During October and November 2003 hundreds of dead and live Northern Fulmars (Fulmarus glacialis) began washing in to beaches in the Monterey Bay National Marine Sanctuary. Fulmars are "tube-nose" seabirds (Family Procellariidae, which includes fulmars, petrels, and shearwaters) that nest on islands from British Columbia to Alaska. Fulmars migrate south from nesting areas during winter and are common off the West Coast of North America during October through March. Periodic die-offs of this species have been reported in past years, and these are often associated with unusual weather patterns.
|Veterinary assistant Eva Berberich examines the wing of a dead fulmar at the necropsy lab at CDFG-MWVCRC in Santa Cruz. photo Hannah Nevins
We investigated this seabird mortality in cooperation with California Department of Fish and Game (CDFG) biologist Jack Ames and veterinary staff at CDFG -- Marine Wildlife Veterinarian Care and Research Center, Santa Cruz (CDFG-MWVCRC). To establish the cause of death, we collected and dissected 186 dead fulmars that had stranded in Monterey Bay. In order to determine
if the abundance of dead fulmars on beaches was unusual, we reviewed BeachCOMBERS (Coastal Ocean Mammal and Bird Education and Research Surveys) data collected since 1997 for comparison to the current data. To make surveys comparable, we standardized deposition rate by the number of kilometers walked. We found that the deposition recorded during the die-off was an order of magnitude greater than our long-term deposition rate for this species.
By examining feather wear, we concluded that most (96 percent) of the birds were young-of-the-year and few (4 percent) were older than one year. We examined the ratio of color morphs (light and dark plumage phases) to ascertain the potential colony of origin for these birds. Geographic differences in the ratio of light to dark morphs vary throughout the breeding range: Bering Sea colonies have few dark morphs (0 -- 0.2 percent), whereas birds from the Aleutian Islands are mostly (99 percent) dark morphs, and those from the Gulf of Alaska and British Columbia are 75
to 85 percent dark morph. We found 92 percent dark
and 8 percent light morphs of fulmars stranding in the sanctuary, indicating that these birds originated from colonies in the Gulf of Alaska. Data from Scott Hatch at the U.S. Geological Survey-Alaska Science Center corroborated our findings. Hatch tracked three adult fulmars with satellite tags from breeding sites in the Semidi Islands in the Gulf of Alaska to central California during the time of the die-off.
We found that all fulmars examined were below normal body mass and had essentially no body fat, indicating severe starvation. Pectoralis muscles were atrophied, suggesting protein catabolism during the starvation event. Stomachs were empty or contained plastic and few other remains. No evidence of disease was found, and starvation was considered to be the most probable and
consistent cause of death in this event.
Because the North Pacific population of Northern Fulmars is estimated at 1.4 million breeding individuals, a periodic die-off such as the one we described during the winter of 2003 is not expected to significantly alter the population. However, events such as these offer great insight into how mortality factors can regulate seabird populations. Persistent storms during September and October along their migration path may have contributed to this starvation event, either by preventing foraging or reducing prey availability. Knowledge of the source of migratory species that inhabit the sanctuary is a first step in understanding how factors outside the sanctuary (such as ocean conditions in the Gulf of Alaska) can influence the abundance and distribution of seabirds
in this area.
Beach COMBERS surveys are conducted by volunteers, with support from the Sanctuary Integrated Monitoring Network (SIMoN) through a research grant to Moss Landing Marine Laboratories.
Hannah Nevins and Jim Harvey
Beach Combers, Moss Landing Marine Laboratories
The arrival of hundreds upon thousands of Sooty Shearwaters (Puffinus griseus) to the Monterey Bay National Marine Sanctuary is an extraordinary annual phenomenon that attests to the global importance of Monterey Bay’s abundant prey resources. Beginning in about April, we begin seeing scattered individuals and small flocks of hundreds to thousands of Sooty Shearwaters that have made their way to the coastal waters of California from breeding colonies in New Zealand, southern Australia, and Chile. (See Figure 1.) Situated along the inside of one of only four eastern boundary currents, the sanctuary hosts some of the world’s
most productive ocean waters; the abundant shoals of anchovy, sardine, rockfishes, krill, and squid in Monterey Bay draw the shearwaters here.
|Figure 1. Sooty Shearwater flock off Moss Landing Marine Laboratories 26 May 2004. Large numbers of shearwaters aggregate, often in dense flocks that can exceed half a million individuals, to feed on shoaling fishes, squid, and euphausiids concentrated in productive marine areas influenced by coastal upwelling. photo Josh Adams
The Sooty Shearwater is the most abundant seabird off the coast of California from May to September. Surveys at sea, however, reveal a 90 percent decline in numbers since the late 1970s. Reasons for this dramatic decline likely include a combination of factors, such as breeding habitat loss, introduced non-native predators on breeding islands, marine climate change, incidental fisheries take, traditional Maori harvest of chicks, and oil pollution. Sooty Shearwaters also may have become more confined to highly productive "refuge" marine areas such as Monterey Bay and San Luis Bay, California and the Cape Blanco-Heceta Bank region off Oregon. And it has been suggested that large numbers of birds shifted to relatively cooler waters in the central North Pacific following the recent warm regime of the Pacific Decadal Oscillation that has affected the California Current ecosystem.
