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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    Temperature effects on egg and larval development rate in European smelt, Osmerus eperlanus, experiments and a 50 year hindcast
    Keller, A.M. ; Molenaar, P. ; Leeuw, J.J. ; Mooij, W.M. ; Rijnsdorp, A.D. ; Wolfshaar, K.E. - \ 2020
    Journal of Fish Biology 96 (2020)6. - ISSN 0022-1112 - p. 1422 - 1433.
    This study investigates the effect of water temperature on the development rate of eggs and larvae, the duration of the endogenous feeding period and its consequences for recruitment of smelt (Osmerus eperlanus) in Dutch lakes IJsselmeer and Markermeer. This study measured temperature-dependent egg and larval development rates as well as mortality rates from fertilization till the moment of absorption of the yolk-sac and from yolk-sac depletion onwards in temperature-controlled indoor experiments. Using multinomial modelling the authors found significant differences in development time of egg development stages under different temperature regimes. Based on historic water temperatures, the model predicted that the larval endogenous feeding period has advanced at a rate of about 2.9 days per decade in a more than 50 year period since 1961, yet there was no change in the duration of the endogenous feeding period. As zooplankton is more responsive to daylight than water temperature cues, a mismatch between the peak of the onset of exogenous
    feeding of smelt and the peak of zooplankton blooms could lead to high mortality and therefore low recruitment of smelt. Such a mismatch might contribute to a decline in the smelt population in Lake IJsselmeer and Lake Markermeer.
    Zandspiering in het Amelander Zeegat : T1-meting voorjaar 2019
    Hal, Ralf van; Volwater, Joey - \ 2019
    IJmuiden : Wageningen Marine Research (Wageningen Marine Research rapport C105/19) - 33
    Sinds 2017 loopt het onderzoeksprogramma Kustgenese 2.0 met het doel ‘Het genereren van kennis om vanaf 2020 goed onderbouwd besluiten te kunnen nemen over beleid en beheer van het Nederlandse zandige kustsysteem’. Onderdeel van dit programma is de van maart 2018 tot februari 2019 uitgevoerde pilotsuppletie in het Amelander Zeegat. Rondom deze suppletie is er onderzoek verricht binnen de onderzoekslijnen morfologie en ecologie. Voor de onderzoekslijn ecologie is o.a. in september 2017 en juni 2018 een bemonstering van zandspiering uitgevoerd om een basisbeeld en uitgangssituatie (T0-situatie), te krijgen van deze soortsgroep in het Amelander Zeegat. Als vervolg hierop is in juni 2019 een bemonstering (T1-situatie) uitgevoerd welke in het voorliggende rapport wordt beschreven. Met behulp van de zandspieringkor is in de nachten van 3 – 5 juni 2019 gevist op 39 locaties. Deze locaties waren vergelijkbaar met die tijdens de bemonstering in september 2017 en juni 2018 aangevuld met vijf locaties op de uitgevoerde pilotsuppletie. Aanvullend is op 37 van deze locaties een sedimentmonster genomen met een Van Veenhapper waarvan de korrelgroottesamenstelling is bepaald. In totaal zijn er 678 zandspieringen gevangen, waarvan 580 gedetermineerd als kleine zandspiering (Ammodytes tobianus), 59 als Noorse zandspiering (Ammodytes marinus) en 39 als smelt (Hyperoplus lanceolatus). Deze waren gevangen in 25 van de 39 trekken, met de hoogste aantallen op de suppletie en de direct ten zuiden en oosten liggende gebieden. De concentratie in dit gebied, met maar beperkte aantallen in zuidelijkere locaties dichter bij het Borndiep is opvallend ten opzichte van de eerdere bemonsteringen. Naast zandspieren werden er ook platvissen gevangen. Schol (Pleuronectes platessa) werd in 38 van 39 trekken gevangen en was in hoge aantallen aanwezig, ook op de suppletie. Schelpdieren werden in lagere aantallen aangetroffen in vergelijking met de eerdere bemonsteringen. Schelpdieren werden ook gevangen op de suppletie. De sedimentsamenstelling liet een vergelijkbaar beeld zien als in september 2017 met fijn zand (125–250 μm) in het grootste deel van de buitendelta, en medium zand (250-500 μm) op enkele locaties in het zuiden. De suppletie wijkt in korrelgrootte niet af van het omliggende gebied. Omdat de korrelgrootte niet onderscheidend is lijkt dit ook geen verklaring voor de hogere aanwezigheid van zandspiering op de suppletie. Eerder in het gebied aangetroffen soorten zijn ook op de suppletielocatie aangetroffen. In het geval van zandspiering zelfs in hoge aantallen. Het aanleggen van de suppletie lijkt dus niet te hebben geleid tot een negatieve verandering in de bemonsterde visgemeenschap.
