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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Managing a complex population strucutre exploring the importance of information from fisheries-independent sources
Hintzen, N.T. ; Roel, B.A. ; Benden, D.P.L.D. ; Clarke, M. ; Egan, A. ; Nash, R.D.M. ; Rohlf, N. ; Hatfield, E.M.C. - \ 2015
ICES Journal of Marine Science 72 (2015)2. - ISSN 1054-3139 - p. 528 - 542.
herring clupea-harengus - state-space model - north-sea - stock assessment - spawning components - management advice - british-isles - celtic sea - dynamics - atlantic
Natural resource managers aim to manage fish stocks at sustainable levels. Often, management of these stocks is based on the results of analytical stock assessments. Accurate catch data, which can be attributed to a specific population unit and reflects the population structure, are needed for these approaches. Often though, the quality of the catch data is compromised when dealing with a complex population structure where fish of different population units mix in a fishery. The herring population units west of the British Isles are prone to mixing. Here, the inability to perfectly allocate the fish caught to the population unit they originate from, due to classification problems, poses problems for management. These mixing proportions are often unknown; therefore, we use simulation modelling combined with management strategy evaluation to evaluate the role fisheries-independent surveys can play in an assessment to provide unbiased results, irrespective of population unit mixing and classification success. We show that failure to account for mixing is one of the major drivers of biased estimates of population abundance, affecting biomass reference points and MSY targets. When mixing of population units occurs, the role a survey can play to provide unbiased assessment results is limited. Either different assessment models should be employed or stock status should be considered from the survey data alone. In addition, correctly classifying the origin of fish is especially important for those population units that are markedly smaller in size than other units in the population complex. Without high classification success rates, smaller population units are extremely vulnerable to overexploitation.
The Influence of Topographic and Dynamic Cyclic Vairables on the Distribution of Small Cetaceans in a Shallow Coastal System
Boer, M.N. de; Simmonds, M.P. ; Reijnders, P.J.H. ; Aarts, G.M. - \ 2014
PLoS ONE 9 (2014)1. - ISSN 1932-6203 - 15 p.
porpoise phocoena-phocoena - whales balaenoptera-acutorostrata - harbor porpoise - habitat preferences - seasonal distribution - scottish waters - dolphin-habitat - british-isles - tidal cycle - fin whales
The influence of topographic and temporal variables on cetacean distribution at a fine-scale is still poorly understood. To study the spatial and temporal distribution of harbour porpoise Phocoena phocoena and the poorly known Risso’s dolphin Grampus griseus we carried out land-based observations from Bardsey Island (Wales, UK) in summer (2001–2007). Using Kernel analysis and Generalized Additive Models it was shown that porpoises and Risso’s appeared to be linked to topographic and dynamic cyclic variables with both species using different core areas (dolphins to the West and porpoises to the East off Bardsey). Depth, slope and aspect and a low variation in current speed (for Risso’s) were important in explaining the patchy distributions for both species. The prime temporal conditions in these shallow coastal systems were related to the tidal cycle (Low Water Slack and the flood phase), lunar cycle (a few days following the neap tidal phase), diel cycle (afternoons) and seasonal cycle (peaking in August) but differed between species on a temporary but predictable basis. The measure of tidal stratification was shown to be important. Coastal waters generally show a stronger stratification particularly during neap tides upon which the phytoplankton biomass at the surface rises reaching its maximum about 2–3 days after neap tide. It appeared that porpoises occurred in those areas where stratification is maximised and Risso’s preferred more mixed waters. This fine-scale study provided a temporal insight into spatial distribution of two species that single studies conducted over broader scales (tens or hundreds of kilometers) do not achieve. Understanding which topographic and cyclic variables drive the patchy distribution of porpoises and Risso’s in a Headland/Island system may form the initial basis for identifying potentially critical habitats for these species.
