Assessing vessel traffic in the Salish Sea using satellite AIS: An important contribution for planning, management and conservation in southern resident killer whale critical habitat

Abstract

In the Salish Sea, a body of water spanning British Columbia, Canada, and Washington State, USA, increasing vessel traffic has the potential to cause many direct and indirect impacts on an endangered population of cetaceans; Southern Resident Killer Whales (SRKW) (Orcinus orca). This study uses satellite Automatic Identification System (AIS) data to provide a detailed description of the volume, distribution and type of vessels within SRKW critical habitat and emphasises the heterogeneity of their movement and presence throughout this area. Further statistical analysis of vessel data within two physically restricted regions (Active Pass and Boundary Pass) showed a particularly strong seasonal influence on vessel presence in Active Pass. This could largely be attributed to the dominance of ferry traffic during summer months in comparison to winter. In Boundary Pass, cargo ships were the predominant type of vessel each year, with their presence increasing over the four-year period analysed. Such information indicates that there is potential for considering seasonal management measures aimed at mitigating threats associated with vessel activity and reducing the risk of impact on SRKW particularly during summer months. Vessel speed was found to vary inconsistently with year, between regions and among vessel groups. However, there was a strong seasonal effect in both regions with vessels generally transiting slower in the winter than summer. This is another important consideration as vessel speed has been directly correlated to strike risk and noise emissions and therefore seasonal speed restrictions could also be explored if the area is navigationally suitable.The data presented here provides specific information related to vessel movement within areas that potentially pose a ‘higher risk’ from vessel related impacts, (e.g. noise pollution, strikes, spills etc.). Furthermore, this study considers the potential for vessel management measures to help mitigate these impacts and makes recommendations for future measures to be targeted at specific areas and vessel types. This sort of information can be used to help inform regional marine spatial planning frameworks, species recovery measures and management plans as well as any other future conservation designations and management schemes both within the Salish Sea but also globally.