• Beach COMBERS Update
• Winter Mortality of Surf Scoters
Volunteers with the Monterey Bay National Marine Sanctuary's Coastal Ocean Marine Bird and Mammal Education and Research Surveys (Beach COMBERS) sample selected beach sections on a monthly basis to record the incidence of dead wildlife. Established in 1997, the program is an important resource for obtaining information -- and detecting trends -- on mortality rates for all marine bird and mammal species in Monterey Bay.
Ocean conditions off California during the spring of 2005 appeared similar to what we might expect during a warm El Niño event, with sea-surface temperatures about 2°C greater than usual. A reduction in the frequency of upwelling-driven winds typical in April to June had significant effects on the seabird community in central California. Beach COMBERS volunteers were the first to record a pulse of unusual mortality for five seabird species (four alcids and one cormorant), compared with baseline data collected during the past eight years.
|Figure 1. Long-term trend in deposition of four resident seabirds showing increased monthly mean deposition (birds per kilometer) in 2005 relative to baseline reported by Beach COMBERS in the Monterey Bay area (beaches 1 to 11, 51 kilometers; May 1997 to July 2005). Significant mortality of several species was similar to that of the 1997-1998 El Niño; however ocean conditions were unlike a true El Niño. Alternating bars indicate years and line hatching indicates no survey data. Note
difference in scale of y-axis among species.
In January and February, the first unusual pattern was detected in two pelagic species: planktivorous (plankton-eating)
Cassin's Auklet, Ptychorhamphus aleuticus, and the piscivorous (fish-eating) Rhinoceros Auklet, Cerorhinca monocerata. (See Figure 1, p. 19.) Cassin's are small alcids (approximately 160 grams) that feed primarily on krill and larval fishes. In general, because of their small size and pelagic habitat, auklets are not
well represented in Beach COMBERS surveys (usually <0.5 birds per kilometer). During a typical year, we find two to 10 Cassin's, with the exception of the 1997-1998 El Niño, when 163 were recorded. In 2005, we documented 82, including 16 freshly deposited birds on Sunset State Beach alone. Rhinoceros Auklet (approximately 800 grams) followed Cassin's and showed the
highest number of deaths in May, June and July (0.15 to 0.8 birds per kilometer).
In May, a wide deposition of unusual numbers of dead Brandt's Cormorants, Phalacrocorax penicillatus, on beaches from central California and Oregon prompted many reports from the public, rehabilitation centers, state agencies and other beach survey
programs. Indeed, our up-to-date beach survey data revealed a
significant increase in the number of cormorants (5.4 birds per kilometer), many of which were adults in breeding plumage.
By July, other fish-eating species, such as the Common Murre, Uria aalge, and the Pigeon Guillemot, Cepphus columba, appeared dead in greater numbers than usual on sanctuary beaches. Based on necropsies performed at the Marine Wildlife Veterinary Care and Research Center (California Department of Fish and Game, Santa Cruz), it became obvious that an entire community of seabirds
off California were dying of starvation. Interestingly, the timing
of mortality among species differed -- a pattern likely related to
differing trophic levels and foraging habitats among the affected species: pelagic species had the earliest mortalities, followed by mid-water piscivores and lastly by nearshore benthic-feeding species.
Was this an El Niño event? Although we did find higher numbers of dead birds among several resident species, migratory Sooty Shearwater, Puffinus griseus, from the southern hemisphere did
not show elevated deposition in 2005. Sooty Shearwater deposition typically increases significantly during El Niño events (e.g., 1997-1998 and 2000). Francisco Chavez and other oceanographers at the Monterey Bay Aquarium Research Institute who are working to understand this year's conditions recognize that despite certain
similarities, this was not an El Niño but rather a more localized event caused by regional (i.e., north-eastern Pacific) atmospheric anomalies. Although normal upwelling conditions appeared to return by July, it was too late for the seabirds that depend upon a food web that is initiated prior to the spring-summer breeding season. Without the pulse of cold, nutrient-rich waters into the system in early spring, forage fish abundances likely were reduced. The NOAA Fisheries laboratory in Santa Cruz reported dismal returns during its annual survey for juvenile rockfishes (Sebastes spp.);
it also documented reduced hake, krill, anchovies and larval flatfishes, according to Steve Ralston at the lab. As a result, many seabirds likely faced a severe food shortage. Many resident seabirds, including murres, auklets, guillemots and cormorants, failed to
nest successfully. Reproductive rates for Cassin's Auklet were the lowest ever recorded in 30 years of monitoring at the Farallon Islands off San Francisco, according to William J. Sydeman at PRBO Conservation Science. Food stress also appeared to result in a significant increase in sub-adult to adult mortality, as evidenced from beached bird deposition. We hypothesized that reduced larval/juvenile recruitment among rockfishes, a key prey shared by
all affected species, was ultimately responsible for this food stress event. The timing and duration of upwelling winds, the dominant physical forcing influencing the Monterey Bay ecosystem, can
ultimately make the difference between a successful breeding
season and a failed one, and dramatic changes likely affect the
survival of resident seabirds.
