Honour's Thesis - University of London (2004)


Throughout its range, the distribution of the harbour porpoise (Phocoena phocoena L.) has contracted significantly in the last century, particularly in the North Sea. Reasons for this decline have been primarily attributed to detrimental anthropogenic activities, but the current lack of data on the species has been noted as the foremost reason for the apparent complacency with which the UK and EC governments have regarded it to date.
In areas where shore sightings of the species are prevalent, quantitative data on the distribution and abundance of this small cetacean will be fundamental to population estimates and ultimately essential to management proposals for their protection. Along the southern coastline of the outer Moray Firth in NE Scotland, the species is found in significant numbers during the summer months. In this respect, the aim of the present study was to determine the coastal distribution and habitat use of the animals in this location; to provide estimates of relative abundance; and to record the general group structure and behaviour of the porpoises encountered.
Line transect surveys were conducted between the months of May and September 2003 using a 5.4 m rigid inflatable boat at speeds of between 8 and 12 km h-1, and in sea states of Beaufort four or less. The transects were undertaken perpendicular to the shore line between the ports of Findochty and Fraserburgh using 4 different survey routes, each approximately 1.5 km apart. The total survey area covered was estimated as 550 km2. When animals were sighted, details such as the GPS position, number of adults and calves, the direction of travel and the activity of the animals present were recorded.
From 123 dedicated survey hours conducted on 38 survey days, a cumulative total of 415 animals were recorded from 134 encounters. Areas adjacent to Whitehills and within Aberdour Bay were identified as potential “hotspots” for the species. The overall abundance was calculated as 0.752 animals per square kilometre, which was significantly higher than in other small-scale investigations of the species. Group sizes of harbour porpoise ranged 1 to 17 animals with a mean of 2.64±1.18; single porpoise and pairs of animals were most frequently recorded. Higher levels of feeding were recorded in May and June, which coincided with known calving periods for the species. 12.68% of all groups encountered contained calves.
In conclusion, the results showed a high level of abundance of harbour porpoises in the study area throughout the summer months. Two main sites of high usage are identified, although further study would be desirable to establish whether the area is also important as a nursery ground for the animals. The evidence so far suggests that the coastline of the outer southern Moray Firth may constitute a potential “safe area” candidate for the species in this NE Scottish location.