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Although the colonisation of coastal rivers on the Atlantic and Mediterranean coast by glass eels, Anguilla anguilla, has been well studied and understood, the colonisation of lagoons by glass eels is much less known. For the first time in
the Mediterranean region, the installation of a glass eel fish-pass in Grau de la Fourcade channels in the Rhô...
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European eel (Anguilla anguilla) populations have suffered a sharp range retraction (90–99%) over the past 40 years. However, in recent years this fish has been detected again in the river Segura (Spain), in both the main river and in channels such as the irrigation canals and ditches that drain the Huerta de Murcia. Even though the water quality o...
Although the colonisation of coastal riv-ers on the Atlantic and Mediterranean coast by glass eels, Anguilla anguilla, has been well studied and understood, the colonisation of lagoons by glass eels is much less known. For the first time in the Mediterranean region, the installation of a glass eel fish-pass in Grau de la Fourcade channels in the Rh...
The European eel ( Anguilla anguilla ) is a critically endangered and declining species. Information from traditional fisheries and a fish monitoring scheme in the Ebro Delta reflect the widely reported eel decline onset in the late 1970s and also a recent, sharp and ongoing decline of similar magnitude (> 80%). This recent trend arises from both f...
Given the poor status of the European eel (Anguilla anguilla)
population, good assessments are essential to optimise recovery measures. Quantifying eel
stock size is challenging given the fractal nature of the distribution of eels,
particularly in The Netherlands with its dense interconnected network of drainage ditches,
rivers and lakes. Dynamic d...
Citations
... Our study indicated that watershed area might not be the major factor affecting elver recruitment abundance, unlike earlier studies that showed elver recruitment was affected by river discharge (Crivelli et al., 2008), which was related to watershed area (Burgers et al., 2014), although reliability of water discharge as an attraction proxy is uncertain (Cairns et al., 2022). Within the three rivers of our study, separated by ~50 km, watershed area of River B was similar to East River, and both were larger than River A, but temporal variation in elver abundance among years did not match the ranking that would be expected if watershed area was important for recruitment. ...
Spatial scales are important for examining health of exploited fishery stocks and guiding management actions. However, information about the optimal spatial scale is still unclear for assessment of transit fisheries, such as elver fisheries of the American eel Anguilla rostrata . We applied a generalized depletion model to assess catch and effort data from three nearby rivers (within 50 km) to test the hypothesis that modeling on pooled and separate data from nearby rivers would give similar estimates of abundance and exploitation rate. Overall, pooling data from rivers within 50 km did not result in large differences (<20% in relative difference) in estimates of abundance and exploitation rate with close mean abundance estimates and similar temporal trends in abundance, exploitation rate, and relative escapement. Pooling nearby river systems can greatly reduce modeling effort, at the cost of ignoring fine‐scale variability in elver recruitment and having coarser spatial scale for the management. When only an index of annual recruitment and exploitation rate are of interest, pooling data may be practical from different locations up to 50 km.
... Some other studies estimated more variable migration speed with values between 0:8 and 4:2 km per tidal cycle in McCleave and Kleckner (1982) and of 0:4 m s , or 34:56 km day , based on the modeling of swimming behavior according to hydrological conditions in Prouzet et al. (2009). In contrast, the colonization of Mediterranean hydrosystems has been little studied, with only a few studies linking environmental factors to the number of glass eels captured (Bardonnet et al., 2005;Bouchard, Drouineau, et al., 2022b;Crivelli et al., 2008;Podda et al., 2020;Zompola et al., 2008). The latter represents a knowledge gap, notably because the selective tidal stream transport (STST, Beaulaton and Castelnaud [2005]) used by glass eels to migrate upstream is probably less efficient in those hydro-systems where the tidal amplitude is very low (20-30 cm) and may be restricted by sluice management (Bouchard, Drouineau, et al., 2022b;Crivelli et al., 2008). ...
