Disease Strikes Again by Steve Johnson at Salton Sea

Once again, an avian botulism started earlier than usual because of outbreak struck the Sonny Bono Salton warmer June temperatures. While past Sea National Wildlife Refuge, an impor- outbreaks generally have killed more tant Pacific flyway stopover for migra- white pelicans, last year’s epidemic tory birds in southern California, last killed mostly brown pelicans that are summer. Since 1996, pelicans and other less than one year old. The outbreak piscivorous (fish-eating) birds at the officially began June 26, and ended Salton Sea have been struck with “type November 22, 2000. C” botulism. Because of their feeding Fifteen Service employees at the This juvenile brown pelican died habitats, pelicans and other piscivorous refuge worked in shifts 18 hours a day before it could be rescued. birds usually don’t contract avian to care for the sick birds. Two Service Photos by Steve Johnson botulism. However, this type doesn’t airboats patrolled the sea all day, every follow the typical avian botulism cycle. day, to round up sick birds and ferry The U.S. Geological Survey’s National them back to the on-site pelican Wildlife Health Center in Madison, rehabilitation hospital. The California Wisconsin, is working to determine Department of Fish and Game (CDFG) exactly how the birds contracted the provided the refuge with an airboat and botulism. Since June 26, 2000, the toxin crew to assist with disease response has killed 717 endangered brown efforts. Workers from the CDFG, Salton pelicans (Pelecanus occidentalis). Of Sea Authority, and Bureau of Reclama- the 1,300 brown pelicans sickened by tion aided refuge staff during this crisis. botulism this year, almost 600 have The open-air bird hospital, built in been successfully rehabilitated and 1997 with money raised by volunteers, released. The total number of brown can accommodate up to 100 sick birds pelicans affected this year was close to at a time. Pelicans spend up to 24 hours the total from the worst year, 1996, at the hospital before being sent to one when 1,429 sickened or dead brown of four off-site, licensed rehabilitation pelicans were retrieved. The last centers, most of which are run by rehabilitated brown pelicans, 15 in all, volunteers. Release sites for fully were released on December 11, 2000. recovered pelicans are located on the The outbreak also sickened and coast near the Tijuana Slough and Seal killed birds from another 35 species, Beach national wildlife refuges in including American white pelicans southern California. (Pelecanus erythrorhynchos). Only birds Birds that contract avian botulism lose that consume tilapia (Oreochromis involuntary muscle control, including mossambicus), a saltwater sport fish eyelid function, have clenched feet, and introduced from Africa, were directly can’t hold up their heads. The disease is affected by the disease. Scientists from not fatal if treated in its early stages. the National Wildlife Health Center The pelicans, however, are not easily traveled to the refuge to take samples captured until they start showing these of the tilapia for analysis. symptoms and are seriously ill. Once Botulism outbreaks have involved captured, the pelicans are taken pelicans every year at the Salton Sea immediately to the refuge’s avian since 1996, but last summer’s outbreak hospital for emergency treatment. This

6 ENDANGERED SPECIES BULLETIN SEPTEMBER/OCTOBER 2000 VOLUME XXV NO. 5 includes flushing their systems with F (38 degrees C) for 4 months run- fresh water and administering antibiot- ning—and driest, with fewer than 3 ics to their eyes, which become dry and inches (7.5 centimeters) of rainfall each infected when the eyelid muscles are year. The Salton Sea is the largest inland paralyzed. Dead and dying birds must body of water west of the Rockies, 35 be retrieved quickly from the sea before miles (56 kilometers) long and 9 to 15 gulls and shorebirds begin feeding on miles (14 to 24 km) wide, with an the fly larvae hatching in the bodies, average depth of about 40 feet (12 m). which can spread the disease. Dead It was created in 1904, when a dike birds are incinerated at the refuge to broke and allowed Colorado River avoid further spread of botulism. water to flow into a natural basin. Since Humans are not generally at risk of that time, 95 percent of other wetlands contracting avian botulism, but staffers in California have been lost to develop- working with sick birds take precau- ment, making the Salton Sea a critical tions against botulism and other stopover for migratory birds and habitat diseases by wearing rubber boots and for nearly 400 species. gloves, and by cleaning all surfaces and equipment with a bleach solution. Steve Johnson is a Wildlife Biologist at Avian botulism breaks out at the the Sonny Bono Salton Sea National A juvenile brown pelican at the field Salton Sea when bacteria and a variety Wildlife Refuge. hospital. This bird is in relatively good of environmental conditions, including condition and has a good chance for heat, come together to cause a massive survival. Note the sicker birds lying growth of algae—an algal “bloom”— down in the background. which robs fish of oxygen. Researchers at the National Wildlife Health Center believe tilapia concentrate toxins from the Salton Sea in their stomachs. When pelicans ingest tilapia that have been oxygen-deprived, the birds are poi- soned. Scientists believe tilapia are easy targets for juvenile pelicans because the fish become sluggish when they are deprived of oxygen. Disease outbreaks are a chronic problem for the Salton Sea. As a closed body of water fed by the Colorado River and surrounding agricultural lands of Imperial County, it has no way to rid itself of excess salt and nutrient build- up. It is 25 percent saltier than the Pacific Ocean due to the tremendous evaporation that takes place during the hot summer months. As the weather heats up, water evaporates, increasing salinity and creating ideal conditions for botulism. Salinity levels at the sea have been increasing yearly.

At 227 feet (70 meters) below sea A Temporary Biological Technician level, the Salton Sea is one of the lowest places a sick brown pelican in a spots in the United States. It also is one pillowcase (or “pellycase”) to prevent of the hottest—summer temperatures the bird’s injury or escape while en top 115 degrees F (47 degrees C) and route to the field hospital. the daily highs stay above 100 degrees

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