5.0 CETACEANS
5.0 CETACEANS
5.1 Twenty-three species of cetacean (i.e., whales, dolphins and porpoises) have been recorded in Scottish waters. Eleven of these are regularly sighted, and six are known to inhabit near coastal waters where domestic ferry services operate (minke whale, short-beaked common dolphin, white beaked dolphin, Risso's dolphin, killer whale and harbour porpoise). Open coast, straits and sounds and sea lochs are the most common habitats. In addition, shallow bays and estuaries are known habitat for harbour porpoises. There are relatively high sighting rates for all named species in the Minches and in the Sea of the Hebrides. Harbour porpoises also have high encounter rates around the Orkney and Shetland coast, as well as in the Firth of Clyde and the numerous sounds (straits) of Argyll and Bute, particularly in the summer months. The size of cetacean populations resident in or transiting Scottish waters is highly variable and likely linked to both distributions of prey and seasonal changes. Two pods of bottle-nose dolphins are known to be resident in Hebridean waters5, and due to their small size are particularly vulnerable6.
5.2 All cetacean species in Scottish waters are protected under national7, UK8 and EU9 law, making it an offence to deliberately capture, kill or recklessly disturb cetaceans10. All species of cetaceans regularly sighted in Scottish coastal waters are listed on the IUCN's Red List as either species of least concern, i.e. low risk of global extinction at present, or as having insufficient data to classify (killer whale only). The UK, as a signatory to the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS), is working towards the prevention of significant disturbance to cetacean populations, particularly disturbances of an acoustic nature, via the implementation of the Marine Strategy Framework Directive's Good Environmental Status (GES) descriptors and through the UK's active participation in the coordination of the protection of small cetaceans through ASCOBANS. GES includes underwater noise and work is progressing on ascertaining whether additional programmes of measures are required.
5.3 The Marine Atlas11 identifies the risk of death or injury from collisions with vessels as a pressure for some species, but notes that this risk is considered to be slight. Noise disturbance from shipping is also an identified pressure. By-catch in commercial fisheries appears to be the main form of direct human-caused mortality in UK waters.
5.4 Evidence suggests that, globally, there is a significant risk of death or injury to cetaceans as a result of collision with vessels12 13. The International Whaling Commission14 recognises the problem of collision for both whales and vessels. The total number of cetacean fatalities caused by vessel collisions is uncertain, especially as collisions with large vessels often go either unnoticed or unreported, particularly for smaller species. Both the Whale and Dolphin Conservation Society (WDCS) and the International Whaling Commission estimate that the numbers of fatalities are likely to be significantly higher than reported15. At the time of writing no evidence has been identified for such collisions in Scottish waters; anecdotal information suggests that cetacean strikes by ferries are rare, but this remains to be confirmed.
5.5 The risk of collision is a function of vessel size, speed, and traffic volume in an area. Studies suggest that most lethal or severe injuries are caused by large ships (80m or longer) and that, in most cases, whales are not seen beforehand or are seen too late to avoid collision. Most minor injuries to whales involved collision with smaller vessels (less than 45m long); when whale fatalities occurred from collisions with smaller vessels, these vessels were usually travelling at high speed. The limited information available indicates that vessels of all sizes and types can strike whales, and that speeds of greater than 13 knots are more likely to result in fatal injuries being sustained by larger whales. The WDCS report suggests that the likelihood of collision is increased by cetaceans becoming habituated to vessel noise, particularly in areas of significant vessel movement, and by younger cetaceans being more inquisitive, which may bring them closer to vessels.
5.6 The key issue arising from the proposals in the Draft Ferries Plan is the increase in the number of vessel movements on existing and/or new routes. As vessel movements increase, the levels of marine underwater noise and the risk of a vessel colliding with a cetacean increases. Over time, this may lead to cetacean populations becoming habituated to vessel noise, particularly in busier areas, which has the potential to further increase the risk of collisions.
5.7 The size and speed of Scottish ferries has been reviewed16 (Table 5; this does not include inter-island ferries). Approximately half of the fleet (21 total) has a design speed of 10 knots or less. Eighteen have a design speed of 14-16 knots; four have a design speed of 24 knots. These last four ply the Ullapool-Stornoway, Stromness-Scrabster and Lerwick-Kirkwall-Aberdeen routes.
| Design Speed (knots) | Number of Vessels |
| 8 | 4 |
| 10 | 20 |
| 14 | 7 |
| 16 | 8 |
| 17 | 3 |
| 24 | 4 |
5.8 The existing and new routes on which the proposals would result in increased numbers of vessels comprise:
- Ardrossan-Brodick (Arran)
- Colintraive to Rhubodach (Bute)
- Cumbrae-Largs
- Oban-Coll and Tiree
- Oban-Craignure (Mull)
- Iona-Fionnphort
- Port Appin-Point (Lismore)
- Mallaig - Muck, Eigg, Rum and Canna (Small Isles)
- Mallaig-Inverie-Tarbet (Knoydart)
- Oban-Colonsay
- Gigha-Tayinloan
- Campbeltown-mainland (Ardrossan or Troon)
Of these twelve routes, seven vessels have a design speed of 14 knots or more. (A vessel speed of 16 knots has been assumed for the new route between Campbeltown and the mainland.)
5.9 A fatal collision (with a cetacean) would have a significant effect on biodiversity. Where fatalities affect smaller pods these effects could be more significant, as smaller pods are more vulnerable and less able to withstand perturbations in population size. For larger populations, it is not thought that ad hoc collisions would have a significant effect on population numbers17. On routes where vessel speed is 13 knots or less, the potential for collision with cetaceans remains, but the risk of fatality is much less. As such, increases in movement on slower routes are not likely to have significant effects on biodiversity as a result of collisions. However, increases on the routes with a vessel speed greater than 13 knots would increase the risk of collisions which could result in fatalities.
5.10 Across all routes where vessel traffic is increased there will also be an associated increase in marine noise. Cetacean populations can become habituated to vessel noise, thereby increasing risk of collisions as they become less responsive to approaching vessels. Vessel noise has been linked to changes in natural behaviours, such as dive times, in cetaceans.18 Therefore, there is potential for increased vessel traffic and the resulting increase in marine noise levels to result in adverse effects on cetaceans However, the significance of this effect is uncertain at this time, as evidence is limited.
5.11 There is currently a lack of evidence regarding the number and severity of collisions between ferries and cetaceans in Scottish waters. Although a risk of increased collision has been identified by this SEA, the significance of effect is uncertain, given the lack of data.
5.12 At this stage it is uncertain whether proposed changes to ferries operations in Scottish waters would be likely to have an adverse effect on cetaceans, either through collisions resulting in death or injury, or through noise disturbance. The Scottish Government will explore with ferry operators, statutory advisers and others if this is an issue and whether information could be collected. If issues are identified, the Scottish Government will explore ways to resolve them. An update will be provided in the final Ferries Plan.