Haul-out Behavior of Harbor Seals (Phoca vitulina) in the San Juan Islands: Differences Between Mothers, Pups, and Lone Adults

Abstract

Harbor seals (Phoca vitulina) are a previously endangered pinniped species native to coastal waters across the United States. Seals haul out onto shore year-round to rest, give birth, nurse, and molt. The San Juan Islands in the Salish have one of the highest densities of harbor seals in the world, making it a prime location to study their behavior. We conducted this study at two locations near San Juan Island, Yellow Island and Goose Island. Our research consisted of two key objectives: 1) contrasting vigilance and behavior among three categories of seals (lone adults, lone pups, and mom-pup pairs) at two locations and 2) contrasting the relationship between abundance and tide height at both locations. At both locations, we collected data on behavior and vigilance levels of different categories of seals (lone adults, lone pups, and mom-pup pairs), along with recording abundance and distribution of hauled out seals. Overall, behavior was consistent at both locations, and seals spent most of their time resting. We found that different haul out sites had a large effect on the vigilance levels, with higher levels in lone pups at Yellow Island, and higher levels in lone adults at Goose Island. Tide height at both locations also influenced seal haul out behavior, as fewer seals hauled out at high tides at Yellow Island, while more seals hauled out at higher tides at Goose Island, supporting that abundance is related to availability of haul out space. These findings are consistent with previous work that has shown harbor seals spend the majority of the time alternating between vigilant and non-vigilant resting, but highlights the role of specific haul out locations in behavioral patterns and distribution.