Marc H Taylor

On the Sensitivity of Field Reconstruction and Prediction Using Empirical Orthogonal Functions Derived from Gappy Data

AbstractEmpirical orthogonal function (EOF) analysis is commonly used in the climate sciences and elsewhere to describe, reconstruct, and predict highly dimensional data fields. When data contain a high percentage of missing values (i.e., gappy), alternate approaches must be used in order to correctly derive EOFs. The aims of this paper are to assess the accuracy of several EOF approaches in the reconstruction and prediction of gappy data fields, using the Galapagos Archipelago as a case study example. EOF approaches included least squares estimation via a covariance matrix decomposition [least squares EOF (LSEOF)], data interpolating empirical orthogonal functions (DINEOF), and a novel approach called recursively subtracted empirical orthogonal functions (RSEOF). Model-derived data of historical surface chlorophyll-a concentrations and sea surface temperature, combined with a mask of gaps from historical remote sensing estimates, allowed for the creation of true and observed fields by which to gauge the ...

Trophic and environmental drivers of the Sechura Bay Ecosystem (Peru) over an ENSO cycle

Interannual environmental variability in Peru is dominated by the El Niño Southern Oscillation (ENSO). The most dramatic changes are associated with the warm El Niño (EN) phase (opposite the cold La Niña phase), which disrupts the normal coastal upwelling and affects the dynamics of many coastal marine and terrestrial resources. This study presents a trophic model for Sechura Bay, located at the northern extension of the Peruvian upwelling system, where ENSO-induced environmental variability is most extreme. Using an initial steady-state model for the year 1996, we explore the dynamics of the ecosystem through the year 2003 (including the strong EN of 1997/98 and the weaker EN of 2002/03). Based on support from literature, we force biomass of several non-trophically-mediated ‘drivers’ (e.g. Scallops, Benthic detritivores, Octopus, and Littoral fish) to observe whether the fit between historical and simulated changes (by the trophic model) is improved. The results indicate that the Sechura Bay Ecosystem is a relatively inefficient system from a community energetics point of view, likely due to the periodic perturbations of ENSO. A combination of high system productivity and low trophic level target species of invertebrates (i.e. scallops) and fish (i.e. anchoveta) results in high catches and an efficient fishery. The importance of environmental drivers is suggested, given the relatively small improvements in the fit of the simulation with the addition of trophic drivers on remaining functional groups’ dynamics. An additional multivariate regression model is presented for the scallop Argopecten purpuratus, which demonstrates a significant correlation between both spawning stock size and riverine discharge-mediated mortality on catch levels. These results are discussed in the context of the appropriateness of trophodynamic modeling in relatively open systems, and how management strategies may be focused given the highly environmentally influenced marine resources of the region.

What model suits ecosystem-based fisheries management? A plea for a structured modeling process

As tools within ecosystem-based fisheries management (EBFM), a wide range of Ecosystem Models (EMs) have been designed to represent ecosystem complexity, but it is not always clear how the outputs of these models can be applied. We address this debate in a literature review to illustrate how a better understanding of ecosystem modeling within the EBFM framework could facilitate the use of EMs in the decision-making process. We classify EMs according to their complexity, and qualitatively evaluate their level of success with regard to five general goals of EBFM. In principle, no single EM is found to successfully accomplish all the EBFM goals. Therefore, we suggest that the way in which ecosystem modeling can effectively contribute to EBFM is through a structured modeling process, which should be pursued according to the context of each specific area. Within this planning strategy a range of Ems should be considered, from rather simple ones with few parameters, whose outputs are scientifically robust but possibly of limited use within the EBFM, to those which include a large number of ecosystem elements yet at the expense of increased uncertainty. If multiple EMs, despite their different assumptions, leads to consistent and converging results then robust management decisions will be supported. The present paper appears particularly useful to anyone confronted with the selection of modeling tools for the implementation of fisheries management strategies considering the particular situation of the fishery.

TropFishR: an R package for fisheries analysis with length‐frequency data

Summary The R package TropFishR is a new analysis toolbox compiling single-species stock assessment methods specifically designed for data-limited fisheries analysis using length-frequency data. It includes methods for (i) estimating biological stock characteristics such as growth and mortality parameters, (ii) exploring technical aspects of the fisheries (e.g. exploitation rate and selectivity characteristics), (iii) assessing size and composition of a fish stock by means of virtual population analysis (VPA), and (iv) assessing stock status with yield prediction and production models. This paper introduces the package and demonstrates the functionality of a selection of its core methods. TropFishR modernises traditional stock assessment methods by easing application and development and by combining it with advanced statistical approaches.

Aqua- and Mariculture Management: A Holistic Perspective on Best Practices

This chapter presents an overview of some of the main issues facing the development of aqua- and mariculture, and provides a framework for improving sustainability from socio-economic and ecological perspectives. We review present global trends in productivity and the institutional and legal frameworks that may affect policy and trade in the coming years. Focus is placed on summarizing recent trends in socio-ecological approaches, such as the “Ecosystem Approach to Aquaculture”, which emphasizes development within the constraints of ecosystem functioning and social well-being. A framework of best practices for long-term sustainability is proposed, which is comprised of steps involving risk assessment, monitoring, and adaptive management. From this holistic perspective, we discuss the future prospects for aquaculture development in terms of its promise of improved food security, nutrition and income.