Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Mosselbanken en oesterbanken op droogvallende platen in de Nederlandse kustwateren in 2016: bestand en arealen
Ende, D. van den; Troost, K. ; Asch, M. van; Brummelhuis, E. ; Zweeden, C. van - \ 2016
Yerseke : Wageningen Marine Research (Wageningen Marine Research report C109/16) - 42
mytilus edulis - mossels - crassostrea gigas - oesters - kustwateren - monitoring - nederland - mussels - oysters - coastal water - netherlands
Als onderdeel van het onderzoeksprogramma WOT (Wettelijke Onderzoeks Taken) worden jaarlijks door Wageningen Marine Research (WMR, voorheen IMARES) de mossel- en oesterbestanden in de Nederlandse kustwateren geïnventariseerd. Voorliggend rapport omvat de resultaten van de inventarisatie van het areaal en bestand aan mosselen (Mytilus edulis) en Japanse oesters (Crassostrea gigas) op de droogvallende platen van de Waddenzee, Oosterschelde en de Westerschelde. Het onderzoek is uitgevoerd in opdracht van het Ministerie van Economische Zaken en is één van de schelpdierinventarisaties die jaarlijks door WMR wordt uitgevoerd in samenwerking met het ministerie. De uitkomsten zijn van belang voor het beleid voor de schelpdiervisserij en vormen daarbij een bron van informatie voor verdere ecosysteem- en effectstudies.
River export of nutrients to the coastal waters of China: the MARINA model to assess sources, effects and solutions
Strokal, Maryna - \ 2016
Wageningen University. Promotor(en): Carolien Kroeze, co-promotor(en): S. Luan; Lin Ma. - Wageningen : Wageningen University - ISBN 9789462579729 - 226
cum laude - nutrients - rivers - coastal water - models - eutrophication - coastal areas - water pollution - china - voedingsstoffen - rivieren - kustwateren - modellen - eutrofiëring - kustgebieden - waterverontreiniging

Rivers export increasing amounts of nitrogen (N) and phosphorus (P) to the coastal waters of China. This causes eutrophication problems that can damage living organisms when oxygen levels drop and threaten human health through toxic algae. We know that these problems result from human activities on land such as agriculture and urbanization. However, the relative importance of these human activities for river export of nutrients to Chinese seas is not well studied. There are two important issues that need further investigation: the relative importance of upstream pollution on downstream impacts and the relative importance of typical sources of nutrients in Chinese rivers that are often ignored in existing modeling studies.

My PhD thesis, therefore, aims to better understand trends in river export of nutrients to the coastal waters of China by source from sub-basins, and the associated coastal eutrophication. To this end, I developed the MARINA model: Model to Assess River Inputs of Nutrients to seAs. For this, I used the existing Global NEWS-2 model (Nutrient Export from WaterSheds) as a starting point.

I formulated five sub-objectives to achieve the main objective:

To analyze the original Global NEWS-2 model for river export of nutrients and the associated coastal eutrophication (Chapter 2);

To develop a sub-basin scale modeling approach to account for impacts of upstream human activities on downstream water pollution, taking the Pearl River as an example (Chapter 3);

To quantify the relative share of manure point sources to nutrient inputs to rivers at the sub-basin scale (Chapter 4);

To quantify the relative share of sources to river export of nutrients at the sub-basin scale (Chapter 5);

To explore optimistic futures to reduce river export of nutrients and coastal eutrophication in China (Chapter 6).

The study area includes rivers draining roughly 40% of China. This includes the most densely populated areas, and areas with intensive economic activities. The rivers include the Yangtze (Changjiang), Yellow (Huanghe), Pearl, Huai, Hai and Liao. In the MARINA model, the drainage areas of the large Yangtze, Yellow and Pearl rivers are divided into up-, middle- and downstream sub-basins. The principle of the sub-basin approach of MARINA is that nutrients from human activities are transported by tributaries to outlets of sub-basins and then to the river mouth (coastal waters) through the main channel. The model takes into account nutrients that are partly lost or retained during transport towards the river mouth. The model quantifies river export of nutrients by source from sub-basins for 1970, 2000 and 2050.