... In contrast, the colonization of Mediterranean hydrosystems has been little studied, with only a few studies linking environmental factors to the number of glass eels captured (Bardonnet et al., 2005;Bouchard, Drouineau, et al., 2022b;Crivelli et al., 2008;Podda et al., 2020;Zompola et al., 2008). The latter represents a knowledge gap, notably because the selective tidal stream transport (STST, Beaulaton and Castelnaud [2005]) used by glass eels to migrate upstream is probably less efficient in those hydro-systems where the tidal amplitude is very low (20-30 cm) and may be restricted by sluice management (Bouchard, Drouineau, et al., 2022b;Crivelli et al., 2008). ...
... Previous studies have shown that eels settle in the Vaccarès pond, where some complete their growth (Bevacqua et al., 2019;Bouchard, Boutron, et al., 2022a;Melia et al., 2006). An artificial channel called the Grau de la Fourcade, located on the town of Saintes-Maries de la mer (Figure 1), represents the main connection between the sea and the inland hydro-system with a weak tidal amplitude (20-30 cm, Bouchard, Drouineau, et al., 2022b;Crivelli et al., 2008). ...
Migration speed can have important evolutionary consequences as it can affect the timing of arrival, remaining energy reserves, and habitat choice. Environmental conditions and individual phenotypic traits can impact the migration speed of individuals. In this way, estimating migration speed is of particular importance, especially for species under strong management strategies and colonizing highly diversified habitats, as is the case for the European eel. However, estimating the migration speed of glass eels, which is the life stage when eels colonize continental habitats, presents challenges due to typically low re‐capture probabilities and difficulties in tagging individuals. Using recruitment time series at two sites, one at the sea connection and another inland, we estimated the temporal lag between the two migration peaks to compute migration speed. Because we worked on the Mediterranean coasts and in a lagoon, the weak tidal amplitudes may inhibit individuals from efficiently performing the selective tidal stream transport. We obtained migration speed values coherent with the few values available in the literature for Atlantic estuaries. The values we obtained that are lower than those obtained for Atlantic estuaries are also coherent with the weak tides along the Mediterranean coasts and lead to necessary further studies to understand the migratory behavior of glass eels in such hydro‐systems.
... The signal to migrate inshore is signalled by numerous environmental cues such as freshwater lure (Tosi and Sola 1993;Sullivan et al. 2006;Crivelli et al. 2008), salinity gradients (Tosi et al. 1990;Edeline et al. 2005), water temperature (Jessop 2003;Briand et al. 2005;Edeline et al. 2006;Laffaille et al. 2007), tidal cycles (Laffaille et al. 2007;Cresci et al. 2017), lunar phases and light intensity (Jellyman and Lambert 2003;Bardonnet et al. 2005;Jellyman et al. 2009). Using Selective Tidal Stream Transport, the eels enter estuaries and the lower tidal reaches of rivers between December and April (Harrison et al. 2014;Trancart et al. 2014). ...
The European eel (Anguilla anguilla) has undergone an unprecedented population decline since the 1980s, with current recruitment levels fluctuating from 3 to 15% of historical levels for the last 20 years. Monitoring of glass eels and elvers as 0 + recruitment is an essential step in helping to understand the trend in recruitment and to better quantify the current recruitment time series. Two locations within the Shannon estuary on the west coast of Ireland were monitored for glass eel recruitment from January to April in 2017 and 2018. This study used a generalised linear mixed model to examine a range of environmental variables impacting on glass eel abundance in transitional waters. Results found that water temperature and moon phase were the most important variables. Tidal height and cloud cover also influenced the abundance of glass eels but to a lesser extent. This study found that focussing survey efforts on nights around the full moon when water temperatures exceed 5℃ will allow a catch which is representative of the population in an estuary. Glass eel monitoring needs a long-term sampling plan in order to account for annual fluctuations apparent in glass eel recruitment.