    The effect of vitamin B12 and folic acid supplementation on routine haematological parameters in older people : an individual participant data meta-analysis
    Smelt, Antonia F.H. ; Gussekloo, Jacobijn ; Bermingham, Lynette W. ; Allen, Elizabeth ; Dangour, Alan D. ; Eussen, Simone J.P.M. ; Favrat, Bernard ; Groot, Lisette C.P.G.M. de; Kok, Frans J. ; Kwok, Timothy ; Mangoni, Arduino A. ; Ntaios, George ; Rest, Ondine van de; Seal, Eric ; Vaucher, Paul ; Verhoef, Petra ; Stijnen, Theo ; Elzen, Wendy P.J. Den - \ 2018
    European Journal of Clinical Nutrition 72 (2018)6. - ISSN 0954-3007 - p. 785 - 795.
    Background/objectives: Low vitamin B12 and folate levels in community-dwelling older people are usually corrected with supplements. However, the effect of this supplementation on haematological parameters in older persons is not known. Therefore, we executed a systematic review and individual participant data meta-analysis of randomised placebo-controlled trials (RCTs). Subjects/methods: We performed a systematic search in PubMed, EMBASE, Web of Science, Cochrane and CENTRAL for RCTs published between January 1950 and April 2016, where community-dwelling elderly (60+ years) who were treated with vitamin B12 or folic acid or placebo. The presence of anaemia was not required. We analysed the data on haematological parameters with a two-stage IPD meta-analysis. Results: We found 494 full papers covering 14 studies. Data were shared by the authors of four RCTs comparing vitamin B12 with placebo (n = 343) and of three RCTs comparing folic acid with placebo (n = 929). We found no effect of vitamin B12 supplementation on haemoglobin (change 0.00 g/dL, 95% CI: −0.19;0.18), and no effect of folic acid supplementation (change −0.09 g/dL, 95% CI: −0.19;0.01). The effects of supplementation on other haematological parameters were similar. The effects did not differ by sex or by age group. Also, no effect was found in a subgroup of patients with anaemia and a subgroup of patients who were treated >4 weeks. Conclusions: Evidence on the effects of supplementation of low concentrations of vitamin B12 and folate on haematological parameters in community-dwelling older people is inconclusive. Further research is needed before firm recommendations can be made concerning the supplementation of vitamin B12 and folate.
    Immunological Properties of Inulin-Type Fructans
    Vogt, L. ; Meyer, D. ; Pullens, G. ; Faas, M.M. ; Smelt, M.J. ; Venema, K. ; Ramasamy, U. ; Schols, H.A. ; Vos, P. de - \ 2015
    Critical Reviews in Food Science and Nutrition 55 (2015)3. - ISSN 1040-8398 - p. 414 - 436.
