Electrotrawling: a promising alternative fishing technique warranting further exploration

Soetaert, Maarten; Decostere, Annemie; Polet, Hans; Verschueren, Bart; Chiers, Koen

doi:10.1111/faf.12047

Cited by 74 publications

(80 citation statements)

References 42 publications

(90 reference statements)

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“…This may be accomplished by either reducing fishing effort, or through technical adaptations reducing the direct impact of the trawl on the seabed. Development of such less destructive trawls is an active field of research [6,35]. Our results indicate that this may actually, dependent on the mode of trophic control and asymmetry in prey profitability, lead to reduced fish abundance and yield.…”

Section: Discussionmentioning

confidence: 84%

When does fishing lead to more fish? Community consequences of bottom trawl fisheries in demersal food webs

2013

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Bottom trawls are a globally used fishing gear that physically disturb the seabed and kill non-target organisms, including those that are food for the targeted fish species. There are indications that ensuing changes to the benthic invertebrate community may increase the availability of food and promote growth and even fisheries yield of target fish species. If and how this occurs is the subject of ongoing debate, with evidence both in favour and against. We model the effects of trawling on a simple ecosystem of benthivorous fish and two food populations (benthos), susceptible and resistant to trawling. We show that the ecosystem response to trawling depends on whether the abundance of benthos is top-down or bottom-up controlled. Fishing may result in higher fish abundance, higher (maximum sustainable) yield and increased persistence of fish when the benthos which is the best-quality fish food is also more resistant to trawling. These positive effects occur in bottom-up controlled systems and systems with limited impact of fish feeding on benthos, resembling bottom-up control. Fishing leads to lower yields and fish persistence in all configurations where susceptible benthos are more profitable prey. Our results highlight the importance of mechanistic ecosystem knowledge as a requirement for successful management.

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Section: Discussionmentioning

confidence: 84%

When does fishing lead to more fish? Community consequences of bottom trawl fisheries in demersal food webs

2013

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“…Wire-shaped electrodes such as those used in the commercial fishery were adapted as described in Soetaert et al (2015). For the shrimp startle pulse, two electrodes of 0.5-m length were placed 0.6 m apart (measured from the center; Figure 1A).…”

Section: Methodsmentioning

confidence: 99%

“…In the SHRI setup this resulted from the reduced distance between the electrodes, which was limited to 0.6 m due to tank size limitations, compared with the 0.7 m used in the field. In the SOLE exposures, a 60 V potential difference on the electrodes was applied, which is higher than the 50-55 V used in electrotrawls (Soetaert et al 2015). Additionally, the sequence of exposures (20 times in one fishing week of 4 d) is most likely more frequent than would occur in the field, where only 0.6% of the seabed is estimated to be trawled more than 20 times a year (Rijnsdorp et al 1998).…”

Section: Survivalmentioning

confidence: 99%

“…These electrotrawls use a bipolar cramp pulse with a frequency of around 80 Hz that elicits a cramp reaction in the fish's muscles which immobilizes it and causes it to bend into a U-shape (Soetaert et al 2016). As a consequence, Sole cannot flee and are more easily scooped up by the foot rope of the fishing gear, which increases catch efficiency (Soetaert et al 2015). In these gears, tickler chains are replaced by electrodes consisting of a series of isolated and conductive parts connected to the beam trawl or its alternative (sumwing, seewing, or multiwing) and towed over the seabed, followed by a footrope (van Marlen et al 2014).…”

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confidence: 99%

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

Soetaert

Verschueren²,

Chiers

et al. 2016

Mar Coast Fish

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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

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“…Other ground gears warrant assessment, and possibly those including angled cups to displace water downwards to stimulate prawns via hydrodynamic pressure instead of physical contact. Another method of minimising ground-gear impacts might be to use electricity (Soetaert et al 2015). Additional experimentation is required to establish the relative species-and size-specific reactions of penaeids and teleosts to gauge the potential for improved selectivity without negative side effects on benthic animals or excessive predation while animals remain 'affected' by the electrical 825 stimulation (Murray et al 2016).…”

Section: Select the Most Appropriate Multi-trawl Configuration 785mentioning

confidence: 99%

Modifying penaeid-trawl spreading mechanisms to improve environmental efficiency

McHugh¹

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The environmental efficiency of demersal trawls can be defined within measures of three response variables: (i) species selectivity; (ii) extent and intensity of habitat impacts; and (iii) energy efficiency. All three variables affect all fisheries, but especially those targeting penaeid prawns (or shrimp).Penaeid-trawl fisheries are globally distributed in tropical and temperate latitudes and involve vessels (~8−25 m) towing small-meshed, single-or multi-funnel-shaped nets on the seabed, horizontally spread by hydrovanes (called 'otter boards'), and less commonly, rigid beams. To date, most of the efforts towards improving the environmental efficiency of penaeid trawls have concentrated on gear selectivity specifically, via bycatch reduction devices (BRDs) in the codend (to address i above).Although somewhat effective (30-70% reductions), BRDs offer few perceived benefits to fishers and, in many fisheries, there is resistance to their adoption.It is known that the anterior trawl section affects all three response variables above, which might concomitantly be mitigated through modifications that could potentially provide fishers with a realised benefit-increased energy efficiency (and therefore greater adoption). A primary objective of this thesis was to investigate the potential for holistically improving penaeid-trawl environmental efficiency through research focussed on the anterior section of the gear; specifically the spreading mechanisms (otter boards, sleds, beams and sweeps).The treatments tested comprised three broad categories: (i) revising otter boards and their rigging;(ii) substituting otter boards with a beam; and then (iii) amalgamating key concepts across both methods. Modifications within the first category included removing sweeps and testing a novel otter board (i.e. the batwing). Within the second category, beams were modified in attempts to maintain target catches while minimising bycatch, habitat contact and energy intensity. The third group of modifications involved exploiting the concepts underlying an identified inherently superior species selection of beam trawls to otter trawls via counter-herding devices, termed 'simple anterior fish excluders'-SAFEs.Where appropriate, the treatments were compared against controls for their utility in mitigating the three response variables. The overall results demonstrated that selectivity can be improved (i.e. bycatch reduction) by using a beam trawl, SAFE or by removing sweeps; habitat impacts will be reduced when using batwings; and, while overall energy intensity was not improved, an important component-drag-can be alleviated using a beam trawl or batwing otter boards. For targeted iii catches, the conventional otter trawls caught more total penaeids, but the beam trawls had comparable penaeid catches when corrected for fuel-to-catch ratios.A key conclusion from the thesis is that no single treatment will be effective for significantly improving all three response variables; however, anterior modifications lowering drag (the beam trawl an...

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Electrotrawling: a promising alternative fishing technique warranting further exploration

Cited by 74 publications

References 42 publications

When does fishing lead to more fish? Community consequences of bottom trawl fisheries in demersal food webs

When does fishing lead to more fish? Community consequences of bottom trawl fisheries in demersal food webs

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

Modifying penaeid-trawl spreading mechanisms to improve environmental efficiency

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