337 



Abstract — Leatherback turtles iDer- 

 mochelys coriacea) are regularly seen 

 off the U.S. West Coast, where they 

 forage on jellyfish (Scyphomedusael 

 during summer and fall. Aerial line- 

 transect surveys were conducted in 

 neritic waters (<92 m depth) off cen- 

 tral and northern California during 

 1990-2003, providing the first forag- 

 ing population estimates for Pacific 

 leatherback turtles. Males and fe- 

 males of about 1.1 to 2.1 m length 

 were observed. Estimated abundance 

 was linked to the Northern Oscil- 

 lation Index and ranged from 12 

 (coefficient of variation [CV] = 0.75) 

 in 1995 to 379 (CV=0.23) in 1990, 

 averaging 178 (CV=0.15). Greatest 

 densities were found off central Cali- 

 fornia, where oceanographic retention 

 areas or upwelling shadows created 

 favorable habitat for leatherback 

 turtle prey. Results from independent 

 telemetry studies have linked leather- 

 back turtles off the U.S. West Coast 

 to one of the two largest remain- 

 ing Pacific breeding populations, at 

 Jamursba Medi, Indonesia. Nearshore 

 waters off California thus represent 

 an important foraging region for the 

 critically endangered Pacific leather- 

 back turtle. 



Abundance^ distribution, and habitat of 

 leatherback turtles iDermoche/ys coriacea) 

 off California, 1990-2003 



Scott R. Benson (contact author)^ 



Karin A. Forney^ 



James T. Harvey^ 



James V. Carretta* 



Peter H. Dutton* 



Email address lor S R. Benson: Scott.Benson@noaa.gov 



' Protected Resources Division 

 Southwest Fisheries Science Center, NMFS, NOAA 

 c/o MLML Norte 

 7544 Sandholdt Rd. 

 Moss Landing, California 95039 



^ Protected Resources Division 

 Southwest Fisheries Science Center, NMFS, NOAA 

 110 Shaffer Road 

 Santa Cruz, California 95060 



^ Moss Landing Manne Laboratories 

 8272 Moss Landing Road 

 Moss Landing, California 95039 



'' Protected Resources Division 

 Southwest Fisheries Science Center, NMFS, NOAA 

 8604 La Jolla Shores Dnve 

 La Jolla, California 92037 



Manuscript submitted 21 August 2006 to 

 the Scientific Editor's Office. 



Manuscript approved for publication 



29 November 2006 by the Scientific Editor. 



Fish. Bull. 105:337-347 (2007). 



The leatherback turtle (Dermochelys 

 coriacea) is listed as a critically endan- 

 gered species on the World Conserva- 

 tion Union Red List 2006 (lUCN'). 

 The Pacific population is at risk of 

 extirpation because of over-harvest 

 of eggs, commercial and residential 

 development on nesting beaches, and 

 incidental bycatch in fisheries (Spo- 

 tila et al., 2000). Declines have been 

 documented at nesting beaches in the 

 eastern Pacific and throughout the 

 Indo-Pacific region, where there has 

 been a complete loss of the Malay- 

 sian nesting population (Chan and 

 Liew, 1996), severe declines at nest- 

 ing beaches in Costa Rica (Spotila 

 et al., 2000) and Mexico (Sarti et al., 

 1996), and lesser declines at western 

 Pacific nesting beaches (Hitipeuw et 

 al., 2007). 



Research on leatherback turtles in 

 the Pacific has typically been limited 

 to nesting beaches and few studies 

 have been conducted in foraging ar- 

 eas. In the eastern North Pacific, 



the leatherback turtle is the most 

 common sea turtle sighted north of 

 Mexico (Stinson, 1984), although no 

 nesting occurs at these latitudes. 

 Sightings and incidental capture da- 

 ta indicate that this species is found 

 as far north as Alaska but has been 

 most frequently encountered off the 

 coast of central California (Stinson, 

 1984; Starbird et al., 1993). Genet- 

 ic analyses of tissues from leather- 

 back turtles stranded on California 

 beaches or caught incidentally in the 

 California-Oregon drift gillnet fishery 

 indicate that these turtles originate 

 from nesting beaches in the western 

 Pacific (Dutton et al., 2000, 2007). 

 Thus, leatherback turtles travel thou- 

 sands of kilometers from western 

 Pacific beaches to forage on season- 



lUCN (World Conservation Union). 

 2006. Species Survival Commission. 

 Red List database 2006. Website: 

 http://www.iucnredlist.org/ (accessed 

 19 November 2006). 