    irritable-bowel-syndrome - aberrant crypt foci - probiotics lactobacillus-rhamnosus - dextran sodium-sulfate - chain fatty-acids - healthy elderly volunteers - colon-cancer patients - tnbs-induced colitis - b-cell responses - fisher 344 rats
    Beneficial effects of inulin-type fructans are discussed in view of studies that applied the oligosaccharides in colon cancer, chronic inflammatory diseases, vaccination efficacy, and prevention of infection and allergy. In the present paper, we discuss their immunomodulating effects. It is suggested that immunomodulation is elicited through indirect and direct mechanisms. Indirect mechanisms encompass stimulation of growth and activity of lactic acid bacteria, but can also be caused by fermentation products of these bacteria, i.e., short chain fatty acids. Evidence for direct effects on the immune system generally remains to be confirmed. It is suggested that inulin-type fructans can be detected by gut dendritic cells (DCs), through receptor ligation of pathogen recognition receptors (PRRs) such as Toll-like receptors, nucleotide oligomerization domain containing proteins (NODs), C-type lectin receptors, and galectins, eventually inducing pro- and anti-inflammatory cytokines. DCs may also exert antigen presenting capacity toward effector cells, such as B cells, T cells, and natural killer cells locally, or in the spleen. Inulin-type fructans may also ligate PRRs expressed on gut epithelium, which could influence its barrier function. Inulin-type fructans are potent immunomodulating food components that hold many promises for prevention of disease. However, more studies into the mechanisms, dose-effect relations, and structure-function studies are required.
    Migration of diadromous and landlocked smelt populations studies by otolith geochemistry
    Phung, A.T. ; Tulp, I.Y.M. ; Baeyens, W. ; Elskens, M. ; Leermakers, M. ; Gao, Y. - \ 2015
    Fisheries Research 167 (2015). - ISSN 0165-7836 - p. 123 - 131.
    eel anguilla-anguilla - laser-ablation icpms - crystal-structure - lake ijsselmeer - fish otoliths - japanese eels - habitat use - water - ratios - strontium
    Laser ablation inductively coupled mass spectrometry (LA-ICPMS) was used to determine Sr and Ba profiles along the growth axis of otholiths of European smelt caught in the Wadden Sea, the IJsselmeer and the Markermeer and to investigate the migration behaviour of the fish between the freshwater lakes and the marine environment. The use of Sr and Ba otolith profiles and their dissolved concentrations in the three aquatic systems provided a robust method for habitat classification and migration behaviour of the 111 individual smelts. No evidence was found of the migration of individuals from the Wadden Sea to the Ijsselmeer due to no marine Sr/Ba signal in the Ijsselmeer smelt. The Ba and Sr concentrations in the otoliths of Wadden Sea smelt suggest a mixture of two populations: juveniles that were born in the Wadden Sea and species that were born in Lakes IJsselmeer or Markermeer and migrated to the Wadden Sea. In the IJsselmeer different types of otolith profiles were observed depending on the migration history of the individuals in that lake: some individuals have probably not moved a lot, others may have used tributaries (e.g. the river IJssel) as spawning grounds or migrated from Markermeer to Ijsselmeer.
    De toendra smelt
    Heijmans, M.M.P.D. ; Beintema, N. - \ 2015
    WageningenWorld (2015)1. - ISSN 2210-7908 - p. 28 - 31.
    permafrost - toendrabodems - bodemverstoring - broeikasgassen - experimenteel veldonderzoek - siberië - permafrost - tundra soils - soil disturbance - greenhouse gases - field experimentation - siberia
    Een kwart van het landoppervlak van het noordelijk halfrond heeft permafrost in de bodem, vooral in Canada en Siberië. De permafrost vormt een meters dikke, ondoordringbare laag. Alleen de bovenste decimeters van de toendra ontdooien in de zomer. Maar dit gebied is erg kwetsbaar voor verstoring. Een kleine verandering kan een groot effect hebben. Dat ontdekten Monique Heijmans en haar collega’s van de leerstoelgroep Natuurbeheer en Plantenecologie. Zij verwijderden de struikjes in een vijftal proefveldjes en volgden die percelen een aantal jaren. Het effect was dramatisch: de permafrost, de permanent bevroren ondergrond, begon te ontdooien en de toendra zakte in elkaar.
