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Least Concern (LC)
Assessors: J. Kiszka Robin Baird Gillian Braulik
Contributors: Philip Hammond Giovanni Bearzi Arne Bjørge Karin Forney Leszek Karkzmarski Toshio Kasuya William Perrin M Scott John Wang Randall Wells Ben Wilson
Reviewers: Randall Reeves

Rationale

The Rough-toothed Dolphin is widely distributed in tropical, subtropical and warm temperate waters. They are generally not common or highly abundant, but can be common around oceanic islands and archipelagos. The sum of existing abundance estimates for Rough-toothed Dolphins is approximately 220,000 individuals. Since estimates are available for only a small proportion of the range of the species, the total abundance is likely considerably greater than this. The species was assessed as Least Concern in 2008 (Hammond et al. 2012). While there is little information available on trends, no major threats have been identified, thus the species is again assessed as Least Concern.

Distribution

Rough-toothed Dolphins inhabit oceanic tropical and warm temperate waters in all three major oceans, mostly between 40°N and 35°S. They also occur in the Gulf of Mexico, the Caribbean Sea, the Red Sea, and the Gulf of California (Watkins et al. 1987, Miyazaki and Perrin 1994, Notarbartolo di Sciara et al. 2017, Jefferson 2018). They are relatively rare in the Mediterranean and are found primarily in the eastern part (Watkins et al. 1987, Kerem et al. 2016).

Population trend

Trend

Abundance estimates for Rough-toothed Dolphins are available for only a relatively small proportion of their range. An estimated 145,900 (coefficient of variation (CV) = 0.32) inhabit the eastern tropical Pacific based on shipboard line-transect surveys undertaken from 1986 to 1990 (Wade and Gerrodette 1993). In the Hawaiian Island Exclusive Economic Zone (EEZ), a shipboard line-transect survey conducted in 2010 resulted in an abundance estimate of 72,528 (CV = 0.39) Rough-toothed Dolphins (Bradford et al. 2017). Mark-recapture analyses from photo-identification surveys conducted between 2003 and 2006 have resulted in estimates of 1,665 individuals (CV = 0.33) around Kauai/Niihau and 198 (CV = 0.12) around the island of Hawaii (Baird et al. 2008). In the northern Gulf of Mexico, a summer line-transect survey conducted in 2009 from the 200 m isobath to the seaward extent of the U.S. EEZ resulted in an estimate of 624 Rough-toothed Dolphins (CV = 0.99; Garrison 2016). Along the U.S. Atlantic coast, a shipboard survey conducted in June-August 2011 between the lower Bay of Fundy and central Florida resulted in an abundance estimate of 271 (CV = 1.00; Hayes et al. 2017). No other abundance estimates are available. The total of the available estimates is 221,186, but this is certainly less than the actual total abundance because large parts of their range have not been surveyed.



Threats

Small numbers of Rough-toothed Dolphins are (or have been) taken opportunistically in directed dolphin hunts in the Solomon Islands, Sri Lanka, St. Vincent and the Grenadines, Taiwan, West Africa, New Guinea, Japan, and possibly St. Helena (Caldwell and Caldwell 1975, Mitchell 1975, Nishiwaki and Uchida 1977, Leatherwood and Reeves 1989, Miyazaki and Perrin 1994, Perrin et al. 2005, Young and Iucidello 2007). Kasuya (2018) reported that in Japan, Rough-toothed Dolphin remains have been found at Taiji, that 4 individuals were taken in 1991 by hand harpoon fishermen in Wakayama Prefecture, and that drive fisheries off the Izu Peninsula killed at least 80 between 1932 and 1972.

Rough-toothed Dolphins sometimes remove bait and catch from fishing gear, particularly longlines, and this sometimes results in their injury or death. In American Samoa between 2008 and 2012, six Rough-toothed Dolphins were reported as injured in the deep-set longline fishery, and this accounted for almost half of the reported cetacean interactions in that fishery (Bradford and Forney 2014, Hayes et al. 2017). The Rough-toothed Dolphin is one of the main species involved in fishery interactions in nearshore Hawaiian waters, stealing bait and hooked fish (Schlais 1984, Nitta and Henderson 1993). Fishermen reportedly shoot dolphins as retaliation (Oremus et al. 2012, Baird 2016, Baird et al. 2008). Mintzer et al. (2018) reported that Rough-toothed Dolphins are sometimes used as bait in longline fisheries.

Rough-toothed Dolphins are killed incidentally in tuna purse seines in the eastern tropical Pacific: 21 were estimated to have been killed during the period 1971–75 and 36 died in a single net haul in 1982. In Ghana, Rough-toothed Dolphins were reported to comprise 6.1% of cetacean bycatches in gillnets (Van Waerebeek et al. 2009, Debrah et al. 2010). From 1992 to 1998 in Ceara State, northeastern Brazil, 13 strandings of this species were recorded, all likely due to gillnet entanglement (Monteiro-Neto et al. 2000). From 1997 to 2015, there were 11 reports of stranding due to bycatch in the eastern Mediterranean Sea (Kerem et al. 2016). Unknown numbers were also taken as bycatch in drift gillnet fisheries in Sri Lanka, Brazil, Taiwan, Cote d’Ivoire, the central North Pacific, and probably elsewhere in tropical and warm-temperate waters around the world (Miyazaki and Perrin 1994, Ilangakoon 1997, Perrin et al. 2005, Van Waerebeek et al. 2009, Kerem et al. 2016).

Uses and trade

The Rough-toothed Dolphin is occasionally taken in small numbers in directed cetacean hunts in Japan, Saint Vincent, Taiwan, West Africa, and possibly elsewhere. It is sometimes used as bait in longline fisheries.

Conservation

The Rough-toothed Dolphin is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES). The biology, life history, population size, and subpopulation structure, as well as migratory behaviour are insufficiently known.

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,]
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