Survival of flatfish and rays in electric pulse fishing

How many of the undersized fish caught survive the process of being discarded? And can we increase their chance of survival?

The Common Fisheries Policy includes what is known as a landing obligation, which means that fishermen must land their unwanted bycatch of any undersized fish that are subject to a quota. The European Commission hopes that this measure will encourage fishermen to reduce unintentional bycatch. Member states can apply to be exempted from the landing obligation for species that are subject to a quota, but have high chances of survival (and thus theoretically help to increase the fish stock if discarded).

The ‘Survival of flatfish and rays in the North Sea fisheries’ project is collecting the scientific information needed to substantiate an application for exemption. The project comprises two main parts:

1. What are the chances of survival for common sole, plaice, turbot, brill and thornback ray?
2. Which changes can be made to on-board processing and fishing methods to increase chances of survival?

What are the chances of survival for common sole, plaice, turbot, brill and thornback ray?

In 2015, Wageningen Marine Research conducted research into the survival of flatfish in pulse fishing (fishing for flatfish whereby the traditional tickler chains in the beam trawls are replaced by electric stimuli). The results of the first study show chances of survival of approximately 15% for undersized plaice and 29% for undersized common sole. It is estimated that 16% of dab survive after being discarded. The research was carried out using an international standardised method.

This initial study is now being followed up to generate a greater understanding of the factors that determine the chances of survival of undersized flatfish. The scientists are trying to work out whether the use of a scoring system to measure the ‘vitality’* of the fish caught would be a suitable, cost-effective way of estimating the chance of survival. The research has been expanded to include three new species: turbot, brill and thornback ray.

Increasing chances of survival

Previous research has shown that the time between common sole and plaice being brought on-board and the moment they are processed appears to affect the chance of survival: the sooner the fish are processed, the higher the chance of survival. The processing itself also has a negative effect on chances of survival. The chances of survival of fish taken from the tank at the start of the process is higher than that of fish collected just before the chute at the end of the process. So it should be possible to increase the chances of survival by modifying the fishing and on-board processing techniques.

This new project is investigating whether modifications to catching and processing really do increase chances of survival. During each research trip, one side of the ship works according to regular practices and the other side deploys modified fishing or processing techniques (depending on the improvement measure). The modified fishing or processing techniques are designed to increase the chances of survival for of undersized fish.

A permit on the grounds of the Experiments on Animals Act was issued for the project, and the project was co-funded by a grant from the European Maritime and Fisheries Fund.

* For all five species