    Permafrost smelt sneller na verstoring toendra
    Heijmans, Monique - \ 2014
    Data evaluation of data limited stocks: Horse mackerel, Seabass, Greater Silver Smelt, Turbot and Brill
    Hammen, T. van der; Poos, J.J. ; Overzee, H.M.J. van; Heessen, H.J.L. ; Rijnsdorp, A.D. - \ 2014
    IJmuiden : IMARES (Report / IMARES Wageningen UR C166/13) - 84
    trachurus trachurus - osmerus - zeebaars - tarbot - scophthalmus rhombus - visbestand - pleuronectiformes - visstand - visserij - trachurus trachurus - osmerus - sea bass - turbot - scophthalmus rhombus - fishery resources - pleuronectiformes - fish stocks - fisheries
    Several commercially important fish stocks are classified by ICES (International Council for the Exploration of the Sea) as “data limited” stocks, which are stocks for which the data are insufficient to perform a full analytical assessment and forecast. In this report available data and literature on North Sea horse mackerel, greater silver smelt, seabass, turbot and brill are analysed. The data in this report may be used in future for catch advice by ICES.
    Genotypic adaptations associated with prolonged persistence of Lactobacillus plantarum in the murine digestive tract
    Bokhorst-van de Veen, H. van; Smelt, M.J. ; Wels, M. ; Hijum, S.A.F.T. van; Vos, P. de; Kleerebezem, M. ; Bron, P.A. - \ 2013
    Biotechnology Journal 8 (2013)8. - ISSN 1860-6768 - p. 895 - 904.
    gastrointestinal-tract - rhamnosus gg - human flora - mice - host - strains - protein - genome - genes - identification
    Probiotic bacteria harbor effector molecules that confer health benefits, but also adaptation factors that enable them to persist in the gastrointestinal tract of the consumer. To study these adaptation factors, an antibiotic-resistant derivative of the probiotic model organism Lactobacillus plantarum WCFS1 was repeatedly exposed to the mouse digestive tract by three consecutive rounds of (re)feeding of the longest persisting colonies. This exposure to the murine intestine allowed the isolation of intestine-adapted derivatives of the original strain that displayed prolonged digestive tract residence time. Re-sequencing of the genomes of these adapted derivatives revealed single nucleotide polymorphisms as well as a single nucleotide insertion in comparison with the genome of the original WCFS1 strain. Detailed in silico analysis of the identified genomic modifications pinpointed that alterations in the coding regions of genes encoding cell envelope associated functions and energy metabolism appeared to be beneficial for the gastrointestinal tract survival of L. plantarum WCFS1. This work demonstrates the feasibility of experimental evolution for the enhancement of the gastrointestinal residence time of probiotic strains, while full-genome re-sequencing of the adapted isolates provided clues towards the bacterial functions involved. Enhanced gastrointestinal residence is industrially relevant because it enhances the efficacy of the delivery of viable probiotics in situ.
    Probiotics can generate FoxP3 T-cell responses in the small intestine and simultaneously inducing CD4 and CD8 T cell activation in the large intestine.
    Smelt, M.J. ; Haan, B.J. de; Bron, P.A. ; Swam, I. van; Meijerink, M. ; Wells, J. ; Faas, M.M. ; Vos, P. de - \ 2013
    PLoS ONE 8 (2013)7. - ISSN 1932-6203
    inflammatory-bowel-disease - influenza-virus infection - cd103(+) dendritic cells - complete genome sequence - lactic-acid bacteria - lactobacillus-plantarum - double-blind - in-vitro - maintaining remission - ulcerative-colitis
    Most studies on probiotics aim to restore intestinal homeostasis to reduce immune-pathology in disease. Of equal importance are studies on how probiotics might prevent or delay disease in healthy individuals. However, knowledge on mechanisms of probiotic actions in healthy individuals is scarce. To gain more insight in how different bacterial strains may modulate the healthy intestinal immune system, we investigated the effect of the food derived bacterial strains L. plantarum WCFS1, L. salivarius UCC118, and L. lactis MG1363, on the intestinal regulatory immune phenotype in healthy mice. All three bacterial strains induced an upregulation of activity and numbers of CD11c(+) MHCII(+) DCs in the immune-sampling Peyer's Patches. Only L. salivarius UCC118 skewed towards an immune regulatory phenotype in the small intestinal lamina propria (SILP). The effects were different in the large intestine lamina propria. L. salivarius UCC118 induced activation in both CD4 and CD8 positive T-cells while L. plantarum WCFS1 induced a more regulatory phenotype. Moreover, L. plantarum WCFS1 decreased the Th1/Th2 ratio in the SILP. Also L. lactis MG1363 had immunomodulatory effects. L. lactis MG1363 decreased the expression of the GATA-3 and T-bet in the SILP. As our data show that contradictory effects may occur in different parts of the gut, it is recommended to study effects of probiotic in different sites in the intestine. Our strain-specific results suggest that unspecified application of probiotics may not be very effective. Our data also indicate that selection of specific probiotic strain activities on the basis of responses in healthy mice may be a promising strategy to specifically stimulate or suppress immunity in specific parts of the intestine
    Target strength and behaviour of smelt
    Gastauer, Sven - \ 2013
    Target strength and vertical distribution of smelt (Osmerus eperlanus) in the IJsselmeer based on stationary 200 kHz echosounder recordings
    Gastauer, S. ; Fassler, S.M.M. ; Couperus, A.S. ; Keller, A.M. - \ 2013
    Fisheries Research 148 (2013). - ISSN 0165-7836 - p. 100 - 105.
