Visual and acoustic monitoring of cetaceans at the Wave Energy Test Site, Co Mayo, Ireland SIMON D. BERROW and JOANNE M. O’BRIEN

Irish Whale and Dolphin Group, Merchants Quay, Kilrush, Co Clare, Ireland and Marine Biodiversity Research Group, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland

Berrow

Contact e-mail: simon.berrow@iwdg.ie Simon.berrow@gmit.ie

Irish waters have some of the largest wave energy resources in Europe with a predicted 400 MWh/m near the west coast. Ireland also has a diverse and abundant marine mammal fauna with 24 cetacean and four seal species recorded to date as well as basking sharks and other marine megafauna. All marine mammal species are protected under national and European law which entitles them, and their habitat, to strict protection. Any development of the wave energy potential in Ireland must take into account any impact on marine megafauna. To prepare a baseline from which change may be monitored we carried out a visual and acoustic survey of the site from October 2009 to November 2010.

INTRODUCTION

CONCLUSIONS

.

POTENTIAL IMPACTS OF WAVE ENERGY

RESULTS: Visual data

Acknowledgment: This work was carried out on behalf of Tonn Energy, ESB International and the Sustainable Energy Authority of Ireland.

1. Visual surveys showed the regular occurrence at the site of harbour porpoise, common and bottlenose dolphin and minke whale. A range of other species including white-beaked, white-sided, striped and Risso’s dolphin and killer, humpback and sei whale also occur.

2. SAM showed both porpoise and dolphin detections were significantly greater along the proposed cable route compared to control sites.

3. We conclude that the features selected as suitable for deployment of by the wave energy devices (WED) were also selected by cetaceans probably for foraging.

4. Monitoring is ongoing for another 12 months to see if this trend is consistent over time.

5. SAM data provides a more robust dataset than visual detections to explore distribution and occurrence at a fine spatial scale.

6. SAM data may also provide a more robust dataset to identify any changes in the use of the site following deployment of WED.

Harbour porpoise were the most frequently recorded cetacean species during visual surveys followed by common and bottlenose dolphin and minke whale. Grey seals were more frequently recorded than common or harbour seals. Basking shark and sunfish were also recorded at the site. Density estimates for grey seal increased from 0.51 seals km2 in July to a maximum of 0.88 seals per km2 in November. A density of 3.20 common dolphins per km2 was estimated in March. Individual bottlenose dolphins recorded at the site had previously been recorded in Counties Galway and Donegal.

The potential effects of wave energy devices (WED) include loss of habitat from physical displacement, collisions, disturbance, electromagnetic fields and noise generated during operation or construction (Inger et al. 2009; Boehlert and Gill 2010; Wilson et al. 2010). However the lack of devices deployed in the sea make it difficult to carry out monitoring of potential effects of WED.

Visual Monitoring

Dedicated line transects surveys using distance sampling were complimented by land-based watches and casual sightings from the area to gain an understanding of the marine megafauna using the site.

Acoustic monitoring

A towed hydrophone was used on dedicated surveys and Static Acoustic Monitoring (SAM) using calibrated CPODs (www.chelonia.co.uk) were deployed at seven sites on LRT acoustic releases (www.sonardyne.co.uk). Offshore and Inshore berths had two control sites 10km either side of the berth and along the same depth contour (Figure 1).

Acoustic detections were expressed as Porpoise Positive Minutes (PPM/day) and Dolphin Positive Minutes (DPM/day).

METHODS

Fig 2. Seabed map showing bathymetric features and cable route

Fig 1. Location of CPODs deployed at test site

Bathymetric feature which

might be important to

cetaceans

RESULTS: Static Acoustic Monitoring

From our knowledge of the distribution of porpoise and dolphins in inshore Ireland we expected more DPM from the three inshore CPODs (Berth C and B and two Controls 2 and 4) and more DPM at Berth A and Controls 1 and 3 (offshore). We did not expect any difference in PPM or DPM between Berths B and C and Controls 2 and 4 nor between Berth A and Controls 1 and 3. Overall detections were greater offshore than mid-shore and both greater than inshore sites. Detections at the berths were greater than at the corresponding control sites.

Table showing PPM and DPM per Inshore, Midshore and Offshore sites

O’Brien

Contact e-mail: Joanne.obrien@gmit.ie