The Recovery Plan for U.S. Pacific Populations of the Leatherback Turtle (NMFS and USFWS 1998) calls for identification of primary foraging areas and monitoring of the status and abundance of foraging populations. Most of the current knowledge about leatherbacks has come from studies on nesting beaches, while very little is known about this species in the marine environment. We have used several approaches, including aerial surveys, molecular genetics, and telemetry to identify key foraging areas in the Pacific. We have determined that waters off central California are a critical foraging area for one of the largest remaining Pacific nesting populations in Papua, Indonesia.
Aerial surveys and satellite telemetry
Line transect aerial surveys conducted since 1990 have identified several nearshore areas along the California and Oregon coast where leatherbacks aggregate seasonally to feed on jellyfish, their preferred prey. We conduct annual surveys to determine the distribution and estimate the abundance of leatherbacks along the central and northern California coast. Since 2000, we have captured and tagged leatherbacks that come into Monterey Bay and areas off the coast south of San Francisco in August and September each year.
This research is multi-faceted as we aim to improve our understanding of the physiology, migration and dive behavior of the leatherbacks in relation to the oceanographic and ecological features of the coastal marine ecosystem, and monitor how these ecosystem processes change through time and effect the abundance and distribution of the leatherbacks.
We have come to better understand what determines when and where the leatherbacks move closer to shore, and why in some years, they are not seen in areas like Monterey Bay. 2006 was a sparse year for leatherbacks at our central California study site, and this was associated with unusual weather patterns and absence of jellyfish. This has stimulated much discussion amongst the scientists involved in our program, and led to further insights in this area.
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Leatherback turtles usually appear in Monterey Bay and California coastal waters during August and September. Scientists from the Southwest Fisheries Science Center’s Marine Turtle Research Program are using molecular genetics and satellite telemetry as research tools to accompany these cryptic animals on journeys of new discoveries as they migrate around the ocean.
Sept. 1st 2006 (WMP): Leatherbacks are known to migrate to Monterey Bay from Indonesia to feed on jellyfish. The upwelling process that is part of the productive Californian coastal ecosystem provides ideal forage habitat for leatherbacks and other marine life.
Sept. 15th 2006 (WMP): The disruption of the seasonal upwelling process within Californian waters is having an adverse effect on marine life and few leatherbacks have been seen.
Sept. 30th 2006 (WMP): The absence of Leatherbacks in Monterey Bay for the first time since the studies commenced in 2000, stimulates discussion on patterns of ocean processes, effects of climate change and the fate of the Leatherback in the Pacific.