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Testing and recommending methods for fitting size spectra to data

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Edwards, AM, Robinson, JPW, Plank, MJ, Baum, JK and Blanchard, JL ORCID: 0000-0003-0532-4824 2017 , 'Testing and recommending methods for fitting size spectra to data' , Methods in Ecology and Evolution, vol. 8, no. 1 , pp. 57-67 , doi: 10.1111/2041-210X.12641.

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Abstract

The size spectrum of an ecological community characterizes how a property, such as abundance or biomass, varies with body size. Size spectra are often used as ecosystem indicators of marine systems. They have been fitted to data from various sources, including groundfish trawl surveys, visual surveys of fish in kelp forests and coral reefs, sediment samples of benthic invertebrates and satellite remote sensing of chlorophyll.Over the past decades, several methods have been used to fit size spectra to data. We document eight such methods, demonstrating their commonalities and differences. Seven methods use linear regression (of which six require binning of data), while the eighth uses maximum likelihood estimation. We test the accuracy of the methods on simulated data.We demonstrate that estimated size-spectrum slopes are not always comparable between the seven regression-based methods because such methods are not estimating the same parameter. We find that four of the eight tested methods can sometimes give reasonably accurate estimates of the exponent of the individual size distribution (which is related to the slope of the size spectrum). However, sensitivity analyses find that maximum likelihood estimation is the only method that is consistently accurate, and the only one that yields reliable confidence intervals for the exponent.We therefore recommend the use of maximum likelihood estimation when fitting size spectra. To facilitate this, we provide documented R code for fitting and plotting results. This should provide consistency in future studies and improve the quality of any resulting advice to ecosystem managers. In particular, the calculation of reliable confidence intervals will allow proper consideration of uncertainty when making management decisions.

Item Type: Article
Authors/Creators:Edwards, AM and Robinson, JPW and Plank, MJ and Baum, JK and Blanchard, JL
Keywords: size spectrum, power law, ecosystem approach to fisheries, ecosystem indicators, individual size distribution, truncated Pareto distribution
Journal or Publication Title: Methods in Ecology and Evolution
Publisher: Wiley-Blackwell Publishing Ltd.
ISSN: 2041-210X
DOI / ID Number: 10.1111/2041-210X.12641
Copyright Information:

Copyright 2016 Her Majesty the Queen in Right of CanadaLicensed under Creative Commons Attribution 4.0 International (CC BY 4.0)https://creativecommons.org/licenses/by/4.0/

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