Recent papers suggest marine events such as a Northward shift in the North wall of the Gulf Stream have caused Leptocephali to follow longer routes exposing them to less favourable conditions and food availability.
The nematode Anguillicola crassus was spread to Eel stocks in Europe from the Japanese Eel imports in the 1980’s. This affects the swim bladder and may cause serious physiological effects and affect the normal migration patterns.
Habitat Loss and barriers
Many scientists attribute the decline to loss of habitat and accessibility. The amount of available habitat is thought to have been reduced by at least 50% during the last century. The habitat area currently available is estimated to be approximately 87 000 Km2. Habitat loss is caused by dams, drainage, and reduced water quality.
Sub lethal poisoning
Due to the high fat content Eels are susceptible to storage of many contaminants namely brominated flame retardants. These can affect gonad development and impair the spawning ability.
Although the above factors are serious and attributed to the decline they are not sufficient to explain the extent and timings of the decline in recruitment.
When arriving Eels are super abundant and freshwater mortality is density dependant then the effects of recruitment variation (due to Elver fishing) on the number of older Eels is negligible. At some point reduced recruitment through fishing will reduce stock and it is thought this point has already been reached. A total of 25 - 30 000t of Eels are exploited every year due to demand for food and even as bait for other species. Elver fisheries account for 800 - 900t per year or 2.7% which equates to 2.4 billion Elvers which is sufficient to restock the whole of Europe at a rate of 0.1kg per hectare.
Eels are not bred in captivity; aquaculture relies on the collection of seed Eels (Elvers) which are then grown on. This means that the species is unsustainable as ALL Eels sold in restaurants, shops and bait suppliers have been taken from the wild initially. Recently, a number of high class restaurants, chefs and even TV programmes are showing Eels on menus throughout Europe adding to the demand on one of our most enigmatic species.
The European Eel is currently deemed the most at risk vertebrate in the country and is currently on the IUCN Red list.