1California Deptartment of Fish and Game (Jessup) Marine Wildlife Veterinary Care and Research Center, Santa Cruz, CA, USA; 2Wildlife Health Center, School of Veterinary Medicine, University of California, Davis, CA, USA; 3Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA; 4International Bird Rescue and Research Center, Berkeley, CA, USA
Monitoring the health of marine ecosystems is a relatively new concept, and the extent to which mortality events involving different species at various trophic levels may serve as a measure of health is only just now being explored. Marine birds may serve as a monitor of short- and longer-term disturbances than may reflect the health of the marine environment. Oil spills and other causes of pollution, and local changes in prey abundance, either as a result of fisheries practices or natural cycles, may severely impact local marine bird populations. Changes in ocean temperature and quality, which may be related to human activity within the near shore environment, as well as global climate change, El Niño events and natural ocean cycles may influence prey abundance and/or algal species and abundance, resulting in red tide events. These events and processes may be of various durations, cyclic, or periodically repeated.
Three recent examples of marine bird die-offs we have explored that have implications for the health of the marine environment are:
1. In August of 1997, approximately 400 common murres (Uria aalge) were found dead in a relatively confined area of the southern end of the Monterey Bay National Marine Sanctuary. This is the first report of inhaled brevetoxin killing birds on the Pacific coast, but in retrospect, brevetoxicosis is suspected in several recent common murre die-offs in California, each involving hundreds of murres and each occurring during months with warmer ocean temperatures.
2. Over an approximately 1-wk period in late October of 1997, five hundred marine birds, predominantly western grebes (Aechmophorus occidentalis), common loons (Gavia imer), and surf scoters (Melanitta perspicillata) became fouled with a fish oil. This product caused water saturation, hypothermia, and associated debilitation, but many birds also suffered enteritis and septicemia due to Salmonella. The combination of physical fouling and acute stress due to oil, bacteremia, and migration related debilitation, resulted in relatively high mortality.
3. Over a 3-mo period in the winter of 1997–1998, a significant percentage of the common murre population off of California’s central coast died as a result of oil and tar contamination. Over 500 live birds, 94% of which were murres, and over 650 dead birds were recovered. Although there was no point source for the petroleum several lines of investigations are being followed. Events of this type have occurred repeatedly in California over the last 5–10 yr, and they may have serious population level effects.