 LS1 LS2 LS3
2500
2000
1500 Hours 1000
500
0 2002 2005 2008
Figure 3.1. Acoustic effort at each of the three listening stations for the months
of June, July, August and September during the three years of monitoring in
Broadhaven Bay.
3.3.2 Acoustic detections
Both dolphin and porpoise detections were successfully logged in 2008. Figure 3.2 shows a screen grab of data downloaded simultaneously from the three T-PODs. Simultaneous detections can be seen from two Listening Stations indicating that full coverage of Rossport Bay was achieved.
44 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Listening Station 1 (North)
Listening Station 2 (Centre)
Listening Station 3 (South)
Days of deployment
Figure 3.2. Screen grab of simultaneous acoustic detections on three T-PODs. Red lines indicate highest probability of being cetacean detections. The x-axis shows number of detections and y-axis time (in days). The T-PODs are deployed about 500m apart and cetaceans were regularly detected simultaneously on at least two of the T-PODs.
0.10 2500 0.09 0.08 2000 0.07 Effort (hours) 0.06 1500 0.05 0.04 1000 0.03 DPM per hour per DPM 0.02 500 0.01 0.00 0
e st r n u er u July g b be J ober m Au ct tem O Sep November Dece
PORPOISES DOLPHINS EFFORT
Figure 3.3. Dolphin and porpoise detections logged to date in 2008. Both species were detected in each month of acoustic monitoring however there was more dolphin echolocation activity during the summer months, while there was more porpoise echolocation towards the winter months.
45 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
In 2008 both dolphins and porpoises were detected at each of the Listening Stations but there is a clear difference in spatial distribution of echolocation activity with dolphin detections concentrated near LS 1 towards the north of Rossport Bay while porpoise detections were highest on LS 2 and 3 in the centre and south side of the bay (Fig. 3.4).
0.10 4000
0.09 3500 0.08 3000 0.07 0.06 2500 0.05 2000
0.04 1500 Effort (hours) DPM per hour per DPM 0.03 1000 0.02 0.01 500 0.00 0 LS 1LS 2LS 3
PORPOISES DOLPHINS EFFORT(HOURS)
Figure 3.4. Detection positive minutes per hour of effort for June – December 2008 at each listening station.
3.3.3 Porpoise detection Porpoise echolocation activity was concentrated towards the autumn/winter and this is evident from the figure below. Although porpoises were echolocating and therefore present in the area from June to December, there were more Detection Positive Minutes (DPM) during autumn.
46 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 3.5. Porpoise DPM and effort per day for survey period June-September 2005 and June-December 2008.
In 2005 fewer porpoise detections were logged however the same pattern emerged where more echolocation activity was logged toward the end of the summer (Fig. 3.5).
3.3.4 Dolphin detection Contrasting with results for porpoises, dolphin echolocation activity in 2008 was concentrated towards the early summer and this is evident from Figure 3.6 below. While dolphins were present in the area from June to December, there were more Detection Positive Minutes towards the start of the summer.
In 2005 fewer dolphin detections were logged compared to 2008, these detections were later in the summer and in early autumn (Fig. 3.6).
47 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Figure 3.6. Dolphin DPM and effort per day for survey period June-September 2005 and June-December 2008.
3.3.5 Comparison with all previous years of acoustic monitoring Harbour porpoises were detected throughout the summer season in all three years of acoustic monitoring. More porpoise detections were logged in 2005 and 2008 than 2002.
0.16 3000
0.14 2500 0.12
2000 Effort (hours) 0.10
0.08 1500
0.06 1000 0.04 DPM perDPM hour (porpoise) 500 0.02
0.00 0 LS 1 LS 2 LS 3
DPM 2002 DPM 2005 DPM 2008 effort 2002 effort 2005 effort 2008
Figure 3.7. Comparison of porpoise detections between the three survey years (during summer months only) at the three listening stations.
48 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
From the three years of acoustic monitoring data collected thus far, most acoustic detections of porpoises were made on the south side of Rossport Bay (Fig. 3.7). Dolphins were also detected in all three years of monitoring however there is clearly an increase in dolphin activity in 2008 with a substantial increase in Detection Positive Minutes per hour of effort with echolocation concentrated at the north side of Rossport Bay. This differs from results in previous years when most detection were made at the south side of the bay (Fig. 3.8).
