English - Caribbean Environment Programme

Harbour porpoises have a gestation period of 10 to 11 months 67 . Calves are seen betweenFebruary and September in UK waters, with a peak in June 68 .Due to the lack of markings that would allow recognition of individual animals (as is possible withmany other cetacean species), it is not presently known whether harbour porpoises display sitefidelity or have regular movement patterns between areas 69 . However, some researchers havereported resighting highly marked individuals over periods of time 70 which may indicate a degree ofsite fidelity. Genetic studies have demonstrated that female harbour porpoises disperse less thanmale harbour porpoises 71 and this may indicate that female harbour porpoises show site fidelity forthe places they calve and nurse their young, returning to preferred areas for these activities 72 .Important foraging habitat for harbour porpoises includes areas of strong tidal currents, usuallynear islands or headlands, where the currents combine with the seafloor topography and seem tocreate conditions where prey become aggregated 73 . At several places around the UK theselocations correspond with high porpoise densities.The patchy nature of survey effort makes it sometimes difficult to determine whether changes insightings rates are indications of seasonal movements or an artefact of the varying levels of searcheffort 74 . An additional issue is that the low profile and small size of the harbour porpoise make themconsiderably more challenging to see in poorer weather and higher seas 75 . Sightings rates thereforedecrease markedly as sea state increases and for this reason, harbour porpoises are likelyunderestimated in offshore areas and winter months when sea states tend to be higher. Difficultiesin sighting harbour porpoises, combined with the general situation of less research conducted awayfrom the coast and in winter due to the rougher seas and expense of working in such conditions, isa significant hindrance to gaining a more complete understanding of this species.Harbour porpoises are typically seen individually or in small groups of up to three animals.Occasionally large groups are sighted, usually associated with foraging. It is not presently known ifthere is a social or co-operative feeding element to these associations, as is the case with manyother cetaceans 76 .2267Jefferson et al, 200868Evans, 1992 (in Goodwin, 2007)69Pierpoint et al, 199870Ibid71Walton, 199772Baines and Earl, 199973Pierpoint et al, 2004; de Boer, 2006; Evans, 1997 (in Evans et al, 2003); Embling et al, 201074Reid et al, 200375Palka, 199676Goodwin, 2007