Guidance to Manage the Risk to Marine Mammals from Man-made Sound Sources in Irish Waters.

Abstract

There has been increasing concern internationally about the potentially harmful effect of man-made sound on the marine environment and species therein that could be sensitive to it. Sound that is derived from human activities (i.e., anthropogenic sound) is not the sole noise source above or below the sea surface. Nevertheless, the level of man-made sound in coastal and marine environments is commonly reported to be increasing, a trend that is partly attributed to a growth in commercial shipping activity1 . Whether it is intended or not, the introduction of man-made sound into the environments occupied by marine mammals (e.g., whales, dolphins, seals) carries with it a potential adverse impact2 . The properties of water allow sounds of various kinds to travel great distances3 across diverse habitats and depth strata. Marine mammals, having evolved from terrestrial predecessors, have adapted to life in the sea by being able to exploit sound properties in water very effectively for their own primary sensory use4 . For example, they depend on and utilise sound for a wide range of critical natural functions including navigation and perception of their environment, communication, prey identification and capture, and the detection of predators. The hearing system of marine mammals, being highly sensitive and adapted to respond to changes in pressure in an aquatic environment, is particularly susceptible to damage3 . The possibility of permanent or even lethal injury in marine mammals as a result of man-made sound has received considerable attention in the scientific and public spheres, due to a number of beaked whale stranding events apparently associated with military use of mid-frequency sonar in the area1,5,6,7,8 . Yet many more routine anthropogenic sounds in the sea, for example seismic surveys9 , pile driving or chemical explosions3,10 , can also cause significant disruption of normal behaviour by marine mammal species. At least 26 species of marine mammal are known to occur in Irish waters. Two seal species, the Grey seal (Halichoerus grypus) and Harbour seal (Phoca vitulina, also known as Common seal) breed around all shorelines of Ireland and use the coastal and offshore waters in their daily lives for foraging, transit between terrestrial resting places (known as haul-out sites), and other behaviours linked to their annual life cycles (e.g., social behaviour, territoriality). Twenty-four species of cetacean (i.e., whales, dolphins and porpoises) have been recorded from Ireland11, 18 of which are more commonly observed, while the remaining six species have rarely been recorded and are currently classed as vagrant (i.e., species well outside their normal natural range). Some species can occur close to shore, and may be found within enclosed bays, harbours and estuaries, such as Dingle Harbour or the Shannon Estuary. Others (e.g., Blue whale, Sperm whale, Humpback whale) may be highly migratory and show a preference for deeper water offshore habitats, or travel hundreds or thousands of kilometres between winter breeding and summer foraging locations, occupying Irish waters during part of their annual cycle. Marine mammals occurring in Ireland have been the focus of considerable research effort over the last three decades and the understanding of species occurrence, abundance and distribution has improved markedly. While detailed knowledge of breeding, foraging, movements and other aspects of the natural history of many Irish species remain to be described, some useful sources summarising the current knowledge and distribution of Irish populations include: Cetaceans NPWS (2008): The status of EU Protected Habitats and Species in Ireland Pollock et al. (1997): Distribution of seabirds and cetaceans in the waters around Ireland Reid et al. (2003): Atlas of cetacean distribution in north-west European waters Ó Cadhla et al. (2004): Cetaceans & seabirds of Ireland’s Atlantic Margin – Volume II 3 O’Brien et al. (2009): Cetaceans in Irish waters: a review of recent research DEHLG (2009): Conservation Plan for Cetaceans in Irish Waters Berrow et al. (2010): Irish Cetacean Review (2000-2009) Wall et al. (2013): Atlas of the distribution &relative abundance of marine mammals in Irish offshore waters Seals NPWS (2008): The status of EU Protected Habitats and Species in Ireland Cronin et al. (2004): Harbour seal population assessment in the Republic of Ireland - August 2003 Ó Cadhla et al. (2008): An assessment of the breeding population of grey seals in the Republic of Ireland Ó Cadhla & Strong (2007): Grey seal moult population survey in the Republic of Ireland Due to concerns regarding the potential detrimental effect on these animals from certain types of acoustic survey equipment, the Department of the Environment, Heritage and Local Government, through review and consultation with key stakeholders, developed a “Code of Practice for the Protection of Marine Mammals during Acoustic Seafloor Surveys in Irish Waters” in August 2007. The following guidance sets out to address several key potential sources of anthropogenic sound that may impact detrimentally upon marine mammals in Irish waters. It incorporates a re-examination of the Code of Practice for acoustic surveys and thereby provides replacement guidance and mitigation measures in this respect. The document will be subject to periodic review to allow its efficacy to be reassessed, to consider new scientific findings and incorporate further developments in best practice.