Wastewater plumes can act as non-physical barriers for migrating silver eel.

Non-physical barriers for migrating fish, such as effluent plumes discharged by sewage treatment plants (WWTPs), are hardly considered, and field studies on this topic are very scarce. The encounter with these plumes however may evoke behavioural responses in fish and could delay or (partially) block the migration. In this study, the behavioural responses of 40 acoustically-tagged silver eel (Anguilla anguilla) were monitored in situ, when confronting a WWTP effluent plume during their downstream migration in the canal Eems, the Netherlands.

Does tagging transparent fish increase predation risk? A laboratory study with glass eel (Anguilla anguilla) and sea bass (Dicentrarchus labrax).

Barriers in the estuaries of the rivers prevent the immigration of glass eels (Anguilla anguilla) arriving on the European coast every spring. This leads to an unnatural accumulation of migrating glass eels below the barriers, and this may lead to additional losses in glass eels by piscivorous fish. The proportion of predation losses can be estimated using mark-recapture techniques and abundance estimates in combination with stomach content analysis of piscivorous fish.