The main six findings of the MARINA results for China are:

Finding 1: Dissolved N and P export by Chinese rivers increased by a factor of 2-8 between 1970 and 2000;

Finding 2: The potential for coastal eutrophication was low in 1970 and high in 2000 in China;

Finding 3: Most dissolved N and P in Chinese seas is from middlestream and downstream human activities;

Finding 4: Manure point sources are responsible for 20-80% of dissolved N and P in Chinese rivers;

Finding 5: In the future, river export of nutrients may increase in the Global Orchestration (GO) scenario of the Millennium Ecosystem Assessment. Current policy plans (CP scenario) may not sufficient to avoid this increase;

Finding 6: In optimistic scenarios (OPT-1 and OPT-2), the potential for coastal eutrophication is low in 2050, mainly as a result of assumed full implementation of: (1) high recycling rates of animal manure (OPT-1 and OPT-2), and (2) high efficiencies of nutrient removal in sewage systems (OPT-2, see Figure 1).

Figure 1. Illustration of future scenarios for coastal water quality in China. GO is Global Orchestration of the Millennium Ecosystem Assessment and assumes environmental actions that are either absent or ineffective in reducing water pollution. CP is based on GO, but incorporates the “Zero Growth in Synthetic Fertilizers after 2020” policy. OPT-1 and OP-2 are optimistic scenarios that assume high nutrient use efficiencies in agriculture (OPT-1, OPT-2) and sewage (OPT-2).

My PhD thesis reveals novel insights for effective environmental policies in China. It shows the importance of manure point sources in water pollution by nutrients. Clearly, managing this source will likely reduce coastal eutrophication in the future. Furthermore, the implementation of advanced technologies is essential when dealing with urban pollution. My PhD thesis may also be useful for other world regions with similar environmental problems as in China. The new, sub-basin scale MARINA model is rather transparent and thus can be applied to other large, data-poor basins that may benefit from the allocation of effective management options. With this I hope to contribute to future availability of sufficiently clean water for next generations, not only in China, but also in other world regions.

