Salish Sea Ecosystem Conference

Is silence golden? The recovery rationale for yielding—and enforcing—the maritime right-of-way to Southern Resident killer whales and their access to prey

Prey availability is recognized as one of three major limiting factors in the recovery of Southern Resident Killer Whales (SRKWs) by the US and Canada. In terms of inter-related, cumulative effects the most recent population viability analysis (Lacy et al. 2017) suggests that improving access to those prey—by reducing (1) the masking effects of vessel noise on echolocation and intra-pod communication, and (2) the physical interference caused by nearby vessels on the water—could magnify the benefits of modest gains in the abundance of the residents’ primary prey, Chinook salmon. The transboundary SRKW Symposium in October 2017 highlighted emerging studies on underwater noise and potential opportunities for mitigation; also reflected in various sessions at this conference. Discussions there also revived regional recognition that—independent of the noise-masking effects of recreational fishing, whale-watching and other types of vessel activities—the physical presence of vessels may also disturb SRKWs. Using the behavior of Northern Resident Killer Whales as a proxy, Williams et al. (2011) found that even kayaks (essentially silent) evoked evasive, energetically expensive “outpace” responses and reduced foraging time. The effects of such disturbance appeared to worsen during periods of low Chinook salmon abundance. While Southern Residents appear to be more boat-tolerant than their northern counterparts, groups of 3-5+ boats still alter the whales’ behavior and reduce the proportion of time spent foraging and—by extension—consumption of prey (per Lusseau et al. 2009). This talk will summarize studies documenting this phenomenon in resident killer whales and other cetaceans. By more definitively documenting the potential pervasiveness and influence of boat presence alone, I seek to outline the benefits and tradeoffs of trying to reduce such potential interference by various precautionary methods: including enhanced regulatory enforcement and incentives for conservative approach-distances, speed limits, and the use of quieter vessel types or engines—and draw attention to the apparent disproportionately high value of reducing vessel disturbance during years of relatively low Chinook abundance.