Article

The potential contribution of small coastal streams to the conservation of declining and threatened diadromous fishes, especially the European eel

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Abstract

Human-generated pressures are continuing to have a detrimental effect on diadro-mous fishes, resulting in legislative initiatives to conserve and manage these species. Field studies to inform these initiatives focus almost exclusively on larger marine, estuarine, and inland waters, neglecting the role of small coastal streams and tributaries in population recovery. As an example of the potential contribution of very small coastal streams to diadromous fish recruitment, we report here on the densities and distribution of European eel Anguilla anguilla L. and flounder Platichthys flesus (L.) in one such stream, "La Warenne," in northeast France in October 1998 and 1999. Both species were found mainly in downstream sites in both years-flounder were captured in low numbers only, but mean CPUE values for eel were similar to the highest densities reported in the ICES WGEEL database for larger rivers of Great Britain, France and Spain in the Interreg Atlantic and North Sea areas. This small dataset illustrates that small coastal streams may represent an important, but overlooked , role in conservation strategies for European eel, and possibly flounder, indicating the need for further field studies and investigations of existing data sources to evaluate the contributions to diadromous fish recruitment of these poorly studied water courses. K E Y W O R D S dune stream, flounder, juvenile fish nursery habitat, Pas-de-Calais

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... In addition, investigations on eels focused almost exclusively on large estuary (e.g., in the Severn Estuary [30] and in the Gironde Estuary [10,25]), neglecting the role of small estuaries, which are the most numerous. Conservation and implementation of management measures for eel populations require an understanding of the importance of small estuaries for eels, particularly in terms of their carrying capacity and growth potential [36,37]. In the present study, we analyzed the European eel abundance and growth attributes in six small estuaries along the French coast of the eastern English Channel and explored whether local habitat characteristics influence them. ...
... In addition, CPUE values were in range with the highest densities previously reported in larger habitats. These results reinforce the idea that small estuaries are important habitats that contribute significantly to the eel population and, therefore, must be considered in both population status assessments, conservation and management strategies for the European eel [36]. ...
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... A lack of reliable monitoring of smaller, more numerous, catchments often means that plans concentrate on larger catchments. This belies the likely collective and cumulative importance of numerous small catchments to eel stocks and overall conservation strategies (Copp, Daverat & Baši c, 2020). This study illustrates the importance of catchment-scale approaches to monitoring using different methods, especially PAS by electric fishing and even limited tracking of eels (see 4.1 above). ...
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The cover image is based on the Short Communication The potential contribution of small coastal streams to the conservation of declining and threatened diadromous fishes, especially the European eel by Gordon Copp et al., https://doi.org/10.1002/rra.3746. Photography by Alan Walker.
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Natural or anthropogenic induced variations in estuaries and the dynamics of marine fish populations potentially promote differences in connectivity between estuaries and marine areas, i.e. in their importance as nursery grounds. Within this context, an integrated assessment of the differential nursery function of the main estuaries along the Portuguese coast for commercial fish species common sole Solea solea, Senegalese sole Solea senegalensis, flounder Platichthys flesus and sea bass Dicentrarchus labrax was performed through several indicators based on available data. Contribution of individual estuaries to marine subpopulations was measured with potential metrics (juvenile density, habitat quantity, juvenile number and habitat quality within estuaries) and effective metrics (estuarine source of young adults in marine environment measured via otolith elemental fingerprints). The relationship between the two types of metrics was also assessed. Estuaries identified as important nursery and/or effective juvenile habitat (EJH) differed with species and no single estuary was best for all, highlighting species-specific regulation of nursery function. Multiple species assessment of nursery and EJH function differed among estuaries. Management and conservation of estuaries should focus on sites with higher contributions to adult subpopulations of multiple species. The importance of defining precise scientific and management objectives was emphasized by the different rankings of estuaries obtained with nursery or EJH criteria. Potential and effective contribution of estuaries were not significantly correlated, but in a quantitative analysis juvenile densities and number of juveniles seem related with effective contribution in some species. An agreement between potential and effective contributions of estuaries is concurrent with the acknowledged minor role of juvenile stage processes in regulation of recruitment to adult subpopulations.