Mosselbanken en oesterbanken op droogvallende platen in de Nederlandse kustwateren in 2015: bestand en arealen
Ende, D. van den; Brummelhuis, E.B.M. ; Zweeden, C. van; Asch, M. van; Troost, K. - \ 2016
Yerseke : IMARES (Rapport / IMARES C168/15) - 45 p.
mossels - oesters - kustwateren - biomassa - inventarisaties - aquatische ecosystemen - nederland - mussels - oysters - coastal water - biomass - inventories - aquatic ecosystems - netherlands
IMARES carried out mussel (Mytilus edulis) and oyster (Crassostrea gigas) stock assessments in the littoral areas of the Dutch Wadden Sea, Oosterschelde bay and Westerschelde estuary in 2015. Both surface bed area as well as total biomass stock were assessed. These surveys are part of the annual shellfish inventories, as commissioned by the Dutch Ministry of Economic Affairs (EZ) and carried out by IMARES, in collaboration with both the fisheries industry and the ministry of EZ. These surveys are conducted to aid policy makers with regard to the shellfish industry, and are an important source of information for further ecosystem studies.
Dynamiek van schelpdierbanken in de nederlandse kustzone
Kamermans, P. ; Goudswaard, P.C. ; Asch, M. van; Bos, O.G. - \ 2015
Yerseke : IMARES (Rapport / IMARES C186/15) - 31 p.
schaaldieren - dynamica - aquatische ecosystemen - kustgebieden - kustwateren - karteringen - nederland - shellfish - dynamics - aquatic ecosystems - coastal areas - coastal water - surveys - netherlands
Bestanden van mesheften, halfgeknotte stranschelpen en andere schelpdieren in de Nederlandse kustwateren in 2015
Troost, K. ; Perdon, K.J. ; Jol, J.G. ; Asch, M. van; Ende, D. van den - \ 2015
Yerseke : IMARES (Rapport / IMARES C143/15) - 37
schaal- en schelpdierenvisserij - visserij - schaaldieren - kustwateren - ensis - spisula - nederland - shellfish fisheries - fisheries - shellfish - coastal water - netherlands
De visserij op schelpdieren in de Nederlandse kustwateren heeft zich ontwikkeld van een vrije visserij tot een sterk gereguleerde visserij waarbij naast economische ook ecologische doelstellingen nagestreefd worden. In het kader van de uitvoering van dit beleid is een bestandsopname van Amerikaanse zwaardscheden (mesheften) (Ensis directus), halfgeknotte strandschelpen (Spisula subtruncata), en de overige veel voorkomende soorten met een potentieel belang voor visserij uitgevoerd.
Reguleringsmechanismen in het kustecosysteem van de Voordelta
Kooten, T. van; Jansen, H.M. - \ 2015
IJmuiden : IMARES (Rapport / IMARES C095/15) - 66
aquatische ecosystemen - benthos - voordelta - kustwateren - zuidwest-nederland - aquatische gemeenschappen - visserij - bodemfauna - rivieren - aquatic ecosystems - coastal water - south-west netherlands - aquatic communities - fisheries - soil fauna - rivers
Wordt het benthos in het Voordelta kustecosysteem gereguleerd door bottom-up of top-down gerelateerde processen, en hoe zal dit systeem reageren op de maatregelen om de bodemberoerende visserij uit te sluiten in het Bodembeschermingsgebied.
Vissen in de 12-mijlszone : inzetverandering visserij na introductie puls
Turenhout, M.N.J. ; Hamon, K.G. - \ 2015
Wageningen : LEI Wageningen UR (Nota / LEI 2015-100) - 12
pulsvisserij - pleuronectiformes - boomkorvisserij - visserijbeheer - kustwateren - noordzee - pulse trawling - beam trawling - fishery management - coastal water - north sea
Door de introductie van puls-techniek lijkt een ruimtelijke verplaatsing van de kottervisserij plaats te vinden (door economische overwegingen van vissers) naar de kustwateren (12-mijlszone). Door de efficiëntere tongvangsten lijkt het niet meer noodzakelijk om ver uit de kust te vissen. Deze verschuiving kan mogelijke risico’s met zich meebrengen door hogere visintensiteit in het kustgebied. Door het Ministerie van EZ is aan LEI Wageningen UR gevraagd om een eventuele verschuiving van de platvisvisserij naar de kustzone (12-mijlszone) in beeld te brengen aan de hand van een QuickScan. Het doel van dit onderzoek is: Een goed beeld geven van de mogelijke toename van inzet (en de daarbij behorende consequenties) van de platvisvisserij in de 12-mijlszone bij de introductie van visserij met puls-techniek.
Het kokkelbestand in de Nederlandse kustwateren in 2015
Asch, M. van; Ende, D. van den; Brummelhuis, E.B.M. ; Zweeden, C. van; Troost, K. - \ 2015
IJmuiden : IMARES Wageningen UR (Rapport / IMARES Wageningen UR C111/15) - 44
kokkels - kustwateren - zeevisserij - visserijbeheer - visbestand - visstand - inventarisaties - nederland - natura 2000 - oosterschelde - westerschelde - waddenzee - clams - coastal water - marine fisheries - fishery management - fishery resources - fish stocks - inventories - netherlands - eastern scheldt - western scheldt - wadden sea