Pyrrolizidine alkaloid variation in shoots and roots of segregating hybrids between Jacobaea vulgaris and Jacobaea aquatica
Cheng, D. ; Kirk, H. ; Mulder, P.P.J. ; Vrieling, K. ; Klinkhamer, P.G.L. - \ 2011
New Phytologist 192 (2011)4. - ISSN 0028-646X - p. 1010 - 1023.
senecionine n-oxide - british-isles - natural hybridization - plant hybridization - chemical diversity - tyria-jacobaeae - asteraceae - speciation - evolution - translocation
Hybridization can lead to novel qualitative or quantitative variation of secondary metabolite (SM) expression that can have ecological and evolutionary consequences.•We measured pyrrolizidine alkaloid (PA) expression in the shoots and roots of a family including one Jacobaea vulgaris genotype and one Jacobaea aquatica genotype (parental genotypes), two F1 hybrid genotypes, and 102 F2 hybrid genotypes using liquid chromatography–tandem mass spectrometry (LC-MS/MS).•We detected 37 PAs in the roots and shoots of J. vulgaris, J. aquatica and the hybrids. PA concentrations and compositions differed between genotypes, and between roots and shoots. Three otosenine-like PAs that only occurred in the shoots of parental genotypes were present in the roots of F2 hybrids; PA compositions were sometimes novel in F2 hybrids compared with parental genotypes, and in some cases transgressive PA expression occurred. We also found that PAs from within structural groups covaried both in the roots and in the shoots, and that PA expression was correlated between shoots and roots.•Considerable and novel variation present among F2 hybrids indicates that hybridization has a potential role in the evolution of PA diversity in the genus Jacobaea, and this hybrid system is useful for studying the genetic control of PA expression
Spring distribution and density of minke whale Balaenoptera acutorostrata along an offshore bank in the central North Sea
Boer, M.N. de - \ 2010
Marine Ecology Progress Series 408 (2010). - ISSN 0171-8630 - p. 265 - 274.
porpoises phocoena-phocoena - white-beaked dolphins - line transect surveys - southern moray firth - harbor porpoises - seasonal distribution - summer distribution - british-isles - dogger bank - abundance
Minke whales were recorded in the central North Sea in an area characterised by frontal features and high productivity northeast of the Dogger Bank (4677 km2). Survey efforts were carried out from 28 March to 2 July 2007, at a finer scale than in earlier studies in the region, using 2 vessels as platforms of opportunity and a dedicated line-transect survey vessel following distance sampling methods. The high density of whales indicated that this offshore bank slope is an important spring habitat for minke whales in the North Sea. In total, 77 sightings of minke whales comprising 130 individuals were recorded. The peak density of minke whales was estimated to be 0.029 whales km–2 (minimum estimate, 95% CI: 0.012 to 0.070) in May. During peak abundance, the minke whales temporarily congregated in the area, suggesting that the whales were taking advantage of the local spring abundance of sandeels. The density found was higher than previous studies have suggested for the central North Sea. The results correspond to recent observations of minke whale redistribution within the North Sea, and these may be related to a decline in sandeel availability elsewhere in the North Sea. Offshore banks that aggregate prey may therefore become increasingly important feeding habitats for minke whales and other top predators in the North Sea. The observed habitat preference of minke whales along this offshore bank appeared to be similar to that observed in coastal areas, and this suggests some degree of generality regarding the preference for this type of habitat
Spawning of North Sea fishes linked to hydrographic features
Munk, P. ; Fox, C.J. ; Bolle, L.J. ; Damme, C.J.G. van; Fossum, P. - \ 2009
Fisheries Oceanography 18 (2009)6. - ISSN 1054-6006 - p. 458 - 469.
