Do all ocean mammals drink saltwater?
The answer is yes. Marine mammals are well adapted to their hyperosmotic environment. To osmoregulate properly in a marine habitat, physiological mechanisms intended to conserve fresh water and thus avoid dehydration are required. However, as challenging as enduring life in a high-salt environment may be, aquatic mammals also diverged and inhabited freshwater niches. Although adapting to freshwater habitats may appear beneficial because conserving fresh water no longer poses a problem, those aquatic mammals that adopted such habitats are confronted with a different osmotic challenge. Living in a salt-‘free’ environment requires the appropriate physiological mechanisms to conserve electrolytes. However, some marine mammals have adapted to yet a third, and potentially greater, osmotic challenge, prolonged fasting in an arid terrestrial environment (i.e. Ortiz et al., 1978). The ability to maintain water balance and electrolyte homeostasis during extended periods of complete abstinence fr
