Assess the yield from eel stocking in a marine fjord (38262)

Project Details


The overall objective of the project was to estimate the outcome of stocking eel in a marine area, to estimate the yield to the fishery and the proportions of eels escaping the fishery. To reach this goal it was necessary to estimate the total catch in the fjord, the fishing mortality and whether eels stay in the fjord area or migrate to adjacent waters.

Stocking is a widely used measure to enhance local eel populations throughout Europe. About 1.5 million elvers are stocked annually in Danish marine waters. There are only vague indications that these stockings actually improve the number of fish that are available to the fisheries and the spawning population.

In 1998 and 1999 a total of 100.000 coded wire tagged eel were stocked in the inner parts of Roskilde Fjord. During 1999-2015 the eel catches made by professional and recreational fishermen were analyzed for recapture of tagged fish in order to establish the ratio of tagged to untagged fish in the eel catches. Based on the knowledge of numbers of fish caught in the yellow eel fishery as well as the silver eel fishery, the yield to the fishery was calculated. Migration patterns of the stocked eel were studied by collecting data from different strata of the fjord and adjacent fisheries, Isefjord and Arresø. Migrating silver eels were Carlin tagged and released to the fishery in September and October. Based on reported recaptures from fishermen an estimate of fishing mortality was established as well as of the number of silver eels leaving the Fjord and migrating toward the Sargasso spawning grounds. The total catches made by recreational fishermen were established through questionnaires to recreational fishermen.

The overall result suggests that about 13 % of the stocking were captured by the fishery in Roskilde Fjord and 5 % left the fjord as silver eels on spawning migration.

This project was coordinated by DTU Aqua and funded by the Danish Rod and Net License Funds.

Research area: Freshwater Fisheries and Ecology
Research area: Coastal Ecology
Effective start/end date01/01/199631/12/2015


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