Test and development of a sediment suppressing system for catch monitoring in demersal trawls

Abstract

Catch monitoring during demersal trawling is important to help fishers around the globe to cope with high bycatches. Information about catch composition during towing will allow fishers to identify and react to the presence of unwanted catch and undertake actions to avoid them during trawling. In demersal trawl fisheries, catch monitoring by the optical devices is typically challenged by the poor quality of underwater observations due to sediment mobilized during the towing process. In this study we develop, test and quantify the effect of a demersal trawl modification including sediment suppressing sheet and an in-trawl image acquisition system for catch monitoring during bottom trawling. The system is demonstrated on low-headline trawls that are typically used in mixed Nephrops-directed fisheries. We show that fitting a sediment suppressing sheet in the front part of the gear reduces the amount of mobilized sediment by half at three test positions inside the gear. When this sheet is used in combination with an in-trawl image acquisition system placed in the aft part of the trawl it is possible to obtain clear images of the catch during demersal trawling on the soft muddy grounds.