cod gadus-morhua - british-isles - larvae - distributions - abundance - location - fronts - oceanography - habitat - biscay
Spawning of fishes takes place across a wide area of the North Sea. However, more intense spawning is seen in restricted areas, indicating that such areas present favorable conditions. To update information on fish spawning in the North Sea and analyze potential linkages to hydrographic characteristics, an internationally coordinated survey was conducted in the winter/spring of 2004. Oblique hauls for fish eggs and larvae and vertical profiles of temperature and salinity were carried out at 393 stations across the entire North Sea. The hydrography was strongly influenced by the interfacing of water masses of different salinity, and frontal zones were seen along all coastal areas and off the Dogger and Fisher Banks. Total abundances of eggs and larvae, including fish species such as cod, haddock, plaice, long rough dab and sandeel, peaked in the vicinity of the frontal areas. Hence our findings indicate that the main spawning locations of fish are linked to recurrent hydrographic features such as salinity fronts. Such a linkage may provide survival advantages, as the fronts present favorable feeding conditions, and the related physical processes may confine egg and larval dispersal and transport them towards suitable nursery habitats
Demographic vulnerability of the clonal and endangered meadow thistle
Jongejans, E. ; Vere, N. de; Kroon, H. de - \ 2008
Plant Ecology 198 (2008)2. - ISSN 1385-0237 - p. 225 - 240.
population viability analysis - extinction risk - sexual reproduction - biological flora - perennial herb - british-isles - plants - dynamics - grassland - fragmentation
For effective management of endangered species it is pivotal to understand why a species is endangered and which key life cycle components are involved in its response to environmental changes. Our objective was to investigate the response of rosettes of the redlisted clonal herb Cirsium dissectum to anthropogenic nutrient enrichment, which threatens its populations, and the consequences of these responses for its population dynamics. We constructed matrix population models with demographic data from three populations and four annual transitions and we decomposed the spatiotemporal variation in projected population growth rates into contributions from life cycle components. These patterns were compared with below-ground rosette dynamics in different fields, and with the below- and above-ground rosette dynamics in a garden experiment with nutrient enrichment and competing grasses. The decomposition analysis revealed that increased clonal rosette formation and decreased rosette survival were driving the spatial variation in the population growth rate. Excavating the below-ground rhizome network revealed a higher rosette turn-over in experimentally fertilized garden plots, which not only resulted in increased plot-level extinction, but also in increased spread of the clonal offspring. This supported the observed trend among field populations: rosette formation trades off with rosette survival. Surviving seedlings were only found in areas where the topsoil had been removed. The endangered C. dissectum is vulnerable when its habitat becomes more productive, because this species does not have the necessary capability to build up biomass. Small-scale disturbances such as created by sod-cutting or trampling cattle are essential for seedling establishment and necessary to render the explorative strategy of rhizomatous clonal spread successful.
Long-term effects of climate change on vegetation and carbon dynamics in peat bogs
Heijmans, M.M.P.D. ; Mauquoy, D. ; Geel, B. van; Berendse, F. - \ 2008
Journal of Vegetation Science 19 (2008)3. - ISSN 1100-9233 - p. 307 - 320.
increased nitrogen deposition - increased n deposition - vulgaris l hull - vascular plants - sphagnum bogs - british-isles - northern peatlands - biological flora - boreal peatlands - solar-activity
Questions: What are the long-term effects of climate change on the plant species composition and carbon sequestration in peat bogs?Methods: We developed a bog ecosystem model that includes vegetation, carbon, nitrogen and water dynamics. Two groups of vascular plant species and three groups of Sphagnum species compete with each other for light and nitrogen. The model was tested by comparing the outcome with long-term historic vegetation changes in peat cores from Denmark and England. A climate scenario was used to analyse the future effects of atmospheric CO2, temperature and precipitation.Results: The main changes in the species composition since 1766 were simulated by the model. Simulations for a future warmer, and slightly wetter, climate with doubling CO2 concentration suggest that little will change in species composition, due to the contrasting effects of increasing temperatures (favouring vascular plants) and CO2 (favouring Sphagnum). Further analysis of the effects of temperature showed that simulated carbon sequestration is negatively related to vascular plant expansion. Model results show that increasing temperatures may still increase carbon accumulation at cool, low N deposition sites, but decrease carbon accumulation at high N deposition sites.Conclusions: Our results show that the effects of temperature, precipitation, N-deposition and atmospheric CO2 are not straightforward, but interactions between these components of global change exist. These interactions are the result of changes in vegetation composition. When analysing long-term effects of global change, vegetation changes should be taken into account and predictions should not be based on temperature increase alone.
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