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Gulf of the Farallones: Ecosystem-Oriented Research

by Jaime Jahncke, PhD

There is abundant evidence indicating that the ocean and its living resources are in trouble. Humans have depleted fish stocks and disrupted the composition and function of entire marine communities, threatening several species of birds and mammals. Managing marine resources at the single-species level has not worked in the past, and new management strategies are needed.

Ecosystem-based management focuses on the protection of ecosystem structure, function, and key processes in order to ensure, among other things, that the ecosystem continues to provide the services humans need. This approach requires knowledge of the physical environment, the biological communities, and the complex relationships among the constituent parts. Ecosystem-oriented research generally involves integrated, multidisciplinary and collaborative studies.

PRBO has been conducting such research in the Gulf of the Farallones. To better understand the marine ecosystem, we study the physical and biological interactions linking oceanographic conditions with the abundance and distribution of top predators (seabirds and marine mammals) and their prey (krill and small and large fishes). Our research will provide the scientific basis for the design and implementation of a marine protected area (MPA) around the Farallon Islands (see page 9).

Aboard small research boats, we travel a grid of transect lines that covers much of the offshore region of the Gulf of the Farallones National Marine Sanctuary, west and north of the Golden Gate. During each cruise, we survey the physical oceanography (water mass, movements, and small features such as fronts); the zooplankton community (animal plankton, particularly krill); and the top-predator community (birds and mammals).

Our physical oceanography data characterize areas with enhanced phytoplankton (plant plankton) production, which may attract zooplankton and their predators. In turn, the zooplankton data provide a link between the physical environment and top predators, helping us understand how changes in ocean water properties may affect the suite of organisms that inhabit the region. Marine birds and mammals are our focal species: we want to know whether they aggregate in predictable areas (based on the oceanographic and zooplankton data) and what makes these particular areas distinct from other parts of the ocean.

Results to date include the finding that late timing of nesting and reduced breeding success of Cassin's Auklets on Southeast Farallon Island in 2005 was associated with decreased krill abundance in the region. Reduced upwelling, high sea surface temperature, and low chlorophyll concentrations led to reduced krill abundance in the upper water column and decreased seabird abundance in the vicinity of the breeding colony in our study area.

This project has also shown that at least five species of seabirds (the Cassin's Auklet, Common Murre, Pigeon Guillemot, and Brandt's and Pelagic cormorants) and two species of marine mammals (the California sea lion and California gray whale) would likely benefit from an MPA in this region.

The Gulf of the Farallones was designated a National Marine Sanctuary, in 1981, to ensure protection from oil and gas exploration and from dumping hazardous wastes. The Sanctuary offers no protection, however, from depletion of prey stocks, mortality in fishing gear (‘by-catch'), disturbance of top-predator feeding aggregations, ship strikes of whales, and pollution. MPAs represent a way of managing marine resources at an ecosystem level, offering potential benefits that range from maintenance of diversity and ecological processes, to replenishment of fish for surrounding commercial fisheries, to opportunities for education and recreation. PRBO's cooperative, multidisciplinary study in the Gulf of the Farallones offers the scientific basis for such ecosystem-based management.