Adrenocortical responsiveness in southern elephant seal mothers and pups during lactation and the effect of scientific handling.

Abstract

We examined the cortisol responses to chemical and physical restraint stress in southern elephant seal Mirounga leonina females and their pups at three stages during lactation. In anaesthetised females the serum cortisol levels changed moderately during the 45-min sampling period following restraint, with average peaks at 23 min after anaesthetic administration. Overall, cortisol was relatively low 2 days postpartum and increased throughout lactation. In physically restrained pups serum cortisol increased rapidly after capture; the response was milder at age 2 days than at 11 days and 21 days. Levels were higher in female pups than in males. In order to test whether cortisol levels and/or responses became chronically (i.e. days to weeks) altered due to restraint, we compared the cortisol response at a late stage of lactation between three groups of mother-pup pairs previously given different levels of chemical (mothers) or physical (pups) restraint stress: control (not handled previously), moderate treatment (previously handled twice), and high treatment (previously handled 3-4 times). Pups of the three treatment groups showed similar adrenocortical responses suggesting no chronic effect of repeated physical restraint, despite the clear acute effects. Mothers of the control and moderate treatment groups showed similar cortisol responses; however, mothers of the high treatment group showed significantly attenuated responses. This indicated that elephant seals tolerated moderate degrees of handling disturbance; however, repeated (3-4) chemical immobilisations in lactating females may reduce their adrenocortical responsiveness for a period of days or weeks.