International Journal of
Biodiversity and Conservation

  • Abbreviation: Int. J. Biodivers. Conserv.
  • Language: English
  • ISSN: 2141-243X
  • DOI: 10.5897/IJBC
  • Start Year: 2009
  • Published Articles: 609

Full Length Research Paper

Interactions between short-beaked common dolphin (Delphinus delphis) and the winter pelagic pair-trawl fishery off Southwest England (UK)

Marijke N. de Boer1,2,3,4*, James T. Saulino3, Mardik F. Leopold1, Peter J. H. Reijnders1,2 and Mark P. Simmonds4
  1Wageningen IMARES, Institute for Marine Resources and Ecosystem Studies, Postbus 167, 1790 AD Den Burg, The Netherlands. 2Department of Aquatic Ecology and Water Quality, Wageningen University, Wageningen, The Netherlands. 3Seven Seas Marine Consultancy, Loe Bar Road, Porthleven, TR13 9EL, Cornwall, United Kingdom. 4Whale and Dolphin Conservation Society, Brookfield House, 38 St Paul Street Chippenham, Wiltshire SN15 1LJ,United Kingdom.
Email: [email protected]

  •  Accepted: 17 July 2012
  •  Published: 31 October 2012

Abstract

 

During offshore and onshore studies (2004 to 2009), the interactions between pair-trawls and short-beaked common dolphins (Delphinus delphis) were studied to better understand the impact of bycatch. A ‘hotspot’ area where pair-trawls overlapped with high dolphin abundance was identified. We made comparisons between boat-based data collected in absence and presence of pair-trawlers. The relative abundance and group-size of dolphins was significantly higher in the presence of pair-trawlers. Dolphins were observed associating with towing and hauling procedures. Significantly, more carcasses occurred in areas with hauling-activity than those without. Body-temperatures obtained from carcasses found near operating pair-trawlers indicated that bycatch mostly occurred at night. During necropsy studies, difficulties were encountered in identifying the fishing-gears responsible. Strandings data highlighted that the number of dead stranded dolphins was probably much higher than previously reported and there was a significant difference in the age and gender-composition of carcasses. Mature/sub-adult males appeared at greater risk from entanglement in pair-trawls offshore, whilst females with young appeared more vulnerable to inshore gillnets. Our findings show that the overlap between pelagic fisheries and the common dolphin hotspot is causing direct mortality through bycatch and, together with recent range-shifts, may have contributed to a localised decline of this species in this winter hotspot since 2007.

 

Key words: Bycatch, common dolphin, Delphinus delphis, pair-trawl fishery, gillnets, strandings, English Channel, conservation, abundance, trawling, mortality.

Abbreviation

Abbreviations: NFR, Non-fisheries related; FR, fisheries related; PO, platform of opportunity; BSS,Beaufort Sea State; CSIP, Cetacean Strandings Investigation Program.