scholarly journals Modelling the recruitment of European eel (Anguilla anguilla) throughout its European range

2017 ◽  
Vol 75 (2) ◽  
pp. 541-552 ◽  
Author(s):  
Virginie Bornarel ◽  
Patrick Lambert ◽  
Cédric Briand ◽  
Carlos Antunes ◽  
Claude Belpaire ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Anguilla Anguilla ◽  
Distribution Area ◽  
European Eel ◽  
Estimation Model ◽  
Glass Eel ◽  
The North ◽  
The Status ◽  
The North Sea ◽  
Sea Area

Abstract European eel (Anguilla anguilla) recruitment has been declining at least since the early 1980s at the scale of its distribution area. Since the population is panmictic, its stock assessment should be carried out on a range-wide basis. However, assessing the overall stock during the continental phase remains difficult given its widespread distribution among heterogeneous and separate river catchments. Hence, it is currently considered by the International Council for the Exploration of the Sea (ICES) more feasible to use glass eel recruitment data to assess the status of the overall population. In this study, we used Glass Eel Recruitment Estimation Model (GEREM) to estimate annual recruitment (i) at the river catchment level, a scale for which data are available, (ii) at an intermediate scale (6 European regions), and (iii) at a larger scale (Europe). This study provides an estimate of the glass eel recruitment trend through a single index, which gathers all recruitment time-series available at the European scale. Results confirmed an overall recruitment decline to dramatically low levels in 2009 (3.5% of the 1960–1979 recruitment average) and highlighted a more pronounced decline in the North Sea area compared to elsewhere in Europe.

scholarly journals An Evaluation of Restocking Practice and Demographic Stock Assessment Methods for Cryptic Juvenile European Eel in Upland Rivers

2020 ◽  
Vol 12 (3) ◽  
pp. 1124 ◽  
Author(s):  
Billy Nzau Matondo ◽  
Jean-Philippe Benitez ◽  
Arnaud Dierckx ◽  
Xavier Rollin ◽  
Michaël Ovidio
Keyword(s):  
Stock Assessment ◽  
Release Site ◽  
Anguilla Anguilla ◽  
Assessment Method ◽  
Assessment Methods ◽  
European Eel ◽  
Mark Recapture ◽  
Glass Eel ◽  
The North ◽  
The North Sea

Restocking of the critically endangered European eel Anguilla anguilla is widespread, but it is rarely scientifically evaluated. Methods used to assess its associated performance by estimating the survival rate and implement restocking for maximum recruitment in rivers have not yet been investigated. Based on two glass eel restocking events using a single release site/point and multiple sites per river performed in upland rivers (>340 km from the North Sea), the recruitment success of stocked eels was scientifically evaluated during a 3-year study using multiple capture-mark-recapture methods and mobile telemetry. We compared the observed data with the data estimated from the Telemetry, De Lury and Jolly-Seber stock assessment methods. For recruitment data, Telemetry was very close to Jolly-Seber, an appropriate stock assessment method for open populations. Using the best model of Jolly-Seber, survival probability was higher (>95%) in both restocking practices, but recruitment yields were higher and densities of stocked eels were lower in multiple sites compared to a single site. Our results suggest that Telemetry can help to rapidly assess cryptic juvenile eel stocks with good accuracy under a limited number of capture-mark-recapture sessions. Artificial dispersal of glass eels on several productive habitats/sites per river appears to be the better-suited practice for restocking.

Challenges to quantifying glass eel abundance from large and dynamic estuaries

2017 ◽  
Vol 75 (2) ◽  
pp. 727-737 ◽  
Author(s):  
Sarah Walmsley ◽  
Julie Bremner ◽  
Alan Walker ◽  
Jon Barry ◽  
David Maxwell
Keyword(s):  
Large Scale ◽  
Anguilla Anguilla ◽  
Commercial Fishing ◽  
European Eel ◽  
Estuarine System ◽  
Glass Eel ◽  
The North ◽  
Adequate Sampling ◽  
South Shore ◽  
Glass Eels

