Clare was on the research vessel Dana to find out how much sediment is suspended by bottom trawling and if contaminants, such as dioxins and metals, buried in the sediment are released in the process. This sort of data is important for effective marine spatial planning and sustainable fisheries management in the Baltic Sea.

The Danish research vessel Dana. Photo: Clare Bradshaw.

Suspended sediment can clog animals’ gills or filtration organs, and stick to and suffocate fish eggs. Contaminants released into the water column can potentially be taken up by animals in the ocean affecting their health and fitness. Dioxins*, for example, are known to cause hormone disruption and have developmental and reproductive effects.

- We fixed our fragile contaminant samplers to custom-made frames and then inside a PVC casing that could withstand the rough treatment of being winched in and out of the ship and being attached to a trawl under water for up to 6 hours (thanks to Nils at SU's workshop!), says Clare Bradshaw.

Three types of contaminant samplers attached to a custom-made frame that was mounted inside a protective casing and attached to the trawl (see next photo). Photo: Clare Bradshaw.

The cruise was one of the fish stock assessments done by SLU's Institute of Marine Research at SLU Aqua twice a year. They examine fish health by measuring the sizes of different organs and parasite loads. They also check if the fish populations are growing and declining, and if the fish are in their reproductive years or not.  

This is a collaboration between Clare Bradshaw at DEEP, Mattias Sköld at SLU-Havsfiskelaboratoriet and Ian Allan at NIVA.

Two of the crew attaching the sampling gear to the trawl door Photo: Clare Bradshaw
On board the research vessel Dana. Photo: Clare Bradshaw.

*Dioxin is formed as an unintentional by-product of many industrial processes involving chlorine such as waste incineration, chemical and pesticide manufacturing and pulp and paper bleaching.