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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Editorial: Global in scope and regionally rich: an IndiSeas workshop helps shape the future of marine ecosystem indicators
Shin, Y.J. ; Bundy, A. ; Piet, G.J. - \ 2012
Reviews in Fish Biology and Fisheries 22 (2012)3. - ISSN 0960-3166 - p. 835 - 845.
size-based indicators - cusum control charts - to-end models - fisheries management - community structure - ecological status - climate-change - fuzzy-logic - food webs - catch
This report summarizes the outcomes of an IndiSeas workshop aimed at using ecosystem indicators to evaluate the status of the world’s exploited marine ecosystems in support of an ecosystem approach to fisheries, and global policy drivers such as the 2020 targets of the Convention on Biological Diversity. Key issues covered relate to the selection and integration of multi-disciplinary indicators, including climate, biodiversity and human dimension indicators, and to the development of data- and model-based methods to test the performance of ecosystem indicators in providing support for fisheries management. To enhance the robustness of our cross-system comparison, unprecedented effort was put in gathering regional experts from developed and developing countries, working together on multi-institutional survey datasets, and using the most up-to-date ecosystem models.
VMStools: Open-source software for the processing, analysis and visualisation of fisheries logbook and VMS data
Hintzen, N.T. ; Bastardie, F. ; Beare, D.J. ; Piet, G.J. ; Ulrich, C. ; Deporte, N. ; Egekvist, J. ; Degel, H. - \ 2012
Fisheries Research 115-116 (2012). - ISSN 0165-7836 - p. 31 - 43.
fishing effort - management strategies - high-resolution - giant petrels - catch - sea - pressure - patterns - impact - scale
VMStools is a package of open-source software, build using the freeware environment R, specifically developed for the processing, analysis and visualisation of landings (logbooks) and vessel location data (VMS) from commercial fisheries. Analyses start with standardized data formats for logbook (EFLALO) and VMS (TACSAT), enabling users to conduct a variety of analyses using generic algorithms. Embedded functionality handles erroneous data point detection and removal, métier identification through the use of clustering techniques, linking logbook and VMS data together in order to distinguish fishing from other activities, provide high-resolution maps of both fishing effort and -landings, interpolate vessel tracks, calculate indicators of fishing impact as listed under the Data Collection Framework at different spatio-temporal scales. Finally data can be transformed into other existing formats, for example to populate regional databases like FishFrame. This paper describes workflow examples of these features while online material allows a head start to perform these analyses. This software incorporates state-of-the art VMS and logbook analysing methods standardizing the process towards obtaining pan-European, or even worldwide indicators of fishing distribution and impact as required for spatial planning. --------------------------------------------------------------------------------
Fishing power increases from technological development in the Faroe Islands longline fishery
Eigaard, O.R. ; Thomsen, B. ; Hovgaard, H. ; Nielsen, A. ; Rijnsdorp, A.D. - \ 2011
Canadian Journal of Fisheries and Aquatic Sciences 68 (2011)11. - ISSN 0706-652X - p. 1970 - 1982.
cod gadus-morhua - demersal fisheries - north-sea - european fleets - management - catch - mortality - lessons - system - impact
During an effort-regulated period from 1996 to 2002, unregistered annual increases of 0.3% of hooks fished per day were demonstrated for the Faroe Islands longline fishery. However, annual increases were higher (1.5%) during a preceding total allowable catch regulated period, thereby invalidating an expectation of the 1996 shift in regulations (output to input control) to have induced increases in the number of hooks set per day. Underlying this result is a substantial increase in total yearly effort (fishing days) and a shift in targeting behaviour from secondary to primary (high value) target species in response to the transition from output to input control. Interview data on technology were combined with logbook data and analysed with generalized linear modelling to demonstrate haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) catch-per-unit-effort increases of 51% and 26%, respectively, following the introduction of skewed hooks and swivel line. The technological introductions were not correlated to regulation shifts. So, rather than the management system in force, an ongoing technological development seems to be the principal driver of fishing power trends. The results highlight the need to explicitly address technological development and targeting behaviour when attempting to meet conservation objectives through input control of fisheries.
