Planning & Assessment Framework

Leatherback Turtle

The leatherback sea turtle (Dermochelys coriacea ; Figure 1) is the largest extant sea turtle in the world and the only remaining species of the soft-shelled sea turtles (family Dermochelyidae). This turtle can reach 150 cm in width across the curved carapace and the flippers can reach 270 cm in length. A full-sized adult can weigh up wards of 900 kg (NMFS 2009a). The Pacific leatherback turtle population forages nearshore in the California Current Large Marine Ecosystem (LME), and generally eats only jellyfish (i.e., hydrozoans or Scyphozoans). On the US West Coast the turtles target seasonally dense aggregations of the brown sea nettle (Chrysaora fuscescens; Figure 2).

Because of the limited temporal and geographic distribution of the key prey source, two areas along the California Current have been proposed to be designated as Critical Habitat under the federal Endangered Species Act (ESA) (Figure 3). The proposed listing specifically mentions ocean renewable (wave and tidal) energy development as a concern (NMFS 2009b). As with other turtles, leatherback turtles could directly interact with wave energy development in several ways, including behavior modification due to Electromagnetic Fields (EMF) or Acoustics or direct effects from Underwater Collision or Entanglement and Entrapment. Indirect effects might include prey changes due to the Artificial Reef Effect or the Fish Attraction Device (FAD) Effect.

Concern is also focused on the interaction of the main prey species, brown sea nettles, with wave energy conversion (WEC) devices due to the possibility of Underwater Collision. The nettles, being soft-bodied plankton, could be swept into WEC devices or infrastructure, and damaged. However, the workshop on wave energy ecological effects offshore Oregon, made the following countervailing observation:

Many of the jellyfish have complex life cycles with a planktonic sexual reproductive stage and a benthic asexual stage. The wave energy structures will definitely be colonized by hydrozoans and likely by the asexual stage of true jellyfish (Scyphozoans). By providing more habitat for the benthic asexual stage, wave energy structures may increase jellyfish population sizes (Boehlert, et al. 2008).

Figure(s):

Figure 1. Leatherback turtle (Dermochelys coriacea)(photo by Scott R. Benson, NMFS Southwest Fishery Science Center).

Figure 2. Brown sea nettles (Chrysaora fuscescens) i the Monterey Bay Aquarium (source Wikipedia Commons, photo by Ed Bierman, Redwood City, CA).

Figure 3. Areas recommended as Critical Habitat for the leatherback turtle (from NMFS 2009a). See key below for explanation.

Key to Figure 3 (above)

Areas recommended as Critical Habitat:

Area 1: Nearshore area from Point Arena to Point Sur California and offshore to the 200 meter isobath. Leatherback presence is based on aerial surveys, shipboard sightings, and telemetry studies. This area is a principal California foraging area (Benson et al. 2007b) with high densities of primary prey species, brown sea nettle (C. fuscescens), occurring here seasonally from April to November (Graham 1994).

Area 2: Nearshore area from Cape Flattery, Washington, to Umpqua River (Winchester Bay), Oregon and offshore to the 2000 meter isobath. Leatherback presence is based on aerial surveys, shipboard surveys, fishery interaction data, and telemetry studies. This area is the principal Oregon/Washington foraging area and includes important habitat associated with Heceta Bank, Oregon. The greatest densities of a primary prey species, brown sea nettle (C. fuscescens), occur north of Cape Blanco, Oregon and in shallow inner shelf waters (Suchman and Brodeur 2005)

Area 7: Nearshore area from Point Arena, California, to Point Vicente, California, exclusive of area 1 (see above) and offshore to a line connecting N38.955/W126.382 and N33.741/W121.893. This area includes waters surrounding the northern Santa Barbara Channel Islands (San Miguel, Santa Rosa, Santa Cruz, and Anacapa Islands). Leatherback presence is based on based on aerial surveys, telemetry studies, and fishery interactions. This area includes prey species within secondary foraging areas characterized by ocean frontal zones west of the continental shelf that are occupied by aggregations of moon jellyfish (A. labiata) and lower densities of brown sea nettles (C. fuscescens). The frontal zones are created by a series of quasi-permanent, retentive eddies or meanders, associated with offshore-flowing squirts and jets anchored at coastal promontories between Point Reyes and Point Sur, which create linkages between nearshore waters of area 1 and offshore waters of the California Current. Telemetry data indicate that this area is commonly utilized by leatherbacks, particularly when jellyfish availability in area 1 is poor. This area also provides passage to/from foraging habitat in areas 1, 5, and 6 (see above), often through the northern Santa Barbara Channel Islands during the spring and early summer months.

(For references cited in these area descriptions, see NMFS 2009a).

References:

· Boehlert, G. W, G. R. McMurray, and C. E. Tortorici (editors). 2008. Ecological effects of wave energy in the Pacific Northwest. U.S. Dept. Commerce, NOAA Tech. Memo. NMFS-F/SPO-92, 174 p.

· NMFS (National Marine Fisheries Service). 2009a. Designation of Critical Habitat for the Leatherback Sea Turtle. Endangered Species Act Section 4(b)()2 Report. National Marine Fisheries Service, Office of Protected Resources. 50 p.

· NMFS (National Marine Fisheries Service). 2009b. Revision of Critical Habitat for Leatherback Sea Turtles. Biological Report. National Marine Fisheries Service, Office of Protected Resources: Southwest Regional Office, Southwest Fisheries Science Center and Northwest Regional Office, Northwest Fisheries Science Center. 28 p.

· NOAA Fisheries Office of Protected Resources Leatherback Turtle Page.

Last modified at 11/9/2011 10:18 AM by Greg McMurray