Seasonal, Mortality, and Tidal Effects on Marine Mammal Abundance and Diversity in San Juan Channel Fall 2015

The San Juan Archipelago (SJA) is a dynamic ecosystem that supports a variety of resident and transient marine mammals. As the Salish Sea and the SJA have extensive cultural and economic ties with marine mammals, it is important to have comprehensive studies on population status throughout different seasons. This fall featured continuing shifts to lower abundance and a more diverse community composition that began in 2014. The three most abundant species for fall 2015 were harbor seals (2.8/km²), steller sea lions (1.96/km²), and harbor porpoises (0.6/km²); however, these were some of the lowest densities in recent history. In addition, six other species of marine mammals were recorded on transect that have not been observed previously from Pelagic Ecosystem Function (PEF) apprentices. This may be related to anomalously warm oceanic conditions. Although mortality does not seem to correlate with low abundance of harbor seals, more detailed analysis should be conducted in future research. Additional studies on fine temporal scales of tidal phases and current speeds and marine mammal abundance found species-specific relationships with tidal phase and current speed. Harbor porpoises aggregated in larger numbers after peak current speed than before while steller sea lions and harbor seals showed different preferences for current speeds