Stock structure analysis of the declining shovel-nosed lobster Thenus unimaculatus (Burton and Davie, 2007) for effective management and conservation along the Indian coast

Morphometry of Thenus unimaculatus

Abstract

The  shovel-nosed lobster Thenus unimaculatus (Burton and Davie 2007) is one of India’s most important commercially exploited lobster species. The declining trends and collapse of the sand lobster fishery have been reported from the north-west coast of India. Several hypotheses have been proposed to explain this decline, but a lack of basic information on population demographics inhibits hypothesis testing. This study attempted morphometric stock structure analysis of T. unimaculatus along the Indian coast, using 673 specimens collected from five locations during 2017-2019. Data was subjected to allometric transformation to remove size effect and further subjected to multivariate analysis, including principal component analysis (PCA) followed by linear discriminant analysis (LDA) using R software. The first eight principal components (PCs) cumulatively explained 73.97% of the total variance. The misclassification rate (MR) of the LDA model performed to optimise separation among different sampling locations and coasts were 0.30 and 0.26 respectively, indicating clear overlap of the stocks. The results of this study revealed the presence of a single spawning stock of shovel-nosed lobster along the Indian coast, providing insights for adopting holistic management strategies to conserve this declining resource.

Keywords: LDA, Population structure, Putative stocks, Slipper lobster, Truss