Mammals

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Harbour porpoise

  • Phocoena phocoena
  • Harbour_porpoise_1
    Surging at the surface, showing the ‘rooster tail’ splash (© John S Young)
    Harbour_porpoise_2
    Harbour porpoise (© John S Young)
    Harbour_porpoise_3
    Harbour porpoise, typical view at the surface (© John S Young)
Category: Cetacea (Whales)
  • Identification:

    The harbour porpoise is the smallest cetacean to occur around the coast of Kent. It has a robust body with a small rounded head and no beak. Its small triangular dorsal fin is centrally placed. The body colour is dark grey merging to a lighter grey on the sides, with the underside being white. Calves and juveniles often have brownish backs. They have a quick surface-rolling action and when alarmed or moving at speed they can produce a distinctive splash that is similar to a ‘rooster tail’ in shape.

    It is generally unobtrusive but breaching behaviour, where the whole body is launched from the water has been observed at Dungeness. In Kent waters, the only species that might be confused with the harbour porpoise is the bottlenose dolphin. It also has a greyish colour and central dorsal fin, but this fin and the whole animal is much larger with a pronounced beak. It also behaves more extrovertly.
  • Head and body length: ♂ 145-163cm ♀ 160-189cm
  • Weight: ♂ 50-54 kg ♀ 50-81 kg
  • Distribution Map: Source: 2002–2012 Kent Mammal Atlas. These maps are provided for reference and do not include more recent recording updates

Habits

Harbour porpoise favour inshore waters, either alone or in small groups. They are not showy animals, with a quiet and unobtrusive behaviour. Their small size makes them very difficult to observe in all but the calmest sea conditions. Unlike many dolphin species they are shy, rarely approaching boats. Larger vessels are generally actively avoided and they will swim rapidly away from them; smaller vessels tend to be ignored allowing closer approach. The species also favours some of the larger river estuary areas of the county.  

Reproduction and life cycle

Few records of juveniles and calves are received so little is known regarding the breeding success of the Kentish harbour porpoise population. However, calves and juveniles are infrequently recorded from Dungeness along with signs of breeding behaviour.  

Distribution, status and conservation

In Kent there are no boat operators that provide a trip to see these marine mammals, although chartered recreational marine fishing trips quite often record porpoise and sometimes other cetacean species. Due to their habit of being an inshore species it is possible to observe harbour porpoise from the shoreline and they can occur anywhere around the Kent coastline and estuaries. The species is regularly observed at St. Margarets Bay, the Upper Thames area, Foreness and Dungeness where a small population occurs all year. In June 2012 up to 39 were observed at Dungeness confirming that this area is important for the species. Harbour porpoise are also seen in the larger river estuaries of the outer Thames, the Medway and in the Swale. ZSL (Thames Marine Mammal Conservation) has conducts regular surveys; their 2022 porpoise survey shows significant densities of porpoise in the Greater Thames Estuary. Porpoise monitoring is now ongoing and improving, with ZSL repeating surveys every five years.

Threats include pollution, by-catch, net entanglement, acoustic disturbance and over-fishing, with at least 10 dead harbour porpoises being washed up annually around the Dungeness peninsula area alone. The exact reasons for these deaths and the impact they have on the local porpoise population are unknown.

 
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