Marine mammal observations at the Central American Pacific Ocean coast reflect the occurrence and migration of whales, dolphins and sea lions (Reilly, Reference Reilly1990; Acevedo-Gutierrez Reference Acevedo-Gutierrez1994; Acevedo & Smultea, Reference Acevedo and Smultea1995; Fertl et al., Reference Fertl, Acevedo-Gutierrez and Darby1996; Acevedo-Gutierrez et al., Reference Acevedo-Gutierrez, Brennan, Rodriguez and Thomas1997; Escorza-Treviño et al., 2001; Saenz et al., Reference Saenz, Wong and Carrillo2004; Quintana-Rizzo & Gerrodette, Reference Quintana-Rizzo and Gerrodette2009; Scott & Chivers, Reference Scott and Chivers2009). Also, 19th Century whaling records considered this zone important for wintering humpback whales from the southern hemisphere (Best, Reference Best2008).

On 21 July 2010, fishermen observed a floating carcass of a large cetacean south of Isla Pirigallo, El Salvador, in the Gulf of Fonseca (Figure 1). One day later, a gray whale (Eschrichtius robustus Lilljeborg, 1861) stranded on Playas Negras Beach, La Union, on the continental mainland, 30 km west of the at-sea sighting (13°09′ 34.2″N, 87°56′ 7.8″W, Fig. 1), which may have been the same animal.

Fig. 1.

Area where fishermen observed a large whale carcass floating at sea off southern El Salvador on 21 July 2010 (1), and Playas Negras (2) where a dead gray whale appeared on 22 July 2010. Bahía de Banderas (3) is the place with the southernmost record for gray whales prior to this report.

This whale was identified as a gray whale by its moderately arched mouthline (Figure 2) and in having eight to nine dorsal knuckles and only three short throat grooves (Figure 3). Balaenopterids bear falcate dorsal fin, but balaenids lack this, also, the former whales present several ventral grooves (throat to chest) and in the latter family are absent (Reeves et al., Reference Reeves, Stewart, Clapham and Powell2002). The specimen was 13.4 m long, making it an adult because among gray whales, the largest reported immature female and male was 12.92 and 11.75, respectively (Rice & Wolman, Reference Rice and Wolman1971). Sex was not determined.

Fig. 2.

A gray whale that stranded at Playas Negras Beach, La Union, El Salvador on 22 July 2010. Photograph by Wendy Toledo.

Fig. 3.

Ventral image of the head of a gray whale that stranded in El Salvador; notice there are only three short throat pleats. Photograph by Wendy Toledo.

The carcass did not have any scars that could help determine the cause of death. Field observations reflect no obvious signs of tooth rakes or scarring to suggest a killer whale (Orcinus orca) attack or that a ship strike was involved. Local authorities buried the carcass and no tissue samples were collected.

Eastern North Pacific gray whales summer in arctic waters of Alaska and Russia, and during the autumn they migrate south to winter in waters off western central California, western Baja California, the Gulf of California and western mainland Mexico, where females have their calves (Calambokidis et al., Reference Calambokidis, Darling, Deecke, Gearin, Gosho, Megill, Tombach, Goley, Toropova and Gisborne2002; Urban et al., Reference Urban, Rojas-Bracho, Perez-Cortes, Gomez-Gollardo, Swartz, Ludwig and Brownell2003; Rodriguez de la Gala-Hernandez et al., Reference Rodriguez de la Gala-Hernández, Heckel and Sumich2008). The find of the dead specimen coincides with the occurrence of gray whales in the North Pacific Ocean (Reeves et al., Reference Reeves, Stewart, Clapham and Powell2002), thus an explanation for this event is unclear. The previous southernmost record of occurrence of live gray whales in the eastern North Pacific was Bahia de Banderas, Jalisco, Mexico (20°45′N 105°34′W; Jones & Swartz, Reference Jones, Swartz, Perrin, Würsig and Thewissen2009), about 2000 km north from the stranding reported in this paper (Figure 1). However, the dead whale could have come from anywhere and not necessarily from Mexico.