Tracking Sooty Shearwater habitat use throughout dynamic upwelling ecosystems in the California Current
- Josh Adams
United States Geological Survey (USGS)
- Jim Harvey
Moss Landing Marine Laboratories, California State University
- CA Sea Grant
Sooty Shearwater (Puffinus griseus) is the numerically dominant avian piscivore in the California Current System (CCS) during the upwelling season from May through September. Its affinity for principal prey associated with productive coastal waters in the vicinity of upwelling centers (e.g., anchovy, sardine, and juvenile rockfishes) leads to spatially predictable and extremely aggregated distributional patterns. Within the Monterey Bay National Marine Sanctuary, hundreds of thousands of shearwaters can form single mega-flocks that extend for several kilometers in narrow bands just off shore.
It has been estimated that Sooty Shearwaters in Monterey Bay consume approximately 4,400 metric tons (MT) of anchovies or 9,000 MT of squid per year. Shearwaters are highly mobile, capable of traveling 800 km per day, and thus are able to respond to changes in oceanic conditions and prey resources over very short time scales (i.e., hours to days) while integrating information about prey availability over large spatial scales (i.e., CCS; 100,000 square kilometers). Thus, movement patterns and habitat use of shearwaters provide a convenient measure of biological response among upper trophic level predators to environmental variability within upwelling systems. These parameters, therefore, can serve as proxy indices that relate to fluctuations in commercially important prey.
Since 2008 scientists have tracked Sooty Shearwaters (Puffinus griseus) within the California Current ecosystem during their summertime feeding period and used the data to locate aggregations of prey species such as anchovy, sardine, krill and squid. Findings are assisting in identifying critical at-sea habitats for the shearwaters and are of direct relevance to developing ecosystem-based management plans of forage species, upon which seabirds and other marine species rely.
Summary to DateIn 2008-09, 57 birds were captured in the Santa Barbara Channel, Monterey Bay and Columbia River plume off Washington, outfitted with small transmitters, and tracked via satellite telemetry as they fed and molted from April to October. The tracking data were analyzed to: 1) identify foraging hotspots, 2) calculate residency times within different habitats, and 3) characterize inter-regional movements. As part of this work, scientists documented the birds’ residency within the West Coast’s five NOAA National Marine Sanctuaries.
The Sea Grant project complements a tracking study begun in 2004 by the scientists that has, among other things, documented the shearwaters’ large-scale migration routes–the longest in the animal kingdom. This migration begins in the birds’ breeding grounds in New Zealand, Chile and other parts of the south Pacific and south Atlantic oceans and ends in the historically highly productive waters around Japan, southeastern Alaska and the western coast of North America.
The new tracking data provide further evidence for the existence of foraging hotspots and their highly variable locations from year to year. In 2008, for example, feeding appeared concentrated north of the Columbia River plume, and in Monterey and San Luis bays. In 2009, it moved to nearshore waters of the Southern California Bight, perhaps in response to a shift in the location of sardines. The birds’ distribution was also more dispersed in 2009.
During the study, the birds ranged from southeastern Alaska to southern Baja California, Mexico. They spent 83% of their time within the U.S. Exclusive Economic Zone (EEZ), which extends 200 nautical miles from the coast; 57% of their time over the shelf (in waters less than 200-meters deep); 35% over the slope (200-1,000 meters), and 8% over the continental rise (depths greater than 1,000 meters). Based on the tracking data, an individual bird typically utilized habitat within more than one of the sanctuaries. In total, however, within the EEZ, the 57 birds spent only a quarter of their residency within the sanctuaries. Of the five sanctuaries, the Monterey Bay National Marine Sanctuary and Channel Islands National Marine Sanctuary were the most heavily used by the birds.
The algorithms for filtering, interpolating and analyzing the telemetry data are being, or will be, applied to the tracking of the gray-faced petrel, Adélie penguin, Hawaiian petrel, pink-footed shearwater, black-footed albatross, Galapagos petrel and Kittlitz’s murrelet. Besides identifying critical seabird habitats, the research may, in some cases, be used to reduce fishing impacts–especially from longlining–to seabirds. The high demand for forage species (for human consumption, aquaculture/livestock production and the omega-3 supplement industry) places added pressure on food resources and habitats for marine species.
Findings from this project can assist in ensuring that adequate biomasses of forage species are left in the ocean to sustain marine life. Last but not least, findings may offer insights into the causes of observed recent declines in sooty shearwaters in the
California Current and at their breeding colonies in New Zealand. The researchers note that other highly abundant bird species have been driven to extinction in the past, and that science such as theirs can be used to protect shearwaters from a similar fate by, for example, providing information on where seabird conservation zones might be most effective.
DiscussionWe anticipate broad benefits to SIMoN and the MBNMS resulting from this study. Sooty Shearwaters have great potential for revealing important oceanographic zones characterized by the greatest rates of energy transfer to upper trophic levels. Shearwaters are an ideal independent biological measure of habitat stability and oceanographic patterns, and this study will provide direct biological information about use of key oceanographic features (i.e., fronts, eddies) and conditions (i.e., upwelling-relaxation, phytoplankton blooms) in west coast marine sanctuaries.
Within the California Current System, fisheries oceanographers and resource managers will benefit from new, detailed information regarding how key upper trophic level seabird predators function within a network of variable coastal shelf marine ecosystems—this information is required for ecosystem-based resource management (i.e., design, implementation, and assessment of functional Marine Protected Areas, trophic impacts of potentially competing fisheries, impacts of regional pollutants to the health of nearshore marine systems).
- Habitat association
- Trophic association
- Migration/movement patterns
Study MethodsWe are using small satellite transmitters (PTTs) to measure and compare continuous movement parameters of shearwaters associated with upwelling conditions within the MBNMS and the CCS. Birds are tracked for appoximately 60 days continuously during June – September. Unlike seabird-habitat associations measured during discrete ship-based observations, telemetric data provide a continuous, longer-term temporal component (40 to 90 d). Telemetry provides unique insight into habitat stability which is needed (1) to identify stable, predictable ocean habitats, and (2) assess environmental processes that influence these habitats and can cause rapid changes in forage fish availability.
Figures and Images
Figure 1. Sooty Shearwaters on the water. Photo: Josh Adams, USGS.
Figure 2. Sooty Shearwater in flight. Photo: M. Baird, Wikipedia Commons.
Figure 3. Index of use by Sooty Shearwaters from San Francisco to Mexico. Courtesy of USGS.