A novel enclosure approach to assessing yellow eel (Anguilla anguilla) density in non-tidal coastal waters

A suitable monitoring approach is urgently needed to quantify the stock size of the European eel in coastal waters as coastal areas are considered to contribute significantly to the overall spawning stock. A novel enclosure fishing method for non-tidal coastal waters was developed for yellow eels. The fishing system consists of two main elements, an outer boundary net (100 m × 100 m, enclosing 1 ha) with fyke net chambers in each corner and six fyke net chains inside the enclosure. The system was tested in a variety of habitat types in the coastal waters of the southern Baltic Sea. In total, 200 samples were taken in 2008-2011, resulting in an overall harvest of 1184 eels. Eels were detected in all previously defined reference areas. Over 95% of the eels were classified as yellow eels. Based on the mesh size, full selectivity for yellow eels over 36 cm was assumed. The observed length distribution followed the expected trend as size classes between 36 and 55 cm accounted for most of the catch. Taking into account the gear selectivity, an overall mean density of 4.7 eels per hectare for yellow eels longer than 36 cm was estimated. Eel density varied considerably, with significantly higher yellow eel densities being observed in open coastal areas compared to the inner coastal waters. The enclosure approach appears suitable for assessing eel densities in non-tidal coastal waters.