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The study of hormones reveals mechanisms by which individuals respond to environmental challenges, breed, and regulate all aspects of their life cycles.⁶ Fecal analysis of corticosteroid and reproductive hormones have proved useful in monitoring the endocrine status of terrestrial and marine mammals.^1,4,5 High levels of stress may affect immune system, reducing resistance to diseases and therefore affect the general health of populations.³ The southwest Gulf of California, Mexico, represents an important area in the life cycle of blue whales during winter and early spring, since it serves as a feeding, breeding and nursing area.² Important coastal developments are proposed in the near future, including hotels and marinas, and an increase in marine traffic as well as whale watching activities are expected. The objective of this study is to determine the baseline of glucocorticoid (cortisol, corticosterone) concentrations in blue whale’s feces and to recognize its physiology in a relatively undisturbed environment. We are investigating if glucocorticoid concentrations vary by reproductive status in blue whales. A total of 31 fecal samples have been collected from 24 adult females, 1 mature male and 6 individuals of unknown sex, during the 2009-2012 period. The samples were dehydrated immediately after being collected and were preserved in vials at room temperature until its extraction, using subsamples of 0.1 g of dry weight diluted in 1ml of methanol. The radioimmunoassay (RIA) technique was validated for cortisol, corticosterone and progesterone, through accuracy and parallelism. We analyzed the concentrations by reproductive status for sexually mature females, lactating and pregnant females. Pregnancy was assessed through progesterone concentrations (p<0.05) (Mean ± SD: 1505.2 ± 1106.6 ng/g), which were significantly higher (p<0.05) than mature (48.7 ± 112.6 ng/g) and lactating females (23.0 ± 14.2 ng/g). The pregnant females also showed significant differences (p<0.05) in corticosterone (49.8± 23.4 ng/g) compared to the mature (17.4 ± 5.2 ng/g) and lactating females (13.2 ± 3.4 ng/g). In contrast, cortisol did not show significant difference between female reproductive stages: pregnant (184.1 ± 48.7 ng/g), mature (224.3 ± 109.0 ng/g), and lactating (114.4 ± 79.3 ng/g).

Palabras clave: stress hormones; feces; blue whales

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