225
Chapter ten: Post-partum
after weaning. During this period, the pup begins to develop the physiology needed to
dive to appropriate depths for foraging, including development of oxygen stores and control of the cardiovascular system (Burns et al. 2004; Tift et al. 2013). The size of the weaned
pup is often an important determinant of the duration of the postweaning fast and the
onset of independent foraging (Noren et al. 2003). In many species, pups undergo a long
migration to foraging areas after departing the breeding site. In these cases, pup body
reserves may still be critical to allowing thermoregulation in cold water and to allow time
for development of foraging skills.
Similar to phocids, otariid mothers also fast from food or water while on-shore.
However, they only remain with their pups for approximately a week, called the perinatal
period, before returning to sea to forage. The duration of the perinatal period varies with
species and environmental conditions, but is typically 5–9 days. The female returns to her
pup, which has been fasting during her absence, and suckles it for 1–3 days. This pattern of
intermittent suckling and foraging continues for 4 months to up to several years. In some
species, like subantarctic fur seals (Arctocephalus tropicalis), these fasting periods for the
pup can be greater than 30 days late in lactation (Verrier et al. 2012). The duration of the
period of parental care varies with latitude, being shortest in the polar species and longest
in the equatorial Galápagos fur seal (Arctocephalus galapagoensis) and sea lion (Zalophus
wollebacki). The need to return frequently to provision their offspring limits otariids to
foraging distances within tens to hundreds of kilometers of their breeding rookeries. This
constraint places a priority on maximizing the efficiency of foraging in order to minimize
the time that the pup is left fasting on-shore. For this reason, otariids are often associated
with highly productive coastal regions of ocean upwelling. To maximize foraging success
during this short period, otariids exhibit high levels of foraging effort and energy expenditure for locomotion when compared to phocids. The importance of successful foraging is
evident in the composition of otariid milk, which increases in fat content with the duration
of the foraging trip (Costa 1991).
Walruses (Odobenus rosmarus) have many reproductive features in common with phocids and otariids; however, they exhibit one critical difference. Pups are born on ice or on
land, but unlike the other pinnipeds, walruses nurse while at sea. The ability to feed at sea
allows pups to accompany mothers on short foraging trips. The perinatal fasting period
is only a few days in walrus and the milk they produce is relatively low in fat (~26%) compared to other pinnipeds. Use of an aquatic lactation strategy has reduced the importance
of fasting metabolism and lactation efficiency in walrus. The ability of young pups to move
around in the marine environment with their mothers provides them the opportunity to
learn about foraging strategies and locations in a way that is not possible in the other pinnipeds. As a result, weaning takes place much more slowly in walrus, with the period of
maternal investment lasting as long as two years.
10.2.2.2 Investment and lactation metabolism
The importance of fasting ability on the breeding strategies used by pinnipeds is reflected
in the strong impact of body reserves at parturition on reproductive effort. A variety of
studies have shown strong impacts of maternal mass and fat content on the level of maternal investment in pinnipeds (e.g., Crocker et al. 2001). Interspecific growth rates are correlated with maternal body size (Kovacs and Lavigne 1986). Additionally, animals with
larger fat reserves are able to invest more in their offspring. This creates an important link
between foraging success and maternal investment and leads to strong impacts of ocean
climate on the magnitude of investment or rates of natality in many species (Le Boeuf and
Crocker 2005). Females that expend too much energy in 1 year may experience reduced
Chapter ten: Post-partum
after weaning. During this period, the pup begins to develop the physiology needed to
dive to appropriate depths for foraging, including development of oxygen stores and control of the cardiovascular system (Burns et al. 2004; Tift et al. 2013). The size of the weaned
pup is often an important determinant of the duration of the postweaning fast and the
onset of independent foraging (Noren et al. 2003). In many species, pups undergo a long
migration to foraging areas after departing the breeding site. In these cases, pup body
reserves may still be critical to allowing thermoregulation in cold water and to allow time
for development of foraging skills.
Similar to phocids, otariid mothers also fast from food or water while on-shore.
However, they only remain with their pups for approximately a week, called the perinatal
period, before returning to sea to forage. The duration of the perinatal period varies with
species and environmental conditions, but is typically 5–9 days. The female returns to her
pup, which has been fasting during her absence, and suckles it for 1–3 days. This pattern of
intermittent suckling and foraging continues for 4 months to up to several years. In some
species, like subantarctic fur seals (Arctocephalus tropicalis), these fasting periods for the
pup can be greater than 30 days late in lactation (Verrier et al. 2012). The duration of the
period of parental care varies with latitude, being shortest in the polar species and longest
in the equatorial Galápagos fur seal (Arctocephalus galapagoensis) and sea lion (Zalophus
wollebacki). The need to return frequently to provision their offspring limits otariids to
foraging distances within tens to hundreds of kilometers of their breeding rookeries. This
constraint places a priority on maximizing the efficiency of foraging in order to minimize
the time that the pup is left fasting on-shore. For this reason, otariids are often associated
with highly productive coastal regions of ocean upwelling. To maximize foraging success
during this short period, otariids exhibit high levels of foraging effort and energy expenditure for locomotion when compared to phocids. The importance of successful foraging is
evident in the composition of otariid milk, which increases in fat content with the duration
of the foraging trip (Costa 1991).
Walruses (Odobenus rosmarus) have many reproductive features in common with phocids and otariids; however, they exhibit one critical difference. Pups are born on ice or on
land, but unlike the other pinnipeds, walruses nurse while at sea. The ability to feed at sea
allows pups to accompany mothers on short foraging trips. The perinatal fasting period
is only a few days in walrus and the milk they produce is relatively low in fat (~26%) compared to other pinnipeds. Use of an aquatic lactation strategy has reduced the importance
of fasting metabolism and lactation efficiency in walrus. The ability of young pups to move
around in the marine environment with their mothers provides them the opportunity to
learn about foraging strategies and locations in a way that is not possible in the other pinnipeds. As a result, weaning takes place much more slowly in walrus, with the period of
maternal investment lasting as long as two years.
10.2.2.2 Investment and lactation metabolism
The importance of fasting ability on the breeding strategies used by pinnipeds is reflected
in the strong impact of body reserves at parturition on reproductive effort. A variety of
studies have shown strong impacts of maternal mass and fat content on the level of maternal investment in pinnipeds (e.g., Crocker et al. 2001). Interspecific growth rates are correlated with maternal body size (Kovacs and Lavigne 1986). Additionally, animals with
larger fat reserves are able to invest more in their offspring. This creates an important link
between foraging success and maternal investment and leads to strong impacts of ocean
climate on the magnitude of investment or rates of natality in many species (Le Boeuf and
Crocker 2005). Females that expend too much energy in 1 year may experience reduced