Installing an eel pass in River Mondego

A passage device, especially dedicated to European eel (Anguilla anguilla L.) was installed at Coimbra Açude-Ponte dam. This eel pass is the first specialized device of this type to be built in Portugal.

The construction of the eel pass in River Mondego aims to have positive effects on eel population, by promoting the dispersion of this species by a larger area, thus avoiding the bio-ecological constraints that usually result from density increase, like: i) decrease of body condition; ii) impairment of growth and sexual maturation; ii) changes of sex-ratio, with the decrease of female proportion; and iv) mortality increase.

Ultimately, such constraints will eventually contribute to a lower rate of reproductive success of this species, adding to the decline of its effective population.

Eel pass (Coimbra Açude-Ponte dam, Mondego).
Eel pass: monitoring cage-trap.
Eel pass: brush substrate.
Eel pass: resting pool.

The vertical-slot fish pass operating at Coimbra Açude-Ponte dam since 2011 has proved to be highly successfull in promoting the passage of most diadromous and potamodromous fish species occurring in this river basin, with the exception of eels of which a smaller number of individuals (ca 700 per year) were observed using the structure. Therefore, complementing the existing fish pass with a specific eel pass promotes the unblocking of nearly 40 km of river length in the main watercourse, plus additional 20 km in the major tributaries, rivers Alva and Ceira, for the European eel.

The instalation of this eel pass will be followed by a monitoring program.