Onderzoeksinstituut IMARES heeft in opdracht van het ministerie van EZ in het voorjaar van 2015 het kokkelbestand (Cerastoderma edule) in de Waddenzee, de Oosterschelde en de Westerschelde geïnventariseerd. De inventarisatie wordt jaarlijks uitgevoerd om te kunnen bepalen hoeveel er gevist mag worden en is daarnaast ook van belang voor evaluatie van beheersmaatregelen en effectstudies in het kader van Natura 2000 en de natuurbeschermingswet. De kokkelbestandsopname wordt sinds 1990 uitgevoerd in de Oosterschelde en de Waddenzee, sinds 1992 in de Westerschelde en sinds 1993 in de Voordelta (als onderdeel van de bestandsopnamen van mesheften en halfgeknotte strandschelpen in de Nederlandse kustzone). Doel van deze inventarisaties ten behoeve van de visserij is het bepalen van de voorjaarsbestanden in deze gebieden, op basis waarvan een schatting wordt gemaakt van de oogstbare bestanden in september.
Aanwijzing nieuwe productiegebieden: Onderbouwing monstername sanitair programma
Dedert, M. ; Blanco Garcia, A. ; Poelman, M. - \ 2015
Yerseke : IMARES (Rapport / IMARES Wageningen UR C086/15) - 54
schaaldieren - schaal- en schelpdierenteelt - fytosanitaire maatregelen - fytosanitair beleid - monitoring - bemonsteren - waddenzee - zuidwest-nederland - noordzee - nederlandse wateren - kustwateren - shellfish - shellfish culture - phytosanitary measures - phytosanitary policies - sampling - wadden sea - south-west netherlands - north sea - dutch waters - coastal water
In dit rapport wordt een onderbouwing met aanbevelingen gepresenteerd van het sanitair monitoringsprogramma voor schelpdieren. De analyse is opgesplitst in de Waddenzee, (Zuidelijk) Deltagebied (Oosterschelde, Grevelingenmeer, Veerse Meer en Westerschelde) en Noordzee.
Waardekaarten Ridens & Recifs
Machiels, M.A.M. - \ 2015
IJmuiden : IMARES (Rapport / IMARES Wageningen UR C073/15) - 18
kaarten (charts) - kaarten - frankrijk - kustwateren - vergelijkend onderzoek - opbrengsten - visvangsten - schol - scophthalmus rhombus - tarbot - charts - maps - france - coastal water - comparative research - yields - fish catches - plaice - turbot
In dit rapport beantwoorden wordt een offerteaanvraag van de Nederlandse Vissersbond van 18 februari 2015 beantwoord waarin zij vroegen om waardekaarten en tabellen van de N2000 gebieden Ridens & Récifs voor de Franse kust.
Waardekaarten van: Outer Thames Estuary, Haisborough, Hammond and Winterton & Margate and Long Sands
Machiels, M.A.M. - \ 2015
IJmuiden : IMARES (Rapport / IMARES Wageningen UR C054/15) - 16
vissersschepen - engeland - kustwateren - kaarten - taxatie - demersale visserij - schol - tong (vis) - tarbot - raja - fishing vessels - england - coastal water - maps - valuation - demersal fisheries - plaice - dover soles - turbot
Dit rapport is geschreven in opdracht van VisNed. IMARES is gevraagd om waardekaarten en tabellen te leveren van alle bodem beroerende Nederlandse visserijschepen binnen de gebieden 1) Haisborough, Hammond and Winterton, 2) Margate and Long Sands voor de Engelse kust en 3) Outer Thames Estuary.
Wettelijke Onderzoek Taken WOT-05 Visserijonderzoek: Werksafspraken en werkplan 2015
Verver, S.W. - \ 2014
IJmuiden : Centrum voor Visserijonderzoek (CVO rapport 14.006)
visserijbeleid - visserij - zeevisserij - kustwateren - aquacultuur - binnenwateren - visserijbeheer - visstand - bijvangst - statistiek - monitoring - onderzoek - duurzaamheid (sustainability) - recreatieactiviteiten - palingen - schaaldieren - fishery policy - fisheries - marine fisheries - coastal water - aquaculture - inland waters - fishery management - fish stocks - bycatch - statistics - research - sustainability - recreational activities - eels - shellfish
Dit rapport beschrijft het werkplan voor 2015 van cluster WOT-05 Visserijonderzoek van Wageningen UR. Wageningen UR voert voor het Ministerie van Economische Zaken (EZ) een aantal programma’s met Wettelijke Onderzoek Taken (WOT) uit. Binnen WOT-05 worden Wettelijke Onderzoek Taken uitgevoerd die betrekking hebben op het beheer van de visserij op zee, in Nederlandse kust- en binnenwateren en de aquacultuur. Het werkplan is een uitwerking van de Uitvoeringsovereenkomst tussen het Ministerie van EZ en de Stichting Dienst Landbouwkundig Onderzoek (DLO), onderdeel van Wageningen UR, voor diensten vanwege wettelijke taken op het terrein van visserijonderzoek voor de periode 2011-2015. Bij deze uitvoerings-overeenkomst zijn voor deze periode werkafspraken gemaakt welke de basis vormen voor de jaarlijkse werkplannen. Daarnaast zijn in deze overeenkomst afspraken gemaakt over de KennisBasis (KBWOT) die specifiek aan dit programma is gekoppeld.
Notitie Evaluatie Proefproject Groepsvorming vergunningen in de Geintegreerde Visserij
Kraan, M.L. ; Paijmans, A.J. - \ 2014
IJmuiden : IMARES (Rapport / IMARES 14/IMA0360) - 28
visserij - vissers - visserijbeheer - schaal- en schelpdierenvisserij - waddenzee - vergunningen - kustwateren - bedrijfsmanagement - fisheries - fishermen - fishery management - shellfish fisheries - wadden sea - permits - coastal water - business management
In 2008 zijn de Stichting Geïntegreerde Visserij en het ministerie van Economische Zaken gestart met een proefproject ‘Pilotproject Geïntegreerde Visserij – groepsvorming vergunningen’. Hierbij werd aan zes wad vissers een experimentele proefvergunning verleend, die hen in staat stelde onderling vergunningen en vangstrechten uit te wisselen. Het doel van het project is het mogelijk maken van de flexibilisering van de bedrijfsvoering van kleine kustvisserijbedrijven. Daarbij gaat het om het delen van de visrechten van individuele vissers in een groep van vissers en het gezamenlijk te beheren. Afgesproken werd dat het project na 5 jaar geëvalueerd zou worden.
