Model prediction vs. reality--testing the predictions of a European eel (Anguilla anguilla) stock dynamics model against the in situ observation of silver eel escapement in compliance with the European eel regulation

A direct monitoring of European silver eel (Anguilla anguilla, L) escapement from rivers and estuaries has been proven to be challenging, and a Europe-wide documentation of escaping silver eel numbers therefore hardly seems realistic. To reinforce management decisions, policy-makers are thus widely reliant on the accuracy of escapement models. A 3-year programme of silver eel escapement monitoring was undertaken to compile model input data and revise an eel population model (German Eel Model II; GEM II) already used in the decision-making process of management authorities. By compiling necessary input data and analysing vital system-specific population characteristics, it was possible to compare the documented silver eel escapement with the modelled potential silver eel escapement. Resulting model predictions were close to actually monitored escapement numbers, which were distinctly lower than reference escapement values for the same freshwater system given in the implementation report of the German Eel Management Plans. Applying different commercial and recreational catch scenarios revealed the sensitivity of the model. The results show the potential of the GEM II and highlight the importance of high-quality input data to use model predictions as the basis for management measures

Ontogenetic loops in habitat use highlight the importance of littoral habitats for early life-stages of oceanic fishes in temperate waters

General concepts of larval fish ecology in temperate oceans predominantly associate dispersal and survival to exogenous mechanisms such as passive drift along ocean currents. However, for tropical reef fish larvae and species in inland freshwater systems behavioural aspects of habitat selection are evidently important components of dispersal. This study is focused on larval Atlantic herring (Clupea harengus) distribution in a Baltic Sea retention area, free of lunar tides and directed current regimes, considered as a natural mesocosm. A Lorenz curve originally applied in socio-economics to describe demographic income distribution was adapted to a 20 year time-series of weekly larval herring distribution, revealing size-dependent spatial homogeneity. Additional quantitative sampling of distinct larval development stages across pelagic and littoral areas uncovered a loop in habitat use during larval ontogeny, revealing a key role of shallow littoral waters. With increasing rates of coastal change, our findings emphasize the importance of the littoral zone when considering reproduction of pelagic, ocean-going fish species; highlighting a need for more sensitive management of regional coastal zones

Linked Data Supported Content Analysis for Sociology

Philology and hermeneutics as the analysis and interpretation of natural language text in written historical sources are the predecessors of modern content analysis and date back already to antiquity. In empirical social sciences, especially in sociology, content analysis provides valuable insights to social structures and cultural norms of the present and past. With the ever growing amount of text on the web to analyze, also numerous computer-assisted text analysis techniques and tools were developed in sociological research. However, existing methods often go without sufficient standardization. As a consequence, sociological text analysis is lacking transparency, reproducibility and data re-usability. The goal of this paper is to show, how Linked Data principles and Entity Linking techniques can be used to structure, publish and analyze natural language text for sociological research to tackle these shortcomings. This is achieved on the use case of constitutional text documents of the Netherlands from 1884 to 2016 which represent an important contribution to the European cultural heritage. Finally, the generated data is made available and re-usable as Linked Data not only for sociologists, but also for all other researchers in the digital humanities domain interested in the development of constitutions in the Netherlands

Status of Biodiversity in the Baltic Sea

The brackish Baltic Sea hosts species of various origins and environmental tolerances. These immigrated to the sea 10,000 to 15,000 years ago or have been introduced to the area over the relatively recent history of the system. The Baltic Sea has only one known endemic species. While information on some abiotic parameters extends back as long as five centuries and first quantitative snapshot data on biota (on exploited fish populations) originate generally from the same time, international coordination of research began in the early twentieth century. Continuous, annual Baltic Sea-wide long-term datasets on several organism groups (plankton, benthos, fish) are generally available since the mid-1950s. Based on a variety of available data sources (published papers, reports, grey literature, unpublished data), the Baltic Sea, incl. Kattegat, hosts altogether at least 6,065 species, including at least 1,700 phytoplankton, 442 phytobenthos, at least 1,199 zooplankton, at least 569 meiozoobenthos, 1,476 macrozoobenthos, at least 380 vertebrate parasites, about 200 fish, 3 seal, and 83 bird species. In general, but not in all organism groups, high sub-regional total species richness is associated with elevated salinity. Although in comparison with fully marine areas the Baltic Sea supports fewer species, several facets of the system's diversity remain underexplored to this day, such as micro-organisms, foraminiferans, meiobenthos and parasites. In the future, climate change and its interactions with multiple anthropogenic forcings are likely to have major impacts on the Baltic biodiversity

Proposal For The Stratification Of The Baltic Sea For The Baltic International Trawl Survey