... Therefore, glass eels can actively swim upstream along shallow shore margins even during the ebb tide because the current speed may not exceed their sustained swimming capability. River flow has been demonstrated to be an attracting cue that may play a positive role on the abundance of glass eels at fisheries (Crivelli et al. 2008;Arribas et al. 2012). Olfactory cues associated with freshwater are also considered important in the modulation of glass eel migratory behaviour (Creutzberg 1961;Crnjar et al. 1992;Tosi and Sola 1993;Sola 1995;Briand et al. 2002;McCleave and Jellyman 2002;Tesch 2003;Edeline et al. 2009). ...
Compared with temperate Anguilla, little is known about the early marine migration and recruitment mechanisms of these tropical eels. To understand the ecological and behavioural mechanisms of their inshore migration in tropical Anguilla, systematic research on their periodicity of inshore migration was conducted for 24 h over 9 to 13 consecutive days before and after the new moon dates four times in one year. Glass eel (juvenile) collections (151 to 4371 specimens during each survey period) in the Poigar River, north Sulawesi Island, Indonesia indicated a lunar periodicity, in which peak recruitment continued for 2 to 4 days during the new moon period; then, the recruitment sharply decreased before and after the new moon. Daily glass eel migration occurred in two peaks during the ebb (20:00) and flood (02:00) tides, while there was no significant different glass eel recruitment between the flood tide and ebb tides. Although the “selective tidal stream transport” that glass eels utilize during the flood tide for recruitment is widely accepted to be the main mechanism of inshore migration behaviour through estuaries to freshwater habitats for temperate glass eels, we did not find this mechanism during this study. These results suggest that the main recruitment mechanism for tropical glass eels may be associated with both endogenous rhythms (biological clock) and exogenous factors (tidal orientation) in the study site. The rhythmic activity of migrating tropical glass eels found in this study also contributes not only to understanding the biological and ecological implications but also provides clues for stock management and conservation of Anguilla, which have been critically declining in recruitment worldwide in recent decades.
... Ces recrutements Rz(y) se subdivisent ensuite entre les bassins versants de la zone selon des poids fonction de la taille des bassins versants. Cette fonction repose sur l'idée qu'à l'échelle plus locale, les civelles peuvent être « attirées » par les grands bassins, soit du fait d'un plus grand débit (Elie and Rochard 1994;Crivelli et al. 2008) ...
Mémoire d'Habilitation à Diriger des Recherches - Ecole Doctorale 304 Sciences et Environnements, Université de Bordeaux
... A ˇ value close to 1 would mean that recruitment is proportional to catchment surface, which can be considered a proxy of available habitat. However, it has previously been observed (at least on small catchments) that river discharge and river plume have an influence on glass eel recruitment (Crivelli et al., 2008;Elie and Rochard, 1994). If river discharge is the main factor influencing the proportions in each catchment, then the power is less than one. ...
... • The Vaccares series was collected by counting glass eels in a trap upstream from a fish pass. The fish pass is located on a sea wall which blocks the sea channel (Crivelli et al., 2008). ...
Given the importance of reliable recruitment estimates when assessing temperate eel stocks and enforcing appropriate management measures, surprisingly few analytical tools have been developed to estimate yearly glass eel recruitment. Of the models that do exist, large-scale models generally rely on strong assumptions relating to fishing activity, while other models generally estimate recruitment at the river basin scale. With the aim of filling this gap, we developed the GEREM (Glass Eel Recruitment Estimation Model) to estimate glass eel recruitment at different nested spatial scales. Our model simultaneously estimates annual recruitment at the river catchment level, at an intermediate spatial scale such as Eel Management Units (EMUs), and at a larger scale (e.g., a country). Provided sufficient data become available in the future, the analysis could be extended to the scale of the distribution area, which would be consistent with the population scale. In this study, the model was applied to France, using various recruitment indices obtained from 1960 to 2013. This provided trends and absolute recruitment estimates consistent with current expert knowledge. A sensitivity analysis was carried out to assess the robustness of results to sources of uncertainty. This type of model fills an important gap in the range of quantitative tools presently available to estimate recruitment. It could be used in the future to establish total allowable catches in countries such as France where glass eels are fished commercially.
