Date of Award


Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Wildlife Ecology and Wildlife Conservation


James R. Gilbert

Second Committee Member

Daniel J. Harrison

Third Committee Member

William E. Glanz


Compared to other phocids seals, the maternal investment strategy of the small bodied female harbor seal (Phoca vitulina) is complex. Females are unable to fast for the entire duration of pup rearing and are therefore reliant on resources in the vicinity of the pupping aggregation to continue provisioning their pup by mid-lactation. At the same time, harbor seal pups are highly active during lactation which increases energetic costs to the female but also offers an opportunity for females to influence the behavioral development of her pup. To understand how females maximize their pup's survival it is important to examine both the physical and behavioral development of harbor seal pups. The goal of my research was to describe the morphological development and ontogeny of diving behavioral for harbor seal pups in Maine in respect to the potential factors influencing these two measures of maternal investment. I conducted my research at pupping sites in the vicinity of Stonington, Maine. During two seasons, 156 pups were captured, weighed and measured, and equipped with identification tags. Birth dates were estimated for all individuals and a subset of animals received VHF radio transmitters and time-depth recorders (TDRs) in order to monitor movements, activity, and diving behavior. Pups were monitored using telemetry and were recaptured opportunistically to recover TDRs and measure growth. There was no difference in the timing o births between years and the mean pupping date was found to be May 23rd (SE = 0.5). Mean birth mass was 11.1 kg (SE = 0.23) and mass gain rate averaged 0.45 kg/d (SE = 0.03). Pup mass gains were found to differ between years and decline late in the pupping season. Additionally, pup mass gain rates were found to be positively associated with increased 'in water' activity after controlling for temporal. Data from TDRs revealed that pups spent a large portion of time in water (61%) during lactation and dove up to 100 m near weaning. Activity and diving behavior was found to be influenced by pup birth mass, mass gain rate, age as well as the depth available and tide heights experienced by pups during TDR deployment. Maximal dive duration and dive depths were highly associated with bathymetry and this factor was the most important in limiting pup diving depths early in lactation. The positive association between pup mass gain rate and activity is likely explained by the intermediary effects of female size and condition on both female attendance and pup growth. Although the lower mean mass gain rates in Maine compared to Canadian populations may be explained by differences in population status, this did not explain the lower range of values observed in this study. Resource limitations in the vicinity of pupping sites may provide an explanation for lower pup development and the significant decline in mass gain rates late in the pupping period in this study.