Marine Mammals in the San Juan Channel

Abstract

Since 2005, one site has been studied in the San Juan Channel, located just off San Juan Island, Washington in the United States. This research has been done by the Pelagic Ecosystem Function Apprenticeship at the Friday Harbor Labs on San Juan Island. Continuing this research and focusing on mammals in the San Juan Channel, individual mammal species were counted in autumn 2011. 2011 abundances were calculated based on these counts, compared to abundances from 2007-2010, and looked at by date of sailing, zone in the study, and tidal phase present during each sailing in each zone. The zones were predetermined by the apprenticeship. Mammal individuals were counted using visual identification taken on day trips in October and November 2011. All mammal species seen across the study site, or transect , were counted during these sailings. The four mammals seen in the San Juan Channel in 2011 were Harbor Seals (Phoca vitulina), Steller Sea Lions (Eumatopias jubatus), Harbor Porpoises (Phocoena phocoena), and Dall’s Poropoises (Phocoenoides dalli). Abundance for Harbor Seals was higher in 2010 and 2011 compared to years 2007-2009. Abundance for Harbor Porpoise’s in 2011 was significantly higher than years 2007 to 2010. Abundance for Steller Sea Lions and Dall’s Porpoise’s remained stable from 2007-2011. Harbor Seals were the most abundant mammal present in the study, and Dall’s Porpoise’s were the least abundant. For the pinniped species, Harbor Seals and Steller Sea Lions showed no net change across season, but showed variation date to date. By zone, Harbor Seals showed some preference for Zone 3 in the study, and Steller Sea Lions showed high preference for Zone 5. By tidal phase, Harbor Seals and Steller Sea Lions both showed 3 preferences that differed in each zone. Abundance in relation to date, zone, and tidal phase for both species are likely effected by two factors; the location of haul out sites, as well as presence of prey.