A group of researchers from the University of Washington, NMFS, and other organizations just released the results of an interesting study on the interplay of vessel traffic, prey abundance, and health of resident Orca populations in Puget Sound. This study looked at the interplay between vessel traffic and prey abundance for resident Orcas in Puget Sound. For those of you not from the Pacific Northwest, this Orca population spends its summers up around the San Juan Islands feasting on Chinook salmon, and forages in a broader range (out to the Washington Coast and as far south as California) during winter through spring.

The study design is fascinating. The researchers used a specially trained dog to locate Orca scat in Puget Sound waters. The dog is trained to point towards where it smells Orca scat (which apparently floats). The scat was then analyzed for various stress markers, one which can be indicative of physiological (i.e., boat traffic) stress as well as nutritional stress, and one that is reflective of nutritional stress only. What the researchers saw was that prey abundance seemed to be the primary source of physiological stress to the Orca population–and, interestingly, that Orcas depended heavily on food sources

With a bit of statistics applied, the data gathered showed that:

Prey availability has a greater physiological impact on SRKWs than does vessel traffic. However, we cannot yet rule out a cumulative effect of vessel traffic on the overall SRKW stress response, particularly during years of relatively low Fraser River Chinook abundance. Exposure to toxicants may also add to these cumulative effects if food deprivation promotes metabolism of lipid stores, releasing sequestered toxicants into circulation. Combined, these results suggest that promoting salmon recovery is vital to the long-term persistence of SRKW. Conservation of early spring salmon runs consumed by SRKW prior to arrival in the Salish Sea may be especially important to these recovery efforts. Future studies should aim to better identify these early spring food sources to better target recovery efforts.

The underlined statement (my edit) is the important one from a policy perspective. Vessel traffic is relatively easy to regulate (particularly whale-watching traffic), but salmon recovery is a much more complicated issue. I’d expect this study to be used by salmon recovery proponents to reinforce those efforts–particularly the Fraser River run in Canada because of its importance to these Orcas. I’d also expect this study to be used by proponents for projects that increase vessel traffic in Puget Sound. such as the planned bulk terminal in Whatcom County, to counter arguments that those projects should not move forward or should otherwise be limited because of concerns about vessel traffic impacts on whales.