Date of Completion
Animal Sciences | Other Life Sciences
The decline of the Western population (144 degrees west longitude) of Steller sea lions is hypothesized to be the result of impaired nutritional status and decline of growth rate, especially in juveniles and subsequent natality. Because changes in components of the somatotropic axis can be predictive of nutritional status and growth rate in this species, 2 groups of free-ranging juvenile Steller sea lions were captured in Prince William Sound, AK. Group 1 (n = 30) was initially captured at 5 mo and recaptured at 10 mo of age, whereas group 2 (n = 9) was captured at 7 and 8 mo of age. At capture, animals were anesthetized, age estimated, and blood and BW collected. Concentrations of GH and IGF-I were quantified (ng/mL) using RIA and IGFBP-2 and -3 were quantified [Arbitrary Units, (AU)] using Western ligand blots. Data were analyzed using the Mixed Procedure in SAS. Mass of Steller sea lions increased (P < 0.01) with age from 69±1.3 kg at 5 mo to 100 ±2.8 kg at 10 mo (group 1) and 93 ±5.8 kg at 7 mo to 101 ±5.7 kg at 8 mo (group 2). Concentrations of IGFBP-2 decreased with age from first to second capture (group 1; 37.8 ±2.5 vs. 36.0 ±2.5; group 2; 43.7 ± 4.8 vs. 39.8 ±4.4 AU; P < 0.01) and across all animals GH, IGF-I and IGFBP-3 averaged 1.6 ±0.1 ng/mL, 165.7 ±10.4 ng/mL, 304.0 ±13.4 AU respectively, but there was no effect (P> 0.1) of age on concentrations of these hormones. Greater concentrations of IGFBP-3 were positively associated with greater growth rate (P= 0.06) across all animals. In group 2, the increase in IGF-I concentrations between captures was positively correlated with growth rate (P< 0.05), indicating that changes in IGF-I and IGFBP-3 may be useful indicators of growth rate in juvenile Steller sea lions. These data provide a more detailed description of the changes in the components of the somatotropic axis and their relationship with growth rate in juvenile Steller sea lions, and may provide insight into survival and the continued decline of the Western population.
Hebert, Katherine Denise, "Finding a Link between the Hormones of the Somatotropic Axis and Growth Rate of Juvenile Steller Sea Lions" (2011). Honors Scholar Theses. Paper 173.