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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Vertically Resolved Prey-Selectivity of Baltic Herring (<em>Clupea harengus</em> L.) and Sprat (<em>Sprattus sprattus</em> L.)
No full textFischereifangtechnik zur Verringerung des Beifangs von Schweinswalen und Seevögeln in der Ostsee: Stellnetzmodifikation und alternatives Fanggerät Fischfalle
No full textGillnets are the main fishing gear for small scale fisheries (SSF) globally. They are affordable, easy to use, have a well-adjustable size selectivity and most importantly a high catch efficiency for their target species. In recent times, they are increasingly criticized for resulting in a significant amount of bycaught marine mammals, diving seabirds, and turtles, threatening many of those megafauna species. Gillnets have the highest bycatch intensity of all fishing gears for these taxa. In the Baltic Sea, gillnet fishing is used to fish i.a. cod (Gadus morhua), herring (Clupea harengus), turbot (Scophthalmus maximus), and plaice (Pleuronecta platessa). It causes considerable bycatch of harbour porpoises (Phocoena phocoena) and one the highest gillnet bycatch rates worldwide for diving seabirds in that sea basin. Several of these bird species and one of the two harbour porpoise sub-populations are classed as endangered and considered particularly threatened by gillnet bycatch. Baltic European Union Member States have legal obligations to mitigate the bycatch of these species.
This thesis focusses on bycatch mitigation approaches for the Baltic Sea. It starts from the assumption that gillnet bycatch is not solvable by one single technical solution. Rather, a “toolbox" of different measures is required.
In line with the toolbox thinking, the thesis took a two-pronged approach: In Part A, an acoustic device for mitigating western Baltic harbour porpoise bycatch in gillnet fishing was tested. In Part B, several alternative gears to gillnets were assessed through a literature review and discussions with gear technologists and fishers. Fish pots were identified as the most suited alternative for Baltic SSF. Cod pots (fish pots for targeting cod) were then developed further to increase their catch efficiency.
In Part A (Paper I), an improvement of the cetacean bycatch reduction technology pinger (acoustic deterrent devices attached to gillnets), the “Porpoise ALert” (now marketed as “porpoise-PAL” by manufacturer F3 Maritime Technology, “PAL” hereafter), was tested. Previous pingers emit artificial sounds with no biological significance for cetaceans. Concerns with view to their effectivity and other non-intended effects detrimental to cetaceans, such as habitat exclusion, have been raised. The PAL has been developed to avoid the pingers’ adverse effects. It is an acoustic device which emits a natural aversive communication signal of western Baltic harbour porpoises.
Central question in Part A was, if the PAL effectively reduces western Baltic harbour porpoises’ bycatch in commercial gillnet fisheries. A fisheries trial was undertaken with three commercial gillnet vessels conducting 778 trips during their standard gillnet fishing operations from 2014 to 2016. The bycatch probabilities of 1,120 PAL-equipped gillnet strings and of 1,529 simultaneously set control strings with no PAL-devices were compared.
In total, 18 harbour porpoises were bycaught in control strings, and five harbour porpoises were taken as bycatch in strings equipped with PALs. Using a generalised linear mixed model (GLMM), it is shown that PAL usage significantly reduces western Baltic harbour porpoise bycatch by 79.7% when spaced with maximum distance of 200 m in between PAL.
The results of Part A further revealed that increasing the distance between PAL-devices to 210 m reduces their bycatch reduction effect to 64.9 %. This adds to findings of studies investigating pingers that distance between acoustic devices is an important factor influencing their bycatch mitigation effect.
No indications were found that the PAL reduces target species catch – an important factor for the uptake of the PAL by gillnet fisheries. The fact that the PAL is currently used by over 100 German SSF vessels underlines the validity of this finding. In conclusion, the PAL significantly reduces harbour porpoise bycatch in gillnets deployed in the western Baltic Sea. It can be used for effective bycatch mitigation in that Sea region, with a comparable efficiency as conventional pingers.
The PAL is the first acoustic device which mitigates bycatch of a cetacean species using the species’ own communication signals. It is an important proof-of-concept opening a distinct new cetacean gillnet bycatch mitigation pathway to be explored in further studies.
While PAL and conventional pingers were not directly compared in this study, it is discussed if the PAL could have comparable or similar detrimental effects. This includes a discussion of a Before-After-Control-Impact (BACI) study of harbour porpoise distribution in the area where PAL are now being used by fishers. Results indicate that habitat displacement does not occur. Evidence is limited though and the BACI study also does not assess possible detrimental habituation to the PAL signal. Habitat displacement and habituation in relation to the PAL require further investigation.
