FORAGING STRATEGIES OF GESTATING FEMALE ELEPHANT SEALS AND THEIR SHORT-TERM REPRODUCTIVE FITNESS IN PENÍNSULA VALDÉS? PATAGONIA

ELENA EDER; MIRTHA LEWIS; MONICA MUELBERT; MARK HINDELL

Cartagena de Indias

Encuentro; XVI Reunión de Especialistas en Mamíferos Acuáticos de América del Sur; 2014

Asociación Colombiana de Zoología

Pregnant females of southern elephant seals display foraging strategies with unknown consequences for reprductive fitness. This relation was investigated in females from Península Valdés? Patagonia? through stable isotope analysis (SIA) of C and N in whiskers and weaning mass (WM) of their pups. WM is a proxy of female foraging success and short-term reproductive fitness. Individual specialization in foraging strategies and trophic niche width of prebreeding females was also assessed. At the end of the breeding season of 2011? a total of 60 weaned pups were capture? measured (standard length SL? maximum girth G)? and sampled for whisker SIA. WM was estimated as 53.896? SL1.063 ? G1.697? and corrected for mass lost after weaning date (WM= estimated mass ? (ek?d)? where k=0.00596 and d= number of days between weaning and measuring). Whiskers were measured? cut into 1 mg +/- 5 % subsamples from the proximal end of the tip? mid and base segments for SIA. Individual variability in foraging strategies was estimated through within whisker variance (WV) of C isotopic values (iv). Both C and N iv were higher in the base reflecting the enrichment effect of the lactation. Overall iv (n= 120 segments) ranged −20.8 to -14.8 ? for C and 10.6 to 19.1 ? for N iv. A cluster (1) of six animals exhibitted high iv for both tip and mid segments (-16.5 to -14.8 ? for C? and 15.9 to 19.1 ? for N)? has been considered extreme specialists (WV range= 0.003 to 0.1) and represented neritic foraging. Cluster 2 included a single pup with low C and N iv (-19.8+/-1.4 ? and 10.9+/-0.5 ?? respectively)? representing offshore foraging? and considered generalist (WV= 1.9). Cluster 3 (n= 53) also represented offshore foraging (range= -19.4 to -16.8 ? for C and 11.4 to 14.5 ? for N iv) but exhibited a broader individual variability with 55% extreme specialists (WV range= 0.00005 to 0.1)? 34% specialists (WV range= 0.1 to 0.7)? and 11% generalist (WV= 0.8 to 1.6). Pups of cluster 1 (coastal/neritic foragers) were heavier (134.33+/-19.6 kg) than offshore foragers from cluster 2 (79 kg) and 3 (116.7+/-17.8 kg). Specializing and sustaining neritic foraging strategies (Patagonian shelf or Shelf break) even at the risk of potentially high intra and inter specific competition? may yield advantages in short-term reproductive fitness to a small fraction of gestating female of elephant seals from Patagonia.