Biased stock assessment when using multiple, hardly overlapping, tuning series if fishing trends vary spatially
Kraak, S.B.M. ; Daan, N. ; Pastoors, M.A. - \ 2009
ICES Journal of Marine Science 66 (2009)10. - ISSN 1054-3139 - p. 2272 - 2277.
north-sea plaice - age data - catch
Fishing-effort distributions are subject to change, for autonomous reasons and in response to management regulations. Ignoring such changes in a stock-assessment procedure may lead to a biased perception. We simulated a stock distributed over two regions with inter-regional migration and different trends in exploitation and tested the performance of extended survivors analysis (XSA) and a statistical catch-at-age model in terms of bias, when spatially restricted tuning series were applied. If we used a single tuning index that covered only the more heavily fished region, estimates of fishing mortality and spawning-stock biomass were seriously biased. If two tuning series each exclusively covering one region were used (without overlap but together covering the whole area), estimates were also biased. Surprisingly, a moderate degree of overlap of spatial coverage of the two tuning indices was sufficient to reduce bias of the XSA assessment substantially. However, performance was best when one tuning series covered the entire stock area
Comprehensive discard reconstruction and abundance estimation using flexible selectivity functions
Aarts, G.M. ; Poos, J.J. - \ 2009
ICES Journal of Marine Science 66 (2009)4. - ISSN 1054-3139 - p. 763 - 771.
north-sea plaice - pleuronectes-platessa - fisheries management - stock assessment - mixed fisheries - beam-trawl - age data - catch - survival - flatfish
The additional mortality caused by discarding may hamper the sustainable use of marine resources, especially if it is not accounted for in stock assessment and fisheries management. Generally, long and precise time-series on age-structured landings exist, but historical discard estimates are often lacking or imprecise. The flatfish fishery in the North Sea is a mixed fishery targeting mainly sole and plaice. Owing to the gear characteristics and a minimum landing size for these species, considerable discarding occurs, especially for juvenile plaice. Discard samples collected by on-board observers are available since 1999 from a limited number of commercial fishing trips. Here, we develop a statistical catch-at-age model with flexible selectivity functions to reconstruct historical discards and estimate stock abundance. We do not rely on simple predefined selectivity ogives, but use spline smoothers to capture the unknown non-linear selectivity and discard patterns, and allow these to vary in time. The model is fitted to the age-structured landings, discards, and survey data, the most appropriate model is selected, and estimates of uncertainty are obtained
The discard problem - A comparative analysis of two fisheries: The English Nephrops fishery and the Dutch beam trawl fishery
Catchpole, T. ; Keeken, O.A. van; Gray, T. ; Piet, G.J. - \ 2008
Ocean & Coastal Management 51 (2008)11. - ISSN 0964-5691 - p. 772 - 778.
north-sea plaice - catch - sole
Discarding is the throwing overboard of unwanted fish or benthic animals [In this study, we define discards in terms of discarded edible fish, crustaceans and benthic organisms. We exclude, therefore, discards of plant material, offal, sea mammals and sea birds.] that have been caught by sea fishing vessels. Some estimates suggest that up to 25% of the global amount of fish caught is discarded annually. In this comparative analysis of discarding in two contrasting North Sea fisheries ¿ the English Nephrops fishery and the Dutch beam trawl fishery ¿ we discuss the effectiveness of measures that might reduce their rates of discarding, including management measures, market forces and fisher's behaviour. Our findings are that despite the many differences between the two fisheries and their respective discard problems, one common thread ¿ the importance of appropriate incentives ¿ runs through both of them.
