An SNH and Marine Scotland commissioned report, conducted by our colleagues at SMRU, has used data from tagged seals to assess the potential for collisions with tidal turbines, using the Pentland Firth as an example.

The aims of this study were to:

  • describe the movements and diving behaviour of harbour seals in a high tidal flow area.
  • combine movement data with population data and estimates of the likelihood of injury.
  • test the methods by estimating the potential mortality rate at a proposed tidal array.
  • compare the results of this method with other collision risk models.

In 2011, SMRU tagged 14 harbour seals at the Gills Bay haul out in the Pentland Firth using SMRU GPS/GSM Phone Tags. The locations of these tagged harbour seals were then plotted alongside a hypothetical tidal array of 86 turbines.

The tags also collected depth and dive duration data. These data helped to estimate the number of times the tagged seals passed through the turbine swept area and been at risk of a collision. The data showed that the tagged seals spent most of their time either at the surface or near the bottom of the water column and the seabed. Other parameters were entered into the collision risk model such as the probability of a collision occurring, the consequence of a collision (fatal or not), the angle of the seal in the water, transit speeds and transit times. This was then scaled up from the 14 tagged seals to the local population size to estimate the potential number of collisions at the hypothetical tidal array.

The study showed that:

The resulting collision risk estimate is substantially lower than estimates derived for the same array site using a collision risk model. The results are specific to that one site, but can be replicated for any site with sufficiently detailed movement and diving data.

Data such as these are vital to make collision risk assessments as realistic as possible by removing previous assumptions (such as random transit angles) and using site specific density and dive data to obtain more realistic collision probabilities.

The authors highlight that a main uncertainty when assessing collision risk is:

The lack of information on avoidance and/or evasion behaviour in the presence of moving turbine blades. Additional research to assess avoidance behaviour and determine the abilities of seals to evade moving blades will be needed to provide robust, defensible scaling factors.

Therefore, while site specific density, movement and dive data help to refine collision risk assessments, there is still a knowledge gap. How animals react to tidal turbines is currently unknown and much research is currently being conducted to address this.

SMRU Consulting are heavily involved in trying to answer this question, through our work on projects such as:

  • Scottish Government Demonstration Strategy – to develop and test methods for tracking the fine scale underwater movements of marine mammals in the vicinity of marine tidal energy devices
  • TEL DeltaStream – designed and developed a monitoring system to detect and track porpoise and dolphins around the operational turbine in real time 24/7