|Scientific Name:||Cephalorhynchus commersonii (Lacépède, 1804)|
|Taxonomic Notes:||Two subspecies are recognized: C. c. commersonii in southern South America and C. c. kerguelenensis in the Kerguelen Islands (Robineau et al. 2007). The Kerguelen subspecies was apparently founded by a few individuals as recently as 10,000 years ago.|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Crespo, E., Olavarria, C., Dellabianca, N., Iñíguez, M., Ridoux, V. & Reeves, R.|
|Reviewer(s):||Taylor, B.L. & Pimper, L.|
Although progress has been made towards increasing what is known about the Commerson's Dolphin since the previous assessments in 1996 and 2008, which resulted in listing it as Data Deficient, the information still falls short of what is needed for a rigorous evaluation against the Red List criteria, particularly with regard to population size, trends, and threats. However, there is evidence indicating that the South American subspecies, which is apparently much more abundant than the Kerguelen subspecies, is still widespread, abundant, and not in decline in major portions of its range. Therefore, the species is listed as Least Concern.In the future, separate assessments of the two subspecies should be a priority. The Kerguelen subspecies is currently listed as Endangered in the regional IUCN Red List for French Southern Territories. Further, population structure within South America may justify separate assessments of geographical subpopulations. Further research is also needed to provide current abundance estimates for a larger proportion of the species’ total range, and more up-to-date, quantitative information on human-caused mortality.
|Previously published Red List assessments:|
|Range Description:||The two disjunct subspecies of Commerson’s Dolphins are separated by 130° of longitude and about 8,500 km distance.|
Cephalorhynchus commersonii commersonii
Occurs in the coastal waters of southern South America and the Falkland (Malvinas) Islands. On the Atlantic coast of South America the northern limit of Commerson’s Dolphins is at approximately River Negro mouth (40°S) (Bastida and Rodríguez 2003). The range extends southward to near Cape Horn (56ºS) including the central and eastern Strait of Magellan and the Falkland (Malvinas) Islands (Goodall et al. 1988, White et al. 2002). Single dolphins and groups of up to hundreds were sighted in the late 1980s and early 1990s along the northern coast of Tierra del Fuego (Goodall 1994). Although sightings in the northern parts of the range often are of small groups or solitary individuals, overall numbers and group sizes increase to the south. In Chile the species is found mostly in Strait of Magellan (Aguayo-L. 1975, Venegas and Sielfeld 1978, Sielfeld 1983, Venegas and Atalah 1987, Thielke 1984, Goodall et al. 1988, Leatherwood et al. 1988, Hucke-Gaete and Vallejos 1997, Aguayo-L. et al. 1998, Gibbons et al. 2000), and nearby Seno Skyring, Fitz Roy channel, Seno Otway, and Seno Almirantazgo (Sielfeld and Venegas 1978, Gibbons et al. 2000).
Reported vagrants (northernmost records) along the Atlantic coast of South America include strandings in Buenos Aires province, Argentina (Brownell and Praderi 1985, Iñiguez et al. 2010) and Brazil (Pinedo et al. 2002). To the south, there are a few reports of this species at South Georgia (Brown 1988) and the South Shetland Islands (Aguayo-L. and Torres 1967, Goodall et al. 1988). However, sightings from the vicinity of South Georgia have been rejected by some workers (Jefferson et al. 1993). In the Pacific, a few records have been reported in the Chiloé area (Talcán, near Chaitén, Capella and Gibbons 1991; north of Quellón, J. Capella pers. comm.) and near San Rafael lagoon (estero Elefantes, F. A. Viddi pers. comm.) (http://especies.mma.gob.cl/CNMWeb/Web/WebCiudadana/ficha_indepen.aspx?EspecieId=157&Version=1).
Genetic analyses have revealed significant differentiation among different studied areas (within Tierra del Fuego and Santa Cruz provinces) over small geographic scales, considering these as subpopulations (Pimper et al. 2010, Cipriano et al. 2011). Coastal distribution around the Falkland (Malvinas) Islands and southern South America suggests that there is little mixing, if any, between the populations in these regions (White et al. 2002). Two “ecological stocks” have been identified based on differences in parasite loads and patterns of prey consumption (Berón-Vera et al. 2001). Skull morphology supports recognition of those two stocks (Pedraza 2008).
Cephalorhynchus commersonii kerguelenensis
Occurs in shallow coastal waters around all of the Îles Kerguelen in the southern Indian Ocean (Rice 1998, Robineau et al. 2007). No sightings or specimens have yet been reported from islands between South America and Kerguelen, such as Crozet, Heard, Amsterdam, or St Paul (Goodall 1994). Dolphins of the Kerguelen subspecies are most commonly sighted in the Golfe du Morbihan, on the eastern side of Kerguelen. Sightings have also been reported in other bays and fjords located along the northeastern and southern coasts of Kerguelen where observation effort is much more limited than in Golfe du Morbihan. Sightings from the open ocean in shelf and slope habitats around Kerguelen are scarce.
Recently, a sighting of a single individual south of Cape Town, in South African waters, was reported, although this should be considered extralimital (de Bruyns et al. 2006).
The distribution map shows where the species has been observed, including both subspecies. States for which confirmed records of the species exist are included in the list of native range states.