1.00 3000 0.90 2500 0.80 0.70 2000 Effort (hours) 0.60 0.50 1500 0.40 1000 0.30
DPM perDPM hour (dolphin) 0.20 500 0.10 0.00 0 LS 1LS 2LS 3
DPM 2002 DPM 2005 DPM 2008 effort 2002 effort 2005 effort 2008
Figure 3.8. Comparison of dolphin detections between the three survey years (during summer months only) at the three listening stations.
3.4 Discussion
3.4.1 Acoustic coverage of Rossport Bay Although 2008 provided challenging weather conditions and technical difficulties, acoustic coverage was possible for 83% of the survey period.
3.4.2 Cetacean detections 2008 Dolphins and porpoises were successfully detected during 2008 using T-PODs and data for the 2008 monitoring period provides interesting results and the opportunity to compare an extensive dataset over three years acoustic survey effort in Rossport Bay. Both porpoises and dolphins are seen to use Rossport Bay during the same time period although there is an indication of some spatial and temporal variations in
49 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. habitat use by the two species. Dolphin detections are more concentrated in the north side of the bay while porpoises are detected more in the centre and south sides of the bay. This is consistent with previous findings in 2002 and 2005 for porpoises. Considerably more dolphin detections were logged in 2008 than in previous years and there was a notable concentration towards the north side of the bay. Further monitoring through 2009 should give a better indication of year round fine-scale habitat use by both porpoises and dolphins in Broadhaven Bay. Sightings of coastal bottlenose dolphins have been known to be concentrated in deep narrow channels and have been significantly related to topography (Hastie et al., 2003) and tidal flows (Wilson et al., 1997, Mendes et al., 2002). Bottlenose dolphin occurrence in the Shannon estuary concentrated in areas of greatest benthic slope and depth (Ingram & Rogan, 2002).
In 2008 extended acoustic monitoring continuing into the autumn and winter is showing signs of a seasonal pattern to dolphin and porpoise distribution in Rossport Bay. Dolphin echolocation activity peaked in early summer while porpoise echolocation activity peaked in late autumn. This shows similarities to results from a study in the Moray Firth, Scotland where bottlenose dolphin sightings peaked in mid- summer while harbour porpoise sightings increased later in the season (Thompson et al., 2004). Hastie et al., (2003) found a peak in bottlenose sightings in July in the Moray Firth, Scotland. Studies in the Shannon estuary have shown a seasonal decrease in numbers between the months of January and April (Englund et al., 2007). There have been records of violent interactions between bottlenose dolphins and harbour porpoises in Scotland where 63% of stranded harbour porpoise on the south east coast showed signs of attack by bottlenose dolphins (Ross & Wilson, 1996). Various hypotheses have been suggested for this behaviour such as possible competition for prey, feeding interference, sexual frustration or play fighting (Ross & Wilson, 1996). A study into the diet of the two species in the Bay of Biscay showed there may be partial dietary overlap so interference competition is plausible (Spitz et al., 2006). Harbour porpoises feed on small schooling fish found close to the sea floor while bottlenose dolphins feed on larger demersal fish and cephalopods and some prey species are common to both diets (Spitz et al., 2006). In Ireland harbour porpoises are known to feed mostly on poor cod (Trispoterus sp.), (Rogan & Berrow, 1996) and while there is no published data on bottlenose dolphins diet in Ireland, in Scotland they are known to feed on cod, saithe and whiting (Santos et al., 2001). Both bottlenose dolphins and harbour porpoises may be feeding in Rossport Bay, however due to differences in dietary preferences they may be feeding in slightly
50 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. different areas. Echolocation activity peaks during foraging (e.g. Nowacek, 2005) so it is assumed that dolphins and porpoises are feeding in this area, especially when there are long periods of recorded acoustic activity per day.
When interpreting results from acoustic monitoring it is important to consider that T- PODs only detect echolocating animals that are facing towards the device. Animals that are not echolocating will not be detected. The absence of detections does not necessarily indicate an absence of animals. It is therefore likely that animals are present, but are not actively echolocating (i.e. they are being quiet or listening out for prey). It is further possible that they might be echolocating in the opposite direction of the T-POD. Finally, it is important to note that the T-POD gives no indication as to group size.