Part B focussed on gear alternatives with lower bycatch risk compared to gillnets. Most gear alternatives are not widely used by SSF in the Baltic Sea because they are not as suitable for small vessels, and they often have low catch efficiency and thus lower economic revenue. They have furthermore lower versatility compared to gillnets. Some can only be deployed in certain areas, for instance only from the coast.
In a first step to find the most suitable alternative, gear alternatives to gillnets were systematically assessed against operational, economic, as well as environmental criteria. Information was collated through a literature review and discussions with gear technologists and professional fishers. The following gears were assessed: pneumatically liftable large scale traps, so-called “pontoon traps”; hook-based gears such as longlines and jigging machines; the active gear Danish seine; and fish pots. Fish pots were identified as the most appropriate alternative gear for Baltic SSF. They offer high versatility, delivery of high-quality catch, and can be used from the smallest fishing vessels. And most importantly in this context they have a low risk of seabird and harbour porpoise bycatch.
The key aim of the studies undertaken in Part B was to improve the catch efficiency of fish pots for cod fishing. This would increase their economic viability and thus their uptake by commercial fisheries. In a literature review of cod pot-catch efficiency studies, influencing factors of pot catch efficiency were identified. This review revealed that fish pot entrances are a key influencing factor. They should ideally lead to easy entry of fish approaching a pot and prohibit their subsequent escape. However, this is rarely attained.
The review further showed that most pot-catch efficiency studies are field trials comparing catches. During these trials, different fish pot types are used under the same conditions in one fishery. Their catch-per-unit-effort (CPUE), i.e., the fish caught per number of pots fished, is the main metric by which their catch efficiency is compared. They do not provide any information about how the target species interact with the fish pots. This information is essential for efficient gear development, including the increase of pot catch efficiency. Catch-comparisons have several other drawbacks, for instance varying fish densities around pots over time, or unknown size and condition of approaching fish.
To avoid these limitations of catch comparison studies, a new and more effective study method was developed: the net pen-based observation method. It allows direct comparison of the behaviour of fish in relation to pot characteristics and consists of physical and statistical elements. The physical setup consists of a custom-made fish pot with two easily exchangeable entrances and an underwater video system with long term recording capabilities. The video system has infrared light (IR) capabilities which allows for unobtrusive day- and night-time observation (Paper II). It allows recording all interactions of fish with the pot entrances, including successful as well as unsuccessful fish entry- and exit attempts. Pot and video system are placed in a net pen, in which fish can be set and their interactions with the pot observed. The statistical components of the method include an ethogram for fish-pot entrance interactions for describing and assessing observed fish interaction with the entrances. Observed entrance catch efficiency – a function of entry- as well as of exit probability through an entrance – is quantified and compared using a bundle of two further analysis methods. The statistical methods permit to “dissect” the event chains of fish interactions with the entrance. The reasons for the observed differences between the entrances can thus be pinpointed. For each experimental trial, the same number of fish are set into the net pen, assuring a constant fish presence at the pot for each trial.
The target species for pot catch efficiency improvements was cod, one of the main target species of Baltic Sea SSF at that time. Two studies were undertaken using this method to improve understanding of cod–pot entrance interaction and to then capitalize on that knowledge to improve cod pots. In the first study (Paper III), the influence of basic parameters of cod pot entrances on catch efficiency was assessed. Parameters analyses comprised funnel presence, funnel length and funnel colour, and funnel type. Fundamental findings were made which enhance the understanding of cod-pot entrance interactions: Foremost, a pronounced diurnal pattern of entrance interactions with few nocturnal entrance passages could be revealed. Also, an unobstructed view of the pot inside or pot outside when cod try to enter or exit the pot, was identified as key factor for entrance passage. Regarding the parameters analysed, it was shown that funnel presence increases cod entrance encounter rate by enlarging the outer opening of the entrance and channelling approaching cod towards the entrance opening. At the same time funnels decrease exit rates, assumedly by deflecting cod away from the inner entrance opening and by reducing the area in which the exit is perceptible to cod inside the pot. Funnels are thus crucial for maximising cod pot catch efficiency. Increasing funnel length further reduces the area inside the pot from which cod can see the exit unobstructed and may further deter cod from exiting by the longer passage length. Funnel netting colour (colours tested: white, green, and transparent netting material) influences entrance passage rates, with significantly higher entrance passage rates for a transparent funnel.
