First Comprehensive Study of Telomere Length Measured by Southern Blot Hybridization and Oxidative Stress Across 12 Captive Marine Mammal Species

ABSTRACT Telomeres, repetitive nucleotide sequences at chromosome ends, shorten with oxidative damage and cell replication, and are increasingly used as biomarkers of stress and physiological state. Despite this potential, telomere length (TL) in marine mammals has been measured using Southern blot hybridization in only a few cases, often from different tissue types, limiting interspecific comparisons. This study provides the first standardized TL dataset for leukocytes from blood samples of 42 captive individuals representing 12 species (six cetaceans and six pinnipeds), analyzed with the same Southern blot protocol. Additionally, plasma reactive oxygen metabolites (d‐ROMs), biological antioxidant potential (BAP), and proportion of lymphocytes among leukocytes—potentially influencing TL—were measured. Species‐mean TLs ranged from 12.1 to 13.9 kb. Bayesian models revealed no statistically meaningful differences in TL, d‐ROMs, BAP, or lymphocyte proportion between cetaceans and pinnipeds. At the individual level, TL showed no significant association with d‐ROMs, BAP, or lymphocyte proportion, but a weak negative association with age. Because all animals were captive, future research incorporating wild individuals will be essential to clarify species‐ or taxon‐specific physiological baselines. This study fills a methodological gap by providing the first multi‐species, standardized reference for TL and oxidative stress markers in marine mammals from the blood cell type.