US Navy

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Marine Species Monitoring

Offshore Distribution of Southern Resident Killer Whales in the Pacific Northwest

Introduction & Objectives

Little was known about the movements and occurrence of southern resident killer whales (SRKW) in the winter prior to this study.  Remotely deployed satellite telemetry tags deployed on SRKW and passive acoustic recorders deployed in areas thought to be used frequently by the whales were used to assess the seasonal occurrence of SRKW. While the primary focus of the research was to detect endangered southern resident killer whales during the winter and spring months, the recorders also provided near year-round monitoring of other sound producing cetaceans and anthropogenic sound sources. These data were used to provide information to better understand SRKW seasonal occurrence in relation to the U.S. Navy’s Northwest Training Range Complex (NWTRC) in the Pacific Northwest.

Technical Approach

SPOT5 satellite telemetry tags were deployed on SRKW in Puget Sound and coastal waters of Washington and Oregon between 2014 and 2016; however further SRKW tagging halted indefinitely by NMFS in 2016. Individual-ID photos and samples of prey remains, feces, mucus, and regurgitation were collected. All locations for satellite tagged SRKW were compiled and duration-of-occurrence and state-space models were developed to identify areas of high use and travel corridors.

In addition to satellite tags, autonomous passive acoustic recorders called Ecological Acoustic Recorders (EARs) were deployed off the coasts of California, Oregon, and Washington. Recordings from the duration of the project as well as archived recordings from previous years were analyzed for presence of SRKW.  These were used to create annual predictive maps and to evaluate the probability of detecting whales.  The acoustic data were also analyzed for the presence of other species of vocalizing whales and dolphins, sonar, and explosives. 

Progress & Results

Between 2012 and 2016, satellite tags were deployed on eight SRKW.  The predictions from the updated space-state movement model indicate that in the winters of 2013 and 2015, tagged SRKWs spent the highest density of time located off the Colombia River and near Westport. Other areas with relatively high occurrence were off the northern coasts of Washington and California.

Acoustic data were obtained from 6-13 recorders deployed off the coasts of Washington, Oregon, and California from 2011-2016 resulting in 11,718 monitoring days.  SRKW were acoustically detected 246 times on recorders deployed in the coastal and slope areas. Nine of the 21 monitoring sites were located in the Northwest Training Range Complex. SRKW were detected at four of the nine sites with 67 detections occurring over 4,314 days.

Northern Resident Killer Whales were the most detected killer whale ecotype followed by transients and SRKW, with a peak in spring for all ecotypes. Most detections of SRKW were at nearshore sites with the exception of increased detections at Cape Flattery Offshore site during late spring to early summer.  Mid-Frequency Active (MFA) sonar and explosive sounds were both detected in the recordings. The majority of MFA events were detected at mid-shelf and offshore sites between February and March. The majority of explosive sounds were detected at mid-shelf and offshore sites and were more common in summer months.

 

Publications:

Shelton et al. 2019.  Using hierarchical models to estimate stock-specific and seasonal variation in ocean distribution, survivorship, and aggregate abundance of fall run Chinook salmon.