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Best practice for the development of management plans for cetaceans within Marine Protected Areas in the Channel region - Cornwall as a case study

Creator : Niki Clear, Abby Crosby, Ruth Williams
Date : 04/03/2015

Fourteen species of cetaceans have been recorded in the waters of English Channel, with the species encountered most frequently being the harbour porpoise (Phocoena phocoena), common dolphins (Delphinus delphis) and bottlenose dolphins (Tursiops truncatus).  Since 1995, Cornwall Wildlife Trust has been collecting data on all cetaceans using Cornish waters through projects including the Marine Strandings Network, Seaquest Southwest and Seaquest Netsafe.  These projects have provided a deeper understanding of cetaceans' distribution and their habitats via visual sightings, acoustic monitoring and strandings investigations.  Cornwall Wildlife Trust has also worked to find solutions to some of the major threats facing these animals in inshore waters, such as entanglement in fishing nets.  Working closely with the local fishing industry, acoustic deterrent devices have been tested as a tool, in addition to Marine Protected Areas (MPAs), with the aim of reducing bycatch of cetaceans in nets to protect cetacean populations.

The reason for marine mammal mortality varies from natural disease to anthropogenic pressures such as pollution and accidental bycatch in fishing gear. The fact that the English Channel lays claim to the world's busiest seaway and is ranked among the highest globally for cumulative human impacts on marine ecosystems increases the level of such pressures to local cetacean populations. Bycatch in particular has been identified as the leading cause of death for stranded cetaceans in Cornwall. In 2012 the cause of death in 30% of necropsied cetacean carcasses was found to be entanglement in fishing gear, and a further 26% had physical external injuries consistent with interactions with fishing gear. The vast majority of these animals were harbour porpoise and common dolphin. Chemical pollution such as from organochlorines has been linked to lower immunity to infectious diseases, which is the second leading cause of death seen in harbour porpoise in the UK. Other threats facing marine mammals within the English Channel include increased marine noise pollution, disturbance and habitat degradation.

In European waters, 46 cetacean species and their habitats are included in various conventions, treaties and agreements, many of which embrace the creation of Marine Protected Areas (MPAs) which are increasingly suggested for use as a conservation management tool. However, collection of necessary local population and distribution data to back up such recommendations is difficult as most cetacean species are highly mobile and spend a substantial time below surface. This makes detection, identification, and group size estimation problematic. The knowledge of cetaceans within Cornish waters has been gathered from casual sightings records, photo-identification work, intermittent effort-based surveys both from land and on boat, and in more recent years acoustic monitoring using underwater acoustic monitoring devices. 

The understanding of cetacean populations is essential for the designation of Marine Protected Areas as management tools for these species. The variability in range and abundance of some species, such as the harbour porpoise has caused problems for site identification for MPAs. However MPAs are undoubtedly an extremely powerful conservation tool where a species has a small home range that can be covered more or less in its entirety or for migratory species with very clearly defined breeding/feeding areas, or where the threats faced are localised and appropriate management can be put in place to counteract those threats. Using a static, site specific MPA for a cetacean population which (i) routinely or seasonally migrates out of the MPA or (ii) where the home range of a population shifts towards areas outside of the MPA, means that such a site becomes inadequate for the protection of the designated species. Therefore, it is essential for these sites to be supported by schemes or plans which will deal with the complex interaction of different management issues so that cetacean populations are maintained, significant threats reduced, and the habitats of cetaceans are preserved.

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updated on 03/05/2015
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