J Comp Physiol B (2017) 187:493–502 DOI 10.1007/s00360-016-1048-3 ORIGINAL PAPER Hooded seal (Cystophora cristata) pups ingest snow and seawater during their post‑weaning fast Pauke C. Schots1 · Marie E. Bue1 · Erling S. Nordøy1 Received: 6 August 2016 / Revised: 21 October 2016 / Accepted: 26 October 2016 / Published online: 9 November 2016 © The Author(s) 2016. This article is published with open access at Springerlink.com Abstract The purpose of this study was to evaluate the maintenance of water balance and excretion of urea during importance of exogenous water intake (snow/seawater) in the post-weaning fast of hooded seal pups. hooded seal (Cystophora cristata) pups during their post- weaning fast. In this study, five hooded seal pups had ad Keywords Tritiated water · Mariposia · Water balance · lib access to snow and seawater for the first 12 and last Hooded seal · Post-weaning fast · Homeostasis 21 days of their post-weaning fast, respectively. Total body water and water flux were determined during both exposure Abbreviations periods by use of the tritiated water method. Blood samples RH Relative humidity were collected to monitor changes in hematocrit, plasma S.A. Specific activity urea and plasma osmolality. Body mass loss was on aver- TBF Total body fat 1 age 0.36 kg day− . Average total body water changed from TBP Total body protein 15.7 to 11.4 L, while total water influx changed from 15 1 1 to 18 mL day− kg− during snow and seawater exposure, respectively. Of this influx an average of 35% can be attrib- Introduction uted to metabolic water, while approximately 8% was due to respiratory water influx. Interestingly, 56 and 58% of the The hooded seal (Cystophora cristata, Erxleben, 1777) total water influx was due to snow and seawater ingestion, lives in the North Atlantic where it breeds in four differ- 1 1 respectively, amounting to 8 mL day− kg− snow (counted ent geographical areas: the Davis Strait, off the coasts of 1 1 as liquid water) and 10 mL day− kg− seawater. Based on Labrador and Newfoundland, the Gulf of St Lawrence, and the results of the plasma parameters it is concluded that the “West-Ice” being the pack ice between Jan Mayen and fasting hooded seal pups maintain water balance and home- Greenland (Bowen et al. 1985; Kovacs and Lavigne 1986; ostasis when access to snow or seawater is permitted. It is Lydersen et al. 1997). The pups from the latter group are further concluded that snow and seawater intake, in addi- born in the second half of March (Rasmussen 1960). As tion to metabolic and respiratory water, is important for a consequence of the unstable and unpredictable environ- ment wherein pups are born, adaptations have evolved to survive. These adaptations consist of a large size at birth, Communicated by G. Heldmaier. prenatal blubber deposits (Oftedal et al. 1993), prenatal moult (Oftedal et al. 1991), short lactation period, and effi- Electronic supplementary material The online version of this cient postnatal fat and energy transfer from milk to body article (doi:10.1007/s00360-016-1048-3) contains supplementary material, which is available to authorized users. tissue (Oftedal et al. 1993). Hooded seals weigh around 20–24 kg at birth. The lactation period is short but intense, * Pauke C. Schots lasting only 4 days. During this period they gain 7 kg per [email protected] day, resulting in a body mass of more than 42 kg at wean- 1 Department of Arctic and Marine Biology, UiT-The Arctic ing (Bowen et al. 1987, 1985; Kovacs and Lavigne 1992; University of Norway, Breivika, 9037 Tromsø, Norway Lydersen et al. 1997). After the lactation period, the hooded 1 3 494 J Comp Physiol B (2017) 187:493–502 seal pups go through a post-weaning fast. The fast lasts for vitulina) did not drink seawater, but derive enough water about 1 month (Bowen et al. 1987; Folkow et al. 2010) in from the food to maintain their water balance. Albrecht 1 which they loose on average 0.4 kg day− (Bowen et al. (1950) observed that harbour seals do not tolerate seawater 1987). During their fast, the hooded seal pups of the “West- and that they vomit and get diarrhoea after orally admin- Ice” population passively follow the pack ice in a south- istering a seawater volume of 3.3% of their body mass. western direction. During this period the pups remain in Storeheier and Nordøy (2001), on the other hand, observed the vicinity of the pack ice where they have access to fresh that after a seawater bolus administration (2% of the body water in the form of snow and ice. From the moment they mass) through a stomach tube in harp seals (Phoca groen- leave the pack ice, however, they are pelagic in open sea- landica), urine osmolality remained stable and above sea- water for 2.5 months before returning to the ice (Folkow water levels. They further observed that the