3.4.3 Comparison with visual data Harbour porpoises are very difficult to detect visually due to their inconspicuous behaviour. In conditions exceeding Beaufort sea state 2 it becomes increasingly difficult to spot porpoises. In addition to their inconspicuous nature, and relatively small fin and body, porpoises can go unnoticed when swell is running in the bay which occurs quite often in Broadhaven Bay due to its north-westerly open aspect to the Atlantic. Results from visual monitoring recorded an increased number of bottlenose dolphin sightings in the vicinity of the listening stations in 2008 (Fig. 2.10) than previous surveys in 2001-2002 and 2005. Although the initial sighting of a group of bottlenose dolphins in late September when photo-identification was successfully conducted was northwest of Rinroe Point (Fig. 2.10), this group also travelled around the point into Rossport Bay. Furthermore, while porpoises had the highest number of recorded sightings for cetaceans in 2008 (Table 2.1) there were no sightings of this species in the area immediately surrounding the listening stations (Fig. 2.13).
51 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
4. PHOTO-IDENTIFICATION OF BOTTLENOSE DOLPHINS
4.1 Introduction The bottlenose dolphin (Tursiops truncatus) is one of five species of marine mammal occurring within Irish waters that is listed as Annex II of the EU Habitat’s directive. A semi-resident population of bottlenose dolphins in the Shannon Estuary is one of six known resident or semi-resident populations of this species in Europe. The most recent estimate for this population was 114 ± 16.9 (SE) dolphins, calculated in 2007 (Englund et al., 2007). Research focussed along the Irish west coast has suggested that Ireland’s Atlantic coastal waters are inhabited by bottlenose dolphins that are not part of the Shannon population. Recent photo-identification surveys on the west coast suggested that a number of overlapping “communities” of bottlenose dolphins occur along the coast with each community loosely resident within a specific area (Ingram et al., 2001). The recurrence of bottlenose dolphins within and adjacent to Broadhaven Bay (Ó Cadhla et al., 2003; Englund et al., 2006; Oudejans, 2008 and anecdotal sighting accounts) suggests that the bay and its adjoining waters represent an important habitat for this species.
While the visual and acoustic survey components of this study give an insight into a species’ frequency of occurrence and distribution within the study area such methods do not allow assessment of population size, status or investigation of residency or site-fidelity. Bottlenose dolphin behaviour and the common occurrence of distinguishing markings on individuals’ dorsal fins facilitate more intensive study of this species by means of photo-identification.
Photo-identification can provide accurate estimation of group size and composition for each sampling session, as well as information relating to mother-calf associations within the group and thus important information about social structure. Furthermore, provided there are at least two sampling occasions, photo-identification presents a means of applying a “mark-recapture” method for estimation of animal abundance within a particular population (Evans & Hammond, 2004) and allows investigation of site-fidelity by individuals or groups. While photo-identification represents a non- invasive method of “marking” animals, the use of animal’s own natural markings has inherent limitations. For example, accurate mark-recapture abundance estimates depend on the assumption that the marking of an individual does not affect its
52 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd. probability of recapture (Evans & Hammond, 2004) and consequently abundance calculations may be over-estimated if a proportion of the animals encountered are poorly marked or unmarked. Inaccuracies in estimation of population size may also occur due to changes in the marking of an animal if these are overlooked due to extended time periods between sampling sessions. Population size estimation may also be biased if the assumption that every animal in the population has the same probability of being “captured” within any sampling occasion cannot be maintained (see comprehensive review in Evans & Hammond, 2004) and the estimate based on well marked fins should therefore be inflated with a separate estimation of the proportion of unmarked animals present in the population.
Photo-identification is an established technique for studying various aspects of bottlenose dolphin ecology, including population status, social structure, range and residency and has been used in a number of studies in UK and Irish waters (e.g. Pesante et al., 2008 (Wales) and Wilson et al., 1997 (Scotland)) including the study of Ireland’s bottlenose dolphins (Berrow et al., 1996; Ingram, 2000; Ingram & Rogan, 2002; Ingram et al., 2001; Ingram et al., 2003; Ó Cadhla et al., 2003; Oudejans, 2008). Photo-identification studies of dolphins in the Shannon Estuary, have provided insight into the population’s status (Berrow et al., 1996; Ingram, 2000; Ingram & Rogan 2003; Englund et al., 2007; Englund et al., 2008), social structure (Ingram, 2000) and patterns of habitat utilisation (Ingram & Rogan, 2002) thereby contributing significantly to the understanding of Ireland’s only known semi-resident bottlenose dolphin population.
