Effect of illegal glass eel (Anguilla anguilla) fishery on estuarine fish stocks: a case study in the Mondego Estuary, Portugal

2018 ◽  
Vol 69 (11) ◽  
pp. 1692
Author(s):  
João Bernardo Neves ◽  
Filipe Martinho ◽  
Miguel Ângelo Pardal
Keyword(s):  
Anguilla Anguilla ◽  
Abundant Species ◽  
Estuarine Fish ◽  
Target Species ◽  
Estuarine Ecosystem ◽  
Glass Eel ◽  
Illegal Fishing ◽  
Wide Range ◽  
Mondego Estuary ◽  
Migratory Season

Illegal fishing is a critical activity that affects a wide range of species, leading to a decline in total abundance and the overexploitation of target and non-target species. In Portugal, despite fishing for eel juveniles not being allowed, a substantial amount of illegal fishing takes place during the migratory season (October–March). The aim of this study was to investigate the effects of glass eel fishing in the Mondego estuary on target and non-target species. Samples were collected between November 2011 and March 2013 during the autumn and winter (dry and regular respectively with regard to hydrological characteristics) in 2 years. No differences in glass eel catches were observed between fishing seasons; however, a higher number of non-target species was observed in 2012–13 (regular year). There was higher species diversity in the regular year, as well as the highest number of individuals. Higher catches of the most abundant species were also observed in the regular year, compared with the dry year, suggesting that the magnitude of the effect of these illegal practices is related to hydrological cycles. Despite the low replication (2 years), the present study shows that non-selective practices have considerable effects on the species captured, as well as on the functioning of the estuarine ecosystem.

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.

scholarly journals Yield per recruit from stocking two different sizes of eel (Anguilla anguilla) in the brackish Roskilde Fjord

2015 ◽  
Vol 73 (1) ◽  
pp. 158-164 ◽  
Author(s):  
Michael I. Pedersen ◽  
Gorm H. Rasmussen
Keyword(s):  
Growth Rate ◽  
Scientific Information ◽  
Anguilla Anguilla ◽  
Silver Eel ◽  
Glass Eel ◽  
Recovery Plan ◽  
Yellow Eel ◽  
Roskilde Fjord ◽  
Yield Per Recruit ◽  
The Eu

Abstract Stocking of young eel is widely practised, as a measure, to meet the management target of the EU eel recovery plan. The target of the recovery plan is to increase the escapement to 40% silver eel biomass, relative to pristine conditions. The scientific information to predict the outcome in silver eel biomass from stocking is limited and may depend on whether translocation of wild glass eel or yellow eel is used, or if the stocked eels used are yellow eel from aquaculture. We evaluated the yield from stocking two different sizes, 3 and 9 g eels from aquaculture. A professional fishery recaptured 12.7% of the 3 g and 9.4% of the 9 g eels, originally stocked. Growth rate and mortality rate were different for the two stocked sizes, favouring the small eels. Brutto yield per recruit (YPR) was 13 and 9.2 g and netto YPR was 9.8 and 0.31 g for 3 and 9 g eel, respectively. We conclude that there seems to be no advantage in using larger 9 g eels compared with small 3 g eels for stocking.

Spatial patterns in estuarine fish faunas in tropical Queensland: a reflection of interaction between long-term physical and biological processes?

1998 ◽  
Vol 49 (1) ◽  
pp. 31 ◽  
Author(s):  
Marcus Sheaves
Keyword(s):  
Fish Assemblages ◽  
Abundant Species ◽  
Common Species ◽  
Estuarine Fish ◽  
Maximum Deviation ◽  
Seawater Salinity ◽  
Spatial Differences ◽  
Upstream Direction ◽  
Catch Rates

Spatial differences in the distribution and abundance of fish faunas of structurally complex habitats in subtidal areas of three tropical estuaries were investigated by using modified Antillean-Z fish traps. The overall species compositions of the three estuaries were similar; however, the distribution and abundance of species differed substantially both within and among estuaries. Although the abundance of most species declined in an upstream direction, the fish assemblages of upstream areas of different estuaries were similar. In contrast, assemblages in seaward regions were quite distinct. Neither temperature nor turbidity were correlated with catch rates of the most abundant species. Although catch rates of some species were significantly correlated with deviation away from normal seawater salinity, in most cases the correlation with maximum deviation in salinity was much stronger. Thus, decreased catches and the absence of some common species from upstream areas may be related to the influence of long-term (months and years) patterns of salinity. Some species were abundant only in one region of a single creek. This may reflect the close proximity of nearby habitats from which recruits may come.

Are polymorphic species of Uropodina (Acari: Mesostigmata) more successful evolutionarily?—A case study of closely related species from the genus Oodinychus Berlese, 1917 based on DNA sequences

2019 ◽  
Vol 24 (5) ◽  
pp. 866
Author(s):  
Jerzy Błoszyk ◽  
Katarzyna Buczkowska ◽  
Anna Maria Bobowicz ◽  
Alina Bączkiewicz ◽  
Zbigniew Adamski ◽  
...  
Keyword(s):  
Dna Sequences ◽  
Related Species ◽  
Habitat Preferences ◽  
Abundant Species ◽  
Systematic Position ◽  
Genetic Differences ◽  
Similar Species ◽  
Closely Related Species ◽  
Wide Range

The study presented in this research paper is the first taxonomic investigation focusing on Uropodina (Acari: Mesostigmata) mites with a brief discussion of the genetic differences of two very closely related species from the genus Oodinychus Berlese, 1917, i.e. O. ovalis (C.L. Koch, 1839) and O. karawaiewi (Berlese, 1903). These two morphologically similar species are quite common and they have a wide range of occurrence in Europe. They also live in almost the same types of habitat. However, O. ovalis usually exhibits higher abundance and frequency of occurrence. The major aim of the study was to carry out a comparative analysis of the systematic position, morphological and biological differences, as well as habitat preferences and distribution of O. ovalis and O. karawaiewi. The next aim was to ascertain whether the differences in number and frequency of these species may stem from the genetic differences at the molecular level (16S rDNA and COI). The study shows that O. ovalis, which is a more abundant species than O. karawaiewi, turned out to be genetically more polymorphic.

Patterns of infracommunity species richness in eels, Anguilla anguilla

2004 ◽  
Vol 78 (2) ◽  
pp. 141-146 ◽  
Author(s):  
J. Norton ◽  
D. Rollinson ◽  
J.W. Lewis
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Frequency Distribution ◽  
Parasite Species ◽  
Anguilla Anguilla ◽  
Component Community ◽  
Southern England ◽  
Wide Range ◽  
The Relationship

AbstractBetween October 1999 and October 2001, a total of 510 European eels Anguilla anguilla were captured in 13 different samples from the rivers Thames (five locations) and Test (one location) in southern England. The relationship between parasite component community species richness (CCR) and maximum infracommunity species richness (ICRmax) compared with that previously observed in bird and mammal hosts. Specifically, the maximum number of parasite species occurring in infracommunities equalled or exceeded half the number of parasite species in the component community at that time, across a wide range of CCR values (2–9 parasite species). Furthermore, the frequency distribution of infracommunity richness (ICR) suggested that the species composition of infracommunities is probably random. These findings suggest that intestinal macroparasite infracommunities in eels are unsaturated and potentially species rich assemblages and, in these respects, share a fundamental similarity with the infracommunities of birds and mammals.

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