Many fisheries around Scotland target several species at the same time. For example, cod, haddock, whiting and Nephrops (prawns) are often caught on the same grounds in the North Sea. However, these species grow at different rates, mature at different sizes and have different shapes. So a mesh size which allows a certain size of haddock to escape may not be appropriate for cod or prawns. Too small a mesh size may lead to discarding of undersized fish while too large a mesh size could mean the loss of marketable fish.
One way to overcome this problem of so-called 'mixed fisheries' is to separate the species before they are caught in the cod-end at the end of the net. Observations of fish behaviour have shown that some species have characteristic behaviour patterns. For example, haddock and whiting rise up in the mouth of the net whereas cod, Nephrops and flatfish stay low down.
Alternatively species may have different swimming abilities. These characteristics can be utilised to allow one species to escape or to separate the species into individual compartments, each with a different mesh size.
Designs of fishing gear are now being developed and tested in close collaboration with fishermen in several Marine Scotland and European Union (EU) funded projects.