Precision and accuracy of fish length measurements obtained with two visual underwater methods

During the VITAL cruise in the Bay of Biscay in summer 2002, two devices for measuring the length of swimming fish were tested: 1) a mechanical crown that emitted a pair of parallel laser beams and that was mounted on the main camera and 2) an underwater auto-focus video camera. The precision and accuracy of these devices were compared and the various sources of measurement errors were estimated by repeatedly measuring fixed and mobile objects and live fish. It was found that fish mobility is the main source of error for these devices because they require that the objects to be measured are perpendicular to the field of vision. The best performance was obtained with the laser method where a video-replay of laser spots (projected on fish bodies) carrying real-time size information was used. The auto-focus system performed poorly because of a delay in obtaining focus and because of some technical problems

Development of management models and assessment methods for red deer on the open hill in Scotland

Models to assist the management of red deer on the open hill in Scotland and methods for estimating red deer abundance were studied in this thesis. Currently red deer abundance is assessed by census methods with no estimate of precision. A coefficient of variation of 11-13% was estimated as the precision of repeated census counts on Rum. Misclassification in census counts was studied. Mean relative differences between two simultaneous independent counts were -0.9% (0.16) for stags, -0.5% (0.10) for hinds and 4.4% (0.61) for calves. Numbers in brackets are standard errors. Aerial line transect methodology for estimating deer numbers was tested. Mean estimates were comparable to a census count. In a case study comparison between line transects and census counts the former were shown to be quicker and cheaper for large areas. Past numbers of red deer on the open hill in Scotland estimated by Markov chain Monte Carlo methods, suggested a 30% increase between 1970 and 1992, followed by a small decrease since. Convergence problems lead to reservations about the results. A postal questionnaire survey provided information about current management practices and data availability. An age and sex structured stochastic population dynamics model for red deer was developed incorporating age, sex and density dependent survival rates and weight dependent fertility rates. An updating algorithm was proposed for calibrating the model parameters for any population using only count and cull information for that population. Prior parameter values were obtained from well studied populations. The updating algorithm was based on approximate sequential Bayesian estimation carried out by simulation. Additional features were linear filtering of population estimates and a smoothed bootstrap to generate model parameter estimates. The linear filtering reduced one step ahead prediction errors. The smoothed bootstrap allowed substantial reduction in the number of simulations. For an example red deer population posterior parameter values produced smaller variances of predicted numbers compared to prior parameter values. The calibrated model was used to investigate the effects of alternative culling strategies for a red deer population

Effects of Ignoring Survey Design Information for Data Reuse

Data are currently being used, and reused, in ecological research at an unprecedented rate. To ensure appropriate reuse however, we need to ask the question: "Are aggregated databases currently providing the right information to enable effective and unbiased reuse?" We investigate this question, with a focus on designs that purposefully favor the selection of sampling locations (upweighting the probability of selection of some locations). These designs are common and examples are those designs that have uneven inclusion probabilities or are stratified. We perform a simulation experiment by creating data sets with progressively more uneven inclusion probabilities and examine the resulting estimates of the average number of individuals per unit area (density). The effect of ignoring the survey design can be profound, with biases of up to 250% in density estimates when naive analytical methods are used. This density estimation bias is not reduced by adding more data. Fortunately, the estimation bias can be mitigated by using an appropriate estimator or an appropriate model that incorporates the design information. These are only available however, when essential information about the survey design is available: the sample location selection process (e.g., inclusion probabilities), and/or covariates used in their specification. The results suggest that such information must be stored and served with the data to support meaningful inference and data reuse.Peer reviewe

Statistical ecology comes of age

The desire to predict the consequences of global environmental change has been the driver towards more realistic models embracing the variability and uncertainties inherent in ecology. Statistical ecology has gelled over the past decade as a discipline that moves away from describing patterns towards modelling the ecological processes that generate these patterns. Following the fourth International Statistical Ecology Conference (1-4 July 2014) in Montpellier, France, we analyse current trends in statistical ecology. Important advances in the analysis of individual movement, and in the modelling of population dynamics and species distributions, are made possible by the increasing use of hierarchical and hidden process models. Exciting research perspectives include the development of methods to interpret citizen science data and of efficient, flexible computational algorithms for model fitting. Statistical ecology has come of age: it now provides a general and mathematically rigorous framework linking ecological theory and empirical data.Peer reviewe

Forage fish interactions: A symposium on creating the tools for ecosystem-based management of marine resources

Forage fish (FF) have a unique position within marine foodwebs and the development of sustainable harvest strategies for FF will be a critical step in advancing and implementing the broader, ecosystem-based management of marine systems. In all, 70 scientists from 16 nations gathered for a symposium on 12–14 November 2012 that was designed to address three key questions regarding the effective management of FF and their ecosystems: (i) how do environmental factors and predator–prey interactions drive the productivity and distribution of FF stocks across ecosystems worldwide, (ii) what are the economic and ecological costs and benefits of different FF management strategies, and (iii) do commonalities exist across ecosystems in terms of the effective management of FF exploitation