Overall, the study results indicate that cod–pot interactions are primarily guided by vision. This improved understanding can directly be used to enhance cod pot fishing strategies. For example, traditional olfactory bait such as cut herring has been shown to lose most of its attracting effect in less than two hours. Cod pots baited with such bait thus should assumedly perform better when set during day and at latest two hours before sunset.
The aim of the second study (Paper IV) was to increase pot catch efficiency by reducing cod pot exit rate without also reducing cod entry rate. Based on the finding of the first study that cod primarily use vision to navigate cod pot entrances, the “Acrylic fingers” (AF) were developed. AF are a novel kind of “fish-retention devices" (FRDs) of a finger like type, so-called “triggers”. In contrast to precursor triggers, AF are made of transparent acrylic glass and are hence almost invisible under water.
The AF were compared to a conventional, commercially available trigger, named “Neptune fingers” (NF) that is clearly visible under water. Both trigger types significantly reduced exit rates compared with an entrance without triggers. However, the rigid NFs also reduced entry rates by visually deterring cod. In contrast, AF did not result in changes of entry rates compared to an entrance without triggers. AFs have higher entry-to-exit ratios than entrances without AF and therefore improve catch efficiency. They almost double it compared to entrances without AF. Moreover, combining AFs with funnels further increased catch efficiency.
Transparent acrylic triggers present a promising innovative approach to increase catch efficiency of cod pots, as well as allowing alternative entrance designs to e.g. support multispecies pot designs. They could increase the uptake of pots in commercial fisheries as environmentally low-impact gear.
Concluding Part B, the findings made in the two studies show the net pen-based observation method’s advantages compared to prior catch comparison studies. With the method, an in-depth understanding of how different entrance parameters affect cod–pot entrance interactions is obtained. It can be used to develop and evaluate improved entrances. It was used to deliver important insights into cod–pot entrance interactions, laying the groundwork for further structural entrance improvements. It also led to the development of a new trigger type which increased the retention efficiency without reducing entry rates. Thus, further pot gear development studies will benefit from using this method.
The findings of Part B also have direct management relevance. Due to the critical conservation status of the Baltic proper harbour porpoise sub-population, gillnets will be prohibited in the future in certain protected areas of the Baltic Sea. These prohibitions will be a strong restriction for Baltic SSF. Fishers will have to switch to alternative passive gear (such as fish pots), if they want to continue fishing in the protected areas. The findings on diurnal entrance passage differences and the improved understanding of entrance interactions can already facilitate fishers’ gear switch to fish pots.
This thesis contributes to the bycatch mitigation “toolbox” and thus addresses the divide between fisheries and nature conservation objectives in the Baltic Sea. The PAL concept as well as the developed pot study method and its findings can furthermore be directly or perspectively transferred to the bycatch mitigation “toolboxes” of other sea regions.Stellnetze sind das weltweit wichtigste Fanggerät der kleinen Küstenfischerei („small scale fisheries“ (SSF)). Sie sind kostengünstig und einfach einzusetzen, ihre hohe Größenselektivität ist gut einstellbar und vor allem weisen sie eine hohe Fangeffizienz für ihre Zielarten auf. In jüngster Zeit wird ihre Verwendung zunehmend kritisiert, denn sie führen zu einem erheblichen Beifang von Meeressäugern, tauchenden Seevögeln sowie marinen Schildkröten, den Fortbestand vieler dieser Megafaunaarten bedrohend. Stellnetze haben die höchste Beifangintensität aller fischereilichen Fanggeräte für diese Taxa. In der Ostsee werden Stellnetze u. a. zum Fang von Dorsch (Gadus morhua), Hering (Clupea harengus), Steinbutt (Scophthalmus maximus) und Scholle (Pleuronecta platessa) verwendet. Die Stellnetzfischerei führt dort zu einem erheblichen Beifang von Schweinswalen (Phocoena phocoena) sowie zu einer der höchsten Stellnetzbeifangraten für tauchende Seevögel weltweit. Mehrere dieser Seevogelarten sowie eine der beiden dortigen Schweinswalunterpopulationen gelten als gefährdet und werden als besonders durch Stellnetzbeifang bedroht angesehen. Die baltischen EU-Mitgliedsstaaten sind rechtlich dazu verpflichtet, die Beifänge dieser Arten zu begrenzen.