... Less information is available for the southernmost estuaries of the eel European distribution area (Arribas et al., 2012) and even less for recruitment and settlement of juvenile eel in coastal lagoons ecosystems, notwithstanding the importance that these habitats play for the eel in the southern part of its distribution area. To our knowledge only Crivelli et al. (2008), Lecomte-Finiger andRazouls (1981) andFiniger (1976) have tried to determine which factors are involved in the glass eel migration to Mediterranean coastal lagoons. ...
... Whatever the general mechanisms and the specific role of environmental cues, recruitment and effective settlement are crucial when estimating eel production and hence breeder escapement and their contribution to the global spawning stock biomass (Aalto et al., 2015). Although overall recruitment may be very low today (Dekker, 2003a), settlement in lagoons has always been partially dependent on factors such as lagoon morphology and hydrology and related to the effects of meteorological patterns on glass eel movement (Finiger, 1976;Crivelli et al., 2008). Taken together, these result in an extremely variable recruitment level to lagoons which in turn makes it very difficult to evaluate if recruitment level is the main limiting factor for eel production in these habitats or simply one of several. ...
... The definitive settlement, when elvers move across nearby areas under freshwater influence, confirms the high importance of the freshwater appeal for driving movements of juvenile eels. According to Tosi et al. (1990), Tosi and Sola (1993) and Sola and Tongiorgi (1996), this is due to specific olfactory cues attracting elvers, which has also been pointed out by Jellyman and Lambert (2003) and Crivelli et al. (2008). Freshwater appeal causes young eel to move differently in lagoons with respect to what is observed in estuarine and river systems. ...
... The type of substratum and the slope angle of these fishways as well as hydraulic recommendations are adapted to the specific requirements of local species based on laboratory experiments (Hamano et al. 1995;Voegtle et al. 2002). However, evaluation of the performances of fishways and description of fish migration dynamics to suggest improvements of structure engineering, attraction discharge management and maintenance (Santos et al. 2002) requires in situ studies (Benstead et al. 1999;Crivelli et al. 2008). To date, monitoring of fishways specially designed for amphidromous gobies has not yet been conducted in field conditions. ...
... Using fishways for studying the upstream migration of fishes Fishways are commonly used to assess diadromous and potamodromous fish migrations (Laine et al. 1998;Santos et al. 2002;Crivelli et al. 2008) along with several others methods such as surveying fishing catches (Aprahamian et al. 2008;Maes et al. 2008), fish telemetry (Chanseau et al. 1999a;Lundqvist et al. 2008) or mark and recapture studies (Chanseau et al. 1999b;Smith & Kwak 2014). In La R eunion Island, fishing for S. lagocephalus and C. acutipinnis upstream of the estuaries is officially forbidden. ...
... Increases in river discharge, i.e. floods, have largely been described as stimulating upstream migration of diadromous fishes in both temperate (Erkinaro et al. 1999;Crivelli et al. 2008) and tropical areas (Delacroix 1987;Fi evet et al. 2000). The effects of small floods on upstream migration of tropical amphidromous gobies remain to be described. ...
Diadromous species of tropical islands face numerous anthropogenic disturbances. Understanding how these disturbances affect the population dynamic of these species is important to develop ecologically based management measures. The upstream migration dynamics of two amphidromous gobies, Sicyopterus lagocephalus (Pallas) and Cotylopus acutipinnis (Guichenot), was described using intensive fishway monitoring (28 sampling dates over
1.5 years, 13 000 S. lagocephalus, 23 000 C. acutipinnis captured). Migration peak occurred for both species during the afternoon at the end of austral winter/beginning of austral summer. Abundance and size of fish caught in the river showed a marked impact of a dam (six sampling dates approximately 4000 individuals of each species captured). This study provides critical data for better management of fishways used by tropical amphidromous gobies. It appears especially important to reduce unwanted rheotactic sources that attract the fish away from the fishway’s entrance.