Ontwikkelingen boomkorvisserij met wekkerkettingen in de Nederlandse kustzone
Quirijns, F.J. ; Machiels, M.A.M. - \ 2014
IJmuiden : IMARES (Rapport / IMARES Wageningen UR C043/14) - 40
boomkorvisserij - vistuig - natura 2000 - kustwateren - visvangsten - visserijbeheer - beam trawling - fishing gear - coastal water - fish catches - fishery management
Om te mogen vissen in de Natura 2000-gebieden in de Nederlandse kustzone, is een vergunning nodig. Nederlandse boomkorvissers hebben zo’n vergunning, welke ze ontvingen op basis van een Passende Beoordeling (PB) uitgevoerd in 2011. In die PB zijn de ontwikkelingen in de hoeveelheid visserij (visserijintensiteit) in de periode 2006-2009 onderzocht. Het ministerie van Economische Zaken wil inzicht in de recente ontwikkelingen in visserij-intensiteit in de boomkorvisserij met wekkerkettingen.
Technisch rapport: Productiemetingen aan mosselzaad-invang-installaties (MZI): 2012
Jansen, H.M. ; Broekhoven, W. van; Brummelhuis, E.B.M. ; Hartog, E. - \ 2013
Yerseke : IMARES (Rapport / IMARES Wageningen UR C031/13) - 34
mosselteelt - mossels - rendement - zaad verzamelen - aquacultuur - zaadbanken - kustwateren - effecten - aquatische ecosystemen - mussel culture - mussels - returns - seed collection - aquaculture - seed banks - coastal water - effects - aquatic ecosystems
Dit rapport beschrijft welke gegevens zijn verzameld ter onderbouwing van de bepaling van effecten van mosselzaadinvanginstallaties (MZI’s) op het ecosysteem. Ook geeft dit rapport een eerste overzicht van de resultaten welke vervolgens door de modelleurs gebruikt worden in de draagkrachtmodellen.
KBWOT 2012: the use of an acoustic technique in mapping beds of razor clams (Ensis sp.)
Troost, K. ; Asch, M. van; Baeye, M. ; Brummelhuis, E.B.M. ; Davaasuren, N. ; Ende, D. van den; Lancker, V. van - \ 2013
Yerseke : Centrum voor Visserijonderzoek (CVO report / Centre for Fisheries Research (CVO) 13.001) - 23
ensis - schaaldieren - onderwaterakoestiek - visstand - monitoring - nederlandse wateren - kustwateren - nederland - shellfish - underwater acoustics - fish stocks - dutch waters - coastal water - netherlands
For the survey of shellfish in the Dutch coastal zone (WOT Ensis), a fixed stratified sampling grid is used. Stratification is based on expectation of occurrence, for which previously observations by Spisula fishermen were used. Spisula subtruncata has largely disappeared and was replaced by Ensis sp. However, the stratified sampling grid is still mainly based on expected occurrence of Spisula. The quality of the data would be improved with an entirely independent basis for the stratification. An improved accuracy of stratified sampling grids will increase the efficiency of the WOT surveys and will also increase the confidence level of stock assessments. This will benefit management of shellfish stocks and fishery and will also enhance the reliability of environmental impact assessment studies. Acoustic techniques are increasingly applied for seafloor mapping and optimum allocation techniques for stock assessments. In the framework of the Belgian Science Policy project EnSIS multibeam technology was successfully used to find an acoustic signal representative of dense Ensis sp. aggregations in Belgian waters. In this study however, only relatively few sampling stations were present in the areas with the acoustic signal; a plea was held for more ground-truthing enabling applications in regular monitoring of Ensis sp. or other benthic species that form dense aggregations. Within the KBWOT Fisheries programme of 2012 we further studied the possibility to apply multibeam technology in the annual WOT stock assessment of Ensis sp. in cooperation with the Royal Belgian Institute of Natural Sciences – Management Unit North Sea Mathematical Models (RBINS-MUMM), that also performed the EnSIS project in cooperation with other institutes such as IMARES. The aim of this project was fourfold: 1. study the ability to discern different types of seafloor (e.g. mud, sand, gravel, shellfish beds infaunal and epifaunal) using a high frequency multibeam acoustic sounding system; 2. assess the applicability of multibeam for stratified sampling in the coastal zone: will it optimize the sampling strategy and enhance efficiency? 3. determine what is needed to develop this innovative technique within IMARES and to apply it for stock assessments of shellfish and possibly other benthic communities (expertise, software, etc); 4. determine with whom to cooperate in future regarding availability of multibeam equipment and analysis techniques.
Fishing for food : feeding ecology of harbour porpoises Phocoena phocoena and white-beaked dolphins Lagenorhynchus albirostris in Dutch waters
Jansen, O.E. - \ 2013
Wageningen University. Promotor(en): Peter Reijnders, co-promotor(en): Marten Scheffer. - S.l. : s.n. - ISBN 9789461734228 - 173
phocoena - lagenorhynchus - dolfijnen - voedingsecologie - diëten - kustwateren - noordzee - oosterschelde - nederland - dolphins - feeding ecology - diets - coastal water - north sea - eastern scheldt - netherlands