Article
Daverat F, Martin J, Fablet R, Pécheyran C. Colonisation tactics of three temperate catadromous species, eel Anguilla anguilla, mullet Liza ramada and flounder Plathychtys flesus, revealed by Bayesian multielemental otolith microchemistry approach. Ecology of Freshwater Fish 2011: 20: 42–51. © 2010 John Wiley & Sons A/S Abstract – The colonisation of Gironde (SW France) river catchment by juvenile, eel, Anguilla anguilla, flounder Platychtys flesus and thinlipp mullet Liza ramada was investigated comparatively using Sr:Ca and Ba:Ca composition of otolith. The relation between Sr, Ba and habitat was investigated based on Sr and Ba water composition sampled each month along the estuary-river gradient. A total of 50 mullets, 30 eels and 47 flounders were collected in the Gironde river catchment. Analysis was performed with a Femtosecond LA-ICPMS along a trajectory from the core to the edge. Sr and Ba water concentrations discriminated three habitats within the Gironde system, the lower estuary, the upper estuary and the freshwater sites. A signal processing method based on Gaussian hidden Markov models was applied to the multielemental life-history data. The linear model used to allocate a Gironde habitat to coupled Sr, Ca values was parameterised with seasonal patterns and magnitude of Sr and Ba water values in the different habitats. The results showed that the three species used three different habitats and they had a large diversity of habitat use patterns with resident and nomadic tactics. Resident tactics were less frequent than nomadic tactics that suggested individual fish used two or more habitats. Mullet used a wider range of habitats in the lower part of the estuary than eel and flounder and switched habitats more frequently. Flounders tended to colonise initially freshwater, and then estuarine habitats later in life while mullets used the entire range of available catchment habitats throughout their life.
Article
The performance of fyke netting was compared with that of electrofishing in an artificially stocked closed pond and in open waters with natural populations in the Thames catchment, England. Seine netting, trapping and fyke nets of different mesh size were also compared using wild populations. Studies of mark-recapture and catch-depletion techniques for estimating population sizes and structures were included. It was concluded that no single technique was ideal because of the difficulties inherent in adequately sampling eels in all aquatic environments. Recommendations are made and the implications of fyke net efficiency for commercial fishing are discussed.
Article
Bio-indicators were measured on juvenile fish to assess the quality of eight coastal and estuarine nursery grounds in the Eastern English Channel and in the Bay of Biscay during 3 years. Growth (size and otolith daily increment width), body condition (morphometric index) and abundance of juvenile common soles were analysed together with xenobiotic concentrations (heavy metals and organic contaminants).Condition indices displayed important variations and did not allow relevant estimation of environmental quality. On the contrary, growth and density indicators showed good steadiness above years but varied among sites. In spite of difficulties of interpreting these indicators on such a meso-scale approach, analyses highlighted the estuaries of Seine and Gironde. In these nursery areas, the levels of contamination were especially high, and the combination of fish growth performances and density was significantly lower than in other sites. The combination of these variables appears to provide reliable indicators of habitat quality and anthropogenic pressure on nursery grounds, especially highlighting contaminated areas. Such indicators may thus contribute to improve assessment of environmental quality of essential fish habitats with the aim of a sustainable management of fisheries resources. A study at a different scale, from this meso-scale nursery approach with more precise analyses, on local habitats, will nevertheless be necessary to optimize the relevance of these indicators for the assessment of essential fish habitat quality.
