The impact of lactation strategy on physiological development of juvenile marine mammals: implications for the transition to independent foraging

Lactating marine mammals provision their offspring either by providing large amounts of lipid-rich milk over a short period during which females fast (capital provisioning), or smaller amounts of less energetically dense milk over an extended period during which females forage (income provisioning). While it has long been recognized that these two strategies carry different costs for the female, the effect of these two strategies on the physiological status of newly weaned pups has rarely been considered. Recent comparative studies on the development of diving capacity, as assessed by measuring total body oxygen stores, have demonstrated that the provisioning strategy does affect pup development. Phocid pups, which grow rapidly during their brief nursing period undergo a strong post-parturition anemia and are weaned with relatively immature oxygen stores, possibly due to limited iron intake. Otariid pups, which grow at a slower pace over a longer period, are weaned with body oxygen stores that are significantly more mature. This suggests that newly independent phocid pups must quickly develop foraging skills in order to acquire the nutrients necessary to mature physiologically. In contrast, newly weaned otariids have more mature oxygen stores, and may have previous foraging experience, which may allow for increased behavioral flexibility. (c) 2004 Elsevier B.V. All rights reserved.