Science Advisory Report 2021/025

Identification of areas for mitigation of vessel-related threats to survival and recovery for Southern Resident Killer Whales

Summary

• Southern Resident Killer Whale (SRKW) critical habitat (CH) in Canadian Pacific waters was identified in the Recovery Strategy and includes portions of the Salish Sea and of the continental shelf around Swiftsure Bank. SRKW occurrence and potential vessel-related impacts were examined in these waters.
• Effort-corrected whale watch and Fisheries and Oceans Canada (DFO) sightings data from May to October 2009 to 2020 were evaluated and identified areas of high relative occurrence of SRKW in the Swiftsure Bank Area, Haro Strait, coastal waters near the Fraser River and other locations.
• Occurrence of SRKW varied temporally, with intensity increasing from May to August. In September, the intensity of occurrence was diminished in the Swiftsure Bank area but continued to increase in the Salish Sea. The temporal variation of occurrence aligns with known migratory patterns of SRKW prey (Chinook Salmon (Oncorhynchus tshawytscha) returning to the Fraser River from May to August and Coho Salmon (Oncorhynchus kisutch) in September).
• Analyses identifying dominant behaviours confirmed Haro Strait as a foraging area. Foraging was also the dominant behaviour in the waters around Swiftsure Bank. The shallows of the Bank, Juan de Fuca Strait, Boundary Pass and Swanson Channel were identified as areas of travel.
• Acoustic detections from recorders deployed at Swiftsure Bank, Port Renfrew, and Jordan River supported the spatial and monthly occurrence results from visual surveys, and the acoustic encounter durations were consistent with outcomes of the behaviour analyses.
• Analysis of Automatic Identification System (AIS) data indicated that Haro Strait experiences a higher vessel presence (AIS Class A and B) per square kilometer when compared to the Swiftsure Bank area. AIS vessel presence at Swiftsure Bank area was dominated by large commercial vessels (Class A), while Haro Strait was primarily dominated by recreational vessels (Class B). Class B vessel presence in both areas increased from May to peak in July and August.
• Noise from AIS Class A vessels, which is comprised of container ships, tankers, vehicle carriers, ferries, tugs, and commercial fishing, naval, government, cargo, and passenger vessels, resulted in a greater decrease in potential communication and echolocation ranges in the Swiftsure Bank area than in Haro Strait for all months. Potential echolocation range also decreased with depth at both locations.
• The eastern slope of Swiftsure Bank (foreslope) was the area most impacted by Class A vessel noise. This area was characterized by high SRKW occurrence, with foraging identified as the dominant behaviour. Other locations in the Swiftsure Bank area exhibited less impacts to the potential echolocation and communication ranges, including the foraging area north of Swiftsure Bank.
• The potential acoustic impact in Haro Strait was lower when compared to the Swiftsure Bank area, despite higher vessel traffic. This is likely the result of differing bathymetry, topography, water properties, and type of vessels.
• Analysis of acoustic recorder data indicated a reduction in the potential echolocation range, especially during daylight hours and on weekends. This reduction is attributed to the presence of recreational vessels.
• There is limited information on the presence of non-AIS vessels in the study area. While aerial surveys provided information on recreational fishing vessels and indicate co-occurrence with some areas of high SRKW intensity, spatial and temporal coverage is minimal.
• The risk of lethal vessel strike is known to increase with vessel speed. The majority of AIS vessels travelling over 10 knots are large commercial vessels (Class A) in both the Swiftsure Bank Area and Haro Strait.
• This co-occurrence approach could be used to evaluate the threat of reduced prey availability.

This Science Advisory Report is from the February 22-26^th, 2021 National Marine Mammal Peer Review on the Identification of Areas to Apply Spatial Management Measures to Protect Southern Resident Killer Whales. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2021/025 (PDF, 2,842 KB)

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