Insights on recent baleen whale (Cetacea: Mysticeti) stranding events along the south-west coast of India

Ratheesh Kumar, R and Sumithra, T G and Utthamapandian, U and Durga, V and Monolisha, S and Anto, Alvin and Vinayak, S and Akhilesh, K V and George, Grinson and Gopalakrishnan, A (2025) Insights on recent baleen whale (Cetacea: Mysticeti) stranding events along the south-west coast of India. Regional Studies in Marine Science, 89. pp. 1-13. ISSN 2352-4855

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Abstract

The present study provides the most recent data (2004–2023) on baleen whale strandings along the Indian southwest coast, a potential biodiversity and marine fisheries production hotspot. The primary survey during 2023 recorded nine stranding events with more stranding between July and November. Morphometric identification classified the stranded whales into Balaenoptera musculus (N = 2) and Balaenoptera edeni (N = 6), and one remained unidentified. Molecular identification confirmed the morphometric identification. There were two subspecies in B. edeni, viz. B. edeni brydei and B. edeni edeni with 3.9 ± 0.73 % intra-subspecies pairwise genetic distance. Data analysis of the last 20 years revealed 33 baleen whale strandings with B. edeni as the most frequently reported (63.63 %). Average stranding during 20 years was 0.0192 ± 0.0162/ km and 1.65 ± 2.38/year/1390 km. There was a ten-fold increase after 2014 (from 0.3/year during 2004–2013 to 3/year during 2014–2023). Temporal analysis revealed a significant difference in strandings across the Indian seasons, with higher numbers during monsoon and lower numbers during summer. Spatial analysis revealed that stranding reports were not evenly distributed, suggesting the need for region-specific management measures. Karnataka and Kerala had the maximum strandings. A strong positive (Kendall's correlation (τ) = 0.57; P = 0.009) and negative (τ = −0.50; P = 0.02) correlations were observed between stranding and chlorophyll concentration and between strandings and sea surface temperature during the 20-year period. Briefly, the results offer interesting insights into baleen whale strandings, which have worldwide relevance in marine ecosystems.

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