Photo-identification of bottlenose dolphins in the Broadhaven Bay area was carried out during the 2001-2002 survey period (Ó Cadhla et al., 2003) and in a 2008 study commissioned by The Heritage Council (Oudejans, 2008). The 2001-2002 research established that the number of “individually-recognisable bottlenose dolphins” encountered within the study area was a minimum of 25 and at most 39. A number of individuals were identified on two or more different survey days during the summer of 2002, suggesting the existence of a distinct group of dolphins with some level of residency or site-fidelity to Broadhaven Bay and its adjacent waters during this period (Ó Cadhla et al., 2003).
53 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
4.2 Methods
4.2.1 Photo-identification field methods Line transect surveys were conducted in Broadhaven Bay when weather conditions were suitable, a detailed description of which is presented in Section 2 above. An auto-focus digital SLR camera (Nikon D70) with a 70-300mm zoom lens was used for photographing bottlenose dolphins during these surveys.
Once bottlenose dolphins were identified the school was approached with caution to minimise potential disturbance. The duration of photo-identification was kept to a minimum, lasting only until observers were satisfied that every individual’s dorsal fin was photographed from either aspect (i.e. right and left side), provided dolphins didn’t exhibit any sign of disturbance. A GPS position for the encounter location and information such as estimated group size and composition were additionally recorded in the field.
4.2.2 Image analysis All photographs were analysed in their digital format using Microsoft Office Picture Manager and Windows Picture and Fax viewer. The images were digitally filed and the quality of each photograph rated on a scale from 1 to 4 in accordance with a standardised method as used by Englund et al., 2008 (Table 4.1).
Table 4.1. Quality scale and relevant criteria of photographs analysed in this report as per Englund et al., 2008
Quality Photograph Grade Criteria
1 Well lit and focused photo taken perpendicular to the dorsal fin at close range
2 More distant and less well lit or slightly angled photograph of the fin
3 Poorly lit or slightly out of focus, or photo taken at acute angles of the fin
4 Poorly focused, backlit or angled photographs taken at long distance to dolphins
54 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
It is important to note that Photograph quality is distinct from Fin grade, which refers to the degree of marking present on a dolphin fin. Fin grade is rated on a scale of 1 to 3 as follows: Grade 1 (Plate 4.1, a) - significant fin damage or deep scarring considered to be permanent; Grade 2 (Plate 4.1, b) - temporary fin markings consisting of deep tooth rakes and lesions with only minor cuts present; Grade 3 (Plate 4.1, c) - superficial rakes and lesions.
a)
b)
c)
Plate 4.1 a, b & c. Examples of differently graded dolphin fins photographed in Broadhaven Bay in September 2008 (a = Grade 1, b = Grade 2, c = Grade 3).
55 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Poor quality images were excluded from photographic analysis. Once a record of all images was completed the best photos for each identifiable individual was assigned a temporary name and included into a photo id catalogue compiled in 2002 and analysed to determine whether any individuals had been “re-captured” in 2008. Further analysis in 2009 will entail a review of the West Coast catalogue (compiled and managed by UCC researchers) to determine if any of the individuals identified in Broadhaven Bay have been encountered in other locations.
4.3 Results & discussion Despite poor weather conditions there were two occasions during 2008 fieldwork when line transect surveys were successfully completed (July 29th and September 25th), the latter of these included the opportunity for photo-identification of bottlenose dolphins. A position for the group was recorded from the survey vessel’s GPS (latitude: 54°18.110 and longitude 009°50.751) and group movements tracked by the cliff observer who reported the initial sighting (Fig. 2.11).
The initial sighting reported an active group of ten individuals, comprised of seven adults, one juvenile and two calves. Once the survey vessel was close enough for the observers to assess group size and composition the dominant behaviour of the group had changed to milling and slow travel, heading west around Rinroe Point inside Rossport Bay. Construction was underway at the time of this encounter approximately 2 km from the animals (see report cover photograph).
The total group size estimate made from photo identification analysis (Table 4.2) was a maximum of 17 marked individuals. Out of these, 12 dolphins were identified from both sides, four from only the left side and one from the right side only. The group additionally included a number of unmarked individuals that could not be reliably identified or matched. The group included seven probable females showing close association with calves or juveniles.
56 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Table 4.2. Summary of individuals identified using only good quality images of at least one fin profile. The fin grade of each individual is displayed as is group composition (N = neonate; C = calf; J = juvenile). Note: * indicate mothers identified within the group through close association with neonates, calves or juveniles.
