Genus Cephalorhynchus includes four geographically distinct species ranging from the cold-temperate to sub-Antarctic waters of the Southern Hemisphere. Of the four, two species are found in South America: the Chilean dolphin (C. eutropia; Gray, 1846) and the Commerson's dolphin (C. commersonii; Lacepede, 1804) (Rice, 1998). The South American subspecies of Commerson's dolphin (C. c. commersonii) is found in shallow waters along the Atlantic coast of South America, from Gulf of San Jose (41[degrees] 26' S) to the southern tip of Tierra del Fuego (55[degrees] S) of Argentina, including the Falkland (Malvinas) Islands (Goodall et al., 1988; Goodall, 1994).
In Chilean waters, Commerson's dolphins occur frequently in the eastern area of the Magellan Strait (Venegas & Atalah, 1987; Goodall et al., 1988; Leatherwood et al., 1988), although small groups have also been observed occasionally inside the channels system (Goodall et al., 1988; Aguayo-Lobo et al., 1998), with the northernmost record near Chiloe Island (42[degrees] 45' S; Capella & Gibbons, 1991) and the southernmost in the Drake Passage to the Pacific (Aguayo-Lobo & Torres, 1967). With the exception of the eastern area of the Magellan Strait, the paucity of records of Commerson's dolphins inside of fjords and channels to south of 40[degrees] S in the Pacific suggests that its occurrence is unusual. In fact, Commerson's dolphins are relatively easy to identify, but there are fewer than 60 reports (Goodall et al., 1988; Aguayo-Lobo et al., 1998) from hundreds of ships, including wildlife observation-oriented cruise ships--birders or naturalists traversing these fjords and channels. Herein, we provide information on the occurrence of Commerson's dolphins in Fitz Roy Channel located between Otway and Skyring Sounds, 60 km northwest of Punta Arenas, Chile, and discuss whether this subspecies can be regarded as resident to this particular area of the Chilean Pacific coast.
Fitz Roy Channel (52[degrees] 43' 17" S, 71[degrees] 23' 19" W; Figure 1) is a narrow passage that connects Otway and Skyring Sounds, two bodies of water with different oceanographic features and regimes (Valdenegro & Silva, 2003). The channel is 21.3 km long with a maximum width of 1,870 m in the south section, a minimum of 441 m in the central part, and a maximum depth of 30 m. The current speed averages 7 km/h, although it can reach 9.3 km/h during tidal changes; and the swell is dictated by the wind. This area does not constitute a maritime traffic route, and maritime access is through the Jeronimo Channel that connects Otway Sound with the western section of the Magellan Strait, and the Gajardo Channel that connects the Xaultegua Gulf with Skyring Sound 86 km to the northwest of Jeronimo Channel.
Non-systematic and systematic surveys were conducted in different years. Non-systematic surveys were undertaken onboard a local tourist vessel M/V Forrest in December 2009 and 2015, January 2011 and 2014, and May 2011 along the entire channel. Here, off-effort sightings of dolphins were made when traveling to and from the vessel's base port. Systematic surveys were carried out monthly (two to four surveys...
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