Monitoring Mortality Events and Oiling of Seabirds and Marine Mammals
Using Beach COMBERS Data

Since May 1997 the Monterey Bay National Marine Sanctuary’s beach monitoring program, the Coastal Ocean Mammal and Bird Education and Research Survey (Beach COMBERS) has obtained important baseline data on deposition rates of beached marine birds and mammals from sanctuary beaches. Local citizen volunteers are trained to conduct systematic monthly beach surveys in order to enumerate and identify all beach cast marine birds and mammals within a three- to four-kilometer stretch of coastline. In May 2001 five additional beaches in the southern portion of the sanctuary were added to the program.

Figure 1. Long-term average deposition rate (Bar) and oiling rate (Line) for ten Sanctuary beaches. Deposition is greatest during El Niño ocean conditions and lowest during major oil events when oiled carcasses are collected from beaches.

During the past six years, the Beach COMBERS project has revealed episodic mortality events related to natural (e.g., 1998 El Niño) and anthropogenic (e.g., oil spills, fishery interactions) factors and provided data to resource managers and scientists. In 1997 Beach COMBERS data were used to assess fishery-related mortality in southern Monterey Bay. In 1998 the program provided information regarding harmful algal blooms and domoic acid toxicity that affected seabirds and marine mammals in the sanctuary. In the summer of 2001 we provided data on hook-and-line entanglements of the endangered California Brown Pelican to the California Department of Fish and Game and size and age class data to University of California Davis researchers. In 2002 Beach COMBERS provided genetic samples to Cheryl Baduini of Claremont College and her colleagues to examine population genetics and colony affiliation of Shearwaters (Puffinus spp.) that travel from colonies in Chile, Australia, and New Zealand. Leg bands recovered from beached birds were useful in documenting movements and survival, contributing to an international effort to understand seabird populations.

During unusual mortality events, Beach COMBERS volunteers collect carcasses for necropsy to determine cause of death. Veterinarians Melissa Miller and David Jessup at the Marine Wildlife Veterinary Care and Research Center in Santa Cruz con-duct necropsies and examine birds for disease. The major cause of death for most beached birds was emaciation, but bacterial and fungal infections also may be factors. Collaborations like these will contribute to a greater understanding of the diseases affecting the seabird community in the sanctuary.

To examine trends in seabird mortality in the sanctuary, we have compared data from the current Beach COMBERS program (1997 to 2002) with past beach survey data collected during 1968 to 1969 and 1974 to 1975 by Victor Morejohn at Moss Landing Marine Laboratories and during 1971 to 1985 by researchers at Point Reyes Bird Observatory (PRBO).

The assemblage of species collected during the past and present beach surveys is similar, with changes in composition mainly relating to seasonal influxes in migratory species and episodic booms or die-offs in other species. One apparent difference in species composition is the past abundance of White-Winged Scoter (Melanitta fusca). In previous studies, this sea duck was often found on beaches during the winter and spring. Today it is rarely found on Beach COMBERS surveys, which probably reflects changes in its population throughout the North American breeding areas. Since 1977 U.S. Fish and Wildlife Service surveys indicate a 2 to 3 percent annual decline in the number of Scoters (both surf and white-winged) breeding in interior Alaska. Surveys of Canadian breeding areas indicate a reduction in the breeding range and significant declines in numbers of breeding birds. Although the reasons for these declines are not certain, habitat degradation, disturbance, and climate change are suspected as contributing factors. With long-term data sets and a historic perspective, we can gain insight regarding problems facing sea ducks and other wintering waterbirds that visit the sanctuary.

Brandt’s Cormorants are among the species affected by oil spills. photo Brad Damitz for NOAA/MBNMS

We have examined trends in oiling rates over our six-year data set (Figure 1) and compared these with past surveys to determine whether there has been a change in the incidence of chronic oiling in Monterey Bay. Chronic oiling (non-source) affects seabirds throughout the year, and deposition increases particularly during months with strong onshore winds. During 1971 to 1985, PRBO reported oiling rates averaging 8 percent in Monterey Bay, with the greatest incidence of oiling for diving birds (Loons 9 percent, small Grebes 7 percent, and Alcids 17 to 20 percent). The present oiling rate (2 percent) of seabirds recorded by Beach COMBERS is relatively low by comparison, possibly indicating that oil pollution prevention measures in the past twenty years have been successful. Common Murres (48 percent) and other divers continue to comprise a significant proportion of the total recorded oiled birds. Smaller species, including small Alcids (14 percent) and small Grebes (16 percent) are proportionally more affected relative to their deposition.

From November 2001 to July 2002 Beach COMBERS detected an increase in oiled seabirds. This event was attributed to an ongoing leaking shipwreck, the Jacob Luckenbach, off the San Mateo County coast. This source of oil contributed to the death of 236 seabirds collected within the Beach COMBER survey area. The species affected by this spill were mainly diving seabirds, primarily Common Murres (91 percent of total), Rhinoceros Auklet (3 percent), Ancient Murrelet (2 percent), Loons (1 percent), and Western and Clark’s Grebes (1 percent). Other species recorded within the survey area were affected to a lesser extent, including California Brown Pelicans, Shearwaters, Fulmars, Gulls, Cormorants, and others (less than 1 percent each). (The immediate threat from the Luckenbach has been removed; see article on page 23.)

Results from the recent Luckenbach spill are consistent with our five-year trend in species-specific oil rates; namely diving seabirds, Alcids, Loons, and Grebes, which spend their time at sea sitting on the water, are the most susceptible to oiling. One caveat to these data is that small-bodied birds (like shorebirds, smaller Alcids, and Storm-Petrels) probably are not represented in the beach bird data simply because they do not persist long on the beach. Mobile birds that are apt to fly when disturbed (e.g., Gulls, Shearwaters) may move out of the area and die before being detected. Within these limitations, we are confident that the Beach COMBER program is making great progress in understanding trends in sources of mortality for seabirds in the sanctuary.

Hannah Nevins and Jim Harvey
Moss Landing Marine Laboratories