    methane bubbles - eutrophic lake - fish - l. - quantification - consequences - population - kinneret - patterns - shallow
    Ventral target strength (TS) of smelt (Osmerus eperlanus) was measured using a bottom deployed Simrad EK60 200 kHz echosounder in the shallow lake Ijsselmeer (The Netherlands). Ventral TS values recorded (TS = 20 log10(L)–74.39) were lower but comparable to previous studies looking at the dorsal TS in other areas. Biological samples were collected simultaneously close to the bottom and close to the surface. The combination of acoustic measurements and catch information revealed a diurnal migration of smelt. Smelt was observed to be more dispersed during the night than during daytime, but showing no clear avoidance pattern for any environmental variable recorded by CTD measurements. Smelt was found in the upper water column during times of highest light intensity. Such behaviour is likely to occur due to a combination of turbid water conditions and predator avoidance, mainly of piscivorous fish species such as pike–perch (Stizostedion luciperca) and perch (Perca fluviatilis)
    The Impact of Lactobacillus plantarum WCFS1 Teichoic Acid D-Alanylation on the Generation of Effector and Regulatory T-cells in Healthy Mice
    Smelt, M.J. ; Haan, B.J. de; Bron, P.A. ; Swam, I. van; Meijerink, M. ; Wells, J. ; Kleerebezem, M. ; Faas, M.M. ; Vos, P. de - \ 2013
    PLoS ONE 8 (2013)4. - ISSN 1932-6203 - 14 p.
    placebo-controlled trial - inflammatory-bowel-disease - blood mononuclear-cells - tlr signaling pathways - lipoteichoic acid - double-blind - dendritic cells - ulcerative-colitis - maintaining remission - acidophilus deficient
    To date it remains unclear how probiotics affect the immune system. Bacterial envelope components may play an essential role, as these are the first to establish bacterial-host cell interactions. Teichoic acids (TAs), and especially lipoteichoic acids, are the most pro-inflammatory components of the gram-positive bacterial envelope. This effect is dependent on D-alanyl substitution of the TA backbone and interactions with TLR2 on host cells. Although the pro-inflammatory properties of TAs have been established in vitro, it remains unclear how TAs affect immunomodulation in vivo. In this study, we investigated the role of TA D-alanylation on L. plantarum–induced intestinal and systemic immunomodulation in vivo. For this, we compared the effect of L. plantarum WCFS1 and its TA D-Alanylation negative derivative (dltX-D) on the distribution of dendritic cell and T cell populations and responses in healthy mice. We demonstrated that the majority of the L. plantaruminduced in vivo immunomodulatory effects were dependent on D-alanylation (D-Ala), as some L. plantarum WCFS1-induced immune changes were not observed in the dltX-D-treated group and some were only observed after treatment with dltX-D. Strikingly, not only pro-inflammatory immune responses were abolished in the absence of D-Ala substitution, but also antiinflammatory responses, such as the L. plantarum-induced generation of regulatory T cells in the spleen. With this study we provide insight in host-microbe interactions, by demonstrating the involvement of D-alanylation of TAs on the bacterial membrane in intestinal and systemic immunomodulation in healthy mice.