The Sooty Shearwater is one of five shearwater species frequently observed in the sanctuary. Shearwaters are members of the Family Procellariidae, often collectively referred to as "tube-noses" for their pronounced nostrils. The function of their unique bill morphology is unknown but may relate to the group’s keen sense of smell -- a trait required for locating patchy prey while navigating over thousands of square miles of open ocean. Alternatively, this structure -- combined with greatly developed olfactory anatomy -- may help these remarkable birds to sense subtle changes in sea-level atmospheric pressure gradients that shape global ocean wind patterns. (Strong winds are required for energy-efficient flight in order to traverse large expanses of open ocean in search of food or during migration.)
Shearwaters were named for their characteristic flight behavior, or "jizz." During flight, a Sooty Shearwater arcs and tips to gather speed as wind velocity increases several meters off the ocean’s surface. At the apex, the bird again tips and dips, accelerating down with wind and gravity to slip in front of a wind wave or ocean swell. Skimming the ocean with its wingtips, the bird "shears" the surface, tips, and accelerates up to repeat this pattern, termed "dynamic soaring."
In 2003 we sought funding to follow up on shearwater research conducted in the mid- to late 1970s. We received the first of two small grants from the California Department of Fish and Game Oil Spill Response Trust Fund, administered through the Oiled Wildlife Care Network (OWCN) at the Wildlife Health Center, School of Veterinary Medicine, University of California Davis to examine the body condition, blood chemistry, diet, and molt pattern of shearwaters in Monterey Bay. This information is necessary to establish reference ranges and target release criteria for rehabilitated birds. With the support of the OWCN, we have established methods to capture wild shearwaters and measure seasonal variability in body condition and blood parameters in relation to feeding habits off California.
|Figure 2. The trans-Pacific pre-breeding migration of twelve Sooty Shearwaters captured and outfitted with satellite radio transmitters near Pismo Beach, California. Track lines show direct movements from California toward New Zealand and as far south as 60 degrees, near the Antarctic convergence. Tracks shown are from approx-imately 1 September 2004 to 3 December 2004. (Data are ongoing, please visit www.seaturtle.org/tracking or www.signalsofspring.net for maps updated daily.)
This past year, we teamed up with K. David Hyrenbach (Duke Marine Laboratory, Beaufort, North Carolina) and Cheryl Baduini (Claremont Colleges Consortium, Claremont, California) to examine the movements and migration of birds captured and outfitted with small satellite radio transmitters off central California. To date we have captured ninety-seven Sooty Shearwaters off Santa Cruz and San Luis Obispo Counties and outfitted twenty sub-adult to adult birds with satellite transmitters.
Six birds captured during the molting period in June and July
off Capitola resided within the sanctuary and adjacent waters off California for one to two months. One individual ranged as far as Vancouver Island, BC, Canada before its transmitter’s battery failed (after seventy-six days; twice its expected duration). By September 2004 oceanographic conditions in Monterey Bay contributed to an impressive, lingering red tide, which we hypothesize might have caused large numbers of shearwaters to leave the area. Our satellite data revealed that San Luis Bay and Pismo Beach were important destinations for birds marked in Monterey Bay.
In early September we traveled to Port San Luis to capture and attach transmitters to fourteen additional shearwaters, in an effort to examine the timing, duration, and route of the annual pre-breeding trans-Pacific migration to Southern Hemisphere breeding colonies. (See Figure 2.) Twelve of fourteen birds departed the California Current System, crossed the equator, and appeared destined for breeding colonies off New Zealand. The first individual to leave California, named Moana-Nui after the Maori words for the Pacific, made it within 1,000 kilometers of New Zealand before heading back east across the ocean toward South America. Was this individual perhaps a Chilean breeder?
This study marks the first time researchers have tracked, in detail, the incredible trans-Pacific migration of individual Sooty Shearwaters. Continuing investigations of the ecology of the Sooty Shearwater -- the dominant member in the sanctuary’s rich avifauna and a shared global natural resource -- will provide important information related to the health of Monterey Bay and surrounding waters. In the future we hope to work more closely with the sanctuary, together with our colleagues in the Southern Hemisphere, to examine post-breeding migration routes from Chile and New Zealand.
Josh Adams1 and Jim Harvey2
1U.S. Geological Survey, Western Ecological Research Center
2Moss Landing Marine Laboratories