Methods for tracking fine scale underwater movements of marine mammals around marine tidal devices

9 Appendix II: Case study - Sound of Islay

To illustrate the use of the technologies discussed in this report we consider as a case study: the proposed deployment of an underwater turbine array at the Sound of Islay (Figure 2) by Scottish Power Renewables. We refer to this site as the Development Area. Details of this development provided in the appendix are taken primarily from Scottish Power Renewables' Environmental Statement (Scottish Power Renewables 2010b). The information provided in the case study reflects the position at the time of this reports preparation.

9.1 Proposed development

The Sound of Islay is approximately 1 km wide and reaches 62m in depth. The maximum flow within the Sound is 3.7m/s.

A total of 10 Hammerfest ¹⁵ 1 MWattHS1000 turbines will be installed in 2013 ¹⁶ (see Figure 3). They will be placed in water in excess of 48m deep and secured with gravity ballast. The tripod support structure dimensions are 15m (W) x 22m (L) on the substructure with a hub height of 22m from the seabed. A rotor diameter of 23m will give the device a total height from the seabed of approximately 33.5m. The rotational speed of the turbine will be 10.2rpm with a maximum blade tip speed of approximately 12m/s. Two subsea cables will connect the array with the grid - probably on the Jura shore.

9.2 Marine mammals

Both harbour seals and, to a lesser extent, grey seals ( Halichoerus grypus) are present the vicinity of the Development Area. The South-east Islay Skerries is a Special Area of Conservation ( SAC) for (approximately 600) harbour seals ( Phoca vitulina) and lies about 18 km to the south of the Development Area. Approximately 50 harbour seals may be seen hauled out within the Sound of Islay. SMRU (unpublished) has shown that harbour seals from this and neighbouring haulout sites do transit through the Sound. Grey seals are more common to the north of the Sound and are a notified feature of the Oronsay and South Colonsay SSSI (20 km to the north).

Harbour porpoise ( Phocoena phocoena), and the bottlenose dolphin ( Tursiops truncatus) are the most common cetacea to use the Sound of Islay. Since there is uncertainty about the rate at which cetacea (and to a lesser extent grey and harbour seals) will transit the Sound we take the precautionary view that all marine mammal classes (seals, toothed and baleen whales) should be targeted in this proposal.

9.3 Proposed monitoring scenario

9.3.1 Caveats and scope

Our proposal is generic. The details depend on:

• The scope of the objective. We take as a working objective: 'tracking fine scale underwater movements of marine mammals around marine tidal devices'. As such we ignore the larger scale questions of the rates of usage within the Sound of Islay and consequential population level effects.
• Cooperation with the operator during the construction phase (especially the provision of brackets to attach PAM hydrophones, active sonar devices or underwater cameras; access to electrical power and communication channels).
• The finances available. No costings are provided here, but we assume there are financial constraints. Thus we consider the minimum scenario (with consequent greater risk) to address the primary objective.
• Successful pilot trials of the technology.

9.3.2 Proposal

In consideration of the planned deployment, biology and technological tools available, we propose the following monitoring scenario for the Sound of Islay.

The ten turbines will be arranged linearly in pairs or triplets. We consider the turbine pair/triplet that is furthest upstream to provide the greatest number of interactions since they will be the first to be encountered. Since the leading structures will alternate with tidal flow we suggest that the detection systems be established at both ends.

• Establish a static PAM array around a turbine to track vocalising odontocetes. The raw PAM data will cabled ashore (probably to the Jura side of the Sound) where it will be processed and stored. An internet connection will permit subsequent remote data downloading and operation monitoring.
  
• Tag with acoustic pingers (type to be decided in trials) thirty harbour seals captured as close as possible to the turbine array. Interactions of these individuals may then be tracked with the PAM arrays. Furthermore, the availability of a PAM at either end of the array will indicate passage time of individual tagged seals along the length of array.
  
  Note that, whilst not the primary objective, an optional, additional tagging of these tagged seals with GPS/ GSM tags would permit the interpretation of fine scale interactions within the context of larger scale movements.
• Establish a Tritech Gemini Active Sonar on the turbine to detect and track all marine mammal species (including baleen whales). As with the PAM array, data would be cabled a shore-based processing centre. Automatic detection software should be developed and established.

We suggest that the Sound of Islay would be an appropriate place to test Impact Detection systems. We thus suggest the following:

• Establish two video cameras pointing up- and down-stream of the turbine. Evaluate the operational environmental window of the video system. Evaluate whether the automatic detection software systems discussed in the PAM array section could be incorporated. The video surveillance system could be triggered by detection events from the active sonar and PAM systems.
• Model and test whether Mechanical Detection using the turbine's sensors will detect the strike of a carcass. This test should also be combined with video surveillance. If successful then trigger logging of the turbine sensors with PAM or Active Sonar detection event.

There is a risk that any impact detection system, even in it passes feasibility test, will fail to encounter a certain proportion of actual impacts. We thus suggest the following:

• A regular survey for carcasses is established around the neighbouring shores where the tidal current are likely to ground ashore any animal killed at the site of the turbine array.

A similar survey was established at Strangford Lough in relation to the establishment of a SeaGen turbine. No seal carcasses were found which presented trauma associated with blade strike.

Figure 2. Site of planned deployment of 10 turbines within the Sound of Islay. Taken from Scottish Power Renewables (2010b).

Figure 3. Artist's impression of an array of Hammerfest HS1000 turbines. Taken from Scottish Power Renewables (2010a)