soft bottoms

Simple equipment

Taking samples with a drop-trap

Simple equipment



A drop-trap is a tool that is used to catch mobile epifauna, organisms that live and move on top of the sediment on soft bottoms. Such organisms are small flatfish, whelks, shore crabs, periwinkles, gobies and shrimps. A drop-trap is easily made out of aluminium plate. A box is formed, but without a bottom or top (a walled square). It should cover an area of 0,5 sq. metres, which means that each side should be 0,71 metres in length. Surveying is accomplished when two people carry the drop-trap on a pole (figure below) above the water surface. When the drop-trap is over an area that is to be surveyed, it is lowered onto the bottom. Care should be taken not to tread on the area to be surveyed. Therefter the edges the drop-trap are controlled so the sides go against the bottom and no organisms can escape. Afterwards a net is used to catch all the enclosed organisms which are placed in jars.
A suitable net is an aquarium or butterfly net, but will probably have to be reinforced with plastic tubing around the opening so as not to be worn out to quickly.

A drop-trap standing on the bottom


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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson