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Plaice Survival in the Irish Seine Net Fishery

Estimated 87% survival rate obtained

Dr Ronán Cosgrove, Fisheries Conservation Manager, BIM

Bord Iascaigh Mhara (BIM), Ireland’s Seafood Development Agency, recently completed a plaice survival study in collaboration with Damien Turner and crew on board bottom seine net vessel, MFV Róise Catríona. Led by BIM’s Martin Oliver, the trial was conducted around 5 hours steaming south of Castletownbere in October 2019. The condition of plaice caught under normal fishing operations was assessed using well established fish vitality/movement and injury assessment protocols.

Most of the plaice were in excellent condition with vigorous body movement. Scale and mucus loss were the predominant injuries. Applying observed plaice survival rates from a Danish seine net study conducted in the Skagerrak inferred a survival estimate of 87% for plaice in the Irish fishery. Directly observed survival rates were not possible in the Irish study due to logistical constraints but survival rates inferred from other fisheries have previously been used by the European Commission (EC) to grant exemptions from the landing obligation. For example, the Skaggerak study results were used to infer plaice survival rates and grant an exemption in a seine net fishery in the English Channel.

The Irish study results will be used to apply for a survival exemption for seine caught plaice off Ireland’s south-west and west coasts where there are risks of choking under the landing obligation due to restrictive plaice quotas of less than 60 t in 2020. Given the specialised nature of the fishery, seine net vessels are limited in their options to avoid unwanted plaice capture. They are generally restricted to targeting mixed demersal fish species, and incapable of switching to Nephrops and benefitting from the suite of selective gears available in that fishery. Also, Irish fishing grounds suited to bottom seining are mainly located off the south-west and west coasts so relocation to areas with more quota availability is not an option.

A previous Irish application for a plaice survival exemption for otter trawlers off the south west coast was rejected on the basis that survival of around 40% would not lead to a sufficient reduction in fishing mortality in a depleted stock. While there are no guarantees, the seine net application will hopefully fare better given a substantially higher survival estimate and superior fish condition in seines compared with trawls. Underwater camera observations have shown that the majority of fish herded by seine ropes enter the belly and codend sections in the closing phase of the hauling operation. Hence, the actual fishing time may be as short as 15 minutes with fish subject to physical stressors in the codend for much shorter periods compared with trawling. This is corroborated in the Skagerrak study where a substantially higher plaice survival rate of 78% was found in a seine net fishery compared with 44% in a bottom trawl fishery in the same area and time of year off the Danish coast.

BIM would like to thank Damien Turner and the crew of MFV Róise Catríona for a productive collaboration, and Shane Murphy for assistance with on board sampling. A full report on this work is available at www.bim.ie/our-publications/fisheries