Harbour porpoises and white-beaked dolphins are the most common small cetaceans in the North Sea and Dutch coastal waters. The distribution and relative abundance of harbour porpoises and white-beaked dolphins from the Dutch coastal waters has changed significantly over the past decades. This thesis describes the past and present feeding ecology of these two species in Dutch coastal waters and investigates whether changes in abundance and relative distribution of porpoises reflect changes in their foodbase. For porpoises, three techniques for dietary analyses were combined, including stomach contents-, stable isotope- and fatty acid analysis, providing the most detailed description of their diet in time and space, elucidating differences between their short- and longer term diet.

Stable isotope analysis (δ13C and δ15N) were carried out in bone and muscle samples collected from porpoises stranded along the Dutch coast. Muscle δ15N values revealed that neonatal enrichment occurred and that larger porpoises, in particular males, seem to feed on lower trophic level species, compared to smaller individuals. Also bone δ15N values show that larger animals had fed on lower trophic levels in distant times. Seasonal variation in bone δ15N and δ13C values revealed two distinct groups of porpoises along the Dutch coast, a winter group (mainly males) that migrated from neighbouring regions and a Dutch subpopulation in summer (Chapter 2).

To assess the contribution of prey species to the porpoises’ diet, stable isotope analysis in both porpoise muscle and prey were carried out. With the use of a mixing model (Stable Isotope Analysis in R, SIAR), we revealed that 70-83% of the diet of porpoises consisted mainly of poor cod, mackerel, greater sandeel lesser sandeel, sprat and gobies. This highlights a higher importance of pelagic, schooling species in the porpoises’ diet compared to stomach contents, where 90.5% of the diet consisted of gobies, whiting, lesser sandeel, herring, cod and sprat. Porpoises thus also feed offshore on pelagic, schooling species, while they feed closer to shore on more benthic and demersal species shortly before they strand. This could be due to the distribution of prey species as well as differences in behaviour of porpoises and their prey between the coastal zone and offshore waters (Chapter 3).

The use of Quantitative Fatty Acid Analysis (QFASA) showed that the diet of porpoises consisted mainly of gobies, mackerel, smelt, herring and dragonet, pointing towards profound differences between the diet as estimated by QFASA and as deduced from stomach contents. This study revealed that the longer term diet of porpoises in Dutch coastal waters consists both of coastal species (e.g. gobies, smelt and dragonet) and also pelagic, schooling species (e.g. mackerel and herring). The results also brought to dawn possible methodological problems in using QFASA for porpoise diet estimation, emphasizing the importance of applying different dietary analysis techniques when studying marine mammal diets and the need for controlled feeding experiments in order to improve the interpretation of dietary analysis results (Chapter 5).