Animal number Left side Right side Grade (1-3) Adult Calf/Juvenile 1A 08-1 √ √ 1 √* - 1AC 08-1 √ √ 3 - N 1C 08-1 √ √ 1 √ - 1D 08-1 √ √ 1 √* - 1E 08-1 - √ 3 √ - 1F 08-1 √ √ 1 √ - 1G 08-1 √ √ 2 √* - 1H 08-1 √ √ 1 √ - 1L 08-1 √ √ 1 √* - 1M 08-1 √ √ 1 √ - 1N 08-1 √ √ 1 √* - 1Q 08-1 √ √ 3 - C 1T 08-1 √ √ 2 √* - 1U 08-1 √ - 3 - N 1V 08-1 √ - 3 √* - 1W 08-1 √ - 3 - J 1X 08-1 √ - 3 √ -
Due to the absence of markings on individual 1E 08-1, identified by the right profile only, this animal could represent the right profile of 1X 08-1 (since 1X was only identified by its left profile), thereby reducing the 2008 group size identified through photographical analysis to a minimum of 16 animals and a maximum of 17. Photo- identification analysis of bottlenose dolphins in Broadhaven Bay carried out in 2002 by Ó Cadhla et al., (2003) identified a minimum of 25 and a maximum of 39 individual dolphins. A total of 28.2% (n=11) of the individuals identified in 2002 had significant fin damage (grade 1) compared to 47.1% (n=8) in 2008. A total of 35.9% (n=14) of individuals identified in 2002 had grade 2 dorsal fins while 11.75% (n=2) of individuals from the 2008 encounter are categorised as grade 2. The number of individuals in 2002 with grade 3 fins was 35.9% (n=14) compared to 41.2% (n=7) in 2008.
Although the number of identified dolphins in 2008 is lower than 2002 it is worth noting that the survey effort in 2002 totalled five successful photo-identification sessions between June and October compared to one single opportunity in 2008.
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4.3.1 Group composition Bottlenose dolphin groups photographed in 2002 comprised of adults and juveniles only with no calves or neonates recorded at the time. However, bottlenose dolphin calves were reported from reliable sources during this period (Ó Cadhla et al., 2003). The 2001-2002 study additionally included observations of white-sided and common dolphin calves and both common and bottlenose dolphin calves were observed in the study area in 2005 (Englund et al., 2006). Sightings of two potential neonatal bottlenose dolphin calves (displaying foetal folds/lines considered a distinctive feature on infant bottlenose dolphins – Mann & Smuts, 1999) were reported for the 2008 survey period (Plate 4.2). Risso’s dolphin calves were also identified from the western shore-based site in 2008 for the first time by the CMRC in Broadhaven Bay.
a) b) Plate 4.2. The first photograph (a) displays a mother (individual 1G 08-1) and a neonate calf with visible foetal lines (individual 1AC 08-1). The second photograph (b) displays another potential neonate calf from the 2008 encounter (individual 1U 08-1). These individuals were all present in the 2008 Broadhaven encounter.
4.3.2 Group size Comparisons of group size estimates in 2002 determined by photographic analysis and visual survey methods (Table 4.3) showed that group sizes approximated in the field from survey vessel or cliff sites were commonly lower than the number calculated from photographical analysis (Ó Cadhla et al., 2003) and the encounter recorded in 2008 followed the same general pattern.
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Table 4.3. Summary of group size estimates for bottlenose dolphins in 2002 and 2008 where boat-based photo-identification surveys were successfully implemented while simultaneous cliff-top surveys were conducted.
Group size Group size Group size estimate – Date estimate - boat estimate – cliff photo-identification
28 June 2002 10 >10 17 13 July 2002 14-15 - 11 19 August 2002 18 15-17 21 03 September 2002 15 15 20 04 September 2002 11 14 16 25 September 2008 15 10 17
Bottlenose dolphin group size and composition was similar between 2008 and previous studies by Ó Cadhla et al. (2003) and Englund et al. (2006) with the additional sighting of bottlenose neonates in 2008. Results from photographic analysis provided more accurate estimates of both group size and composition than those recorded from boat or cliff observation. This further highlights the importance of boat surveys and photo-identification methods as valuable additions to cliff-based observation. Group composition recorded from the boat included ten adults, two juveniles and three calves compared to the result of 13 adults, one juvenile and two probable neonates estimated through photographical analysis. The general group composition was however recognised from the cliffs although less precise, with seven adults, one juvenile and two calves recorded.