Ziel dieser Dissertation ist die Entwicklung neuer Ansätze zur Beifangverringerung. Ausgangspunkt ist die Annahme, dass Stellnetzbeifang nicht durch einen einzelnen technischen Lösungsansatz ausreichend vermindert werden kann. Zielführend ist vielmehr die Entwicklung eines Werkzeugkastens unterschiedlicher Maßnahmen.
In Teil A dieser Dissertation (Paper I) wurde der “Porpoise ALert” (jetzt vom Hersteller F3 Maritime Technology unter dem Namen “porpoise-PAL” vertrieben; “PAL” hiernach) als eine Weiterentwicklung der sog. „Pinger“-Technologie getestet. Pinger sind an Stellnetze zu befestigende Geräte zur akustischen Vergrämung von Walen, Delfinen und Schweinswalen. Dazu senden herkömmliche Pinger künstliche Geräusche ohne biologische Bedeutung aus. Es bestehen wissenschaftliche Bedenken im Hinblick auf ihre Wirksamkeit und andere unbeabsichtigte Auswirkungen auf die damit zu schützenden Meeressäuger, wie zum Beispiel weiträumige Habitatvertreibung. Ziel der Pinger-Weiterentwicklung PAL war die Vermeidung dieser negativen Pingereffekte. Dazu sendet der PAL natürliche, aversive Kommunikationssignale von Schweinswalen der westlichen Ostsee aus.
Leitfrage von Teil A war, ob der PAL den Beifang von Schweinswalen der westlichen Ostsee in der kommerziellen Stellnetzfischerei wirksam reduziert. Dazu wurde ein Fischereiversuch mit drei Fahrzeugen der kommerziellen Stellnetzfangflotte durchgeführt, die von 2014 bis 2016 insgesamt 778 Tages-Fangreisen im Rahmen ihrer üblichen Fischereiaktivität durchführten. Die Beifangwahrscheinlichkeit von insgesamt 1.120 PAL-ausgestatteten Stellnetzfleeten sowie 1.529 Kontrollfleeten ohne PAL wurde verglichen.
Über die gesamte Versuchsdauer wurden insgesamt 18 Schweinswale in Kontrollfleeten sowie fünf Schweinswale in PAL-Fleeten beigefangen. Mittels eines „generalised linear mixed model” (GLMM) wurde nachgewiesen, dass PAL den Beifang von Schweinswalen der westlichen Ostsee um 79,7% signifikant verringern, wenn der Abstand zwischen an den Fleeten aufeinanderfolgenden PAL nicht mehr als 200 m beträgt.
Die Studie von Teil A zeigt des Weiteren, dass eine Erhöhung der Distanz zwischen aufeinanderfolgenden PAL auf 210 m den Beifang-verringernden Effekt auf 64.9% verringert. Diese Erkenntnis unterstützt die Ergebnisse früherer Pingerstudien, die zeigten, dass die Distanz zwischen aufeinanderfolgenden Pingern ein wichtiger Einflussfaktor auf deren Beifang-verringernden Effekt ist.
In der Teil-A Studie wurden keine Hinweise darauf gefunden, dass PAL die Stellnetzfängigkeit auf die Zielarten verringert – ein wichtiges Ergebnis für den Einsatz von PAL in der Stellnetzfischerei. Die Tatsache, dass über 100 deutsche Stellnetzfahrzeuge in der westlichen Ostsee die PAL mittlerweile schon seit mehreren Jahren einsetzen, belegt dies. Somit kann geschlussfolgert werden, dass der PAL Stellnetz-Schweinswalbeifang in der westlichen Ostsee signifikant verringert. Der PAL kann für effektive Schweinswalbeifangvermeidung in dieser Region genutzt werden, mit vergleichbarer Effektivität zu konventionellen Pingern.
Der PAL ist das erste akustische Gerät, dass den Beifang von Schweinswalen mittels ihrer eigenen kommunikativen Lautäußerungen verringert. Er stellt somit ein wichtiges „proof-of-concept” dar und eröffnet damit einen neuen Ansatz zur Beifangvermeidung von Walen, Delfinen und Schweinswalen.
