scholarly journals Changes in the juvenile fish assemblage of a Mediterranean shallow Posidonia oceanica seagrass nursery area after half century

2019 ◽  
Vol 20 (3) ◽  
pp. 603
Author(s):  
CARLOS DÍAZ-GIL ◽  
AMALIA GRAU ◽  
ANTONIO MARIA GRAU ◽  
MIQUEL PALMER ◽  
REMEDIOS CABRERA ◽  
...  
Keyword(s):  
Environmental Variability ◽  
Juvenile Fish ◽  
Anguilla Anguilla ◽  
Posidonia Oceanica ◽  
Nursery Area ◽  
Environmental Drivers ◽  
European Eel ◽  
Habitat Transformation ◽  
Seagrass Meadows ◽  
Sampling Zone

The within-year dynamics of the juvenile fish community over a shallow nursery seagrass-dominated habitat (Posidonia oceanica) in a Mediterranean Bay was compared between two surveys separated 50 years (1960 and 2012-2013). A nocturnal survey over depths ranging from 2 to 10 m over patched seagrass meadows was conducted for one year (2012-2013) through 72 epibenthic tows spread fortnightly in 4 close-by stations, mimicking a survey, conducted in 1960, in terms of sampling intensity, sampling zone, temporal coverage and sampling gear. Although a large proportion of fish species was similar among surveys, remarkable and statistically significant differences were detected. A striking feature was that one of the most common and abundant sparidae species nowadays, Diplodus annularis, did not appear in 1960. Other strong differences included the disappearance of European eel Anguilla anguilla in the recent survey. Further, one of the most valuable species for artisanal fisheries in the area, the black scorpionfish Scorpaena porcus, was almost 10 times less abundant in 1960. A finer-scale study of the 2012-2013 survey allowed a quantitative analysis between species composition and potential environmental drivers through Redundancy Analysis that described well the current pattern of time-dependent recruitment pulses in nearshore meadows from the area through a year, with marked effects of surface temperature and photoperiod. The comparison between surveys suggests that some strong differences between surveys are unlikely attributable to interannual stochasticity in recruitment or environmental variability but may be related with i) unaccounted for habitat transformation and/or ii) the strong decrease of juvenile fishing mortality in this shallow nursery area since the enforcement of bans on littoral epibenthic trawling activities characteristic of this area.

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

2011 ◽  
Vol 92 (4) ◽  
pp. 843-851 ◽  
Author(s):  
Peter A. Henderson ◽  
Shaun J. Plenty ◽  
Lyn C. Newton ◽  
David J. Bird
Keyword(s):  
Environmental Variability ◽  
Cooling Water ◽  
Anguilla Anguilla ◽  
Fish Population ◽  
European Eel ◽  
Power Station ◽  
Population Number ◽  
Population Collapse ◽  
Recruitment Failure ◽  
The North

A 30-year study of the estuarine population of yellow eel, Anguilla anguilla, abundance in Bridgwater Bay, Somerset, UK, shows that the population number has collapsed. Since 1980, the decline has averaged 15% per year. The abundance of eel in 2009 is estimated at only 1% of that in 1980. This is one of the greatest systematically quantified crashes of a fish population ever reported. Collections of eels impinged on cooling water filter screens were made monthly at Hinkley Point power station between 1980 and 2010 and from Oldbury power station between 1996 and 1998. Eels are always present in the Severn Estuary, although there are large seasonal variations in abundance. At Oldbury, in the upper estuary, eels are least abundant in January. In contrast, in the outer estuary in Bridgwater Bay, eels are most abundant between November and March. The size-distribution of yellow eels ranged from <200 to >700 mm indicating an age-range since the glass eel stage of 2 to >25 years. The mean size-range has not changed since the 1980s indicating that the population collapse is not caused by a sudden recruitment failure. It is suggested that there has been a continual long-term failure of recruitment to compensate for losses. The reason for this is unidentified, but is unlikely to be changes in the North Atlantic Oscillation or other natural environmental variability. A major effort to improve eel survival to adulthood is required if this species is not to gently fade to extinction. This would likely involve a cessation of elver fishing, a reduction in the volume of estuarine water extracted for power station cooling and other purposes during which eels are entrained and killed, and the removal of obstructions which increase mortality during migration.

scholarly journals Cause or consequence? Exploring the role of phenotypic plasticity and genetic polymorphism in the emergence of phenotypic spatial patterns of the European eel

2017 ◽  
Vol 74 (7) ◽  
pp. 987-999 ◽  
Author(s):  
Maria Mateo ◽  
Patrick Lambert ◽  
Stéphane Tetard ◽  
Martin Castonguay ◽  
Bruno Ernande ◽  
...  
Keyword(s):  
Life History ◽  
Phenotypic Plasticity ◽  
Habitat Selection ◽  
Life History Traits ◽  
Environmental Variability ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Anthropogenic Pressures ◽  
The Impact