The Broadhaven catalogue complied following photo-identification effort in 2002 (Ó Cadhla et al., 2003) was used to determine if any individuals identified in 2002 were re-captured in 2008. Although no re-occurrence of individuals was found it should be noted that the dataset was very small for 2008 and that over five years have passed between sampling periods, a time period over which marks are likely to change thus making matching more challenging.
59 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Plate 4.3. Photograph showing both left and right side profile of individual 1M 08-1 from the Broadhaven encounter in 2008 (Grade 1 fin).
4.3.3 Site-fidelity A comprehensive photo-identification project conducted concurrent to the CMRC effort in Broadhaven Bay was initiated by Oudejans, (2008) to examine population size, habitat use and site fidelity of bottlenose dolphins in the waters of Co. Mayo. This study encompassed a wider geographical area than the current CMRC study and identified one small group of bottlenose dolphins of which two individuals were re-sighted together on eight occasions in Co. Mayo waters between May 28th and July 29th.
On the afternoon of the 27th of July CMRC observers sighted and for a brief time tracked a group of three bottlenose dolphins (believed to be those identified and re- captured by Oudejans (2008)) as they travelled out of view toward Ballyglass harbour. Construction work in the bay was postponed on this day as this group were in close proximity to the construction zone (Coppock pers. comm. 2008).
Re-sightings of these dolphins during the summer months of 2008 (observed in Blacksod Bay and Ballyglass harbour) “indicate that at least a small part of the population show some level of residency” (Oudejans, 2008). These findings support the suggestion in 2002 (Ó Cadhla et al., 2003) that bottlenose dolphins show some level of seasonal residency or site-fidelity within the bay itself and its adjacent waters.
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4.4 Conclusions of photo-identification
1. Despite poor weather conditions during the field season of 2008 resulting in less opportunity to conduct boat surveys; photo-identification of bottlenose dolphins was successfully implemented on one occasion resulting in the identification of a maximum of 17 individuals.
2. A relatively high proportion of animals had permanent to semi-permanent natural markings allowing for individual identification and potential matching of dolphins between years and locations.
3. Newborn (neonate) bottlenose dolphin calves were recorded in 2008 reinforcing previous suggestions that Broadhaven Bay is a potentially important nursery area for this species.
4. Although none of the photographically identified animals in 2002 were “re- captured” in 2008, individuals identified in 2002 were “re-captured” by UCC researchers elsewhere in Irish waters (UCC unpublished data) indicating that the population of bottlenose dolphins occurring in Broadhaven Bay may have a much larger geographical range.
5. Photo-identification allows for the best estimate of group size and composition compared to approximating group specifics from cliff observations, thus indicating that overall numbers of individuals recorded by cliff based observers tend to be underestimates of the true number of cetaceans actually present in the bay. The uncertainties apparent in recording group composition from cliff sites may have resulted in underestimation of the proportion of calves or neonates present in some of the groups recorded.
6. While the 2008 photo-identification dataset is small, limiting the level of analysis that can be performed, additional surveys over the coming months (2009-2010) will further contribute to this dataset and aid in interpretation of data collected previously.
7. Not only will the increased effort of photo-identification in the 2009-2010 field seasons improve knowledge about the local bottlenose population in Broadhaven Bay, it will also contribute valuable data and enhance understanding of bottlenose dolphin populations in Irish coastal waters.
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5. CONCLUSIONS AND RECOMMENDATIONS
Ecological significance of Broadhaven bay
The 2008 survey results reaffirm the ecological significance of Broadhaven Bay SAC and its adjacent coastal waters in providing important habitat for a range of marine mammals. Species diversity recorded in 2008 was comparable to previous study periods supporting the suggestion that marine mammal diversity reported is high relative to records from studies at other Irish coastal locations. The significance of Broadhaven Bay as a nursery ground for a variety of dolphin species was again highlighted in 2008 with the first sightings of neonate bottlenose dolphins and Risso’s dolphin calves so far recorded by the CMRC. This supports findings of previous studies where the presence of bottlenose dolphin and common dolphin calves were recorded in 2005; and white-sided dolphin and common dolphin calves were recorded in 2002.
