Current status and temporal trends in stocks of European eel in England and Wales

Abstract

Bark, A., Williams, B., and Knights, B. 2007. Current status and temporal trends in stocks of European eel in England and Wales. – ICES Journal of Marine Science, 64: –. An extensive 4-year programme of catchment surveys, data collection, and model development for eels was undertaken to establish the status of the stocks in England and Wales, so that appropriate management action can be taken. Nine test catchments representing different geographical areas and catchment types were studied, covering 14 rivers, two estuaries, and a fresh-water lagoon. Data were collected via electric fishing, fykenetting, fixed eel racks, and elver traps. In all, 13 500 eels were caught, weighed, and measured, and the sex and age of a subsample of 1400 determined. Despite declining recruitment, eel stocks in some, perhaps many, west coast rivers are probably still at or near to carrying capacity, with male-dominated populations. In other rivers, particularly those towards the southeast of England, current and historical data indicate declining female-dominated stocks. For rivers where recruitment is not limiting, there appears to be a direct relationship between the standing stock of eels and the mean nitrate level. This relationship potentially facilitates the application of a biomass-based biological reference point for eels for application to individual catchments. The data also suggest that it may be possible to develop reference points based on mean eel length or sex ratio.

Evidence for a population collapse of European eel (Anguilla anguilla) in the Bristol Channel

“…The dramatic decline of yellow eels within the Bristol Channel contrasts with the findings of Bark et al (2007) for the tributaries of the upper Severn Estuary, in which sampling was carried out during 1998, 1999 and from 2002 to 2004. This study concluded that the estuary's upper tributaries were at, or approaching their carrying capacity and stressed the importance of later life stage recruitment from estuaries in maintaining freshwater stocks. It would appear from the data presented in Figure 7 that if the River Severn relies on recruitment of yellow eels from its estuary and the Bristol Channel, then a future decline in the associated riverine stock may be expected.…”

“…Despite the marked decline in the recruitment of glass eels and the general view that yellow eel stocks are declining throughout Europe, Bark et al (2007) have shown that yellow eel populations have remained stable in some UK river systems. They concluded that, despite declining levels of recruitment, many west coast rivers were still at, or near their carrying capacity.…”

Dynamics of upstream movements of the European eel Anguilla anguilla in an inland area of the River Meuse over the last 20 years

“…In this context, it is difficult to understand, at inland sites, the effects of the long-term reduction in glass eel recruitment on the upstream movement process of the yellow eel stage. The initiation and cessation of annual upstream movements of eels in riverine systems is controlled by environmental variables such as water temperature and river discharge (Naismith and Knights 1988; Bark et al 2007;Nzau Matondo et al 2014). As a consequence, fish pass monitoring may play an important role by providing useful information on the upstream migration behavior of the riverine yellow eel (Welsh et al 2015) in the context described above.…”

Status of eel fisheries, stocks and their management in England and Wales

“…The Scenario-based Model for Eel Populations (SMEP) (Aprahamian et al, 2007) and GlobAng (Lambert and Rochard, 2007) share common approaches to modelling eel production within river basins. While there is a lot of growth data eels from UK rivers (Aprahamian, 1988(Aprahamian, , 2000Bark et al, 2007), there is a limited understanding of other processes, or how they might be influenced by density and habitat. Furthermore, the application of spatial models such as these requires the quantification of the eel-producing habitat, and ideally an understanding of the potential production of the various habitats, including how this potential varies with distance from the sea, etc.…”