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Marine Mammal Physiology: Requisites for Ocean Living
to occur incidentally as a function of capturing and eating prey while submerged. Fasting
dolphins consumed seawater at rates ranging between 4.5 and 13 ml/kg/day (Telfer et al.
1970; Hui 1981), which are not exceptional and more indicative of volumes more closely
related to incidental ingestion than active consumption. In fin and sei whales, which primarily consume crustaceans that have a high salt content, mariposia only contributes to
1%–2% of estimated total water ingestion (Kjeld 2003) and only 2%–3% in bottlenose dolphins (Ridgway 1972) suggesting that mariposia is a very small fraction of water intake
across cetaceans. In the harbor seal, seawater ingestion accounted for 9.2% and 7.3% of total
water flux in fed and fasted animals, respectively, suggesting that the small volume of seawater intake is the consequence of incidental ingestion and that mariposia is not essential
to maintain water balance (Depocas et al. 1971).
Because most marine mammals can concentrate their urine greater than seawater, and
thus, potentially gain free water from active consumption, mariposia may not only serve in
an osmoregulatory capacity. Mariposia has been reported in pinnipeds inhabiting temperate regions, and thought to counter thermal stress. Seawater drinking has been reported
in the Galápagos fur seal (Arctocephalus galapagoensis) that inhabit a tropical region, but
it is not observed in the Antarctic fur seal (Arctocephalus gazella) living in colder regions
(Costa and Gentry 1986; Costa and Trillmich 1988). Fasting or dehydration may also induce
mariposia. Mariposia was reported in dehydrated harp seals (How and Nordøy 2007) and
in a number of fasting otariids (Gentry 1981). Hooded seals with no access to seawater
exhibited an increase in blood osmolality and plasma urea, and the values returned to
normal when the seals were allowed access to seawater (Storeheier and Nordøy 2001; How
and Nordøy 2007). Additionally, dehydrated hooded seals drank on average 1900 ml of
seawater a day (Verlo 2012). Skalstad and Nordøy (2000) calculated that hooded and harp
seals may drink 300 ± 55 and 900 ± 12 ml/day, respectively, amounting to 14% and 27% of
total water turnover, respectively, at low ambient temperature.
The herbivorous dugong, whose habitat is strictly marine, may require more water
than carnivorous marine mammals to facilitate the efficient fermentation of sea grasses.
Additionally, the anatomy of the dugong kidney suggests that they can drink seawater
and gain free water (Lanyon et al. 2006). In contrast, the West Indian manatee that does
not drink appreciable volumes of seawater (Ortiz et al. 1999) is found in both hypo- and
hyperosmotic environments. The relatively high water turnover rate recorded in dugong
suggests the presence of mariposia or sufficiently high metabolic rate to maintain water
balance (Lanyon et al. 2006). Although manatees have the high ability to concentrate their
urine above seawater (Irvine et al. 1980), water turnover rates are not indicative of active
seawater consumption (Ortiz et al. 1999), and it is likely that they need to excrete excessive
salt that is the consequence of the ingestion of plants in marine and estuarine environment
(Reich and Worthy 2006).
The sea otter may be the only marine mammal that actively consumes seawater to
eliminate urea–nitrogen load (Costa 1982). As sea otters can excrete Na + and Cl − in much
greater concentrations than that in seawater, they can obtain a net gain in free water by
consuming seawater (Costa 1982).
Although the number of marine mammals that inhabit strictly freshwater or have
ready access to freshwater environments is small, freshwater drinking is common among
those species that have been studied, including pinnipeds that inhabit on ice packs. The
harp seal consumes freshwater in the form of ice cubes while in captivity (Renouf et al.