Obwohl PAL und konventionelle Pinger in der Studie von Teil A nicht direkt verglichen wurde, wird argumentativ erörtert, ob der PAL vergleichbare oder sogar gleichartige schädliche Effekte bewirken könnte. Bei einer Before-After-Control-Impact (BACI) Studie von Schweinswalverbreitung in dem Gebiet, in dem der PAL seit mehreren Jahren eingesetzt wird, wurden keine Belege für Habitatsvertreibung gefunden. Die Belege der BACI-Studie sind jedoch nicht stark aussagekräftig und eine potentiell schädliche Habituation der Schweinswale an das PAL-Signal konnte nicht untersucht werden. Somit bedürfen mögliche Habitatsvertreibung und Habituation weiterer Untersuchungen, um ausgeschlossen werden zu können.
In Teil B der Dissertation lag der Fokus auf möglichen Fanggerätealternativen mit geringerem Beifangpotential im Vergleich zu Stellnetzen. Die meisten bekannten Fanggerätealternativen werden von der kleinen Küstenfischerei der Ostsee nicht genutzt, da sie für den Einsatz von kleinen Fischereifahrzeugen weniger geeignet sind. Auch haben sie meistens eine geringere Fangeffizienz und ihr Einsatz ist somit ökonomisch weniger rentabel. Des Weiteren weisen sie oft eine geringere Einsatzvielseitigkeit auf: Manche Fanggerätealternativen können nur in bestimmten Gebieten eingesetzt werden, zum Beispiel nur in flachen Küstengewässern.
Im ersten Schritt wurde zur Identifikation des als Stellnetzalternative am besten geeigneten Fanggeräts, Fanggerätealternativen systematisch nach operativen, wirtschaftlichen und ökologischen Kriterien bewertet. Grundlage für die Bewertung war eine Literaturrecherche sowie Diskussionen mit Fischereifangtechnikern und professionellen Fischern. Die folgenden Fanggeräte wurden analysiert: pneumatisch-hebbare Großreusen, sog. „Ponton-Fallen“, Fanggeräte mit Haken wie Langleinen und sog. „Jigging-Maschinen“, das aktive Fanggerät Snurrewade oder „Danish seine“ sowie Fischfallen. Letztere wurden als beste Stellnetzalternative für die kleine Küstenfischerei der Ostsee identifiziert. Sie sind ebenso vielseitig einsetzbar, liefern den hochwertigsten Fang und können selbst von kleinsten Fischereifahrzeugen eingesetzt werden. Und im Kontext dieser Dissertation entscheidend: Fischfallen haben ein geringes Risiko für Beifang von Schweinswalen sowie tauchender Seevögel.
Wichtigstes Ziel der im zweiten Schritt in Teil B unternommenen Studien war, die Fangeffizienz von Fischfallen bei der Dorschfischerei zu erhöhen. Denn damit würde ihre Wirtschaftlichkeit verbessert werden und somit auch ihre Aufnahmewahrscheinlichkeit durch die Stellnetzfischerei. Mittels einer Literaturstudie von Fischfallen-Fangeffizienzstudien wurden Einflussfaktoren identifiziert und bewertet. Fischfalleneingänge wurden dabei als zentraler Einflussfaktor herausgearbeitet. Fischfalleneingänge sollen idealerweise den Eintritt von sich der Fischfalle nähernden Fischen in die Fischfalle möglichst erleichtern und einen darauffolgenden Austri
Activity pattern of the harbour por-poise Phocoena phocoena in the coastal waters of Fyn (Denmark)
No full textThe harbour porpoise Phocoena phocoena is the only cetacean species, which occurs regularly
in the Baltic Sea. Its abundance has decreased dramatically within the last several
decades, so that it was classified as “Critically Endangered” in the Baltic Sea in 1996. In
order to recover the harbour porpoise population, it is protected in the EU waters by several
national and international agreements. These agreements demand the immediate creation
of marine protected areas for the harbour porpoise, which is only possible with the
knowledge about its abundance, distribution and activity pattern. In this study, the activity pattern of the harbour porpoise in the coastal waters of Fyns
Hoved, Denmark was investigated acoustically with C-PODs as well as visually with a theodolite.
