The effect of pulse stimulation on marine biota - Research in relation to ICES advice - Progress report on the effects on benthic invertebrates
Experiments were carried out in July 2009 on a range of benthic invertebrates (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 based on the Verburg-Holland stimulus.
Groups of twenty animals per species were exposed to three treatments of four 1 s bursts of electrical pulses using a pulse simulator: nearby (0.10-0.20 m distance), at medium distance (0.20-0.30 m), and further away (0.40 m) of the electrodes. A 1 s pulse burst is deemed to represent the in situ passage of the pulse field of the gear beneath a non-moving fish. A control group was used for all species to correct for handling effects. The animals were caught with methods minimizing catch effects, and kept in water quality controlled circulating sea water tanks, and regularly fed. Survival, food intake and behaviour were monitored for a period of some two weeks after the exposure. The data were analysed with generalized linear models in the SAS statistical package.
For two species (ragworm and European green crab) a 3-5% statistically significantly lower survival was found compared to the control group, when all exposures were lumped together. For the near field exposure a 7% lower survival was also found for Atlantic razor clam. For the other species (common prawn, subtruncate surf clam, common starfish) no statistically significant effects of pulses on survival were found. Surf clam seemed not to be affected at all, common prawn seemed to show lower survival in the highest exposures (near and medium field), while common starfish showed lower survival, but not for the highest (near field) exposure.
Food intake turned out to be significantly lower (10-13% less) for European green crab, except in the far field exposure for which the reduction (~5%) was non:significant. No effect at all was found for ragworm, surf clam and razor clam, lower food intake for common prawn, and higher for common starfish, but all these results were statistically non-significant.
Surf clam and starfish did not show any behavioural reaction at all, they did not move. The other species showed very low responses in the far field exposure range. In the medium and near field ranges the reactions were stronger. Food intake and behaviour recovered after exposure.
In general terms the effects of the pulse stimulus in terms of mortality and food intake can be described as low. It is therefore plausible that the effects effects of pulse beam trawling, as simulateed in this study, are are far smaller than the effects of conventional beam trawling.