Besides new insights in the feeding ecology of porpoises, stable isotope analysis also elicited a non-food related conservation ecology issue. Distinct δ13C values in muscle of porpoises stranded in the Eastern Scheldt revealed that these porpoises foraged there for a longer period. This distinct δ13C signature of animals from the Eastern Scheldt was not observed in bone tissue, which suggests a relatively recent shift in habitat use rather than life-long residency of porpoises within the Eastern Scheldt. The high number of strandings within the Eastern Scheldt revealed a higher mortality rate compared to the Dutch coastal zone, indicating that along with other changes in the physical environment, the building of the storm surge barrier may play an important role in determining the residency of porpoises in the Eastern Scheldt, and that the area might act as an ecological trap for porpoises entering it. This is an example of the impact on marine species due to protection structures that emerge and respectively increase worldwide in response to the effects of global warming and climate change. It highlights that even semi-open structures, which are meant to ameliorate habitat loss, degradation and fragmentation, may still affect the abundance and distribution of migratory marine mammal species (Chapter 4).

The analysis of stomach contents of white-beaked dolphins showed that their diet was dominated by Gadidae. All other prey species combined contributed little to the diet by weight. The two most important prey species based in weight were whiting and cod. In numbers, gobies were most common, but these contributed little to the diet by weight. The overall diet showed a lasting predominance of whiting and cod, without clear changes over time (35 years) or differences between sexes or size-classes of dolphins and revealed that white-beaked dolphins in the south-eastern North Sea are specialist feeders, with a strong preference for whiting and cod (Chapter 6).

Stomach contents of juvenile white-beaked dolphins in our study revealed that at the age of about 1.5 years old, they had started feeding on solid food by taking a variety of small fish and invertebrate prey, mostly shrimp and squid. Immatures in our study, estimated to be 2-4 years old, still take small prey, including small gadoids, but also take larger gadoids. Calves apparently gradually learn to eat big fish by taking prey that is much smaller than those normally taken by their mothers. This study illustrates novel techniques for diet estimation to reconstruct sizes of shrimp and whiting from tail flaps and eye lenses, respectively (Chapter 7).

Most dietary studies on porpoises and white-beaked dolphins are deduced from stomach contents. This thesis has demonstrated that using indirect methods for studying the feeding ecology of marine mammals is a valuable addition to the more direct approach using stomach contents. It supports the need for multi-method approaches because by using only one technique, key prey species in the predator-prey relation may be missed or underestimated. Future ecological and fishery impact assessment studies and management decisions for the conservation of porpoises and white-beaked dolphins should acknowledge a difference between their long- and short-term diet. Large improvement in the interpretation of the results from diet analyses can be established either by controlled feeding experiments with animals in captivity or by studies that help to understand the common principals in dietary analyses (e.g. digestion rates, turnover rates of tissues, tissue-dependent isotopic fractionation between predator and prey and lipid metabolism within the animal) and variation of these between species.