Mitigation measures to protect marine mammals
Mitigation measures designed to protect marine mammals - as specified by the Department of the Environment, Heritage & Local Government’s NPWS - continue to present a practicable means of safeguarding animals if the preventative actions recommended are correctly implemented. In accordance with these guidelines the provision of Marine Mammal Observers (MMOs) aboard vessels for inshore construction works is representing a favourable measure towards ensuring compliance. However, an understanding on the behalf of vessel operators and construction operations crew of their respective responsibilities to comply with relevant codes of practice is nevertheless vital for these measures to be effective.
Recommendation for future monitoring in Broadhaven Bay SAC
It is suggested that any future monitoring efforts shall employ the same general methodology as in previous survey periods in order to enable comparisons within and between years. Where differences in species’ sighting rates were recorded in 2008, relative to previous years, continued monitoring will provide for evaluation of their significance relative to construction. In this respect, the provision of continued monitoring over a period comparable to the 2001-2002 study signifies an important opportunity.
62 Marine Mammal Monitoring in Broadhaven Bay SAC, 2008. Project Report to RSK Environment Ltd.
Continued photo-identification of dolphins provides an important tool for evaluation of possible residency or site-fidelity, which may provide further insights into potential marine mammal population disturbance occurring as an impact of construction.
Continued acoustic monitoring of the construction area in Rossport Bay is still considered essential. A new version of the acoustic devices “C-PODs” will be included from the 2009 field season. The use of these devices will improve the quality of acoustic data gathered and will enable better distinction between dolphin species than was possible using T-PODs only, since these could only provide reliable distinction between porpoises and dolphins. When the C-PODs take the place of the T-PODs, after a period of field calibration it is envisioned that these may be used in other locations within or in the vicinity of Broadhaven bay, providing insights into larger scale patterns of occurrence and distribution of echolocating cetaceans in these waters.
It is suggested that measurements of noise levels related to marine construction works should be made. This would add valuable information to the overall monitoring programme and would give a better insight into the potential impacts on marine mammals in the area. Also, a more detailed log of operations than has previously been available would be valuable in the analysis of collected data.
Finally, as has been stressed previously, any completed installation of a gas pipeline should be followed by a long term monitoring programme involving regular annual surveys in order to provide data on seasonal, annual and long-term distribution and population trends and aid in the evaluation of the effectiveness of conservation strategies put in place.
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6. ACKNOWLEDGEMENTS The research team would like to thank Shell Exploration and Production Ireland Ltd. and RSK Environment Ltd. for commissioning the study. In particular, our thanks go out to Dave Watson, Andy Bendell and Alec Moore at RSK for productive co- operation regarding the monitoring plan and for other important discussions during the survey period and report writing. Also, we would like to thank Agnes McLaverty at Shell for helpful advice and support and Conor Byrne for feedback and updates regarding construction vessels in the bay. Thanks to Michelle Cronin for advice and help during the project and with the final report. Thanks also to John Coppock for sightings information and valuable contacts during the works. A very special thank you to Machiel Oudejans for his multiple roles throughout the project, especially the effort at the beginning of the project and on moorings and acoustic equipment, photo- identification and literature provided to the Broadhaven team. We are also incredibly appreciative of the efforts of Oliver Ó Cadhla for initial orientation, advice and discussion throughout the project and participating during line transects. Many thanks also to Fleur Vissure for lending the team her camera during photo-identification and special thanks to Simon Ingram for allowing us to borrow a theodolite for use at Gubastuckaun. We’re also grateful of the efforts from Pat Cowman for boat work; Brain Smith for mooring development and boat work and Anthony Irwin for his advice regarding reinforced moorings. Also to Eamon Reily and other land-owners who made it possible for the researchers to access and use suitable cliff-based sites for observation, for their occasional company on the cliff and help with a car stuck in the bog in November, a sincere thank you to the locals involved from Ceathrú Thaidhg. All our friends in the area will never be thanked enough for their warm welcome back, magnificent hospitality and in particular to the Sweeney family for storage of equipment and use of the Internet in the beginning of the project. Finally, we thank all those who reported additional sightings of cetaceans in and around the coastal waters of Broadhaven Bay.
Photographic credits Photographic images used in this report are credited as follows: Cover photo, Plate 2.1 and 2.5 © Mary Coleman; Plate 2.4, 4.1, 4.2 and 4.3 © Machiel Oudejans; Plate 2.3, 2.7, 2.8, 2.10 and 2.11 © Anneli Englund; Plate 2.2, 2.9 © Evelyn Philpott and Plate 2.6 © Oliver Ó Cadhla.
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Website References www.npws.ie
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