ICES - Report of the Study Group on Electrical Trawling 2011 (SGELECTRA)
The Study Group on Electrical Trawling (SGELECTRA) chaired by Bob van Marlen, and Bart Verschueren, met from 7–8 May 2011 at the Marine Research Institute of Reykjavik, Iceland. A total of seven participants attended from Netherlands, Belgium, Germany, Scotland, Russia and Lithuania.
Following the ICES Advice on Pulse Trawling on flatfish of 2006 further studies were carried out by IMARES, the Netherlands on catsharks (Scyliorhinus canicula L.), cod (Gadus morhua L.) and a range of benthic species (ragworm (Nereis virens L.), common prawn (Palaemon serratus L.), subtruncate surf clam (Spisula subtruncata L.), European green crab (Carcinus maenas L.), common starfish (Asterias rubens L.), and Atlantic razor clam (Ensis directus L.) under pulse stimulation of the Verburg-Holland system.
These studies were reviewed and discussed at WKPULSE.
Further studies were conducted on cod in 2010 that were presented and discussed here. Juvenile cod (10–12 cm) were affected to a lesser degree by electric pulse stimulation than larger individuals (44–51 cm). By increasing pulse frequency or decreasing pulse amplitude harmful effects on larger cod can be avoided. A remaining question is whether these pulse settings would still enable catching the target species sole and plaice.
A presentation was also given about the development of a pulse trawl for the brown shrimp (Crangon crangon L.) fishery in Belgium and the beginning of sea trials in the Netherlands.
In addition a report was given on electric fishing for razor clams (ensis) in Scotland, and work in Russia and Lithuania from 1972–1988. A vast body of reports in the Russian language exist that might contain valuable information for this group.
The work already done in EU DEGREE-project and study FISH/2009/07 LOT3 for flatfish fishery was extended. A new scenario was run (scenario 2c) with pulse trawling replacing standard beam trawling in the 24–40m and >40m métiers of 80–90 mm mesh size using the model of Piet et al., 2009. The results indicate that cod landings and discards can be reduced by ~7%. It was advocated to update the models used with results from new full-scale tests.
It was intensively discussed how electric fishing gears can be regulated and controlled to avoid negative impacts. A major problem is that the impact of electric pulses potentially depends on a variety of parameters. Relevant puls characteristics and other variables were identified such as: amplitude in V, electric field strength in V/m, pulse frequency in Hz, pulse duration in μs, pulse form, method: continuous or intermittent, the configuration of the electrodes (diameter, length, insulator/conductor mounting etc.), as well as: species, length in cm, seawater temperature, conductivity of organism, seawater conductivity, position of organism in electric field, sediment characteristics and conductivity, and towing speed. It is quite clear, that it is not optimal to specify all these parameters in legislation and difficult to control them. Therefore, it is hoped that simpler limits can be found, such as capacitor
size, as these will physically limit any increase in the output energy the system can deliver. It may be the case that for different species groups (shrimps, flatfish) different limits need to be defined.
The reviewing experts recommended to:
- Continue work on TOR’s a), ... , e)
- Follow and participate in the debate of the Dutch Working Group on Control & Enforcement
- Consider producing an ICES Cooperative Research Report (CRR) on electric fishing, possibly through working by correspondence
- Meet again spring 2012 (prior to WGFTFB), possibly in conjunction with WGFTFB
- Consider including other experts (e.g. on fish physiology, modelling effects).