Mechanical effects

In collaboration with the fishing industry, two field experiments have been conducted to measure the sediment penetration and direct benthos mortality induced by both conventional tickler chain beam trawl and the pulse trawl gear. The results are:

  • Because pulse trawls are lighter and are towed at a slower speed (5 knots or less) than the traditional tickler chain beam trawls (towing speed between 6 and 7 knots), pulse trawls have a smaller annual footprint in terms of the area affected.
  • Pulse trawls show a reduced penetration into the sediment and a reduction in the bycatch of benthos.
  • Although no significant differences in trawl path mortality of benthos was found, power analysis showed that a larger sample size would be required to detect a difference in mortality imposed by the pulse trawl as compared to the traditional beam trawl.
  • Because pulse trawlers may be used in other habitats than conventional tickler chain trawls, the change in effort distribution over the habitats needs to be taken into account when estimating the change in impact of fishery for sole when the beam trawl is replaced by the pulse trawl.
  • Electrical stimulation may also be successfully applied in the fishery for brown shrimp to improve the selectivity and reduce the bycatch and the contact with the seafloor.