Final report on impact of catchment scale processes and climate change on cause-effect and recovery-chains
Verdonschot, P.F.M. ; Keizer-Vlek, H.E. ; Spears, B. ; Brucet, S. ; Johnson, R. ; Feld, C. ; Kernan, M. - \ 2012
Brussel : European Commission - 116
ecologisch herstel - beheer van waterbekkens - rivieren - meren - estuaria - kustwateren - degradatie - biologische indicatoren - verzuring - eutrofiëring - morfologie - ecologische beoordeling - ecological restoration - watershed management - rivers - lakes - estuaries - coastal water - degradation - biological indicators - acidification - eutrophication - morphology - ecological assessment
Catchment wide integrated basin management requires knowledge on cause-effect and recovery chains within water bodies as well as on the interactions between water bodies and categories. In the WISER WP6.4 recovery processes in rivers, lakes and estuarine and coastal waters were evaluated. The major objectives were: - to analyse and compare (cause-effect and) recovery chains within water categories based on processes and structural and functional features; - to detect commonalities among different chains in different water categories ( to compare recovery chains between water categories); - to link recovery chains to over-arching biological processes and global change; - to develop a method to combine recovery effects in a summarising ‘catchment’ metric. The main stressors studied to reach these objectives were acidification, eutrophication and hydromorphological changes.
Effect of variations in concentration of algae and silt on filtration and growth of the razor clam (Ensis directus, Conrad)
Kamermans, P. ; Dedert, M. - \ 2012
Yerseke : IMARES (Report / IMARES Wageningen UR C017/11) - 69
ensis - voedselopname - algen - silt - groeitempo - filtratie - kustwateren - noordzee - food intake - algae - growth rate - filtration - coastal water - north sea
As part of a collaboration between the research programme Knowledge for Primary Processes Silt of Rijkswaterstaat Waterdienst NWOB (department of Infrastructure and Environment, MinIenM, RWS) and the Monitoring programme Sand extraction RWS and the LaMER Foundation, RWS-WD NWOB requested further research into the relation between food availability and Ensis production. The aim is to better understand the effect of different algae and silt concentrations on filtration and growth rates and improve prediction of effects. Laboratory experiments were carried out with Ensis directus to estimate food intake rate and growth rate as a function of food density and clam size. Growth experiments carried out in 2010 showed that the species seems to be very fragile as shown by the low growth rates and high mortality rates. Improvements designed to optimize the experimental conditions, survival rates and experimental set-up were implemented in 2011. These were: experimental animals were collected with a box corer instead of a suction dredge; animals were kept in cylinders without sediment, but their shells were closed with elastic bands during the filtration experiments; circular tanks were used with increased water movement; the diet during the growth experiment consisted of two species of algae. Two food levels were tested: low food availability (6.5 μg Chla/l) and high food availability (16.5 μg Chla/l) at four silt concentrations (0, 50, 150 and 300 mg/l). Only the highest silt concentration induced a reduction in filtration rate. Food level did not influence filtration rate of Ensis, but intake rate is higher at the high food concentration, because more algal cells are present in a certain volume of water. Longterm (10 weeks) exposure to silt concentrations of 300 mg/l showed significantly higher growth than the 150 mg/l treatment indicating that exposure to a high silt concentration did not induce a reduction in growth. Long-term (10 weeks) exposure to a food level of 6.5 ug chla per liter reduced shell growth of Ensis compared to growth at 16.5 ug chla per liter. The filtration and growth rate results are used in a modelling study on growth and condition of Ensis during sand extraction 2013-2017 (Schellekens, in prep). The conclusions of this study give more notion of the effects of sand extraction in the coastal zone of the North Sea on the viability of the razor clam Ensis directus. Sand extraction always goes together with an increase of silt concentration in the water column. This reduces the light conditions for algal growth which reduces the food availability for Ensis. The laboratory experiments suggest that Ensis is more sensitive to a reduction in algal concentration than to an increase in silt concentration. Some discussion is given on the implications of the results for the management of sand extraction.
Schelpdierwateronderzoek 2011
Poelman, M. ; Hoek-van Nieuwenhuizen, M. van; Gool, A.C.M. van - \ 2012
Yerseke : IMARES (Rapport / IMARES Wageningen UR C047/12) - 33
schaaldieren - waterkwaliteit - kustwateren - schaal- en schelpdierenteelt - ecotoxicologie - fecale coliformen - monitoring - westerschelde - oosterschelde - voordelta - waddenzee - shellfish - water quality - coastal water - shellfish culture - ecotoxicology - faecal coliforms - western scheldt - eastern scheldt - wadden sea
In november en december 2011 is onderzoek verricht naar de schelpdierwaterkwaliteit in de Nederlandse kustwatergebieden. Doel hiervan is het vaststellen van de gehalten aan fecale coliformen, zware metalen en gehalogeneerde organische stoffen in schelpdiervlees. Daarnaast zijn zintuiglijke waarnemingen op het schelpdiervlees en veldmetingen voor de verschillende parameters in het oppervlaktewater uitgevoerd. De monitoring data is getoetst aan de bestaande normen. De monitoring heeft plaatsgevonden op 12 locaties in gebieden waar schelpdierproductie/visserij voorkomt, namelijk de Westerschelde, Grevelingen, Oosterschelde, Voordelta en de Waddenzee.
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