English - Caribbean Environment Programme

East EnglandThe seasonal pattern in the southern North Sea appears to be for an early spring peak in numbersin coastal waters to be followed by a northward migration towards more offshore waters. However,whilst some studies report that numbers of harbour porpoises in coastal waters around the southernNorth Sea then remains low for the summer 130 , others have found a second peak to take place offeast England in August and September, possibly highlighting a regional difference 131 .The major SCANS surveys undertaken in the summers of 1994 (SCANS) and 2005 (SCANS II)across the North Sea and European Atlantic continental shelf waters provided some interestinginsights into possible large-scale changes in harbour porpoise distribution in the North Sea overrecent years (see Figures 4.3-4.4, p.21 and 4.5-4.6, p.22). The 1994 survey 132 recorded moderatenumbers of harbour porpoises off east England and in the central/southern North Sea region (0.387animals/km 2 and 0.34 animals/km 2 ). Yet when SCANS II took place in 2005 133 , numbers in the southNorth Sea had increased greatly and densities of 0.562 animals/km 2 were recorded, while in thenorthern North Sea a corresponding decrease was detected. This may indicate a redistribution ofporpoises from north to south, which is thought to be most likely due to changes in the distributionor availability of prey 134 . Highest densities in 2005 stretched from The Wash and north Norfolkcoast, north and west to the Dogger Bank region 135 . Many sandbanks exist in this area, importanthabitat for sandeel and other prey species utilised by harbour porpoises, other marine mammals,seabirds and fish 136 .Other studies have highlighted the importance of the Dogger Bank area to harbour porpoises,other cetaceans and many species of seabirds, and multi-species feeding associations have beendocumented here 137 . Surveys over the German sector of the Bank found high densities of porpoises(1 - 1.5 animals/km 2 ) 138 . The German side of the bank has been designated as an SAC and theDutch and UK areas of the bank have also been proposed for an SAC, but not with harbour porpoisesas a qualifying feature 139 . An acoustic study based on offshore installations on the Dogger Bankrecorded porpoises regularly around the installations and considered these may be importantforaging areas for this species 140 . The authors also noted that if porpoises cluster around theseinstallations as their research suggests, these animals may be omitted by population surveys suchas SCANS as survey vessels would have to remain outside the 500m exclusion zone.Trying to understand these large-scale changes in distribution, and the driving forces behind them,will only be possible by repeating North Sea wide surveys such as SCANS on decadal or morefrequent basis, and also by investigating porpoise-prey dynamics. The SCANS surveys — designedto provide large-scale population estimates — provide no information on the relative importance ofhabitats at a fine scale. It may be that smaller areas within the North Sea are important to harbourporpoises. Smaller scale surveys are also necessary to determine if some areas remainimportant to harbour porpoises throughout these larger scale fluctuations.A review and analysis of over 20 years of harbour porpoise data from around the UK identifiedthree areas off the east coast of England that are potentially consistently important to harbourporpoises – east of Northumberland, east of Yorkshire, and particularly, east of the Wash near theNorfolk coastline. Porpoises have been recorded in these locations for some or most months of theyear, with concentrations in several months, and records over several years 141 . For east of theWash these concentrations occur during the April to September key calving period for harbourporpoises 142 . High densities of harbour porpoises during the summer, the time of year whenthese animals breed and produce young, suggest these waters may be important for thesefunctions and this should be investigated further.South east EnglandDeclines in harbour porpoise abundance have been observed in the southern North Sea regionsince the 1950s, for reasons not understood 143 . For the last few years, sightings and strandingsdata from Belgian and Dutch waters have indicated an increase in numbers for the southern NorthSea, and the SCANS II survey results (see East England section) support this. However, the130Haelters and Camphuysen, 2009131Evans and Wang, 2002132Hammond et al, 2002133SCANS II, 2006134Ibid135Ibid136JNCC, 2010137Camphuysen et al, 1995; Gubbay et al, 2002138Gilles et al, 2008139JNCC, 2010140Todd et al, 2009141Evans and Wang 2002142Ibid143Haelters and Camphuysen, 200927