animals were et al. 2010). able to concentrate urinary sodium and chloride to levels To survive in a hyperosmotic environment, physiological above seawater. Additional support for the tolerance of sea- adaptations are required to conserve water and avoid dehy- water was found by Depocas et al. (1971). They found that dration. In pinnipeds, water can leave the body through harbour seals do in fact ingest seawater. However, since three different routes: respiratory evaporation, cutaneous this volume was small, it was concluded that this was an evaporation and urine production. Although hooded seals accidental ingestion due to the intake of food under water have sweat glands (Kovacs and Lavigne 1986), pinnipeds and not due to deliberate mariposia. They also concluded do not appear to sweat (Ridgway 1972; Whittow et al. that fasting harbour seals derive enough oxidative water to 1972). One of the water conserving adaptations found in maintain their water balance. These conclusions were the pinnipeds is nasal counter current heat exchange. Through general assumptions in later studies on water flux, water this morphological adaptation the expired air temperature is balance and food intake in marine mammals (Folkow and lowered, which reduces the respiratory water loss (Folkow Blix 1987; Hong et al. 1982). and Blix 1987; Huntley et al. 1984). Another morpho- However, other studies on several marine mammal spe- logical characteristic are the reniculate kidneys, found in cies have shown that mariposia does occur (Costa 2009; cetaceans and pinnipeds (Ortiz 2001). Reniculate kidneys Suzuki and Ortiz 2015). It has been observed that Aus- have an increased medullary thickness allowing the pro- tralian fur seals (Arctocephalus forsteri), Steller sea lions duction of urine with an increased osmolality to reduce (Eumetopias jubatus), Northern fur seals (Callorhinus urinary water loss (Bester 1975; Vardy and Bryden 1981). ursinus) and California sea lions (Zalophus californianus) Marine mammals are able to produce urine with an osmo- drink both from tidal pools and from the sea (Gentry 1 lality well above that of seawater (1000 mOsm kg− ) (Ortiz 1981). Skalstad and Nordøy (2000) showed that maripo- et al. 1996; Skog and Folkow 1994; Storeheier and Nordøy sia accounts for 14 and 27% of the water influx in young 2001). The highest urine osmolality measured in a marine fed hooded seals and harp seals, respectively. Common 1 1 mammal was 2658 mOsm kg− in a common bottlenose dolphins (Delphinus delphis) drink up to 0.8 L day− (Hui dolphin (Tursiops truncatus) (Ridgway 1972). The high- 1981), whereas pilot whales (Globicephala scammoni) 1 est osmolality registered in seals was that of the Baikal seal can drink up to 1.8 L day− (Tefler et al. 1970). Sea otters 1 (Pusa sibirica), measuring 2374 mOsm kg− (Hong et al. (Enhydra lutris), feeding on clams, derive 33.8% of the 1982). total water influx from the ingestion of seawater (Costa During fasting, water conservation mechanisms need to 1982), and Bentley (1963) concluded, based on the urine be even more efficient since there is no free water entering concentration, that fasting humpback whales (Megaptera the animal with food. One of the mechanisms found in fast- novaeangliae) swallow seawater, but without a net water ing northern elephant seal (Mirounga angustirostris) pups gain. is a reduction in glomerular filtration rate, which reduces For an animal to obtain a net gain of water from maripo- the urinary water loss (Adams and Costa 1993; Pernia sia, it should not only be able to concentrate urine above the et al. 1980). Another characteristic of the fast is that pro- concentration of seawater. The concentration of Na+ and tein catabolism decreases (Adams and Costa 1993), reduc- Cl− in urine should also be higher than in seawater (Albre- ing the nitrogen load on the kidneys. The reduced nitro- cht 1950; Tarasoff and Toews, 1972). Although the latter gen load, together with an increased urine osmolality, also is usually not the case, How and Nordøy (2007) observed decreases urinary water loss. that dehydrated harp seals can concentrate Na+ and Cl− A urine osmolality above that of seawater is a prerequi- in their urine to 540 and 620 mM, respectively, which is site for a net water gain from mariposia (voluntary drinking above the concentrations found in seawater (444 mM Na+ of seawater). Despite that seals are capable of producing and 535 mM Cl−). Thus, harp seals were able to restore urine with an osmolality above that of seawater Irving et al. water balance through mariposia. Other suggested reasons (1935) concluded that young captive harbour seals (Phoca for mariposia are facilitating thermal regulation in fasting 1 3 J Comp Physiol B (2017) 187:493–502 495 animals that inhabit warm environments (Gentry 1981), designed board.