Laboratory Study of the Impact of Repetitive Electrical and Mechanical Stimulation on Brown Shrimp Crangon crangon

Abstract

Pulse trawling is currently the best available alternative to beam trawling in the brown shrimp Crangon crangon and Sole Solea solea (also known as Solea vulgaris) fisheries. To evaluate the effect of repetitive exposure to electrical fields, brown shrimp were exposed to the commercial electrodes and pulse settings used to catch brown shrimp (shrimp startle pulse) or Sole (Sole cramp pulse) 20 times in 4 d and monitored for up to 14 d after the first exposure. Survival, egg loss, molting, and the degree of intranuclear bacilliform virus (IBV) infection were evaluated and compared with those in stressed but not electrically exposed (procedural control) and nonstressed, nonexposed (control) brown shrimp as well as brown shrimp exposed to mechanical stimuli. The lowest survival at 14 d (57.3%) occurred in the Sole cramp pulse treatment, and this was significantly lower than in the group with the highest survival, the procedural control (70.3%). No effect of electrical stimulation on the severity of IBV infection was found. The lowest percentage of molts occurred in the repetitive mechanical stimulation treatment (14.0%), and this was significantly lower than in the group with the highest percentage of molts, the procedural control (21.7%). Additionally, the mechanically stimulated brown shrimp that died during the experiment had a significantly larger size than the surviving individuals. Finally, no effect of the shrimp startle pulse was found. Therefore, it can be concluded that repetitive exposure to a cramp stimulus and mechanical stimulation may have negative effects on the growth and/or survival of brown shrimp. However, there is no evidence that electrical stimulation during electrotrawls would have a larger negative impact on brown shrimp stocks than mechanical stimulation during conventional beam trawling.Received November 15, 2015; accepted May 16, 2016

Comparison of mechanical disturbance in soft sediments due to tickler-chain SumWing trawl vs. electro-fitted PulseWing trawl

“…The inferred reduction in mortality rate is related to the effect of mechanical disturbance, primarily due to the replacement of tickler chains. Whether electrical stimulation results in any additional mortality under marine circumstances is yet unknown, but laboratory evidence suggests that exposure to a pulse stimulus will not result in a measurable additional mortality (Soetaert et al 2015b(Soetaert et al , 2016ICES, 2018).…”

Reducing bycatch in beam trawls and electrotrawls with (electrified) benthos release panels

“…Exposure of sole to a broad range of electric stimuli could also not provoque lesions or mortality (Soetaert et al, 2016a). Finally, no increased impact of electric cramp stimuli compared to conventional mechanical stimulation has been evidenced for invertebrate species either (Smaal and Brummelhuis, 2005;van Marlen et al, 2009;Soetaert et al, 2014;2016c). The second part of the present study therefore investigated the effect of an electric cramp stimulus on the escape behaviour of marketable sole through the panel.…”

“…This does not surprise as lab experiments reported that the behavioural reaction to a cramp stimulus of most benthic invertebrates was limited: Echinodermata showed no reaction, molluscs retreated in their shells and crabs demonstrated no or hampered movement (Smaal and Brummelhuis, 2005;van Marlen et al, 2009). Shrimp however, show jump and escape behaviour when exposed to electric stimuli Soetaert et al, 2014Soetaert et al, , 2016c, which may promote escape through the panel, the side or the back of the net resulting in the observed higher loss.…”

“…Drop-out openings without netting and large diamond and square escape zones just behind the groundrope have proved to be ineffective in releasing bycatch causing unacceptable losses of commercial catch (Fonteyne and Polet, 2002;van Marlen et al, 2005). Square-meshed windows inserted in the lower panel just in front of the cod-end, also known as benthos release panels (BRPs), have given much better results.…”

“…In the past, two main drawbacks have hampered the implementation of the BRP gear modification. First and foremost, catches of Dover sole (Solea solea L.), the most important economic species, fall by between 20 and 45% (Fonteyne and Polet, 2002;van Marlen et al, 2005). Second, the implementation of a rectangular square-meshed panel in a traditional beam trawl with a round footrope proved to be suboptimal: BRP rigging resulting in slack and subsequent bag formation in the lower panel, just in front of the BRP, causing abrasion and unacceptable wear of the net fabric (H. Polet Pers.…”