|In marine ecosystem studies that PRBO conducts, both on Southeast Farallon Island and at sea, we have documented extreme variability in ocean conditions over the last six years. In 2005 and 2006, weak upwelling and abundant fish benefited murres and cormorants but resulted in unprecedented failure for Cassin's Auklets. In contrast, in 2008 and again this year, strong upwelling and abundant krill benefited auklets and whales but resulted in extreme failures (especially in 2009) for Common Murres and Brandt's Cormorants. Working with our USFWS and NOAA partners, PRBO is able to detect changes in the marine environment through our seabird monitoring and oceanographic surveys together.—Jaime Jahncke, PhD, Director of PRBO's Marine Ecology Division|
June 18th: another overcast and windy summer morning on the Farallones; the height of the seabird breeding season. I'm sitting at North Landing surveying one of our Common Murre productivity plots up on Tower Point, a steep cliff about 100 meters away. Through a telescope, I'm noting which birds are present at the breeding sites we follow, and whether they still have eggs and chicks. I'm making good time, happy that a few "problem birds" have stood up to show that they are still incubating eggs. At site 27, it seems my luck is continuing—there's the chick right out in the open. But where are its parents? The chick is only six days old and still coated in down, definitely too young to be left unattended.
|Farallon murres closely attend their chicks, as a rule—but 2009 was the exception. Photo by Ron LeValley|
It is rare for murres to attack chicks from unattended neighboring sites, but this year we saw the behavior daily through a few weeks in June. Why? In a world where breeding sites in dense colonies are vigorously defended, why would chicks be left unattended? The answer is likely fish—in particular, the northern anchovy. During the past few years, murres have fed large chicks mostly anchovies, and these forage fish have been abundant. But there has been a dramatic shift this year, with anchovies disappearing almost completely. Adult murres brought smaller prey and fed their chicks less (some barely at all). Many birds, instead of brooding their chicks throughout the day, would take leave from the colony, likely having to work harder to find food for themselves in one of the poorest breeding years in decades for murres at the Farallones.
|Blue whale. Photo by Mike Baird.|
Such is the "reality of death." On now to the "wonder of life." It's August 2nd, 10:00 AM, and I'm up at the Lighthouse staring through a scope again. The Black Oystercatcher I'm watching, on its second nest attempt over on Aulon Islet, has not yet stood to show me its eggs (how the power to levitate birds at will would simplify a seabird biologist's life!). Then, out of the corner of my eye I see it: a geyser in Fisherman's Bay. Spinning around, I catch the blue whale in full view at the surface—over 65 feet long, a blue-gray submarine—within a half-mile of the island. "Blue whale!" I bellow to the interns doing a Pigeon Guillemot diet watch halfway down Lighthouse Hill, and they hurry to get a good look at the largest creature that has ever lived. The blue whales have returned to the Farallones! And this is the closest we have seen them in at least five years.
|Russ Bradley atop Lighthouse Hill, the highest point on Southeast Farallon Island.|
As with many events in the marine ecosystem, the explanation for this is food. While populations of anchovy have plummeted this year, krill are abundant. Strong krill densities off the continental shelf have meant a good breeding year for Cassin's Auklets, a sizable return of feeding blue whales, and many more humpback whales arriving in the Gulf of the Farallones in August. p>How can krill be abundant while large forage fish are absent from the system? What is the root of this food-web mismatch? As we watch the Common Murres and blue whales, and all Farallon life, new questions about the changing marine ecosystem remind us always to expect the unexpected.