Adult hooded seals (Cystophora cristata) may dive for ~1hr to depths of more than 1000 m. To achieve this they store large amounts of oxygen bound to hemoglobin (Hb) in the blood and to myoglobin (Mb) in their skeletal muscles, and economize with these stores through cardiovascular and metabolic adjustments during dives. Their pups are born extremely precocial and display a rapid increase in diving duration and depth shortly after weaning (Folkow et al. 2010 ), which takes place after a lactation period of only 3–4 days. Blood Hb levels are at birth already at the level of adults, but muscle Mb levels are only at 25% of the adult value (Burns et al. 2007). To investigate factors governing the development of Mb, muscle biopsies were collected at intervals from Musculus longissimus dorsi (LD) of weaned captive hooded seal pups that were kept in an indoor pool. In addition, liver samples were collected from wild neonate and captive juveniles, for analysis of liver iron stores. Captive pups showed a rapid initial increase in Mb levels in LD, from 25.5 ± 3.4 mg/g (n=4) to 43.7 ± 6.4 mg/g (n=4) within the first month, which corresponded to 82% of their Mb levels at one year of age (53.3 ± 7.9 mg/g (n=4)). This development coincides with the rapid initial increase in dive durations of free-living hooded seal pups (Folkow et al. 2010), which suggests that the Mb level influences their diving behavior. The liver iron content was extremely high in young compared to adult animals (1.06 ± 0.6 mg/mg (n=12) vs. 0.06 ± 0.02 mg/g (n=3), mean difference 0,99 ± 0,14 mg/mg). This suggests that the rapid postnatal Mb development in hooded seal pups is supported by prenatally formed liver iron stores.

References: 

Burns, J. M., Lestyk, K., Folkow, L. P., Hammill, M. O. & Blix, A. S. 2007. Journal of Comparative Physiology B 177, 687–700 Folkow, L.P., Nordøy, E.S. & Blix, A.S. 2010. Polar Biology 33, 433–411