Examination of Blubber Fatty Acids in Pregnant and Lactating Alaskan Harbor Seals (Phoca vitulina)

Pregnancy and lactation are energetically expensive for female mammals and greatly influence the evolution of species-specific reproductive strategies. Phocid (true seals) lactation is generally short in duration and relies heavily on stored energy, whereas otariid (sea lions and fur seals) lactation is generally much longer, and energy is supplemented by foraging. While a phocid, the smaller body size of the harbor seal (Phoca vitulina) is assumed to preclude the maintenance of lactation solely from stored energy. For this reason, their lactation strategy is believed intermediate to that of otariids and phocids. The purpose of this study was to characterize blubber fatty acids (FAs) of pregnant and lactating harbor seals and determine if lactating blubber FA profiles more closely resemble phocids or otariids. Blubber FA differences between female reproductive states (lactating, n = 18; pregnant, n = 7; non-lactating-non-pregnant, n = 17), mother-pup pairs (n = 6), and families (otariid, n = 3; phocid, n = 3) were evaluated using permutation analysis of variance (PERMANOVA). Compared to lactating females, pregnant harbor seals had elevated polyunsaturated FAs (PUFAs) and decreased monounsaturated FAs (MUFAs) in their blubber, suggesting pregnant harbor seals may prioritize PUFA storage in the blubber. Additionally, when compared to their pregnant counterparts, lactating harbor seals had lower PUFA, as well as saturated FAs (SFAs) and MUFA <= 16C, suggesting lactating harbor seals may utilize blubber FAs similar to other phocids. Lastly, while blubber SFA and MUFA concentrations may be conserved among pinniped families, PUFA concentrations among lactating phocids and otariids appear to be similar, suggesting lactating species may selectively mobilize PUFA from the blubber in a similar way despite family or lactation strategy. Understanding how family and body size influence the lactation strategy of a species provides greater insight into the physiological and behavioral limitations a species may have to both internal and external forces during such a critical time in its life history.

Automated summary

Pregnancy and lactation are energetically expensive processes for female mammals and have significant impacts on species-specific reproductive strategies. The lactation strategy of harbor seals is believed to be intermediate between sea lions and true seals. This study characterized the fatty acid composition of blubber in pregnant and lactating harbor seals and compared it to other pinnipeds. The results showed that pregnant harbor seals prioritize the storage of polyunsaturated fatty acids (PUFAs) in their blubber, while lactating harbor seals exhibit similar fatty acid profiles to other true seals.