Principal Investigators: Scott Benson, Tomo Eguchi, & Jeffrey Seminoff (SWFSC)


Project title

Assessing changes in the abundance and foraging habitat of western Pacific leatherback turtles off the U.S. West Coast in the context of a strong El Niño and decadal-scale climate variation

Background

Pacific leatherback sea turtles, part of NOAA’s “Species in the Spotlight” initiative, are identified as being under the greatest threat of extirpation across worldwide sea turtle populations. Past research has provided information on the physical and biological habitats of Pacific leatherbacks, and helped to identify Critical Habitat along the U.S. West coast. Reconsideration of the timing and spatial extent of the Pacific Leatherback Conservation Area (PLCA) has led to a need for model-based tools that help predict leatherback habitat use and limit overlap between leatherback turtles and fishery activities. However, the California Current ecosystem varies over seasonal, interannual, and decadal time scales, which Pacific leatherbacks are responsive to by changing habitat use. Therefore, models must incorporate this temporal climate variability in order to accurately predict habitat use. The proposed research is designed to conduct studies of leatherback turtle distribution, density, abundance, and movements in the context of climate variation to ensure that future management actions can be based on the best available and appropriate scientific information spanning a range of oceanic conditions.


Leatherback and jellyfish

Research Objectives

This projects directly links to the NOAA Marine Turtle Research Themes (B) Life History and Vital Rates; (C) Abundance; and (D) Anthropogenic Impacts as outlined in NMFS’s 2013 Sea Turtle Assessment Status and Research Needs document. The objectives are to:
1. Assess distribution, abundance and foraging behavior of western Pacific leatherback turtles foraging off the U.S. West Coast during current/predicted warm-water conditions (aerial line-transect surveys and animal-borne video).
2. Determine the distribution, species composition, and relative density of leatherback prey during warm-water conditions (aerial line-transect surveys and animal-borne video).
3. Examine trends in leatherback abundance relative to oceanographic indices, such as NOI, PDO, ENSO to inform habitat-use models (aerial line-transect surveys and regression models).
4. Determine leatherback movements within, and timing of arrival and departure from, central California foraging areas relative to oceanic conditions (satellite telemetry).

Project significance, impacts, and applications

The proposed project will provide novel and necessary data to evaluate the adequacy of the recently designated critical habitat area and its robustness in a variable and changing climate. Further, as NMFS seeks to enhance swordfish fisheries along the U.S. West Coast, this study will support the development of robust leatherback habitat-use models that capture a broader range of oceanic conditions within the California Current Ecosystem, including potential effects of climate change (Hazen et al. 2012). Such models are essential to minimize spatio-temporal overlap of fisheries and endangered leatherbacks, which is critical because the local limit reference point (mortality limit to avoid adverse consequences), is less than 1 individual per year within the West Coast U.S. EEZ (Curtis et al. 2015).

In conducting informal or formal ESA consultations, NMFS is required to use the best available scientific or commercial data when conducting jeopardy analyses. This project will provide high quality and timely data on leatherbacks during ecosystem conditions that are markedly different than those during previous studies of western Pacific leatherbacks, leading to less uncertainty for the agency when reaching conclusions about potential impacts of activities. Finally, as mentioned above this project meets research and management data needs outlined in multiple NMFS documents.