Harbor seal (Phoca vitulina) behavior in response to vessel disturbance at Yellow Island and Goose Island, WA, USA

Abstract

The Salish Sea is an area with high vessel traffic, which can potentially cause negative shifts in the energetic budgets of many marine mammal species. This includes harbor seals, which use haul out sites to rest and rear their pups, and have been shown to exhibit increased vigilance and flushing in response to vessel disturbance. Therefore, vessel traffic in close proximity to harbor seal haul outs may be detrimental, especially when vessels are not in compliance with current regulations, such as the 91.4 m buffer zone set by the Marine Mammal Protection Act (MMPA). While the harbor seal population in the Salish Sea is believed to be at equilibrium, and is therefore not of great conservation concern, the management and protection of the species can set an important precedent for how other pinnipeds, both recovered and otherwise, are treated. To understand the impacts of vessel traffic on harbor seal behavior in the Salish Sea, we conducted a comparative study of harbor seal behavior in response to vessel disturbances at Yellow Island and Goose Island in the San Juan Islands, WA, USA. Tracking vessel traffic within 400 m of each haul out site, we monitored behavioral responses both during and after vessel disturbances and mapped the distribution of seals throughout our observational period. We found that, while vessel traffic differed at both sites, kayaks were the vessel type which most frequently came within the regulatory buffer zone. This is important considering kayaks also caused the most extreme behavioral responses observed. Additionally, while behavioral trends in response to vessel disturbances varied between sites, harbor seals show possible signs of habituation over time in comparison to previous studies as well as in areas of higher vessel traffic. These findings help contribute to the understanding of the impacts of vessel disturbance in the Salish Sea and may have important implications for management.