Article
It is shown that the catch-effort electrofifhing methods, which are those most often employed for estimates of riverine fish density and biomass, are often not precise. These multiple sampling procedures are time- and manpower-consuming, and can change the habitat and fish community structure. The results, collected in rivers of different size and character, show curvilinear relationships between the average specimen size and the percentage, number and biomass of fish caught by one electrofishing. Using such relationships minimizes the alteration of fish community structure by the sampling procedure. Conditions which must be fulfilled for proper use of the proposed relationships are discussed.
Article
In this paper, we review the role of fish populations in generating ecosystem services based on documented ecological functions and human demands of fish. The ongoing overexploitation of global fish resources concerns our societies, not only in terms of decreasing fish populations important for consumption and recreational activities. Rather, a number of ecosystem services generated by fish populations are also at risk, with consequences for biodiversity, ecosystem functioning, and ultimately human welfare. Examples are provided from marine and freshwater ecosystems, in various parts of the world, and include all life-stages of fish. Ecosystem services are here defined as fundamental services for maintaining ecosystem functioning and resilience, or demand-derived services based on human values. To secure the generation of ecosystem services from fish populations, management approaches need to address the fact that fish are embedded in ecosystems and that substitutions for declining populations and habitat losses, such as fish stocking and nature reserves, rarely replace losses of all services.
EuroDiad 4.0 User's Guide. Report on Assessing and Enhancing Ecosystem Services Provided by Diadromous Fish in a Climate Change Context. Deliverable reference: WP 5-Action 1
  • B Barber
  • G Lassalle
  • P Lambert
  • E Quentin
  • J King
  • W Roche
  • E Pereira
Barber, B., Lassalle, G., Lambert, P., Quentin, E., King, J., Roche, W., … Pereira, E. 2020. EuroDiad 4.0 User's Guide. Report on Assessing and Enhancing Ecosystem Services Provided by Diadromous Fish in a Climate Change Context. Deliverable reference: WP 5-Action 1. Retrieved from https://diades.eu/wp-content/uploads/2020/07/Dia dES-5.1-EuroDiad-User-Guide_Final_CorrectedJune2020.pdf
Regulation (EU) no 1237/2010 of the European Parliament and of the Council of December 15, 2010 amending council regulation (EC) no 2187/2005 as regards the prohibition of highgrading and restrictions on fishing for flounder and turbot in the Baltic Sea, the belts and the sound
  • EC
EC. (2007). Council regulation (EC) no 1100/2007 of September 18, 2007 establishing measures for the recovery of the stock of European eel. Official Journal of the European Union, 248, 17. EC. (2010). Regulation (EU) no 1237/2010 of the European Parliament and of the Council of December 15, 2010 amending council regulation (EC) no 2187/2005 as regards the prohibition of highgrading and restrictions on fishing for flounder and turbot in the Baltic Sea, the belts and the sound. Official Journal of the European Union, 348, 34.
Un étrange poisson: L'anguille ses mœurs et son intérêt économique
  • Hornyold G.
Hornyold, G. (1931). Un étrange poisson: L'anguille ses moeurs et son intérêt économique. La Terre et la Vie, Revue d'Histoire Naturelle, 11, 657-674.
A review of the European flounderPlatichthys flesus-biology life history and trends in population
  • D J Skerritt
Skerritt, D. J. (2010). A review of the European flounder Platichthys flesusbiology, life history and trends in population. Eastern Sea Fisheries Joint Committee Report. Newcastle University. Retrieved from https://www.eastern-ifca.gov.uk/wp-content/uploads/2016/03/Flou nderLitReviewDS.pdf
Comment on stock assessment of eels in the Baltic by
  • H Svedäng
  • M Cardinale
Svedäng, H., & Cardinale, M. (2016). Comment on stock assessment of eels in the Baltic by Westerberg and Wickström (2015): Do we need more unknowns? ICES Journal of Marine Science, 73(6), 1610-1612.
  • Baras E.
Council regulation (EC) no 1100/2007 of September 18, 2007 establishing measures for the recovery of the stock of European eel
  • EC