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

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.

[1]  W. Dabin,et al.  The significance of stranding data as indicators of cetacean populations at sea: Modelling the drift of cetacean carcasses , 2012 .

[2]  N. Sillero,et al.  Common dolphin (Delphinus delphis) habitat preferences using data from two platforms of opportunity , 2012 .

[3]  G. Pierce,et al.  Quantifying likely cetacean range shifts in response to global climatic change: implications for conservation strategies in a changing world , 2011 .

[4]  Villy Christensen,et al.  From common to rare: The case of the Mediterranean common dolphin , 2011 .

[5]  B. Godley,et al.  Cetacean sightings and strandings: evidence for spatial and temporal trends? , 2011, Journal of the Marine Biological Association of the United Kingdom.

[6]  D. Lusseau,et al.  Underestimating the damage: interpreting cetacean carcass recoveries in the context of the Deepwater Horizon/BP incident , 2011 .

[7]  R. Wells,et al.  Genetic Evidence Highlights Potential Impacts of By-Catch to Cetaceans , 2010, PloS one.

[8]  M. Simmonds,et al.  Short-beaked common dolphin ( Delphinus delphis ) occurrence in the Moray Firth, north-east Scotland , 2010 .

[9]  A. Aguilar,et al.  Incidental bycatch of short-beaked common dolphins (Delphinus delphis) by pairtrawlers off northwestern Spain , 2010 .

[10]  Simon Jennings,et al.  Developing reliable, repeatable, and accessible methods to provide high-resolution estimates of fishing-effort distributions from vessel monitoring system (VMS) data , 2010 .

[11]  Alfredo López,et al.  Trends in cetacean sightings along the Galician coast, north-west Spain, 2003–2007, and inferences about cetacean habitat preferences , 2010, Journal of the Marine Biological Association of the United Kingdom.

[12]  C. Fortuna,et al.  By-catch of cetaceans and other species of conservation concern during pair trawl fishing operations in the Adriatic Sea (Italy) , 2010 .

[13]  M. Simmonds,et al.  The Conservation of British Cetaceans: A Review of the Threats and Protection Afforded to Whales, Dolphins, and Porpoises in UK Waters, Part 1 , 2010 .

[14]  I. Cascão,et al.  Sex bias in biopsy samples collected from free-ranging dolphins , 2010, European Journal of Wildlife Research.

[15]  Mónica A. Silva,et al.  Importance of biological parameters in assessing the status of Delphinus delphis , 2009 .

[16]  C. MacLeod,et al.  Fine-scale habitat selection by white-beaked and common dolphins in the Minch (Scotland, UK): evidence for interspecific competition or coexistence? , 2009, Journal of the Marine Biological Association of the United Kingdom.

[17]  P. Duignan,et al.  Causes of mortality in stranded Common Dolphin (Delphinus sp.) from New Zealand waters between 1998 and 2008 , 2009 .

[18]  Lluís Yedra Cardona,et al.  Factors determining the interaction between common bottlenose dolphins and bottom trawlers off the Balearic Archipelago (western Mediterranean Sea) , 2008 .

[19]  T. Brereton,et al.  Changes in the occurrence of common dolphins, striped dolphins and harbour porpoises in the English Channel and Bay of Biscay , 2008, Journal of the Marine Biological Association of the United Kingdom.

[20]  P. Garcia,et al.  Insights on common dolphin (Delphinus delphis) social organization from genetic analysis of a mass-stranded pod , 2008, Behavioral Ecology and Sociobiology.

[21]  A. Aguilar,et al.  Pingers as deterrents of bottlenose dolphins interacting with trammel nets , 2008 .

[22]  Y. Morizur,et al.  Tests d'efficacité du répulsif acoustique CETASAVER à bord des chalutiers commerciaux français Résultats obtenus au cours des années 2007 et 2008 , 2008 .

[23]  Brendan J. Godley,et al.  Spatio-temporal analysis of cetacean strandings and bycatch in a UK fisheries hotspot , 2008, Biodiversity and Conservation.

[24]  P. Hammond,et al.  Abundance and habitat preferences of the short-beaked common dolphin Delphinus delphis in the southwestern Mediterranean: implications for conservation , 2008 .

[25]  G. Pierce,et al.  Intraspecific dietary variation in the short-beaked common dolphin Delphinus delphis in the Bay of Biscay: importance of fat fish , 2008 .