Understanding how changing ocean conditions affect seabirds can provide important indicators of the dynamics of forage fishes. Not only seabirds, but commercial and recreational fishermen and local economies, depend on ocean conditions that foster abundant forage fishes. We will continue collecting systematic information on beached bird deposition to understand what seabirds can tell us about the ecosystem within our sanctuary. This example from the Beach COMBERS highlights how information about seabirds can contribute toward a better understanding of food-web dynamics, trophic interactions, marine productivity and forage fish availability -- essential aspects required for a complete understanding of the effects of fluctuations in the marine ecosystem.
Hannah Nevins And Jim Harvey
Beach COMBERS, Moss Landing Marine Laboratories
This work was supported in part through a grant from the Monterey Bay Sanctuary Foundation, Sanctuary Integrated Monitoring Network (SIMoN). Substantial in-kind support was
provided by Moss Landing Marine Laboratories and California Department of Fish and Game, Marine Wildlife Veterinary
Care and Research Center. This work was made possible by the dedicated volunteer beach surveyors of Beach COMBERS and Beach Watch programs.
|Winter Mortality of Surf Scoters |
Since its inception in 1997, the Coastal Ocean Marine Bird and Mammal Education and Research Surveys (Beach COMBERS) project has documented some interesting trends in deposition of dead birds and mammals on beaches within the Monterey Bay National Marine Sanctuary. (See previous article.) The growing long-term data set allows researchers to identify unusually large mortality events, or die-offs. For example, during the winter of 2003-2004, Beach COMBERS documented a die-off of Northern Fulmars, Fulmarus glacialis, an order of magnitude greater than usual. (See Ecosystem Observations 2004, p. 18.) Another notable die-off involved unusually high numbers of dead Surf Scoters, Melanitta perspicillata, during the winter and spring of 1998.
|Surf Scoters are sea ducks that breed in Alaska and northern Canada and winter in coastal areas as far south as Baja, Mexico. (Photo Laird Henkel)
Surf Scoters are sea ducks that breed in Alaska and northern Canada and winter in coastal areas as far south as Baja, Mexico. They are common in Monterey Bay nearshore waters from November through April. In April 1998, Surf Scoter deposition
on Monterey Bay beaches spiked to 3.6 birds per linear kilometer, more than 20 times the five-year mean for this species. While the Beach COMBER data are excellent for identifying these unusual mortality events, without information on natural population fluctuations, it can be difficult to determine if these die-offs are related
to an acute event, such as an oil spill or disease, or if they are
the natural result of higher-than-normal numbers of live birds occurring locally.
In the case of the 1998 Surf Scoter die-off, we were fortunate to have data on the concurrent abundance of Surf Scoters in Monterey Bay. Surveys were conducted from a small open skiff in a 100-meter strip transect 500 meters offshore, from Capitola to Monterey. These surveys were conducted during the early spring of 1998 and then from February 1999 through March 2001. With these data, we were able to investigate the relationship between numbers of dead scoters found on local beaches and densities of live scoters in Monterey Bay. Deposition rate (number of birds per linear kilometer) was exponentially related to at-sea density during the previous month. (See Figure 1.) These data indicate that winter mortality of Surf Scoters in central California may be density-dependent: as the number of Surf Scoters in the bay increases, the mortality rate (number found dead per number found alive the previous month) also increases. This relationship is weak, and more data would be useful to determine whether the
relationship truly is density-dependent. If density dependence is occurring, it could be a result of increased competition for food, which would affect baseline health, or an increased transmission rate of parasites.
|Figure 1. Relationship of deposition of beach-cast Surf Scoters to at-sea density in the previous month, from 26 surveys between March 1998 and January 2001
So what caused this unusual mortality event in 1998? We examined the gastrointestinal tracts of more than 30 Surf Scoters collected on Monterey beaches in 1998 and found remarkable densities of acanthocephalan parasites in their intestines. (Most had 15-20
parasites per centimeter of intestine.) Stomach contents and observations of live scoters indicated that, in Monterey Bay sandy beaches, they feed primarily on sand crabs (Emerita analoga), which carry cysts of acanthocephalan parasites. These small
worms often infect Surf Scoters and have also been implicated in sea otter (Enhydra lutris) deaths. Although Surf Scoters are a
natural host of these parasites, which are ingested as cysts in
sand crabs, death may have been due to perforation of intestinal walls and peritonitis as a result of these infections. Increased Surf Scoter numbers in Monterey Bay may have allowed easier transmission of parasites.
These preliminary data illustrate the usefulness of concurrent monitoring programs in the sanctuary. Although this study focused on data from 1998 through 2001, the Beach COMBERS project continues to collect data that could be used for similar assessments in the future. Further use of at-sea surveys conducted concurrently with beached-bird monitoring projects can help determine if observed die-offs represent unusual mortality events or are simply proportional to fluctuating local population levels. In addition, further research on the baseline health of animals such as Surf Scoters will be useful in determining causes of death during mortality events.
Laird Henkel, Hannah Nevins, Jim Harvey and Scott Benson
Moss Landing Marine Laboratories