The arms race between fishers
Rijnsdorp, A.D. ; Poos, J.J. ; Quirijns, F.J. ; Hille Ris Lambers, R. ; Wilde, J.W. de; Heijer, W.M. den - \ 2008
Journal of Sea Research 60 (2008)1-2. - ISSN 1385-1101 - p. 126 - 138.
north-sea plaice - hake merluccius-bilinearis - maturation reaction norms - fishing vessels - mixed fisheries - fleet dynamics - behavioral inferences - population-dynamics - beam trawlers - catch
An analysis of the changes in the Dutch demersal fishing fleet since the 1950s revealed that competitive interactions among vessels and gear types within the constraints imposed by biological, economic and fisheries management factors are the dominant processes governing the dynamics of fishing fleets. Double beam trawling, introduced in the early 1960s, proved a successful fishing method to catch deep burying flatfish, in particular sole. In less than 10 years, the otter trawl fleet was replaced by a highly specialised beam trawling fleet, despite an initial doubling of the loss rate of vessels due to stability problems. Engine power, size of the beam trawl, number of tickler chains and fishing speed rapidly increased and fishing activities expanded into previously lightly fished grounds and seasons. Following the ban on flatfish trawling within the 12 nautical mile zone for vessels of more than 300 hp in 1975 and with the restriction of engine power to 2000 hp in 1987, the beam trawl fleet bifurcated. Changes in the fleet capacity were related to the economic results and showed a cyclic pattern with a period of 6¿7 years. The arms race between fishers was fuelled by competitive interactions among fishers: while the catchability of the fleet more than doubled in the ten years following the introduction of the beam trawl, a decline in catchability was observed in reference beam trawlers that remained the same. Vessel performance was not only affected by the technological characteristics but also by the number and characteristics of competing vessels.
Standardizing commercial CPUE data in monitoring stock dynamics: Accounting for targeting behaviour in mixed fisheries
Quirijns, F.J. ; Poos, J.J. ; Rijnsdorp, A.D. - \ 2008
Fisheries Research 89 (2008)1. - ISSN 0165-7836 - p. 1 - 8.
beam trawl fleet - north-sea - competitive interactions - demersal fisheries - effort allocation - fishing vessels - gadus-morhua - catch - impact - plaice
Catch per unit effort (CPUE) is commonly used as an indicator for monitoring developments in stock size. To ensure proportionality between average CPUE and total stock size, two processes that should be accounted for are the degree of targeting behaviour of the fleet and the management-induced responses in fishing behaviour. We studied the effect of restrictive individual quotas and targeting behaviour on average CPUE in the Dutch beam trawl fleet. Fishing opportunities varied in time and across species due to changes in quotas. Using catch and effort data by fishing trip of the total fleet and haul-by-haul data from a reference fleet, targeting behaviour of the beam trawl fleet was quantified for sole and plaice, at various space and time scales. Sole was targeted on all scales examined, whereas plaice was only targeted on a micro-scale of 10 × 10 nautical miles. When sole quota restrictions were relaxed, the fleet increasingly targeted sole instead of plaice. Targeting indices for sole and plaice were negatively correlated. Our findings indicate that catch and effort data by fishing trip are sufficient to characterise targeting behaviour on a macro-scale, whereas haul-by-haul data are needed to quantify the targeting on a micro-scale (30 × 30 nautical miles). The micro-scale targeting index can be used to standardize macro-scale CPUE data for bias due to variations in directed fishing among local fishing grounds.
Evaluating the science behind the management advice for North Sea cod
Reeves, S.A. ; Pastoors, M.A. - \ 2007
ICES Journal of Marine Science 64 (2007)4. - ISSN 1054-3139 - p. 671 - 678.
sequential population analysis - stock assessment - atlantic - catch - recruitment - fisheries
Since 1974, annual assessments have constituted the core of the scientific advice underpinning management of the North Sea cod stock. Here, we base our evaluation of the assessments' performance on the quality of the advice and on the wider issue of how science is used to produce management advice. At the same time, we consider catch-at-age analyses and catch forecasts in the context of the amount of person-time and expertise available at the relevant working group meetings. The results indicate that, generally, the catch forecasts have been positively biased and that the bias has been driven by three main factors: (i) substantial overestimates of terminal stock size since the late 1990s, (ii) overestimates of incoming recruitment, and (iii) overestimates of growth. information for other North Sea stocks (haddock, plaice, and sole) suggests that bias is a problem generally, not one unique to cod. Our results include a discussion of ways to use science more effectively in supplying management advice.
