Methods for estimating a critical value for determining the freshwater/estuarine habitat residence of American eels from otolith Sr: Ca data
Resource
Estuarine Coastal and Shelf Science, 133,293-303
Journal
Estuarine, Coastal and Shelf Science
Journal Volume
133
Pages
293-303
Date Issued
2013
Author(s)
Abstract
Linear discriminant analysis (LDA) and habitat discrimination critical value (HDCV) methods are alternatives for evaluating the migratory history, such as the proportion of residence in freshwater (%fwr) and estuarine/marine habitats, of individual American eels (Anguilla rostrata) via the analysis of otolith Sr:Ca data. The LDA process requires Sr:Ca data from both freshwater and estuarine/marine groups while the mean+cSD method requires only a freshwater standard. For the two group (freshwater, estuarine/marine), single predictor variable (Sr:Ca) case, the LDA process defaults to Fisher's linear discriminant where the HDCV equals the average of the group mean Sr:Ca values. The difference between freshwater and estuarine resident eel mean otolith Sr:Ca values, based on 13 published studies and the current study (n=14), decreased with increasing freshwater group otolith mean (r=0.80, p<0.001), reflecting a relatively constant estuarine group mean (r=0.38, p=0.17). A process is proposed for estimating a HDCV from freshwater group otolith Sr:Ca mean and SD values based on empirical linear relations between the LDA, HDCV and freshwater mean (n=14, r=0.90, p<0.0001) and c and SD (n=14, r=-0.89, p<0.0001) from the equation HDCV=mean+cSD. Variation in the sample sizes of otolith Sr:Ca values used in the discriminant process of estimating a HDCV, while statistically significant, had trivial effect sizes that were likely of little biological consequence. However, larger sample sizes are preferred over smaller sample sizes. Estimates of %fwr increased with increases in the HDCV. Differences in %fwr estimates over a range of HDCVs were highly statistically significant and effect sizes increased with increased HDCV difference. As HDCV levels increased, growth rate estimates increased for a given %fwr value. A HDCV difference of ≤0.5×10-3 produced a small effect size. Accurate estimation of a HDCV is fundamental to the assessment of the habitat residence and inter-habitat movement of American eels and perhaps of other diadromous fishes and helps minimize bias in dependent estimates of other useful statistics such as the percentage of freshwater residence (%fwr) and growth rate. © 2013 Elsevier Ltd.
Subjects
American eel; Diadromous fish; Linear discriminant analysis; Otolith; Sr:Ca ratios
SDGs
Other Subjects
discriminant analysis; eel; fish; freshwater; growth rate; habitat; movement; otolith; population size; Anguilla; Anguilla rostrata; Pisces
Type
journal article
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Jessop BM,Shiao JC, Iizuka Y. 2013. Methods for estimating a critical value for determining eel SrCa ratio. Est Coastal and Shelf Sci. 133_293_303.pdf
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