The European eel (Anguilla anguilla), and generally, temperate eels, are relevant species for studying adaptive mechanisms to environmental variability because of their large distribution areas and their limited capacity of local adaptation. In this context, GenEveel, an individual-based optimization model, was developed to explore the role of adaptive phenotypic plasticity and genetic-dependent habitat selection, in the emergence of observed spatial life-history traits patterns for eels. Results suggest that an interaction of genetically and environmentally controlled growth may be the basis for genotype-dependent habitat selection, whereas plasticity plays a role in changes in life-history traits and demographic attributes. Therefore, this suggests that those mechanisms are responses to address environmental heterogeneity. Moreover, this brings new elements to explain the different life strategies of males and females. A sensitivity analysis showed that the parameters associated with the optimization of fitness and growth genotype were crucial in reproducing the spatial life-history patterns. Finally, it raises the question of the impact of anthropogenic pressures that can cause direct mortalities but also modify demographic traits and act as a selection pressure.

scholarly journals Movements of Non-Migrant European Eels in an Urbanised Channel Linking a Mediterranean Lagoon to the Sea

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 839
Author(s):  
Raphaël Lagarde ◽  
Jason Peyre ◽  
Elsa Amilhat ◽  
François Bourrin ◽  
François Prellwitz ◽  
...  
Keyword(s):  
Water Temperature ◽  
Regression Tree ◽  
Anguilla Anguilla ◽  
Environmental Drivers ◽  
European Eel ◽  
Anthropogenic Pressures ◽  
Boosted Regression Tree ◽  
Mediterranean Lagoons ◽  
Regression Tree Analysis ◽  
Management Plans

Transitional ecosystems and, particularly, Mediterranean lagoons represent important habitats for the European eel (Anguilla anguilla) population. In these habitats many anthropogenic pressures can disturb eel movements and, in turn, negatively affect the population. Despite the importance of movements during the non-migrant growing stage in eels, this topic is understudied in Mediterranean lagoons. We thus aim to describe the diel and seasonal phenology and the effect of environmental drivers on non-migrant eel movements. Videos obtained from an Adaptive Resolution Imaging Sonar (ARIS) acoustic camera that continuously recorded from October 2018 to April 2020 were processed to evaluate the daily number of eels swimming toward the lagoon. More than 60% of the 7207 eels observed were females with a size >45 cm. Movements were year-round and predominantly during the night. A Boosted Regression Tree analysis demonstrated that, among the 10 environmental drivers studied, flow velocity, water temperature, discharge of the main tributary, wind velocity and atmospheric pressure, had the strongest influence on eel movement activity. Non-migrant eel movements should be better incorporated into lagoon management plans through actions such as limiting dredging activities from 18:00 to midnight, especially when the water flows toward the lagoon and when the water temperature is higher than 12 °C.

Metazoan Parasites and Health State of European Eel, Anguilla Anguilla (Anguilliformes, Anguillidae), From Tonga Lake and El Mellah Lagoon in the Northeast of Algeria

2018 ◽  
Vol 52 (4) ◽  
pp. 279-288 ◽  
Author(s):  
F. Bakaria ◽  
S. Belhaoues ◽  
N. Djebbari ◽  
M. Tahri ◽  
I. Ladjama ◽  
...  
Keyword(s):  
Brackish Water ◽  
Parasite Species ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Health State ◽  
Component Community ◽  
Metazoan Parasites ◽  
Parasite Communities ◽  
High Dominance ◽  
Argulus Foliaceus

Abstract The aim of the study was to examine metazoans parasite communities of European eels (Anguilla anguilla) in freshwater (Tonga Lake) and brackish water (El Mellah lagoon) in the northeast of Algeria. Six parasite taxa were collected: one monogenean, Pseudodactylogyrus sp.; two crustaceans, Ergasilus sp. and Argulus foliaceus; two nematodes, Cucullanus sp. and Anguillicola crassus; one cestode, Bothriocephalus claviceps. Th e most prevalent parasite taxa in freshwater were Pseudodactylogyrus sp., A. crassus and Bothriocephalus claviceps; whereas in the brackish water, eels were infected mainly with A. crassus. Th e characteristics of the parasite component community structure revealed low parasite species diversity and high dominance values in eels from the two localities. Both communities were dominated by a single parasite species: Tonga eels by the monogenean Pseudodactylogyrus sp. and El Mellah lagoon eels by the nematode A. crassus, verified by high Berger-Parker dominance values of 0.76 and 0.87 respectively.

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