Edinburgh Napier University

  1. The impact of anthropogenic activity associated with the construction of a proposed tidal turbine on harbour seals (Phoca vitulina) was investigated using controlled disturbance trials.
2. Trials were conducted by approaching hauled out seals by boat at a speed of five knots until all seals had entered the water. Trials were carried out at a frequency of once every three days when weather permitted and the post disturbance haulout behaviours of the seals were documented. The time taken for numbers to recover to pre-disturbance levels was determined by monitoring haulout sites using time-lapse photography. In addition, seals were tagged with GPS phone tags providing haulout location and at-sea movement data allowing investigation of how disturbance may influence haulout site choice and seal distribution.
3. Mean post-disturbance recovery of seals was 52% (95%CI 35-69%) within 30 minutes. However, mean recovery only returned to 94% (95%CI 55-132%) of pre-disturbance levels after four hours.
4. Telemetry tagged seals displayed a high degree of haulout site fidelity. Disturbance trials did not have a significant effect on the probability of seals moving to a different haulout site.
5. The results of this study suggest that increased boat activity that causes seals to enter the water at a higher than normal frequency will not cause individuals to relocate to another haulout site. Seals continued to return to the original site despite repeated disturbance trials suggesting that increased boat activity is likely to repeatedly impact on the same seals with the largest effect being to reduce the amount of time available to seals to haul out.
6. This study recommends that monitoring effort to mitigate against increased levels of disturbance caused by boat activity need only be on a local scale relative to any proposed development.