Molecular identification of a fin whale stranded in Veracruz, southern Gulf of Mexico

Abstract

Baleen whale strandings are rare in the southern Gulf of Mexico and can provide valuable molecular information where species are infrequently documented. We analyzed tissue from a highly decomposed whale stranded on the central coast of Veracruz, Mexico, by amplifying and bidirectionally sequencing the mitochondrial DNA control region. A total of four chromatogram reads were generated: one forward and one reverse read for each of the two overlapping amplicons (5′ and 3′). Accordingly, nucleotide positions located within the overlap between fragments were independently covered by up to four reads, whereas positions outside the overlap were supported by the corresponding forward and reverse reads. A nucleotide BLAST search identified the specimen as a fin whale (Balaenoptera physalus), showing 99% identity to the mitochondrial reference sequence MF409243.1. Three nucleotide substitutions relative to that reference occurred at positions 15499 (A>G), 15650 (T>C), and 15754 (C>T). The three nucleotide substitutions were each supported by high-quality base calls and by all independent reads covering the corresponding position. In a maximum-likelihood analysis, the Veracruz sequence clustered within a clade containing sampled North Atlantic fin whale control-region sequences. The specimen’s estimated length (~11 m) was consistent with a young individual, although decomposition prevented definitive age classification. The mitochondrial result indicates affinity with sampled North Atlantic diversity but does not establish geographic origin or stock identity. These results provide molecular confirmation of a rare fin whale occurrence in the southern Gulf of Mexico and demonstrate that highly decomposed stranding material can retain sufficient good quality mitochondrial DNA for reliable species identification. Systematic tissue preservation and archiving during stranding responses can therefore improve verified occurrence records in poorly documented regions. This case underscores the scientific value of collecting and preserving stranded specimen samples from vulnerable species that are exposed to heavy maritime traffic, artisanal fisheries, and ongoing oceanographic variability in poorly documented regions of the Gulf of Mexico.