PROJECTS

Harbor porpoises (Phocoena phocoena) are now the most frequently sighted cetacean in Hood Canal, with recent surveys showing increased abundance with seasonal fluctuations; the highest porpoise densities occur in and near DBRC and Bangor in the late-spring through early fall (Rone et al. 2023).

Bigg’s killer whales (also known as Transient or mammal-eating killer whales, Orcinus orca) have been increasing their use of Hood Canal and the lower Salish Sea in recent years. This trend is likely related to increases in the populations of their prey, primarily seals, sea lions, and harbor porpoise. Unlike the Southern Resident killer whales, which have historically rarely entered the Hood Canal area, Bigg’s are now regularly sighted within Hood Canal, with some visits apparently lasting more than a month based on sighting reports.

Both species are sensitive to anthropogenic sound. Harbor porpoises have peak sensitivity extending roughly from 16 to ~140 kHz (Benhemma-Le Gall et al. 2021; Brandt et al. 2013; Culik et al. 2001; Dyndo et al. 2015; Elmegaard et al. 2023; Kastelein 2013), while killer whales hear broadly from ~5–81 kHz (peak sensitivity around 15–20 kHz) (e.g. Harris et al. 2015; Miller et al. 2014; 2012; Branstetter et al. 2017).  Many such sounds occur in Hood Canal, including noise from recreational and commercial vessel traffic as well as sounds unique to naval training and testing activities. Harbor porpoises exposed to disturbing sounds typically cease echolocation and leave an area of acoustic disturbance, leading to foraging disruption- a response that is particularly costly for species with high foraging rates or limited foraging ranges if sound exposure is prolonged or frequent within their preferred habitat (Wisniewska et al. 2016). Findlay et al. ( 2024) documented a 34% reduction in the harbor porpoise population (displacement and/or decrease in echolocation) when exposed to acoustic deterrent devices (500 Hz- 40 kHz) at received levels > 108 dB re 1 μPa Root Mean Square (RMS). Harbor porpoise reacted to pingers (50 and 120 kHz with a source level of 144 dB re 1 µPa RMS @ 1 m) up to 520 m away (Brennecke et al. 2022).

Military underwater vehicle communications testing within the DBRC often operates at frequencies between 16 and 32 kHz with sound pressure levels ranging from 140 to190 dB (P. Mulcahy, pers. comm.), well within the hearing range of harbor porpoises and at or above levels that displaced or disrupted harbor porpoise in prior studies. These sound sources may be active for hours or days at a time, creating the potential for extended displacement from what are typically high-density habitats. Another interesting finding of the 2023 surveys was that very high densities of harbor porpoise occurred in the waters immediately to the south and north of Bangor; however, sightings were virtually non-existent in the waters to the west of the facility that functionally connect these two high-density regions (Figure 1). This suggests the region immediately adjacent to Bangor may be uniquely disturbing to harbor porpoise. The known use of potentially disturbing sound sources and the apparent exclusion of harbor porpoise from the area around Bangor suggest a better understanding of the effects naval activities in Hood Canal have on harbor porpoise is needed.

Characterizing the soundscape and linking it to distribution and behavior is therefore essential for effective monitoring and mitigation.

Goals and Objectives

1.  Test an integrated, multi‑method monitoring program that characterizes cetacean distribution, movement, and behavior in relation to the Hood Canal soundscape, with emphasis on Navy activity areas.
2.  Quantify fine‑scale distribution and movement of harbor porpoises using shore‑based theodolite tracking at up to three elevated sites near Hazel Point or other high‑density locations based on Rone et al. (2023).
3.  Measure diving, movement, and acoustic exposure context of Bigg’s killer whales through the deployment of suction cup attached sound and motion tags (SMRT).
4.  In collaboration with NUWC Keyport, integrate visual, acoustic, and tag datasets to assess exposure–response hypotheses and refine a design for a possible full behavioral response study (BRS).