[26]  De Boer,et al.  Winter abundance estimates for the common dolphin (Delphinus delphis) in the western approaches of the English Channel and the effect of responsive movement , 2008 .

[27]  G. Waring,et al.  Incidental Take of Marine Mammals in Foreign Fishery Activities Off the Northeast United States , 1977-88 , 2008 .

[28]  Brendan J. Godley,et al.  A Step Towards Seascape Scale Conservation: Using Vessel Monitoring Systems (VMS) to Map Fishing Activity , 2007, PloS one.

[29]  E. Rogan,et al.  Megafauna bycatch in drift nets for albacore tuna (Thunnus alalunga) in the NE Atlantic , 2007 .

[30]  Mike Pawson,et al.  Migrations, fishery interactions, and management units of sea bass (Dicentrarchus labrax) in Northwest Europe , 2007 .

[31]  A. Read,et al.  Reproduction in short-beaked common dolphins (Delphinus delphis) from the western North Atlantic , 2007 .

[32]  B. Godley,et al.  Effects of pingers on the behaviour of bottlenose dolphins , 2007, Journal of the Marine Biological Association of the United Kingdom.

[33]  Sharon L. Hedley,et al.  Modeling distribution and abundance of Antarctic baleen whales using ships of opportunity , 2006 .

[34]  Simon Northridge,et al.  Bycatch of Marine Mammals in U.S. and Global Fisheries , 2006, Conservation biology : the journal of the Society for Conservation Biology.

[35]  M. Leopold,et al.  Bruinvisstrandingen in Nederland in 2006: achtergronden, leeftijdsverdeling, sexratio, voedselkeuze en mogelijke oorzaken , 2006 .

[36]  J. Robin,et al.  Stomach contents of English Channel cetaceans stranded on the coast of Normandy , 2005, Journal of the Marine Biological Association of the United Kingdom.

[37]  G. Pierce,et al.  Climate change and the cetacean community of north-west Scotland , 2005 .

[38]  P. Guglielmi,et al.  Driftnet fishing and biodiversity conservation: the case study of the large-scale Moroccan driftnet fleet operating in the Alboran Sea (SW Mediterranean) , 2005 .

[39]  A. Ross.  The Net Effect ? A review of cetacean bycatch in pelagic trawls and other fisheries in the north-east Atlantic , 2004 .

[40]  P. Corkeron,et al.  Influence of trawling on the behaviour and spatial distribution of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Moreton Bay, Australia , 2003 .

[41]  R. Reeves,et al.  Ecology, status and conservation of short-beaked common dolphins Delphinus delphis in the Mediterranean Sea , 2003 .

[42]  Alfredo López,et al.  Fishery by-catches of marine mammals in Galician waters: results from on-board observations and an interview survey of fishermen , 2003 .

[43]  Mónica A. Silva,et al.  Patterns in the mortality of common dolphins ( Delphinus delphis ) on the Portuguese coast, using stranding records, 1975-1998 , 2003 .

[44]  G. Pierce,et al.  Results of a short study on by-catches and discards in pelagic fisheries in Scotland (UK) , 2002 .

[45]  Alfredo López,et al.  Trends in strandings and by-catch of marine mammals in north-west Spain during the 1990s , 2002, Journal of the Marine Biological Association of the United Kingdom.

[46]  P. Corkeron,et al.  Trawling and bottlenose dolphins' social structure , 2001, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[47]  D. Neumann.  Seasonal movements of short‐beaked common dolphins (Delphinus delphis) in the north‐western Bay of Plenty, New Zealand: Influence of sea surface temperature and El Niño/La Niña , 2001 .

[48]  A. Aguilar,et al.  Spanish driftnet fishing and incidental catches in the western Mediterranean , 1999 .

[49]  A. S. Couperus,et al.  Incidental catches of marine-mammals in pelagic trawl fisheries of the northeast Atlantic , 1999 .

[50]  S. Leatherwood,et al.  Cetacean Interactions with Trawls: A Preliminary Review , 1997 .

[51]  A. S. Couperus.  Interactions Between Dutch Midwater Trawl and Atlantic White-sided Dolphins (Lagenorhynchus acutus) Southwest of Ireland , 1997 .

[52]  T. Kuiken,et al.  Mass mortality of common dolphins (Delphinus delphis) in south west England due to incidental capture in fishing gear , 1994, Veterinary Record.

[53]  A. S. Couperus.  Killer whales (Orcinus orca) scavenging on discards of freezer trawlers north east of the Shetland islands , 1994 .