Harbour porpoise are the most commonly spotted cetacean species in the Clyde. There is a lack of data on this species but we know that they are resident throughought the year and evidence suggests that the area is crucial for feeding, breeding and calving. The Clyde Marine Mammal Project is conducting research on the abundance and distribution of this species and assessing how our resident harbour porpoise is responding to changing environmental and other pressures.
190 individual propoises were sighted in the Clyde in 2015 with many calves and juvenile family groups. Unfortunately, many neonatal and young porpoises have died or become stranded. The Clydes population does not seem to experience the same predation pressure compared to other areas in Scotland but more likely to suffer physical injury from fast moving boats, being caught in fishing gear and sensitive to underwater noise pollution.
Female porpoises tend to be slightly larger than males and can reach 1.8 metres in length and weigh up to 70kg. Porpoise have a small round head on a stout chunky body. They usually have a grey to dark-brown back, fading to a lighter greyish belly, often with speckling along the flanks. They have a small triangular dorsal fin .
Habitat and Distribution
Harbour porpoises are resident and widespread in Scottish coastal waters with high concentration in the inner Hebrides. Its is not fully understood how much movement there is between the porpoise groups in the Clyde, Hebrides and Irish Sea. Oppurtunisitic sightings data suggest that male porpoises migrate off shore during the winter months but females remain in the Clyde with their juvenile offspring.
Harbour porpoises are elusive creatures and often only seen briefly when they surface to breath which is usually accompanied by a puffing sound. They have a characteristic rolling motion when surfacing but not generally noted for thier acrobatics. They are often spotted alone, in pairs or small groups. Occasionally you can observe larger groups of anything between 10-30 animals.
Food and Foraging
The harbour porpoise is a bit of a generalist and diet consists of over 20 species fish, squid, crustaceans, shellfish and octopus. When they are diving to feed they surface to breath for 10-20 seconds before diving for up to 6 minutes. They use echolocation to search for food and have small spade like teeth that are used to catch prey items. In Scotland, Killer whales are the main predator of porpoises but interaction between bottlenose dolphins and grey seals have also been documented.
Harbour porpoises are easily disturbed and killed by human activities because their feeding behaviour can bring them into contact with fishing gear and risk of entrapment. The harbour porpoises in the Clyde are located in areas of relatively high shipping traffic, coastal development, industry and other sources of disturbance. Echolocation is the primary sense used when searching for prey items but may become confused by high-speed propeller, military activity and acoustic deterrent devices used around fish farms.
Porpoises are not mentioned in the Firth of Clyde Marine Spatial Plan (2010) other than in a comment from Furnace Community Council who noted that they were more numerous in the 1950’s before the complete collapse of Loch Fyne herring fishery. They were included in the Marlin Review of Clyde Biodiversity but data was discarded and not included in final plan because porpoise abundance and distribution could not be measured accurately or quickly enough. Harbour porpoises are included in some of the Clyde Local Authorities Biodivesity Action Plans (LBAP) but noticeably absent from Inverclyde Council, Refrew Council and West Dunbartonshire Council LBAP lists. No Special Areas of Conservation (SAC) or other considerations have been made to conserving porpoises in the Clyde.
Harbour porpoises are protected under UK and EU law:
- Schedule 5 of the Wildlife and Countryside Act 1981
- Nature Conservation (Scotland) Act 2004
- 1992 EU Habitats and Species Directive
- On the Scottish Biodiversity List
- On Nationally Important Marine Features List (c NIMF)
- Are listed in the OSPAR convention lists
- Are listed on UK Biodiversity Action Plan (UK BAP)
- Are listed on Ayrshire, Argyll & Bute, Dumfries & Galloway’s Local Biodiversity Action Plans (LBAP)
We will be using established methods and collecting data from dedicated boat surveys, the principle objectives of this study:
- To map the abundance, distribution and activity of harbour porpoises in the Clyde Estuary and surounding seas.
- To identify sites of high fidelity and/or potential “hotspots” for the animals.
- To record the number and association of calves in the study area, to relate habitat use to the presence of prospective nursery areas.