The growth rate of lactating pups of the South American sea lion (Otaria flavescens) depends on the feeding strategy of the female.

DRAGO, M., L. CARDONA, E.A. CRESPO, S. AMEGHINO, N. GARCÍA & A. AGUILAR.

San Sebastián

Congreso; 21 ANNUAL CONFERENCE OF THE EUROPEAN CETACEAN SOCIETY; 2007

EUROPEAN CETACEAN SOCIETY

A study was conducted in Northern Patagonia to determine the influence of female feeding strategy on the growth rate of lactating pups in the South American sea lion. The ä13C and the ä15N signals of plasma and erythrocytes from 27 suckling pups were determined with the objective of assessing the composition of the mother?s diet. To do so, it was assumed that the isotopic signatures of the pup reflected those of mothers? milk and that the latter was in its turn reflecting the nutrients incorporated by the mother approximately 1 week (plasma) and 1-2 months (erythrocytes) prior to collection. Parallel to this, the isotopic signal of potential prey was analysed to establish baseline values. Also, pups were weighted and the specific growth rate at the age of 21 days was computed. The IsoSource programme was used to calculate the relative contribution of each prey species to the mother?s diet. Total fractionation factors for plasma were assumed to be 4.6 for ä15N and 0.5 for ä13C, and for erythrocytes were assumed to be 3.4 for ä15N and 1.2 for ä13C. IsoSource revealed that a lowly negative ä13C signal was due to a high consumption of benthic prey, mainly Enterocotpus megalocyathus. In females, the contribution of this species to diet increased after parturition (31±10% before and 53±14% after; Student t test, t=-8.315; p<0.001), but individual variability was large both before and after parturition. Also, a negative correlation was found between the specific growth rate of pups and the plasma ä13C (r2=0.482; p=0.003) and ä15N (r2=0.350; p=0.016) signals, thus indicating that a higher consumption of benthic prey negatively affected pup growth rate. Therefore, we conclude that the foraging strategy of lactating females has a dramatic influence on the growth rate of the pups.