Population dynamics of eel (38260)

Project Details

Description

The project has 3 main goals: 

1) Evaluation of the feasibility of eel stocking
In compliance with the National eel MP, 1.3 million pre-fed eel are stocked annually in lakes and rivers. In coastal areas 0.2 million are stocked.  Very little is known about the feasibility of these stockings. Due to the long life cycle of eels, both short and long term experiments are carried out.  
Short-term: Wild and cultured (pre-fed) eels of similar size (2-5 gram) are stocked in a number of large open ponds (old trout farm) and their growth and survival is recorded during their first year. Similar experiments are performed with wild glass eels stocked in different densities in the ponds.
Long-term: Small CW-tagged eel were stocked in the river Gudenåen in 2001, 2002 and 2011. The return from these stockings in the form of migrating silver eels are monitored by scanning eel caught in a trap(at a hydropower station), operating every autumn from 2006-2013. Further more the silver eels caught in the trap are PIT tagged and recorded when reaching the lowermost obstacle in the river (Tange HPS).
In Ribe Å, in Vester Vandet lake and in Karrebæk estuary CW-tagged eel were stocked in 2011 and 2012. The monitoring of catches for tagged eel started in 2015 and will continue for several years to get an estimate of how much the stocked eel contribute to the fisheries and how the ratio wild/stocked is, giving an indication of the natural recruitment.

2) Monitoring of recruitment/elvers
The recruitment of eel has been continually declining since early 80’ies and is now at a historical low.Monitoring of the number of elvers/glass eels arriving every year is therefor every important for the whole of EU. In DK we have two stations, where upstream migrating elvers are caught and recorded on a daily basis. Both stations are on the Danish East Coast. On the Westcoast the immigration is monitored by electric fishing/sampling in small streams in early summer.

3) Monitoring of the prevalence of the swim bladder parasite Anguillicola in Danish eels
The swim bladder worm Anguillicola crassus was introduced to Europe from the far east in the beginning of the 1980´s. The parasites are thought to be one of the causes of the decline of the European eel population.Therefore the colonisation of Anguillicola in Denmark has been monitored in fresh and marine water bodies to assess the abundance of parasites and the general health of parasitized eels. The geographical distribution and the stability of the parasite abundance are of international interest due to the decline of the eel stock, but also because large effort is done to secure that the 1.5 million annually stocked eel are free of parasites. 

This project is coordinated by DTU Aqua and funded by the Danish Rod and Net Fishing Licence Funds.

Research area: Freshwater Fisheries and Ecology
StatusActive
Effective start/end date01/01/1988 → …