C-PODs are passive acoustic monitoring devices, which can automatically detect
harbour porpoises by recording the echolocation clicks they produce. 10 C-PODs were deployed
throughout 24 hours over a period of five weeks in Fyns Hoved. The visual observation
was conducted during the day on an around 19 m high cliff in the study area. The results have shown a diel as well as a geographical activity pattern of the detected
harbour porpoises. More harbour porpoises were detected during night and evening than
during morning and day. The detections of harbour porpoises were significantly higher at the
deeper C-POD stations than at the remaining, shallow stations during the evening. The comparison
of the acoustic with the visual harbour porpoise sightings have demonstrated that
the ability to sight harbour porpoises visually is limited to a maximum distance to the observer
of between 266 m and 325 m. These findings have extended the current knowledge about the diel activity pattern of the
harbour porpoise. It can be hypothesized that the harbour porpoise may be feeding pelagic
prey in deeper waters at night, while it may be hunting mainly benthic prey in shallow waters
during the day. Its hunting method during the day could be mainly visually or with the
special feeding behavior. During this “bottom-grubbing”, the harbour porpoise scans the
sea bottom by swimming in a vertical position with the mouth close to the bottom. The visual
hunting as well as the “bottom-grubbing” would both have the consequence that the
harbour porpoise could not be detected by the C-PODs. These findings should be taken
into consideration when planning further monitoring studies of the harbour porpoise. However,
more research on this topic needs to be undertaken before a general conclusion can
be made. It is recommended to compensate this potential limitation of the C-PODs during
the day with visual monitoring methods to secure precise data collection.Der Schweinswal Phocoena phocoena ist die einzige Walart, die in der Ostsee regelmäßig
vorkommt. Seine Abundanz hat innerhalb der letzten Jahrzehnte dramatisch abgenommen,
so dass er seit 1996 in der Ostsee als „stark gefährdet“ eingestuft wird. Damit die
Schweinswalpopulation sich wieder erholen kann, werden die in den EU-Gewässern lebenden
Schweinswalen durch verschiedene nationale und internationale Abkommen geschützt.
In diesen Abkommen wird die sofortige Einrichtung von Meeresschutzgebieten für
den Schweinswal gefordert, was jedoch nur möglich ist, wenn seine Abundanz, sein Vorkommen
und seine Aktivitätsmuster bekannt sind. In dieser Studie wurde das Aktivitätsmuster von Schweinswalen sowohl akustisch mit C-
PODs als auch visuell mithilfe eines Theodolits in den Küstengewässern von Fyns Hoved
in Dänemark untersucht. C-PODs sind passive akustische Monitoring Geräte, die
Schweinswale erkennen, indem sie deren Echoortungsklicks aufnehmen. 10 C-PODs wurden
über einen Zeitraum von fünf Wochen 24 Stunden lang in den Küstengewässern von
Fyns Hoved ausgebracht. Die visuelle Beobachtung fand tagsüber auf einer ca. 19 m hohen
Klippe im Untersuchungsgebiet statt. Die Ergebnisse zeigen sowohl ein Tag/Nacht- als auch ein geographisches Aktivitätsmuster.
Es wurden mehr Schweinswale am Abend und in der Nacht als am Morgen und am
Tag registriert. Am Abend wurden häufiger Schweinswale an den tieferen C-POD Stationen
entdeckt als an den flacheren Stationen. Der Vergleich zwischen der akustischen und
der visuellen Schweinswalsichtungen hat gezeigt, dass die Beobachtung von Schweinswalen,
auf eine maximale Entfernung von 266 m bis 325 m zum Beobachter beschränkt ist.
Die Erkenntnisse haben den aktuellen Wissensstand über das Aktivitätsmuster von
Schweinswalen erweitert. Es ist anzunehmen, dass der Schweinswal nachts vor allem
pelagische Beute im tieferen Wasser frisst, während er am Tag hauptsächlich benthische
Beute im flachen Wasser jagt. Sein Jagen am Tag könnte mehrheitlich visuell basiert sein
oder ist mit einem speziellen Fressverhalten zu erklären, dem „bottom-grubbing“. Dabei
„tastet“ der Schweinswal den Meeresboden mithilfe seines Sonars ab, in dem er vertikal
mit der Schnauze nah über den Meeresboden schwimmt. Sowohl das visuelle Jagen als auch „bottom-grubbing“ haben zur Folge, dass der Schweinswal nicht von C-PODs erkannt
werden kann. Diese Erkenntnisse sollten bei der Planung zukünftiger Monitoringstudien mit
Schweinswalen berücksichtigt werden. Dennoch muss mehr Forschung zu diesem Thema
durchgeführt werden, bevor allgemeine Schlussfolgerungen gemacht werden können. Es
wird empfohlen, dass die möglichen Einschränkungen von C-PODs während des Tages mit visuellen Monitoringmethoden ausgeglichen werden, um eine genaue Datensammlung
zu gewährleisten
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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