Food, feeding and growth of the eel (Anquilla anguilla L.) in a Dutch eutrophic lake

This thesis describes the food, foraging and growth of the eel (Anguilla anguilla). Attention is paid to the abundance and distribution of the food organisms and the feeding and growth of other fish species. The investigations were carried out in the Tjeukemeer (21 km2) in the northern part of the Netherlands. This lake is the main object of study of the Tjeukemeer laboratory, part of the Limnological Institute of the Royal Netherlands Academy of Arts and Sciences. The Royal Academy funded the research on eel, the Ministry of Health and the Environment funded the zooplankton research.The Tjeukemeer is a shallow (1-2 m) , turbid (Secchi-disc 0.30 - 0.40 m), hypertrophic lake. It is part of a system of canals and reservoirs (lakes) receiving surplus water in late autumn, winter and early spring from a watershed covering 3060 km 2. Via this system the water is drained into the Waddensea or pumped into the IJsselmeer. When during spring and summer the evaporation exceeds precipitation, the whole system is drained with water from the IJsselmeer. These inputs have great impact on the physico-chemical conditions, but also on the fish fauna of the lakes. The smelt (Osmerus eperlanus) immigrates passively from the IJsselmeer as a massive flow of larvae. This immigration is dependent on weather conditions, therefore the abundance of the smelt is highly variable.The shoreline of the Tjeukemeer is poorly developed, the emergent vegetation covers 0.5% of the surface; since the early 1970s the submerged aquatic vegetation is greatly reduced and now virtually absent.The eel population in the Tjeukemeer, like in other large Dutch lakes, is heavily exploited. The population is dominated by small eels between 200 and 300 mm. Eels smaller than 120 mm are scarce. The proportion of eels larger than 300 mm ranges between 7 and 30% of the catch.Irrespectively their body length, the eels prefer as food invertebrates, at least 7 mm large, living on the water bottom surface. In the Tjeukemeer the larvae (later instars) and pupae of the chironomids Chironomusplumosus , Einfeldiacarbonaria and Glytotendipespallens , and the amphipod Gammarustigrinus are most frequently consumed.In 1979 larger bivalve mollusks are of secondary importance in the eel diet, while in 1980 and 1981 the>200 mm eels can switch to predation on smelt ( O. eperlanus ). Eels smaller than 340 mm become gape- limited in predation on smelt because the smelt grows faster than the eel mouth.The searching and catching behaviour of small eels foraging on chironomids was investigated in aquaria. The feeding efficiency, expressed as the time interval between finding and swallowing the larva, rapidly decreases when larvae are burrowed in the substrate. The eel has no preference for pupae, if larvae and pupae are offered in the same way, i.e. both easily available for the eels.In the stomach contents of the eels from the lake the proportion of pupae in the total chironomid biomass is 60-90%. The preference for pupae is explained by the availability of pupae, in comparison with the chironomid larvae, which are often deeply burrowed in the bottom substrate.The growth of eel was investigated by means of otolith readings and cohort analysis. The otoliths from 905 eels were sawn and polished or manually ground to determine the age by counting winter rings. The growth of Earlier studies on fish and zooplankton showed the great impact of the predation by smelt on the density of the Daphnia , in the crustacean zooplankton. Daphnia also is an important part of the diet of larger bream ( A. brama ) . In 1980 and 1981, when the smelt population increases, the zooplankton is hardly available to the bream. A large part of the bream population switches to a diet of chironomids. The chironomid population becomes overexploited.The overexploitation of the chironomids caused bad feeding conditions for eels confined to prey on invertebrates. The low growth rate of small eels is explained by these feeding conditions. We observe that even small eels start to prey on smelt in 1980 and 1981, but become gape-limited. Larger eels (>340 mm) show a better growth when feeding on fish.The effects of the inputs of water from other origins in the Tjeukemeer on the horizontal distribution of crustacean zooplankton were studied. Only during short periods in summer, the population densities appeared to be influenced by the inflow of water from the IJsselmeer. In periods with a precipitation surplus (autumn and winter) the zooplankton community was "diluted" by the inflow of surplus water from the watershed. The influence on the rest of the aquatic fauna of the lake was only slight.Patchiness in the zooplankton distribution occurs in the Tjeukemeer due to inhomogeneities in physico-chemical parameters. However, the lake is shallow and strongly influenced by windinduced turbulence. The zooplankton appears to be more homogenous than in other lakes elsewhere in Europe. These lakes were often deeper or contained more sheltered parts.In the last chapter the role of the eel in the ecosystem is discussed. Although competition between eel and bream for food (chironomids) occurs, it is suggested that changes in the vegetation and nutrient loading of the lake and the heavy commercial exploitation of the eel population have a negative influence on the amount of eel, while the bream is favoured by the effects of eutrophication.</TT

Early carboniferous brachiopod faunas from the Baoshan block, west Yunnan, southwest China

38 brachiopod species in 27 genera and subgenera are described from the Yudong Formation in the Shidian-Baoshan area, west Yunnan, southwest China. New taxa include two new subgenera: Unispirifer (Septimispirifer) and Brachythyrina (Longathyrina), and seven new species: Eomarginifera yunnanensis, Marginatia cylindrica, Unispirifer (Unispirifer) xiangshanensis, Unispirifer (Septimispirifer) wafangjieensis, Brachythyrina (Brachythyrina) transversa, Brachythyrina (Longathyrina) baoshanensis, and Girtyella wafangjieensis. Based on the described material and constraints from associated coral and conodont faunas, the age of the brachiopod fauna from the Yudon Formation is considered late Tournaisian (Early Carboniferous), with a possibility extending into earlyViseacutean.<br /

Search for the Chiral Magnetic Effect in Au+Au collisions at sNN=27\sqrt{s_{_{\rm{NN}}}}=27 GeV with the STAR forward Event Plane Detectors

A decisive experimental test of the Chiral Magnetic Effect (CME) is considered one of the major scientific goals at the Relativistic Heavy-Ion Collider (RHIC) towards understanding the nontrivial topological fluctuations of the Quantum Chromodynamics vacuum. In heavy-ion collisions, the CME is expected to result in a charge separation phenomenon across the reaction plane, whose strength could be strongly energy dependent. The previous CME searches have been focused on top RHIC energy collisions. In this Letter, we present a low energy search for the CME in Au+Au collisions at $\sqrt{s_{_{\rm{NN}}}}=27$ GeV. We measure elliptic flow scaled charge-dependent correlators relative to the event planes that are defined at both mid-rapidity $|\eta|<1.0$ and at forward rapidity $2.1 < |\eta|<5.1$. We compare the results based on the directed flow plane ($\Psi_1$) at forward rapidity and the elliptic flow plane ($\Psi_2$) at both central and forward rapidity. The CME scenario is expected to result in a larger correlation relative to $\Psi_1$ than to $\Psi_2$, while a flow driven background scenario would lead to a consistent result for both event planes[1,2]. In 10-50\% centrality, results using three different event planes are found to be consistent within experimental uncertainties, suggesting a flow driven background scenario dominating the measurement. We obtain an upper limit on the deviation from a flow driven background scenario at the 95\% confidence level. This work opens up a possible road map towards future CME search with the high statistics data from the RHIC Beam Energy Scan Phase-II.Comment: main: 8 pages, 5 figures; supplementary material: 2 pages, 1 figur

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe