|Abstract or Summary
- The marine environment is under increasing pressure from human activities worldwide, particularly in coastal waters, creating a need to better understand fine-scale distributions of highly mobile species that occur in the area, as they are frequently most threatened. Harbor porpoise (Phocoena phocoena) occur frequently in Oregon’s nearshore habitat, but due to limited survey data, the temporal and spatial distribution of these small cetaceans is not well understood. Sensitivity of harbor porpoise to anthropogenic noise and entanglement is well established, generating concerns for the spatial overlap between future coastal development projects and preferred coastal habitat. Passive-acoustic monitoring and standard line transect surveys were conducted from 2014 to 2015 providing information at a range of spatial and temporal scales of harbor porpoises distribution in Newport, Oregon’s neritic waters. The integration of visual and acoustic survey methods is advantageous in that it creates high spatial and temporal resolution, reduces methodology bias (acoustic surveys provide temporal coverage, visual survey provide spatial coverage), and results in a more robust data set. A total of 42 visual transect surveys were conducted in the study area resulting in over 65 individual sightings. Data collected from visual detections were compiled in 1 km bins relative to environmental conditions including bathymetry, distance to shore, distance to rocky reef, surface salinity, temperature, and florescence concentration. Acoustic survey efforts occurred May through October of 2014 using digital monitoring devices (DMONs) deployed at two neighboring but bathymetrically different locations off the Oregon coast: (1) a site on the 30 m isobath in close proximity to an offshore rocky reef, and (2) a site on the 60 m isobath in an open sandy environment. Acoustic data were analyzed with respect to two dynamic cyclic variables (diel and tidal phase). Over 1500 echolocation click trains were detected and analyzed for patterns of occurrence and behavior, using inter-click intervals to differentiate between navigating and foraging activities. Using either acoustic or visual data, species distribution models were generated to describe harbor porpoise habitat use patterns. Visual surveys revealed harbor porpoise distribution in this area is likely to be influenced by nearshore rocky reefs and fine scale (1 Km) oceanographic conditions of temperature and salinity. Acoustic results revealed that porpoise presence at the nearshore reef was driven by tidal forcing, while harbor porpoise presence offshore was associated with night time foraging. Taken together, these results suggest harbor porpoise habitat use is modulated by specific dynamic environmental conditions that maximize foraging efficiency. Results of this study provide needed baseline data on harbor porpoise occurrence and movement patterns in Oregon, the ecological drivers of those patterns, and critical areas or temporal periods necessitating focused protection from current and developing anthropogenic activities along the Oregon coast.