An experiment on effort allocation of fishing vessels: the role of interference competition and area specialization
Poos, J.J. ; Rijnsdorp, A.D. - \ 2007
Canadian Journal of Fisheries and Aquatic Sciences 64 (2007)2. - ISSN 0706-652X - p. 304 - 313.
ideal free distribution - southern north-sea - spatial-distribution - location choice - fleet dynamics - beam trawlers - fisheries - catch - consequences - movement
A temporarily closed area established to protect spawning Atlantic cod (Gadus morhua) in the North Sea allowed us to study the response of the Dutch beam trawl fleet exploiting common sole (Solea solea) and plaice (Pleuronectes platessa). A number of vessels left the North Sea 1 month earlier than the normal seasonal pattern. The vessels that continued fishing in the North Sea were concentrated in the remaining open areas. In the first week after the closure, the catch rate decreased by 14%, coinciding with an increase in crowding of 28%. Area specialisation affected the response of individual vessels because vessels without prior experience in the open areas showed a larger decline in catch rate compared with vessels that previously fished in these open areas and were more likely to stop fishing during the closed period. The decrease in catch rate in response to the increase in competitor density allowed us to estimate the strength of the interference competition.
Estimating stock parameters from trawl cpue-at-age series using year-class curves
Cotter, A.J.R. ; Mesnil, B. ; Piet, G.J. - \ 2007
ICES Journal of Marine Science 64 (2007)2. - ISSN 1054-3139 - p. 234 - 247.
north-sea - fishing mortality - natural mortality - catch
A year-class curve is a plot of log cpue (catch per unit effort) over age for a single year class of a species (in contrast to the better known catch curve, fitted to multiple year classes at one time). When linear, the intercept and slope estimate the log cpue at age 0 and the average rate of total mortality, Z, respectively. Here, we suggest methodological refinements within a linear least squares framework. Candidate models may include a selectivity term, fleet-specific parameters, and polynomials in year to allow for gradual variations of Z. An iterative weighting method allows for differing precisions among the different fleets, and a forward (one-step ahead) validation procedure tests predicted cpue against observed values. Choice of the best approximating model(s) is made by ranking the biological credibility of each candidate model, then by comparing graphic plots, precision of prediction, and the Akaike Information Criterion. Two example analyses are (i) a comparison of estimated and true results for five stock simulations carried out by the US National Research Council, and (ii) modelling three beam trawl surveys for plaice (Pleuronectes platessa) in the North Sea. Results were consistent with known, age-related, offshore migrations by plaice. Year-class curves are commended as a widely applicable, statistically based, visual, and robust method
Annual trends in catchability and fish stock assessments
Marchal, P. ; Ulrich, C. ; Korsbrekke, K. ; Pastoors, M.A. ; Rackham, B. - \ 2003
Scientia Marina 67 (2003). - ISSN 0214-8358 - p. 63 - 73.
trawl fishery - age data - catch - model - cod - populations - information - selectivity - parameter - dynamics
A key assumption of many fish stock assessment models is that catchability is constant over time. We assume here that trends in catchability may occur through fishing power creeping. The tuning fleets, which are prone to fishing power development, may be identified using the "Hybrid" method. A range of catchability trends, including values derived from the "Hybrid" method, is then implemented to standardise the fishing effort of some tuning fleets used in the stock assessments performed by XSA (eXtended Survivors Analysis). Stocks being assessed are the North Sea cod, saithe, plaice and sole. The performances of the new and traditional XSA assessments are compared using criteria based on the precision of catchability estimates, stationarity of Log-catchability residuals and retrospective patterns relative to fishing mortality, spawning stock biomass and recruitment estimates. The performances of the North Sea cod, plaice and sole assessments could be enhanced by accounting for an overall annual increase in the catchability of some of the tuning fleets. No significant trends could be detected in the catchability of the tuning fleets relative to the assessment of the North Sea saithe. By contrast with the traditional assessment, the spawning biomass of cod is expected not to have increased between 1997 and 1998, while the fishing mortality of sole is expected to have increased over the same period.
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