Flatfish fishery: impact and challenges

Flatfish are by far the most targeted marine organisms by the Belgian fishermen. Sole (Solea solea)
and plaice (Pleuronectes platessa) indeed take first place with regard to landings value and landings
weight, respectively. Both demersal fish species are mainly caught using beam trawls with tickler
chains. However, this fishing technique has several well known disadvantages including seabed
disturbance (caused by the deep penetration of the chains in the bottom), excessive discards (due
to lack of species and size selectivity) and high fuel consumption. Improvements have been made to
the fishing gear in order to reduce water resistance and to increase selectivity for species and size
resulting in less fuel consumption and by-catch reduction, respectively. However, these adjustments
were not assigned as sufficient. Alternative passive techniques such as fly shooting, gill nets or long
lines are available which are more selective, result in almost no seabed contact and markedly less
fuel consumption. However, these latter techniques currently are hardly economically feasible (gill
nets and long lines) or too dependent on the weather conditions to be fully effective (fly shooting).
Adequate long-term solutions hence are indispensable to ensure a sustainable and profitable future
for the flatfish fishery. The most promising alternative meeting both the fisherman’s aspirations
and the need for ecological progress is pulse fishing. In this fishing technique, the tickler chains are
replaced by electrodes towing over the sea floor and inducing electrical pulses, which elicit an
upward movement of the fish enabling its catch without spading the bottom. Pulse fishing, using
high frequency and voltage pulses, is currently evaluated for catching sole. Hitherto, several plus
points are discernible in comparison to the classical trawl fishery: marked decrease in seabed
disturbance, reduction of bycatch of undersized sole and plaice and invertebrate benthos and
halved fuel consumption (van Stralen, 2005). Unfortunately, also negative effects such as dislocated
spinal cords, hemorrhages and mortality were observed in certain exposed fish species, especially
cod (van Marlen et al., 2007; de Haan et al., 2008;). These adverse effects need to be tackled in
order to be able to define pulse fishing as an environmental friendly fishing technique. Further
studies hence are needed to define and optimize pulse characteristics for stimulating flatfish that
are not harmful for (other) exposed marine organisms.