There were a total of 10 sightings of white-beaked dolphins during the survey, comprising a minimum estimate of 70 animals.  The sightings were restricted to the northern part of the Minch between the Butt of Lewis and Kinlochbervie, and were limited to only two ¼ ICES rectangles.  However, the relative abundance of white-beaked dolphins within those areas was high.  Although adverse weather conditions during August did limit the extent of the survey coverage, the survey was successful in locating an area of white-beaked dolphin concentration in the northern part of the Minch, in a similar region to where white-beaked dolphin abundance was high during the 1980s and 1990s.  The distance from shore of the sightings ranged from 22 to 32 km with a mean of 26 km.  This area is approximately mid-way across the Minch, indicating that white-beaked dolphins showed a strong preference for open habitat located outside of the immediate coastal zone.  The water depth for white-beaked dolphin sightings ranged from 107 to 135 m with a mean of 122.5 m, reflecting the pelagic distribution of this species. The number of dolphins recorded differed significantly between water depth categories, with more animals than expected occurring in the ≥100 m depth category.  White-beaked dolphins were recorded in a rather narrow water temperature range varying between 13.2 and 13.5°C, with a mean of 13.4°C.  More animals than expected were observed in the 13.0–13.9°C water temperature category.

The group size of white-beaked dolphins ranged from two to 12 animals, with a mean of 7.0 animals. The proportion of calves identified within five groups varied from 25 to 50%, indicating that some white-beaked dolphin pods in the Minch consisted entirely of mother-calf pairs. Only three individuals were photo-identified from permanent markings on the dorsal fin, with a further five individuals tentatively identified from temporary markings (N=2) and/or permanent features (N=3) that were visible (but ill-defined) in poor-quality images. Vocalisations by this species were generally sparse, comprising sporadic whistles and some short click trains. Opportunistic broadband recordings showed that white-beaked dolphin whistle harmonics were visible at frequencies up to 35 kHz, while the broadband clicks contained high energy levels up to around 160 kHz.

Location of white-beaked dolphin sightings

There were a total of 11 sightings of short-beaked common dolphins during the survey, comprising a minimum estimate of 1,486 animals.  Common dolphins were the most numerous cetacean species recorded in the Minch, and sightings were widely distributed across the survey area.  The widespread occurrence of common dolphins recorded during the survey in the Minch during August 2007 was notably different from surveys carried out in the 1980s and 1990s, and indicative of a marked increase in the occurrence of this species off the west coast of Scotland.  The distance from shore of common dolphin sightings ranged from 1 to 28 km, with a mean of 13 km.  The water depth of common dolphin sightings ranged from 70 to 240 m with a mean of 116.3 m, and significantly more animals than expected were observed in depths greater than 50 m. Sea water temperature at the location of common dolphin sightings varied from 12.0 to 14.2°C with a mean of 13.5°C, and common dolphins showed a significantly higher occurrence in temperatures <14°C indicating a preference for cooler waters.

The recorded group size during common dolphin sightings was high, ranging from 3 to 450 with a mean of 135.1 animals.  A total of 24 common dolphins were photo-identified from permanent markings on the dorsal fin. A further 18 individuals were tentatively identified from large temporary markings (N=11) and/or permanent features (N=7) that were visible (but ill-defined) in poor-quality images.  Most common dolphins bore numerous tooth rakes and small scars, and these were not considered suitable for long-term photo-identification.  Many individuals had ‘clean’ fins that lacked nicks or notches.  Acoustic recordings were made during five common dolphin encounters, and this species was often detected acoustically long before visual sightings were recorded.  All common dolphin recordings contained almost continual tonal calls, although the quality of these varied from faint whistles to very loud whistles when animals were close to the boat.  Loud click trains and burst-pulse sounds were also recorded, as dolphins investigated the hydrophone.  Opportunistic broadband recordings made during the survey showed that common dolphins whistles included harmonics whose frequency range extended to at least 40 kHz and their click trains contained significant energy at frequencies as high as 140 kHz. 

Location of common dolphin sightings

There were a total of three sightings of Risso’s dolphins during the survey, comprising a minimum estimate of six animals.  The sightings were located off the Eye Peninsula, off Cape Wrath and in the centre of the Minch.  The sightings of this species were fewer than expected, since Risso’s dolphins are known to inhabit the waters around the Eye Peninsula and Lewis on a regular basis.  The distance from shore of the three Risso’s dolphin sightings ranged from 0.8 to 26 km, with a mean of 11 km.  The water depth of the sightings ranged from 31 to 111 m with a mean of 62.7 m, and the water temperature at the location of the sightings varied from 12.4 to 13.2°C, with a mean of 12.9°C.

The recorded group size of Risso’s dolphin sightings ranged from 1 to 3, with a mean of 2.0 animals.   Risso’s dolphin behaviour was generally elusive with the animals surfacing unpredictably and infrequently, and moving large distances while subsurface.  Consequently, it did not prove possible to approach and stay with this species for the purposes of photo-identification.

Location of Risso's dolphin sightings

There were a total of 121 sightings of harbour porpoises during the survey, comprising a minimum estimate of 246 animals.  This was the most frequently sighted cetacean species in the Minch during August 2007.  Porpoise distribution was widespread, with sightings occurring throughout the surveyed area.  The relative abundance of harbour porpoises was highest to the west of Lochinver, and the waters west of Skye and around Raasay also held high concentrations of porpoises.  The distance from shore of harbour porpoise sightings ranged from 0.6 to 24 km with a mean of 6 km.  This species was therefore found in a variety of habitat types from the immediate coastal zone to open waters in the centre of the Minch.  The water depth of the sightings ranged from 23 to 262 m with a mean of 104.8 m.  The sea water temperature at the location of porpoise sightings varied from 12.1 to 14.6°C, with a mean of 13.6°C.  Harbour porpoise group size ranged from 1 to 12, with a mean of 2.0 animals.  The majority of sightings comprised singles (41%) or pairs (37%) of animals.  Eighteen percent of the sightings included a calf, which is consistent with the May to July calving period documented for British waters.

Location of harbour porpoise sightings

There were a total of 10 minke whale sightings during the survey, comprising a minimum estimate of 11 animals.  Sightings of minke whales were widespread in the Minch, with five animals being observed in a relatively small area during transits around Raasay and west of Skye.  The distance from shore of minke whale sightings ranged from 1 to 23 km with a mean of 10 km.  This species therefore occupies a variety of habitat types within the Minch including coastal and open water areas.  The water depth of the sightings ranged from 32 to 259 m with a mean of 100.3 m, and the water temperature at the location of the sightings varied from 12.4 to 14.0°C with a mean of 13.3°C.  No particular habitat preferences were therefore apparent for minke whales. Of the ten recorded minke whale sightings, nine involved single animals and there was a single observation of a pair of whales.

Location of minke whale sightings

A wide range of other marine species occur in the Minch, and these were recorded whenever they were observed.  There were a total of 15 sightings of seals during the survey, comprising three common seals and 12 grey seals.  Many additional adult grey seals were also observed in the fishing harbours of Stornoway and Kinlochbervie.  Seal sightings were widespread, although most occurred in waters adjacent to the coast.  A large basking shark was observed swimming slowly at the surface on 2 August, 1 km west of the mainland to the north of Kebock Head on Lewis.  A well decomposed dead basking shark was recorded between Skye and the west coast mainland on 11 August.  An ocean sunfish was observed on 9 August, halfway between the Eye Peninsula and the Point of Stoer.