    Connectivity between Migrating and Landlocked Populations of a Diadromous fish Species Investigated Using Otolith Microchemistry
    Tulp, I.Y.M. ; Keller, A.M. ; Navez, J. ; Winter, H.V. ; Graaf, M. de; Baeyens, W. - \ 2013
    PLoS ONE 8 (2013)7. - ISSN 1932-6203
    lake ijsselmeer - netherlands - patterns - water - sea
    Smelt Osmerus eperlanus has two different life history strategies in the Netherlands. The migrating population inhabits the Wadden Sea and spawns in freshwater areas. After the closure of the Afsluitdijk in 1932, part of the smelt population became landlocked. The fresh water smelt population has been in severe decline since 1990, and has strongly negatively impacted the numbers of piscivorous water birds relying on smelt as their main prey. The lakes that were formed after the dike closure, IJsselmeer and Markermeer have been assigned as Natura 2000 sites, based on their importance for (among others) piscivorous water birds. Because of the declining fresh water smelt population, the question arose whether this population is still supported by the diadromous population. Opportunities for exchange between fresh water and the sea are however limited to discharge sluices. The relationship between the diadromous and landlocked smelt population was analysed by means of otolith microchemistry. Our interpretation of otolith strontium (88Sr) patterns from smelt specimens collected in the fresh water area of Lake IJsselmeer and Markermeer, compared to those collected in the nearby marine environment, is that there is currently no evidence for a substantial contribution from the diadromous population to the spawning stock of the landlocked population.
    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 - phocoena - lagenorhynchus - 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.

    Recent developments in basophil research : do basophils initiate and perpetuate type 2 T-helper cell responses?
    Beek, A.A. van; Knol, E.F. ; Vos, P. de; Smelt, M.J. ; Savelkoul, H.F.J. ; Neerven, R.J.J. van - \ 2013
    International Archives of Allergy and Immunology 160 (2013)1. - ISSN 1018-2438 - p. 7 - 17.
    thymic stromal lymphopoietin - antigen-presenting cells - chronic allergic inflammation - human blood basophils - in-vivo - cytokine production - dendritic cells - mast-cells - helminth infection - histamine-release
    Basophils account for only 0.1–1% of all peripheral blood leukocytes. They were considered to be a redundant cell type for a long time. However, several findings show a non-redundant role for basophils in type 2 T-helper cell (Th2) immune responses in helminth infections, allergy and autoimmunity. Both immunoglobulin-E-dependent and -independent pathways have been described to contribute to basophil activation. In addition, several recent studies reported that basophils can function as antigen-presenting cells and are important in the initiation of Th2 immune responses. However, there are also conflicting studies that do not corroborate the importance of basophils in Th2 immune responses. This review discusses the role of basophils in Th2 immune responses in view of these recent findings
    Influence of temperature on egg-development of European smelt (Osmerus eperlanus)
    Keller, A.M. - \ 2012
    L. plantarum, L. salivarius, and L. lactis Attenuate Th2 Responses and Increase Treg Frequencies in Healthy Mice in a Strain Dependent Manner
    Smelt, M.J. ; Haan, B.J. de; Bron, P.A. ; Swam, I. van; Meijerink, M. ; Wells, J. ; Faas, M.M. ; Vos, P. de - \ 2012
    PLoS ONE 7 (2012)10. - ISSN 1932-6203
    inflammatory-bowel-disease - lactobacillus-casei shirota - influenza-virus infection - placebo-controlled trial - complete genome sequence - blood mononuclear-cells - dendritic cells - double-blind - immune-system - acid bacteria
    Many studies on probiotics are aimed at restoring immune homeostasis in patients to prevent disease recurrence or reduce immune-mediated pathology. Of equal interest is the use of probiotics in sub-clinical situations, which are characterized by reduced immune function or low-grade inflammation, with an increased risk of infection or disease as a consequence. Most mechanistic studies focus on the use of probiotics in experimental disease models, which may not be informative for these sub-clinical conditions. To gain better understanding of the effects in the healthy situation, we investigated the immunomodulatory effects of two Lactobacillus probiotic strains, i.e. L. plantarum WCFS1 and L. salivarius UCC118, and a non-probiotic lactococcus strain, i.e. L. lactis MG1363, in healthy mice. We studied the effect of these bacteria on the systemic adaptive immune system after 5 days of administration. Only L. plantarum induced an increase in regulatory CD103+ DC and regulatory T cell frequencies in the spleen. However, all three bacterial strains, including L. lactis, reduced specific splenic T helper cell cytokine responses after ex vivo restimulation. The effect on IFN-¿, IL5, IL10, and IL17 production by CD4+ and CD8+ T cells was dependent on the strain administered. A shared observation was that all three bacterial strains reduced T helper 2 cell frequencies. We demonstrate that systemic immunomodulation is not only observed after treatment with probiotic organisms, but also after treatment with non-probiotic bacteria. Our data demonstrate that in healthy mice, lactobacilli can balance T cell immunity in favor of a more regulatory status, via both regulatory T cell dependent and independent mechanisms in a strain dependent manner.
