Date of Award


Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)


Wildlife Ecology and Wildlife Conservation


James R. Gilbert

Second Committee Member

Sean Todd

Third Committee Member

William E. Glanz


As gray seal (Halichoerus gypus) populations continue to grow in the Gulf of Maine, it is necessary to quantie changes to the regional ecology for both management and conservation purposes. This study compares haul-out patterns, presents summer activity budgets, and contrasts intra- and interspecific aggressive interactions among the harbor seal (Phoca vitulina) and gray seal population on Mount Desert Rock, Maine. These data were collected using Altman's scan method and focal animal sampling.

Time to low tide and day of year influenced both harbor seal and gray seal haul-out patterns on Mount Desert Rock. For both species, more seals hauled-out closer to low tide. Day of year was correlated positively with numbers of harbor seals and negatively with numbers of gray seals.

Overall activity budgets are presented for both species; the harbor seal budget agrees well with previously published data and the gray seal budget is the first documented for this species during summer months, but is generally similar to winter breeding season budgets. Intrinsic and environmental factors influenced harbor seal behavior patterns. Gray seals had little, if any, effect on harbor seal behavior patterns and were only important in one of three models describing harbor seal sleep budgets. Harbor seal behavior budgets and rates were most broadly-affected by number of adjacent seals. At moderate densities of 3-5 adjacent seals, focal harbor seals slept more in longer, fewer bouts, while reducing overall time scanning via fewer bouts. Sleep budgets were also positively correlated with total number of seals on a haul-out ledge, day of year, wind speed, and cloud cover and negatively correlated with absolute time to low tide and air temperature. Sleep bouts occurred more frequently during higher tides and during calm wind conditions. Scanning budgets were positively correlated with higher tide states and the absence of fog and negatively correlated with number of seals on a ledge, wind speed, day of year, and cloud cover.

Harbor seal sleep and scan behaviors varied over the course of a day. The activity cycle was independent of tide state and was characterized by alternating peaks of sleep and scan behavior. Sleep peaked near midday in both years and this may explain why maximum haul-out numbers occur near midday in numerous other studies.

Although gray seals did not affect harbor seal behavior patterns, male gray seals clearly were dominant to harbor seals during aggressive interactions. Intra- and interspecific interactions involving only two individuals were similar in duration. Harbor seals responded aggressively less frequently when a gray seal changed body position than when another harbor seal performed the same behavior. Harbor seals may recognize and avoid confrontations with significantly larger opponents.