Variation in body mass and food intake of northern fur seals (Callorhinus ursinus)

Abstract

Estimates of prey and energy consumption are important for effective management and conservation of marine mammals and the ecosystems they inhabit. We used routinely collected husbandry data on body mass, food intake (kilograms), and energy intake (megajoules) from northern fur seals (Callorhinus ursinus) in zoological institutions to examine how these variables changed throughout the year, and with age, sex, and reproduction. Fur seals exhibited seasonal changes in all three variables, but the magnitude and timing of trends varied among age and sex groups. Notably, adult males exhibited rapid increases in body mass leading up to the breeding season. Fur seals were most efficient at converting energy intake to mass gain in the spring and least efficient in the fall. Intake increased into adulthood as animals grew in body mass. Sex‐specific differences in intake were detectable early in development, likely related to size dimorphism. Pregnancy was energetically inexpensive compared with lactation, with food and energy intake rapidly increasing post parturition to values that were double those during early pregnancy. This study highlights the importance of accounting for different age, sex, and life history stages when estimating prey consumption of northern fur seals.

Estimating reproductive costs in marine mammal bioenergetic models: a review of current knowledge and data availability

“…In one of the few studies on the cost of pregnancy in free-ranging marine mammals, Shero et al (2018) documented an increase in diving effort by pregnant Weddell seals (Leptonychotes weddelli) compared with nonreproductive females, particularly during the last trimester, which was attributed to an increase in gestational energy demand. There are fairly consistent observations across species that food intake decreases in the days to weeks leading up to birth, regardless of whether it fluctuates at other time periods (Ronald and Thomson, 1981;Joseph et al, 1987;Kastelein et al, 1990Kastelein et al, , 2000bRobeck et al, 2005;McHuron et al, 2022b). For some species, increases in food intake may not be related to the costs of gestation but rather due to an increase energy storage during gestation for the subsequent lactation interval (Noren et al, 2014).…”

“…Changes in food intake of gestating marine mammals in human care are inconsistent, with conclusions typically drawn from a small number of individuals across only part of gestation. Some studies report no change or even decreases in food intake (in kg prey) during gestation (Joseph et al, 1987;Cheal and Gales, 1991;Kastelein et al, 1993Kastelein et al, , 2002Kastelein et al, , 2003, while others report increases, particularly later in gestation (Asper et al, 1988;Kastelein et al, 1990;Reddy et al, 1993;Kastelein et al, 2000a;McHuron et al, 2022b). There have also been conflicting findings within a species, such as for killer whales where Kastelein et al (2003) and Williams et al (2011) found no change in food intake while Asper et al (1988) documented increases beginning in the 13th month of gestation.…”

“…During lactation, most studies of marine mammals in human care report increases in food intake above prelactation levels (e.g. Kastelein et al, 2000b, Kastelein et al, 2000a, 2003Williams et al, 2007;McHuron et al, 2022b). Species that rely more heavily on energy reserves during lactation may be an exception, since much of the energy for lactation is stored prior to parturition (Kastelein et al, 1990).…”

“…Asper et al (1988) found that consumption of a single lactating killer whale peaked around 110 to 118 kg day −1 , approximately 80% higher than intake during early gestation, with consumption remaining elevated (at 95 kg day −1 ) for six months past the time of weaning at 1.5 years of age. Reports from other species also show peak consumption estimates close to or in excess of 100% higher than nonreproductive periods (Kastelein et al, 2000b(Kastelein et al, , 2003McHuron et al, 2022b). Few comparative studies of food intake in wild marine mammals exist.…”

What are the Metabolic Rates of Marine Mammals and What Factors Impact this Value: A review

“…heart rate, respiration rate, caloric intake) or behavioral (e.g. swim speed, measures of body movement or acceleration) characteristics ( Williams et al, 1993 ; Boyd et al, 1999 ; Butler et al, 2004 ; Fahlman et al, 2008 ; Young et al, 2011 ; Dalton et al, 2014 ; Noren et al, 2014 ; Kastelein et al, 2018 ; McHuron et al, 2022 ). Unfortunately, there are inherent inaccuracies when using such proxies due to unvalidated or weak relationships and substantial variation between individuals (McPhee et al 2003).…”