Proposed Abstract Title

Interrelationships of Marine Mammals, Pelagic Fish, and Tides at Different Spatial Scales in San Juan Channel, Fall 2015

Type of Presentation

Poster

Session Title

General species and food webs

Location

2016SSEC

Description

San Juan Channel (SJC) in the Salish Sea is habitat to multiple species of marine mammals, which exhibit different patterns of aggregation. To determine if mammal distribution is driven by prey distribution, a survey using direct mammal observations and acoustic backscatter as a proxy for fish biomass was conducted along a 21.5km transect (split into 6 zones) in SJC. The most abundant mammals seen and tracked in this study were Steller Sea Lions (Eumetopias jubatus), Harbor Seals(Phoca vitulina), and Harbor Porpoise(Phocoena phocoena). Three spatial scales were used in this study: the entire transect (20+ km), zones (3-4 km), and individual kilometers. No direct correlations between fish density and mammal density were found at any scale. Previous studies in the area have suggested that tidal forcing concentrates forage fish in areas of greater topographic relief and mammal feeding behavior may be influenced by these effects. Mammal and fish distributions were compared with tidal current speed at the three spatial scales. Cetacean density directly correlated with tidal current speed at the largest spatial scale, while pinniped density correlated at the kilometer level in the narrowest part of the channel. Direct correlations were found between fish density and tidal current speed around bathymetric features at the lower two scales. This study showed key examples of how physical oceanographic processes affect the distribution of mammals and forage fish in a bathymetrically diverse and tidally active inland sea.

Keywords: mammals, Phoca vitulina, Eumetopias jubatus, Phocoena phocoena, acoustics, pelagic fish, tides, predator-prey, San Juan Channel, Salish Sea

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Interrelationships of Marine Mammals, Pelagic Fish, and Tides at Different Spatial Scales in San Juan Channel, Fall 2015

2016SSEC

San Juan Channel (SJC) in the Salish Sea is habitat to multiple species of marine mammals, which exhibit different patterns of aggregation. To determine if mammal distribution is driven by prey distribution, a survey using direct mammal observations and acoustic backscatter as a proxy for fish biomass was conducted along a 21.5km transect (split into 6 zones) in SJC. The most abundant mammals seen and tracked in this study were Steller Sea Lions (Eumetopias jubatus), Harbor Seals(Phoca vitulina), and Harbor Porpoise(Phocoena phocoena). Three spatial scales were used in this study: the entire transect (20+ km), zones (3-4 km), and individual kilometers. No direct correlations between fish density and mammal density were found at any scale. Previous studies in the area have suggested that tidal forcing concentrates forage fish in areas of greater topographic relief and mammal feeding behavior may be influenced by these effects. Mammal and fish distributions were compared with tidal current speed at the three spatial scales. Cetacean density directly correlated with tidal current speed at the largest spatial scale, while pinniped density correlated at the kilometer level in the narrowest part of the channel. Direct correlations were found between fish density and tidal current speed around bathymetric features at the lower two scales. This study showed key examples of how physical oceanographic processes affect the distribution of mammals and forage fish in a bathymetrically diverse and tidally active inland sea.

Keywords: mammals, Phoca vitulina, Eumetopias jubatus, Phocoena phocoena, acoustics, pelagic fish, tides, predator-prey, San Juan Channel, Salish Sea