Reactions of harbour porpoise (Phocoena phocoena) to vessel traffic in the coastal waters of South West Wales, UK

Only a limited number of studies on the effects of boats on cetaceans have been published, most concentrating on dolphin species (Family Delphinidae), with restricted research findings published regarding harbour porpoises (Phocoena phocoena). From February 2011-May 2013, a count of boats (n = 2153) was conducted from seven land-based sites - Port Talbot deep water harbour, Tutt Head, Mumbles (39% of all vessel traffic occurred here), Pwll Du Head, Southgate, Port Eynon Point, Rhossili and Burry Holms, all located in the Swansea Bay and South Gower area of the UK - to give an analysis of boat traffic volume. A variety of vessel types was observed: large commercial cargo ship, kayak, recreational fishing, commercial fishing, rib, jet-ski, speedboat, cruiser, yacht, cargo or stand-up paddle board (SUP). Interactions between vessels and porpoise were noted during these surveys. During 729 h of survey effort (268 total surveys), 38% (n = 103) of surveys had no corresponding porpoise sightings, while 62% (n = 165) were porpoise positive. With regard to vessel/porpoise interactions, there were 39 occasions when porpoise exhibited only neutral or negative behaviour. Groups of two porpoise were the modal group size, accounting for 61% (n = 24) of porpoise/vessel interactions, with peak interactions documented in May (n = 9) and July (n = 8). Vessel type and speed rather than presence seemed to be the relevant factors; 75% of all negative reactions were in response to high-speed planing-hulled vessels, the remainder being neutral responses.