    The social network of smelt: connectivity between migrating and fresh water populations
    Tulp, I.Y.M. ; Keller, A.M. ; Navez, J. ; Winter, H.V. ; Graaf, M. de; Baeyens, W. - \ 2012
    Data availability for the evaluation of stock status of species without catch advice: Case study: turbot (Psetta maxima) and Brill (Scophthalmus rhombus)
    Hammen, T. van der; Poos, J.J. ; Quirijns, F.J. - \ 2011
    IJmuiden : IMARES (Rapport / IMARES Wageningen UR C101/11) - 35
    visstand - tarbot - scophthalmus rhombus - gegevensanalyse - gegevens verzamelen - noordzee - fish stocks - turbot - scophthalmus rhombus - data analysis - data collection - north sea
    Several commercially important demersal fish stocks for the North Sea fisheries are classified as “category 11” in the light of the EU policy paper on fisheries management (17 May 2010, COM(2010) 241). For stocks in this category, there is no STECF (Scientific, technical and economic committee for fisheries ) management advice, due to the unknown status of the stocks. The reason for this is that the data and information available to perform analytical stock assessments are highly uncertain or lacking. This document describes existing data and options for collecting new data for the evaluation of the state of category 11 stocks. We focus on turbot and brill in the North Sea. Existing data from logbooks and the market sampling program can be used to estimate LPUE series used in age-based stock assessment methods, similar to other commercially important flatfish species such as plaice and sole. Landings Per Unit of Effort (LPUE) data of the Dutch beam trawl fleet > 221 kW were standardised for engine power and corrected for targeting behaviour as described below and graphically shown in Figure 3.2.1. The methods are similar to those used to analyse commercial LPUE data for North Sea plaice, described in Quirijns and Poos (2010). Landing rates (LPUE) by market category were calculated for the period 2002-2010. The corrected LPUE series indicate an increase in commercial LPUE for both species during the period 2002-2006. For turbot, the LPUE stays stable in the first five years, increases between 2006 and 2008, and decreases afterwards. The increase in brill LPUE is larger, and occurs throughout the study period. Compared to other commercially important flatfish species relatively few brill and turbot market samples are taken. This reduces the ability to track the cohorts in the LPUE series of the older ages which is a prerequisite for reliable stock assessment estimates. Also, the time series currently spans only 9 years. Collection of additional data may therefore be desirable. Expanding the BTS survey will provide industry independent data and would therefore give easily interpretable results. The option of an industry survey is also a good option if the survey is already being executed for sole and plaice. However, both options are costly. Therefore, the option of increasing the samples of turbot and brill at the auction is relatively easy and relatively inexpensive and therefore at present the most promising. The methods used for this document will not per definition be applicable for all category 11 species. For dab, flounder, lemon sole and tub gurnard, samples at the auctions are taken to collect biological data. For these species it may be possible to raise the data in a similar way as was done in this report to estimate the age composition of the stock. For other species (witch flounder, horse mackerel, silver smelt, red mullet and squid) there is no market sampling. For these species, other methods will have to be developed.
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