Stock delineation of striped snakehead, Channa striata using multivariate generalised linear models with otolith shape and chemistry data

Salman Khan,Mohammad Afzal Khan,Devendra Kumar Patel,Kaish Miyan,Hayden T Schilling,Ben Maslen

doi:10.1038/s41598-021-87143-9

Abstract

Otoliths are commonly used to discriminate between fish stocks, through both elemental composition and otolith shape. Typical studies also have a large number of elemental compositions and shape measures relative to the number of otolith samples, with these measures exhibiting strong mean–variance relationships. These properties make otolith composition and shape data highly suitable for use within a multivariate generalised linear model (MGLM) framework, yet MGLMs have never been applied to otolith data. Here we apply both a traditional distance based permutational multivariate analysis of variance (PERMANOVA) and MGLMs to a case study of striped snakehead (Channa striata) in India. We also introduce the Tweedie and gamma distributions as suitable error structures for the MGLMs, drawing similarities to the properties of Biomass data. We demonstrate that otolith elemental data and combined otolith elemental and shape data violate the assumption of homogeneity of variance of PERMANOVA and may give misleading results, while the assumptions of the MGLM with Tweedie and gamma distributions are shown to be satisfied and are appropriate for both otolith shape and elemental composition data. Consistent differences between three groups of C. striata were identified using otolith shape, otolith chemistry and a combined otolith shape and chemistry dataset. This suggests that future research should be conducted into whether there are demographic differences between these groups which may influence management considerations. The MGLM method is widely applicable and could be applied to any multivariate otolith shape or elemental composition dataset.

Highlights

Otoliths are commonly used to discriminate between fish stocks, through both elemental composition and otolith shape
This study demonstrated how multivariate generalised linear models (MGLMs) can be applied to otolith chemistry and otolith shape data to test for differences between groups of samples
We showed that distancebased analyses including PERMANOVA are not appropriate for our otolith chemistry data due to violations of the assumption of homogeneity of variance stemming from a non-linear mean–variance relationship in the data

Summary

Introduction

Otoliths are commonly used to discriminate between fish stocks, through both elemental composition and otolith shape. Typical studies have a large number of elemental compositions and shape measures relative to the number of otolith samples, with these measures exhibiting strong mean– variance relationships These properties make otolith composition and shape data highly suitable for use within a multivariate generalised linear model (MGLM) framework, yet MGLMs have never been applied to otolith data. Minor and trace elements laid down within the protein matrix become a permanent record of the chemical characteristics of the environment experienced by the fish[14,15] While both physiological and environmental factors influence the elemental composition of o toliths[16,17], if fish inhabit different water masses. By combining both otolith shape and chemistry data in the same analysis, the ability to differentiate groups of fish can sometimes be improved[22]

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