Abstract European eel Anguilla anguilla recruitment into the rivers of the northeastern Atlantic has declined substantially since the 1980s. Monitoring of recruiting juveniles, or glass eels, is usually undertaken in small estuaries and rivers. Sampling of large-scale estuaries is rare, due to the size of the sampling area and the resources needed to provide adequate sampling levels. Here we describe surveys for glass eels in the UK’s largest estuarine system, the Severn Estuary/Bristol Channel. We sampled across a 20 km-wide stretch of the estuary in 2012 and 2013, using a small-meshed net deployed from a commercial fishing trawler, and the surveys yielded over 2500 glass eels. Eels were more abundant in the surface layer (0–1.4 m depth) than at depth (down to 8.4 m depth), were more abundant close to the south shore than along the north shore or middle of the estuary, and were more abundant in lower salinity water. Numbers were higher in the second year than in the first and eels were more abundant in February than April. The difficulties and logistics of sampling in such a large estuary are discussed, along with the level of resources required to provide robust estimates of glass eel abundance.

On the distribution of the European eel (Anguilla anguilla) and its fisheries

2003 ◽  
Vol 60 (7) ◽  
pp. 787-799 ◽  
Author(s):  
Willem Dekker
Keyword(s):  
Meta Analysis ◽  
Anguilla Anguilla ◽  
Western Mediterranean ◽  
Qualitative Description ◽  
Suitable Habitat ◽  
European Eel ◽  
Silver Eel ◽  
Southern Limit ◽  
Glass Eel ◽  
The North

For the distribution of the European eel (Anguilla anguilla), only Schmidt (1909) has conducted substantial investigations, yielding a qualitative description (Atlantic and Mediterranean coasts of Europe and Northern Africa). In this article, a meta-analysis of reported fishing yields is presented, showing a major concentration of glass eel yield in the Bay of Biscay (and possibly farther south) and of yellow and (or) silver eel yield in the western Mediterranean. Fisheries target the glass eel stage at highest stock density and shift to the silver eel stage at low density. Because there is no suitable habitat in the Sahara, the southern limit is, contrary to Schmidt's belief, primarily determined by continental conditions. From the centre of the distribution to the north, a long and slow decline in density occurs. The mismatch between northern temperatures and the species' preference, in combination with the very low abundance, indicates that the European eel is best seen as a warm-water species, like most other eel species (Anguilla spp.), showing a considerable northern diaspora.

scholarly journals Mapping silver eel migration routes in the North Sea

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Pieterjan Verhelst ◽  
Jan Reubens ◽  
Johan Coeck ◽  
Tom Moens ◽  
Janek Simon ◽  
...  
Keyword(s):  
North Sea ◽  
Anguilla Anguilla ◽  
European Eel ◽  
English Channel ◽  
Migration Routes ◽  
Silver Eel ◽  
The North ◽  
Wide Range ◽  
Recent Developments ◽  
The North Sea

AbstractRecent developments in tracking technology resulted in the mapping of various marine spawning migration routes of the European eel (Anguilla anguilla). However, migration routes in the North Sea have rarely been studied, despite many large European rivers and hence potential eel growing habitat discharge into the North Sea. In this study, we present the most comprehensive map to date with migration routes by silver European eels in the North Sea and document for the first time successful eel migration through the English Channel. Migration tracks were reconstructed for 42 eels tagged in Belgium and 12 in Germany. Additionally, some eels moved up north to exit the North Sea over the British Isles, confirming the existence of two different routes, even for eels exiting from a single river catchment. Furthermore, we observed a wide range in migration speeds (6.8–45.2 km day−1). We hypothesize that these are likely attributed to water currents, with eels migrating through the English Channel being significantly faster than eels migrating northward.

scholarly journals Influence of oceanic factors on Anguilla anguilla (L.) over the twentieth century in coastal habitats of the Skagerrak, southern Norway

2010 ◽  
Vol 278 (1704) ◽  
pp. 464-473 ◽  
Author(s):  
Caroline M. F. Durif ◽  
Jakob Gjøsæter ◽  
L. Asbjørn Vøllestad
Keyword(s):  
Time Series ◽  
North Atlantic Oscillation ◽  
North Sea ◽  
North Atlantic ◽  
Anguilla Anguilla ◽  
Sargasso Sea ◽  
Glass Eel ◽  
The North ◽  
The North Sea ◽  
The North Atlantic

