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Effects on eggs and larvae

Research on larval stages and juvenile stage of Atlantic Cod

Desender et al (2017) exposed three embryonic stages, four larval stages, and one juvenile stage of Atlantic Cod to a homogeneous electrical field of 150 Vpeak/m for 5 seconds, mimicking a worst-case scenario. The results:

  • No significant differences were detected in embryo mortality rate between control and exposed groups. However, for the embryonic stage exposed at 18 day postfertilization, the initial hatching rate was lower.
  • Larvae that were exposed at 2 day and 26 day post hatch exhibited higher mortality rates than the corresponding non-exposed control groups.
  • In the other larval and juvenile stages, no short-term impact of exposure on survival was observed. Morphometric analysis of larvae and juveniles revealed no differences in measurements or deformations of the yolk, notochord, eye, or head.

Although exposure to a worst-case electrical field did not impact survival or development for six of the eight young life stages of Atlantic Cod, the observed delayed hatching rate and decreased survival for larvae might indicate an impact of electric pulses and warrant further research.

Research on pelagic and demersal eggs

For eggs that float in the water column (pelagic eggs), it can be concluded that given the decay of the electric field strength, the intensity and distribution of pulse trawling and the distribution of the pelagic stages and spawning duration of sole, it is highly unlikely that pulse trawling will have an adverse effect on the survival of eggs and larvae (ICES, 2020).   

A small number of North Sea fish species, such as herring and sandeel, lay their eggs on the seafloor (demersal eggs). The probability that sucheggs will be exposed to a pulse stimulus will be larger than pelagic eggs, but the population level effects of pulse trawling on demersal eggs will be negligible (ICES, 2020). 

Research on eggs of rays

Based on the increase in stock development in combination with the lack of overlap between the pulse fishery and the early life stages of ray species in the North Sea, it can be inferred that it is unlikely that the introduction of the pulse fisheries impacted the survival of egg capsules of the ray stocks that are abundant in the southern North Sea (ICES, 2020)