Body condition as an index of winter foraging success in crabeater seals (Lobodon carcinophaga)

 

Birgitte McDonald1*, Daniel E. Crocker2, Jennifer M Burns3, and Daniel P. Costa1

 

1Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Long Marine Laboratory, 100 Shaffer Road, Santa Cruz, CA 95060 USA

2Department of Biology, Sonoma State University, 1801 East Cotati Avenue, Rohnert Park, CA 94928 USA

3Department of Biological Science, University of Alaska, 3211 Providence Dr., Anchorage, AK 99508 USA

 

Body composition is a direct measure of body condition and as such integrates seasonal variation in foraging success and energy expenditure. In phocids, body condition is a critical determinant of both reproductive effort and ability to survive periods of poor foraging success. We determined body composition in 29 crabeater seals, Lobodon carcinophaga, during austral autumn (April-May 2002) and late winter (August-September 2001, 2002) off the Antarctic peninsula by measuring blubber depth and taking morphometric (length, girth) measurements. In 15 of these seals, we also measured body composition using the labeled water dilution technique. The two methods produced similar body composition estimates, with an average difference of 7%. There were no differences in body composition between adult males and females or between autumn and late winter. However, adults had proportionately more blubber than juveniles (38.4 2.0% vs. 31.2 0.4 %). These findings suggest that by autumn, adult seals have replenished their energy stores following reproduction and molt. Similarly, the absence of seasonal variation in adults indicates that seals are successfully foraging throughout winter. In addition to providing insight into seasonal and age related variation in body composition, this study provides baseline body condition data that can be used to measure impacts of natural or anthropogenic environmental change on one of the large consumers of Antarctic krill.

 

Primary author contact information:

Birgitte McDonald

COH Long Marine Lab

100 Shaffer Rd.

University of California, Santa Cruz

Santa Cruz, CA 95060

Telephone: 1.831.459.2691

Fax: 1.831.459.3383

mcdonald@biology.ucsc.edu

 

 

STATUS UPDATE:

11/10/06: Received U.S. GLOBEC contribution number; number added to final version.