Beam Reach

No fish, no blackfish?

I’ve asked a lot of people why the southern resident killer whales spend so much of their time swimming up and down the west side of San Juan Island. Most folks suggest that they’re here because the fish are here. Ask long-time population surveyor Ken Balcomb of the Center for Whale Research what motivates the orcas to be resident and you’ll get the succinct synopsis he passes on from First Nations elders: “No fish; no blackfish.” Yet I’m amazed at how little is known about what fish are present at any particular time in this part of the San Juan Islands, not to mention the Salish Sea in general.

From April through October the three resident pods are most frequently found along this coastline, the eastern side of Haro Strait. Their most common dance is known as the “west side shuffle” in which the pod(s) travel back and forth from somewhere near Eagle Point in the south to Henry Island in the north, often pausing to forage, socialize, or mill, but rarely resting. I’ve yet to hear of the residents transiting the same body of water on the Canadian (west) side (though transients often do), and I doubt it’s because the Canadians don’t treat their sewage as much as we do.

The orcas often make intermittent excursions further afield. They loop out to visit Hein and Middle banks offshore. They zip west past Race Rocks for a listen along south Vancouver Island. Or they voyage northward to the Fraser River delta before circumnavigating the archipelago via Rosario Strait. But they always seem to return to the west side — the core of their summertime range.

There might be non-fishy reasons orcas might like the west side of San Juan Island. Perhaps they appreciate the great acoustics along the steep unsedimented submarine coastline. Maybe they have a rubbing “beach” like the Northern residents, but hidden deep off of False Bay. Or maybe the west side is just a cross-roads: a familiar pathway that you take whether you’re headed out to the Pacific and the Elwha, up to the Fraser or Nooksack, or down to the Skagit and Puget Sound.

How could we demonstrate that prey availability is the factor that focuses the southern residents attention on the west side of San Juan Island? What kind of fish are they eating? Why and when are which fish available; and implicitly, how do the killer whales navigate the complex distribution of salmon in the Salish Sea? More practically, which (endangered?) fish population segments should we be saving for our endangered whales?

Our primary approach to answering such questions is to discern what the southern residents eat and then observe the behavior of those prey items along the west side. Secondarily we gather basic information about distributions of potential prey in case the prey sampling studies have biases that lead us to overlook important food sources.

The growing body of information about what orcas eat is the best evidence we have of what prey they are after. The current scientific consensus — from analysis of scraps, underwater video, the rare stranded whale’s stomach contents, and poop — is that southern resident killer whales really like Chinook salmon. In the best synopses I’ve seen (of data predominantly from May-October) Ford et al (1998) and Ford and Ellis (2006) suggest that Chinook are preferred at all times except perhaps in the late fall when chum salmon return to many local rivers (and the residents, especially J pod, begin making southward forays into Puget Sound). There also hints that bottom fish such as halibut, lingcod, and dover sole are taken occasionally.

A big problem is that not many people are doing a good job of monitoring what fish are present in the Salish Sea (as opposed to Northwest rivers) generally, and in Haro Strait specifically. A major goal of the spring 2008 Beam Reach program was to test new acoustic tools that could help us fill the observational gap. I’ll post separate articles with detailed results this summer, but for now here is a synopsis of the two new tools we tested:

First, through a new partnership with Seattle-based Biosonics, we used a 200 kHz scientific echosounder to measure fish densities in Haro Strait.  Mounted on a pole and pointed straight downward, the echosounder projected sound in a 6-degree-wide beam and received the echoes from fish, plankton, and the sea floor. With real-time display and data logging, we were able to survey fish distributions in Haro Strait (and map bathymetry and bottom type) both in the presence of orcas and when they weren’t around. Thanks to the generous donation of equipment and software, we were able to observe remarkably complex distributions of fish along the west side and to quantify fish densities in a preliminary suite of foraging locations.

Another active acoustic technology we tested was an acoustic tag that can transmit a depth measurement from inside a fish. We purchased two tags from Vemco and guided by instructor Eric Eisenhardt, implanted them surgically in lingcod near Lime Kiln State Park. With the mobile tracking unit that Vemco kindly provided for free, we were able to monitor the two young fish for about a month and learned they make only occasional depth excursions while remaining in the area where they were caught and released. The fish stayed near 18 and 40 meters depth throughout our study, suggesting that when killer whales make deep dives (>100 meters) to the local bottom (Baird, 2003) are probably not related to foraging for young lingcod on the west side of San Juan Island in the spring.

References:

Baird, Robin W., M. Bradley Hanson, Erin E. Ashe, Michael R. Heithaus, and Gregory J. Marshall (1993) STUDIES OF FORAGING IN “SOUTHERN RESIDENT” KILLER WHALES DURING JULY 2002: DIVE DEPTHS, BURSTS IN SPEED, AND THE USE OF A “CRITTERCAM” SYSTEM FOR EXAMINING SUB-SURFACE BEHAVIOR. Report to the National Marine Fisheries Service, National Marine Mammal Laboratory, 7600 Sand Point Way N.E., Building 4, Seattle, WA, 98250 USA.

Ford, John K. B., Graeme M. Ellis, Lance G. Barrett-Lennard, Alexandra B. Morton, Rod S. Palm, and Kenneth C. Balcomb III (1998) Dietary specialization in two sympatric populations of killer whales (Orcinus orca) in coastal British Columbia and adjacent waters. Can. J. Zool. 76(8): 1456–1471 | doi:10.1139/cjz-76-8-1456.

Ford, John K. B., Graeme M. Ellis (2006) Selective foraging by fish-eating killer whales Orcinus orca in British Columbia. Marine Ecological Progress Series, 316:185-199.