Device to cut dolphin deaths

Wednesday 27 February 2002

Scots marine biologists are joining forces with fishermen to develop a new device that will help prevent dolphins becoming caught in trawl nets.

Dr Simon Northridge of the Sea Mammal Research Unit (SMRU) at the University of St Andrews has been awarded a £33,000 grant by the Department for the Environment, Food and Rural Affairs (DEFRA) with a contribution from the Joint Nature Conservation Committee (JNCC) to work with the Scottish Pelagic Fishermen’s Association (SPFA) to design and implement an exclusion grid which could help prevent hundreds of dolphin deaths in UK and French waters each year.

The project also involves the UK’s Sea Fish Industry Authority (SFIA), who specialise in designing and testing improved types of fishing gear, and the Norwegian Institute of Marine Research (IMR), experts on reducing bycatch in trawl fisheries.

Two years ago, the SPFA, concerned by reports of occasional accidental dolphin captures by their members, invited SMRU to place observers on boats in their fleet to determine the extent of any dolphin deaths in pelagic fishing nets. Under a separate contract with DEFRA, SMRU have placed independent observers on 13 UK pelagic trawlers fishing for mackerel, herring, sprats, pilchards, blue whiting, bass and anchovy. Observers have so far monitored 210 trawl tows during 195 days at sea.

In all of the fisheries monitored bar one, no dolphin bycatches have been observed. In one fishery, the bass fishery in the Channel which operates from December to March, skippers’ fears were realised when 12 of 116 hauls that were monitored also held dead common dolphins. Skippers requested some action to try to reduce the numbers of animals being caught and, in 2001, SMRU observers deployed acoustic pingers around the mouth of the trawl. These devices have been shown to reduce dolphin bycatch in stationary nets, but ultimately were not effective in eliminating dolphin deaths from the moving trawls.

A second plan has therefore been developed to bring in outside expertise to design and implement an exclusion grid. Exclusion or selection grids are used in many fisheries around the world to exclude unwanted fish or other animals from the catch. Grid selection devices were first used in the early years of the 20th century but were refined by the Norwegian Institute of Marine Research in the 1980s after innovations in grid design conceived by Norwegian fishermen from the Nordmore region of Norway. Nordmore grids are now widely used, and even compulsory, in many shrimp fisheries around the world to reduce wasteful killing of fish. A variation of the design is also used to exclude turtles from shrimp trawls. In New Zealand, an IMR grid design has been successfully used to reduce sea lion bycatch in a pelagic trawl fishery for squid by over 90%.

The SMRU, IMR, SFIA and the SPFA have designed a grid system specifically to address common dolphin bycatch in the bass trawl fishery, with the intention of guiding common dolphins out of the net before they become hopelessly caught. Hydrodynamic tests to ensure smooth operation will be conducted with a scale model at the SFIA Flume Tank testing facilities in Hull, and a prototype device will be tested by one of the two Scottish pair trawl teams working in the Channel during March. Observers on the second pair will continue to monitor dolphin bycatches in an unmodified net. A report on these preliminary trials will be completed by May. If the device seems successful, SMRU will seek to establish a joint project with the much larger French bass fishing fleet to develop the design further.

Dr Northridge of SMRU said, “Every year, hundreds of dolphins are found in French and also UK waters that have clearly died in fishing operations. We do not know which fisheries most of these animals come from, but it is clear that some of them probably come from the UK bass fishery. The only sensible way to resolve this problem is to work with the fishermen to try to find a way of preventing these accidents. We hope that if we can show the way forward in this one very small fishery, that other foreign fleets may be persuaded to try the same methods”.

Meanwhile, Derek Duthie of the SPFA said, “The industry takes its environmental responsibilities seriously and has been active in collaborating with scientists to assess the nature and scale of the problem over several years. Extensive monitoring has confirmed what we already knew; that cetacean by-catch is not an issue in the main UK pelagic fisheries. A problem has however been identified when fishing for sea bass and we have been trying to find a solution to this one small area of operation. The development of the exclusion grid will, we hope, provide the answer.”



Common dolphins are the most abundant of all 83 species of cetacean (whales, dolphins and porpoises). They are especially numerous in the southwest of Britain and out into the deep Atlantic Ocean. In summer time they can be found from the tropics as far north as the Faeroe Islands and Iceland, whilst in winter they are mainly found south of the Ireland.

Common dolphins are sociable animals, and it appears that groups of several animals usually get caught together, averaging 4 to 5 individuals.

A major international survey that was led by SMRU in 1995 concluded that there were 75,000 common dolphins in a part of the western Channel in the summer, whilst further offshore a French survey estimated there were more than 65,000 common dolphins present in 1993.

Common dolphins in the Channel feed mainly on sardines and horse mackerel, with smaller amounts of mackerel and Norway pout – generally fish less than 25cm in length. They do not feed on the much larger sea bass that is the target of the bass fishery.

The UK pelagic fisheries sector is dominated by Scottish boats, mostly skipper-owned, or owned by small businesses based in the fisheries dependent areas along the shores of the Moray Firth and the Shetland Islands. The fleet consists of around 40 vessels. The main target species are herring and mackerel, and this year the UK’s quota of these species is c. 200k tonnes and 80k tonnes respectively. A small number of vessels (4 this year) prosecute sea bass between the seasonal main fisheries.

Two years ago, SMRU, with industry partners, ran a successful programme to reduce the bycatch of a related species, the harbour porpoise, in stationary gill nets. Using acoustic warning devices the bycatch rate was reduced by over 90%.

Issued by Beattie Media on behalf of the University of St Andrews For more information please contact Claire Grainger on 01334 462530, 07730 415 015 or email [email protected] Ref: dolphins/standrews/chg/27feb2002

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