- Land-based marine mammal surveys of the Fall of Warness were carried out from 15th July 2006 to 13th July 2007, encompassing a total of 240 days, and 928 hours of observation. These are a continuation of previous surveys of the site that ran from 11th July 2005 to 14th July 2006 and encompassed 219 days and 964 hours of observations.
- Grey seals, harbour seals, harbour porpoises, minke whales, white-beaked dolphins, killer whales, Risso’s dolphins and basking sharks were all seen during the study period. All species of marine mammal (and basking sharks) observed in the study area are protected under international and/ or national legislation.
- Chi-squared (E2) tests were used to investigate the patterns underlying seal and harbour porpoise observation data. Generalised Additive Models (GAMs) were fitted to the entire two year dataset to explore these patterns further. There was insufficient information on the other species to support anything beyond descriptive statistics.
- Grey seals were the most frequently observed species, with a significant peak in occurrence during their breeding season from September and October. Sightings were concentrated close to the shore area, especially to Muckle Green Holm. The probability of sighting grey seals was greatest while the tide was ebbing, and on calm afternoons. The rate of sighting grey seals has declined over the period of the study.
- Harbour seals were rarely observed between December 2006 and February 2007, though overall the numbers of sightings have been decreasing. They were most commonly seen during high tide and at the ends of the day. The small numbers of sightings was probably responsible for the lack of any other significant factors in the data analysis.
- Harbour porpoises were mainly observed on calm days during the summer and were observed to be mainly in small groups. The small number of sightings of this species meant that it was not possible to determine any other significant factors in the data analysis.
- Occasional sightings of minke whales, white-beaked dolphins, killer whales, Risso’s dolphins, and basking sharks are consistent with existing knowledge of these species behaviour and distribution in Orkney waters.
- The potential effects of tidal stream devices on large-bodied animals in the water column are a subject of considerable concern that requires a careful approach to management and mitigation. The methodological approaches developed in this study to help assess these effects are at the leading edge of the field. We suggest that they have broad application to most circumstances in which tidal power generation is being considered.