1990). Under captive/experimental conditions, harbor seals maintained at high ambient temperature drank freshwater (Irving et al. 1935) or after ingestion of 1 l of seawater
(Albrecht 1950). In the West Indian manatee, water turnover rates were greater in animals
Marine Mammal Physiology: Requisites for Ocean Living
to occur incidentally as a function of capturing and eating prey while submerged. Fasting
dolphins consumed seawater at rates ranging between 4.5 and 13 ml/kg/day (Telfer et al.
1970; Hui 1981), which are not exceptional and more indicative of volumes more closely
related to incidental ingestion than active consumption. In fin and sei whales, which primarily consume crustaceans that have a high salt content, mariposia only contributes to
1%–2% of estimated total water ingestion (Kjeld 2003) and only 2%–3% in bottlenose dolphins (Ridgway 1972) suggesting that mariposia is a very small fraction of water intake
across cetaceans. In the harbor seal, seawater ingestion accounted for 9.2% and 7.3% of total
water flux in fed and fasted animals, respectively, suggesting that the small volume of seawater intake is the consequence of incidental ingestion and that mariposia is not essential
to maintain water balance (Depocas et al. 1971).
Because most marine mammals can concentrate their urine greater than seawater, and
thus, potentially gain free water from active consumption, mariposia may not only serve in
an osmoregulatory capacity. Mariposia has been reported in pinnipeds inhabiting temperate regions, and thought to counter thermal stress. Seawater drinking has been reported
in the Galápagos fur seal (Arctocephalus galapagoensis) that inhabit a tropical region, but
it is not observed in the Antarctic fur seal (Arctocephalus gazella) living in colder regions
(Costa and Gentry 1986; Costa and Trillmich 1988). Fasting or dehydration may also induce
mariposia. Mariposia was reported in dehydrated harp seals (How and Nordøy 2007) and
in a number of fasting otariids (Gentry 1981). Hooded seals with no access to seawater
exhibited an increase in blood osmolality and plasma urea, and the values returned to
normal when the seals were allowed access to seawater (Storeheier and Nordøy 2001; How
and Nordøy 2007). Additionally, dehydrated hooded seals drank on average 1900 ml of
seawater a day (Verlo 2012). Skalstad and Nordøy (2000) calculated that hooded and harp
seals may drink 300 ± 55 and 900 ± 12 ml/day, respectively, amounting to 14% and 27% of
total water turnover, respectively, at low ambient temperature.
The herbivorous dugong, whose habitat is strictly marine, may require more water
than carnivorous marine mammals to facilitate the efficient fermentation of sea grasses.
Additionally, the anatomy of the dugong kidney suggests that they can drink seawater
and gain free water (Lanyon et al. 2006). In contrast, the West Indian manatee that does
not drink appreciable volumes of seawater (Ortiz et al. 1999) is found in both hypo- and
hyperosmotic environments. The relatively high water turnover rate recorded in dugong
suggests the presence of mariposia or sufficiently high metabolic rate to maintain water
balance (Lanyon et al. 2006). Although manatees have the high ability to concentrate their
urine above seawater (Irvine et al. 1980), water turnover rates are not indicative of active
seawater consumption (Ortiz et al. 1999), and it is likely that they need to excrete excessive
salt that is the consequence of the ingestion of plants in marine and estuarine environment
(Reich and Worthy 2006).
The sea otter may be the only marine mammal that actively consumes seawater to
eliminate urea–nitrogen load (Costa 1982). As sea otters can excrete Na + and Cl − in much
greater concentrations than that in seawater, they can obtain a net gain in free water by
consuming seawater (Costa 1982).
Although the number of marine mammals that inhabit strictly freshwater or have
ready access to freshwater environments is small, freshwater drinking is common among
those species that have been studied, including pinnipeds that inhabit on ice packs. The
harp seal consumes freshwater in the form of ice cubes while in captivity (Renouf et al.
1990). Under captive/experimental conditions, harbor seals maintained at high ambient temperature drank freshwater (Irving et al. 1935) or after ingestion of 1 l of seawater
(Albrecht 1950). In the West Indian manatee, water turnover rates were greater in animals