... A key unknown factor for estimation of eel production in lagoons is actual eel settlement, a process affected by the interaction of several factors including local habitat quality and hydrodynamics, small-scale spatial and temporal heterogeneities in recruitment and global population dynamics of the eel panmictic stock. Though recruitment is thought to be at very low quantitative levels today (Dekker, 2003b), settlement has always been partially dependent on external factors such as lagoon morphology and hydrology and the influence of meteorological patterns on glass eel movement (Finiger, 1976, Crivelli et al., 2008. The result is an extremely variable level of recruitment to lagoons in the present as well as in the past, making it very difficult to evaluate if recruitment is the main limiting factor for eel production or simply one of several. ...
... Although we cannot rule out regional differences in recruitment patterns and trends, consensus an 90% drop in recruitment with respect to pre-1980s levels is strong within the ICES/EIFAC Working Group on eel (ICES, 2012) and is supported by a number of scientific publications (Bonhommeau et al., 2008a, b); available data did not allow us to assess whether the drop in recruitment at the Mediterranean level was more severe than that of central and northern Europe. At the local level, year-to-year variation or a decrease in glass eel recruitment to lagoons can also be due to a general decline in management efficacy, particularly affecting the efficiency of tidal channels (Crivelli et al., 2008). ...
The European eel Anguilla anguilla is thought to be in a multi-decadal decline across its range. Although its northern Atlantic sub-populations are well-studied,
little is known about the historical trend and current status of eel stock in the Mediterranean Sea. To fill this gap, we
gathered catch data for 86 lagoon fisheries in nine countries across the Mediterranean basin and analysed historical trends
and geographical and environmental patterns. We found a region-wide decline in eel catch, beginning in the mid-1970s and exceeding
the simultaneous decline in non-eel fisheries, as well as lower productivity in larger lagoons and those in the southern Mediterranean.
Additionally, we developed a population dynamics model to provide a preliminary estimate of pristine, potential, and actual
escapement of spawning adults (silver eels) across the Mediterranean basin under historical and current conditions. Model
results suggest that current escapement is 35% of escapement at pristine biomass levels, <40% target set by EC regulation
1100/2007. Furthermore, we estimate that a complete closure of lagoon fisheries would achieve 57% of pristine escapement under
current recruitment levels. Though preliminary, this analysis represents a first step towards a full assessment of the role
of the Mediterranean sub-population in overall eel stock recovery.
... River flow has been demonstrated to be an attracting cue that may play a positive role on the abundance of glass eels at fisheries (Crivelli et al. 2008;Arribas et al. 2012). However, high flows can have a countering effect on tidal flow in the 'upstream' direction thereby reducing the conveyor belt effect of STST. ...
Recruitment of the three northern hemisphere eel species (European eel Anguilla anguilla, American eel Anguilla rostrata and Japanese eel Anguilla japonica) has reduced significantly over the past thirty-five years. The stock of the European eel is described as being outside safe biological limits, with urgent action required by European Union Member States to assist recovery of the panmictic stock. Stock recruitment models and estimates of silver eel output from a river catchment are strongly influenced by the degree of certainty in estimating key population parameters of each life history stage. Therefore, management decisions aimed at enhancing eel populations rely on sound scientific evidence, based upon a fundamental understanding of the complex anguillid eel life cycle. This review paper focuses on the estuarine entry phase of the eel life cycle and synthesises the current scientific knowledge with regard to glass eel migratory behaviour, sampling methods and abundance estimates within estuaries. Although the behavioural and environmental processes modulating glass eel migration patterns are reasonably well understood, site specific factors play a significant role in determining fine scale distribution patterns at an individual estuary level. Given the large resource commitment required to adequately sample this key life history stage, behavioural studies of migration patterns on a local scale are crucially important to aid the design of robust sampling programmes aimed at quantifying seasonal abundance and annual recruitment.