The European eel ( Anguilla anguilla L.) is distributed in coastal and inland habitats all over Europe, but spawns in the Sargasso Sea and is thus affected by both continental and oceanic factors. Since the 1980s a steady decline has been observed in the recruitment of glass eels to freshwater and in total eel landings. The eel is considered as critically endangered on the International Union for the Conservation of Nature and Natural Resources Red List of species. The Skagerrak beach seine survey from Norway constitutes the longest fishery-independent dataset on yellow/silver eels (starting in 1904). The Skagerrak coastal region receives larvae born in the Sargasso Sea spawning areas that have followed the Gulf Stream/North Atlantic Drift before they penetrate far into the North Sea. The Skagerrak coastal time series is therefore particularly valuable for exploring the impacts of oceanic factors on fluctuations in eel recruitment abundance. Analyses showed that Sargasso Sea surface temperature was negatively correlated with eel abundance, with a lag of 12 years revealing a cyclic and detrimental effect of high temperatures on the newly hatched larvae. The North Atlantic Oscillation index and inflow of North Atlantic water into the North Sea were negatively correlated with eel abundance, with a lag of 11 years. Increased currents towards the North Atlantic during high North Atlantic Oscillation years may send larvae into the subpolar gyre before they are ready to metamorphose and settle, resulting in low recruitment in the northern part of the distribution area for these years. The Skagerrak time series was compared with glass eel recruitment to freshwater in the Netherlands (Den Oever glass eel time series), and similar patterns were found revealing a cycle linked to changes in oceanic factors affecting glass eel recruitment. The recent decline of eels in the Skagerrak also coincided with previously documented shifts in environmental conditions of the North Sea ecosystem.

scholarly journals Decreasing predation levels and increasing landings challenge the paradigm of non-management of North Sea brown shrimp (Crangon crangon)

2014 ◽  
Vol 72 (3) ◽  
pp. 804-823 ◽  
Author(s):  
Axel Temming ◽  
Marc Hufnagl
Keyword(s):  
North Sea ◽  
Stock Assessment ◽  
Total Mortality ◽  
Brown Shrimp ◽  
Distribution Area ◽  
Distribution Data ◽  
Mammal Species ◽  
Potential Growth ◽  
The North ◽  
The North Sea

Abstract The North Sea brown shrimp fishery is currently regulated neither with quotas nor with effort management. The current paradigm of non-management was based on an analysis of the total predation by cod and whiting in relation to commercial catches for the period 1970–1995 and the estimated total dominance of natural mortality. However, since this period, the North Sea ecosystem has undergone pronounced changes with overfishing and climate change causing a substantial decline in predator stocks, namely cod and whiting. In addition, both predators have shifted their range of distribution causing a reduced overlap with brown shrimp. Here, we extend the previous assessment of brown shrimp predation for the years 1996–2011 using updated stock assessment and predator distribution data. For the first time, predation estimates are used together with commercial landings to partition independent estimates of total mortality into fishing and predation mortality. We demonstrate that the decline of key predators of brown shrimp in combination with a shift in the distributional range of the predators has caused a new situation, in which the fishery has become the main mortality source of adult brown shrimp (>50 mm). Average landings since 2000 have been ∼40% higher than in the 1980s and 1990s, indicating that humans have at least partly taken over the share previously taken by juvenile whiting and cod. We discuss that this situation is likely to continue, because three marine mammal species have built up a combined population of over 80 000 individuals, which hunt for potential brown shrimp predators mainly in the distribution area of brown shrimp. The application of two yield-per-recruit models of different complexity indicates potential growth overfishing of brown shrimp and reopens the discussion of management.

scholarly journals Gadoid dynamics: differing perceptions when contrasting stock vs. population trends and its implications to management

2014 ◽  
Vol 71 (6) ◽  
pp. 1433-1442 ◽  
Author(s):  
Steven J. Holmes ◽  
Colin P. Millar ◽  
Robert J. Fryer ◽  
Peter J. Wright
Keyword(s):  
North Sea ◽  
Stock Assessment ◽  
Research Vessel ◽  
Vital Rates ◽  
The North ◽  
Depth Contour ◽  
Spawning Stock ◽  
Population Structures ◽  
The North Sea ◽  
Local Pressures

Recent research suggests that ICES stock definitions for cod, haddock, and whiting of “west of Scotland” and “North Sea”, do not reflect underlying population structures. As population responses to different vital rates and local pressures would be expected to lead to asynchrony in dynamics, we examined trends in local spawning-stock biomass (SSB) among putative subpopulations of the three species. Delineation of subpopulation boundaries around spawning time was made based on genetic, tagging, and otolith microchemistry studies together with density distributions of species based on research vessel survey data. Subpopulation specific indices of SSB were derived using numbers-at-age and maturity observations from the same research vessel data and asynchrony was assessed by fitting a smoother to log SSB for each subpopulation and testing whether the smooths were parallel. Results for cod support the hypothesis of distinct inshore and larger offshore subpopulations and for whiting for northern and southern North Sea subpopulations with a boundary associated with the 50 m depth contour. In haddock, no difference in SSB trends between the North Sea and west of Scotland was found. For cod and whiting, subpopulation SSB trends differed substantially within current stock assessment units, implying reported stock-based SSB time-series have masked underlying subpopulation trends.

Subsidence and sea-level rise in the Thames Estuary

1972 ◽  
Vol 272 (1221) ◽  
pp. 121-130 ◽  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Average Rate ◽  
Thames Estuary ◽  
The North ◽  
Storm Waves ◽  
Late Cretaceous Period ◽  
The North Sea ◽  
Sea Area ◽  
Cretaceous Period

The development of the area, of the Thames Estuary is briefly traced since the late Cretaceous period, with its present outline being due to a combination of factors. The overall subsidence of the North Sea area, the ‘Alpine5 fold movements, and the transgression of the sea since the retreat of the Weichselian icesheets have all contributed. The positions of the shore-line during the critical phase, 9600 b.p. to 8000 b.p., of this last transgression of the sea are shown. Subsequent to this main transgressive phase, erosion of the shoreline has been rapid due to storm-waves and tidal current action. An estimation of the average rate of subsidence and/or sea-level rise is given based on the concept of sedimentary equilibrium in which a figure of 12.7 cm (5 in) per century is arrived at.

scholarly journals When will the eel recover? A full life-cycle model

2007 ◽  
Vol 64 (7) ◽  
pp. 1491-1498 ◽  
Author(s):  
Mårten Åström ◽  
Willem Dekker
Keyword(s):  
Life Cycle ◽  
Distribution Area ◽  
European Eel ◽  
Life Cycle Model ◽  
Cycle Model ◽  
Glass Eel ◽  
Full Life Cycle ◽  
Long Run ◽  
Spawning Stock ◽  
Full Life

Abstract Åström M., and Dekker W. 2007. When will the eel recover? A full life-cycle model. – ICES Journal of Marine Science, 64: 000–000: –. The European eel population has declined over the past decades in most of its distribution area, and the stock is outside safe biological limits. The EU has taken up the challenge to design a management system that ensures the escapement of 40% of spawning-stock biomass, relative to unexploited, unpolluted circumstances in unobstructed rivers. This ultimately aims to restore the spawning stock to a level at which glass eel production is not impaired, i.e. to restore to full historical glass eel recruitment. To explore the trajectory from the current depleted state to full recruitment recovery, we developed a simple model of stock dynamics, based on a simplified stock–recruitment relationship and the conventional dynamic pool assumptions. Recruitment trajectories under different future fishery regimes are explored, for the medium (one generation time) and long time-span (until full recruitment recovery). Reducing fisheries to zero, recovery is expected within ∼80 years, whereas under an ultimately sustainable fishing regime of just 10% of the current rate of fishing mortality, recovery may take more than 200 years. Moreover, management regimes, apparently leading to slight recovery of the stock in the coming 5–15 years, might still be unsustainable in the long run.

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