Damage done to stocks of deep-water fish by the “ghost fishing” of lost or abandoned gillnets may not be as widespread as previously thought according to the results of a recent EC-funded pilot research project.
'Ghost fishing' occurs when nets become lost on the seabed but continue to trap fish that eventually die and are removed from the stock – a problem which was identified on the Rockall fishery off the northwest coast of Ireland following a survey by the Irish Sea Fisheries Board (BIM) in 2005, which recovered 261 metres of netting for every kilometre of seabed surveyed.
“Deep Clean” – the most extensive co-ordinated survey of ghost fishing to date within the EC, and undertaken between the Marine Institute and BIM in Ireland and Seafish and CEFAS in the UK – set out in 2008 with the twin objectives of; conducting targeted retrieval exercises of lost, discarded and abandoned nets in deep-water gillnet fisheries greater than 200 metres depth and to accurately estimate the quantity and range of ghost nets in these fisheries. As part of the project, a review of various types of recovery gear was undertaken to identify the most efficient ways of retrieving lost nets.
“One of the first goals of the project was to identify areas where ghost fishing might be a problem,” said Norman Graham of the Marine Institute, who coordinated the project. “To do this, we used information from a range of sources, including vessel monitoring data, ‘on the ground’ experience and interviews with commercial fishermen”.
While the industry was able to provide general information, very little detail on specific locations of lost nets was made available. "Experiences in Norway have shown that without this, the success of surveys as a mitigation exercise can be limited – akin to looking for a needle in a hay stack," says Graham.
"Norwegian surveys benefit from having a detailed data collection programme and the rate of ghost nets recovered are 100 times greater. So, while the extent of lost nets may not be widespread, we can not rule out localised ‘hot spots’."
Those areas included the Rockall and George Bligh Bank, North Shetland, the South and West Porcupine and the Rosemary Bank and South East Rockall area. The project also identified data on the location of sensitive deep sea habitats, such as coldwater coral reefs so as to avoid damaging these areas during the survey. Two charter vessels were then selected following an EU-wide call for tenders to conduct the four surveys and in all, 82 survey days were completed within four months over the summer of 2008. During that period 390 separate transects were undertaken as part of the survey and recovery operations, covering over 2,600km of seabed in total.
Seabed surveys were carried out at the beginning of the study using underwater camera systems. Once these were complete by mid-May retrieval of any identified ghost fishing nets began using a variety of gear including specially designed “creeper arrays”. These arrays, which were towed behind the survey vessels, consisted of a heavy horizontal iron bar dragging a number of smaller spiked bars along the bottom and above which a floating underwater camera was suspended to record results.
Information gained from the Deep Clean project suggests that in those nets that were retrieved, the extent of ghost fishing was low – consisting mainly of crabs. The overall conclusion of the project is that in general terms the issue of ghost fishing associated with lost gill nets does not constitute a high source of unaccounted catches for species such as monkfish, although given the poor status of some species such as deepwater shark, even small catches could be significant.
“It’s interesting to compare these results with the original BIM survey in Rockall in 2005,” said Graham. “At that time, significant quantities of abandoned nets were encountered that appeared to have been left on the seabed for some time. The fact that no abandoned nets were encountered in 2008 suggests that either this is no longer a problem in the fishery or that the industry notice provided an incentive for fishers to remove all gears from the area – making it difficult to draw any firm conclusions on whether deliberate abandonment is still a problem."
The project partners would like to thank all those who contributed to the success of the work, including fishermen from the Irish, Scottish and Spanish industries who supplied information; the deep-water gillnet sub group of the North Western Waters Regional Advisory Council (MWWRAC) and particularly the crews of the fishing vessels who undertook the survey work.