No abstracts are to be cited without prior reference to the author.Different national demersal trawl surveys are carried out in different parts of the Baltic Sea since 1962. These national surveys of the different countries were planned regarding the special scientific interests of the institutes. The results of these surveys were used to calculate indices of the year class strength of cod and other species. The estimated indices were used as tuning variables in the VPA, to assess the discards in the commercial fishery and the total mortality. Furthermore, these values were used as recruitment index, for estimating the food consumption of young cod,-for estimating the maturity ogive, and for quantifying the exchanges between both Baltic cod stocks. The first attempts to co-ordinate the different national surveys were carried out 1985 and were continued in the following years with different intensity in the following years. Besides the standardization of the gears used and the inter-calibrations between the national and the new standard gear a common survey design is necessary. The development of the standard gears and the inter-calibrations of the gears were carried out by an EU funded study project. The goal of the analyses presented is the optimization of the relationship between the possible amount for the surveys (vessel days, man power, . ..) and the accuracy of the estimated indices. Using the available data from the BITS database the variance structures of the CPUE (catch per hour) were analysed in the different sub-divisions. The aim of the analyses was to find parameters which are correlated with the species density and the variance structure of the CPUE. These results are the basis for the development of the stratified survey design with the goal: the optimization of the relationship between the possible amount for the surveys (vessel days, man power, . ..) and the accuracy of the estimated indices

Exchanges Between The Western And Eastern Baltic Cod Stocks Using The Lenght Distributions Of Trawl Surveys

No abstracts are to be cited without prior reference to the author.By investigations of the microstructure of otoliths from juvenile cod which were caught in the Bomholm Sea (eastern Baltic cod stock) it could be proved that a part of these individuals must be spawned in the Kieler or Mecklenburger Bight (western Baltic cod stock) (Oeberst & Bottcher 1998). The possibility of the transport of different development stages of cod within the about 100 days of the pelagic life phase were confirmed by water transport model calculations (Hinrichsen et al. 1999)

Fecundity Of Baltic Cod Differences Between Ices Sub-Divisions And Variations From 1993 To 1999

No abstracts are to be cited without prior reference to the author.About 1500 gonads of Baltic cod were analysed for estimating the absolute and relative individual fecundity. The female cods were mainly sampled in the Belt Sea, ICES Subdivision (SD) 22 and in the Arkona Sea, SD 24. Additional samples were also taken in adjacent areas, in the Kattegat, SD 21, and in the Bornholm Sea, SD 25. The investigations started in 1992 and until 1999 cruises were carried out to catch female cods in the different sub-divisions every year. The age of the female cods varied from 1 to 11 years. The minimum total length was 21 cm. The largest cod had a total length of 116 cm. The gonads were prepared and preserved in formalin – seawater – solution (4%) and the number of eggs in a gonad was estimated using the method as described by Bleil and Oeberst (1993). Besides the total length the total body weight and further parameters were used for describing the variability of the absolute and relative individual fecundity. A further focus of the analyses is the comparison of the individual fecundity in the different sub-divisions of the Baltic Sea. These results can be important for the stock assessment and also for the separation of both the Baltic cod stocks. Since from 1992 to 1999 very different year class strengths of cod have been observed in the Baltic Sea it was also analysed whether significant variations of the individual fecundity existed from year to year or the individual fecundity was comparable in all years. The analyses showed that the gonadosomatic index is a useful parameter for assessing the physiological status of the maturity development within the maturity stage IV. Furthermore, it could be shown that the developments of the individual fecundity of the western and eastern Baltic cod stocks were different. In contrast to the stable individual fecundity of the western cods the absolute and relative fecundity of the eastern repeat spawners increased from 1993 to 1999, significantly. The reason of this development seems to be the dramatic decrease of the eastern cod stock. and the more successful reproduction of cods that produce oocytes with a lower dry weight in combination with a higher relative fecundity

Relations Between The Year Class Strength Of The Western Bal Tic Cod And Inflow Events In The Autumn

No abstracts are to be cited without prior reference to the author.The year class strength of the western Baltic cod stock varied considerably in the last years. After a strong year class 1994 a very low year class 1995 followed. Stronger year classes growing up again 1996 and 1997 In the following paper possible reasons for this fluctuation are analysed. Experiments according to spawning activities of captive cod under controlled condition in a marine hatchery suggested, that the year class strength is also influenced by the body condition (energetic status) of the females at the beginning of spawning activities. Furthermore it was possible to demonstrate, that the body condition influences the portion of oocytes in the gonads which is really spent in the spawning season. The investigations showed additionally that the fertilisation rate of spawned eggs is also dependent of the body condition of female cod. Following these results the relations between the fluctuating year class strength of cod in the western Baltic Sea and the temporal shift of the annual maturity development as well as the different portion of females, which takes part in the spawning activities, were analysed. It seems to be that inflow events in the autumn cause temporal shifts of annual maturity development and changes in the portion of really spawning individuals in the following spnng