Native:Argentina; Chile; Falkland Islands (Malvinas); French Southern Territories (Kerguelen)
Vagrant:Brazil; South Africa
|FAO Marine Fishing Areas:|
Atlantic – southwest; Indian Ocean – Antarctic; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
Commerson's Dolphin seems to be the most abundant species of the genus Cephalorhynchus (Dawson 2009) although much of its range has not been surveyed and there are only a few estimates of abundance. Leatherwood et al. (1988) conducted aerial surveys in the northeastern Strait of Magellan, Chile, in January-February 1984 and estimated 3,211 (standard error (SE) = 1,168) dolphins for that area at that time. Venegas and Atalah (1987) estimated abundance in the same area between 12-14 May 1987 as 313 (SE = 99). Later, Venegas (1996) estimated abundance there in late December 1989 as 718 ± 196 individuals. Another survey conducted in June 1996, in the same area, produced an estimate of 1,206 (95% confidence interval (CI) 711-2,049) individuals (Lescrauwaet et al. 2000). Apparently, none of those estimates was corrected for availability or perception bias. Unfortunately, it is difficult to reach any conclusion about population trend due to the differences in methods and analytical approaches used in the various studies
In Argentine waters, a series of aerial surveys carried out from the mid 1990s to mid 2000s resulted in an estimate of 40,000 individuals between the coastline and the 100 m isobath between 43°S and 55°S (Pedraza 2008). This estimate was derived from three sets of summer surveys different strata as follows: northern Chubut (seven flights between 1994 and 2000), northern Santa Cruz (four flights between 1994 and 1997) and southern Patagonia (i.e. southern Santa Cruz and Tierra del Fuego) (two flights in 2001). The resulting density estimates were 0.052 dolphins/km² (coefficient of variation (CV) = 43.3%), 0.716/km² (CV = 56.05%) and 2.071/km² (CV 27.35%), respectively (Pedraza 2008). There was a latitudinal gradient in density with hundreds of individuals near the northern border of the range and at least 15,000 in Tierra del Fuego (Pedraza 2008). More recently, eight scientific cruises along the Patagonian shelf during austral summer and fall (November-April), 2009-2015, recorded sightings of 88 schools (212 individuals) of Commerson’s Dolphins in 8,535 km surveyed. The Commerson’s Dolphin sightings were all less than 60 km from shore. Fitted models indicated overall abundance of 21,933 individuals CV = 74%, 95% CI = 6,013–80,012) (Dellabianca et al. 2016). The abundance estimates by Pedraza (2008) and Dellabianca et al. (2016) are in the same order of magnitude. However, given the differences in methods, areas surveyed, and level of precision reported by Dellabianca et al. (2016), no conclusion concerning trend in abundance is possible.
Marine mammal and seabirds surveys around the Falkland (Malvinas) Islands found Commerson’s Dolphins to be one of the most frequently observed cetaceans, particularly in inshore waters, with 336 Commerson’s Dolphins recorded, on 100 occasions, during at-sea surveys carried out monthly between February 1998 and January 2001 (White et al. 2002).The status of the Kerguelen Islands subspecies is less clear than that of the South American subspecies. As of 1985, there had been more than 100 reported sightings, the largest group of about 100 dolphins having been seen near the edge of the shelf (Goodall 1994, Robineau 1989). A seasonal pattern has been documented in the occurrence of Commerson’s Dolphins in the Golfe du Morbihan area, suggesting movements to and from this shallow, semi-enclosed bay. Since 1985, many more observations have been reported in the Golfe du Morbihan, as Commerson’s Dolphins are commonly encountered from boats from the permanent research station that operate within the bay, and a few observations have been reported from other coastal and shelf areas around Kerguelen (V. Ridoux, unpubl. data). Recent capture-mark-recapture analyses based on photo identification studies of dolphins in the Golfe du Morbihan estimated this local population at 69 ± 13 individuals in 2013 (Paul Tixier, pers. comm). No similar figure exists for the rest of the C. c. kerguelensis distribution. The Kerguelen subspecies is restricted in range and is therefore probably very small in number and relatively vulnerable to any anthropogenic threats.
|Current Population Trend:||Unknown|
|Habitat and Ecology:|
Commerson's Dolphins are found in cold inshore waters along open coasts, in sheltered fjords, bays, harbours and river mouths, and occasionally in the lower reaches of rivers. Within the Strait of Magellan, they prefer the areas with strong currents, such as the Primera and Segunda Angostura (First and Second Narrows), where the current can reach or exceed 15 km/hr (Goodall 1994). At the Falklands (Malvinas) Islands this species was found to have a highly coastal distribution, with the majority of records from partially enclosed waters and within 10 km of the coast, with no records further than 25 km offshore (White et al. 2002). Off mainland South America, Commerson’s Dolphins were observed entirely in shelf waters < 200 m deep and most frequently close to shore (less than 60 km) (Dellabianca et al. 2016). Commerson’s Dolphins were recorded 24 km upriver in Deseado (Iñíguez and Tossenberger 2007).Off the South American mainland, Commerson's Dolphins appear to prefer areas where the continental shelf is wide and flat, the tidal range is great, and temperatures are influenced by the cool Malvinas Current. In coastal Patagonia, they are found principally in areas with continental runoff such as at the mouths of rivers in Chubut and Santa Cruz, including the Deseado, Santa Cruz, Coyle, and Gallegos. Pedraza (2008) concluded that coastal fronts affect the density and abundance of their food resources and determine the distribution pattern of the species. Highest densities in her study were observed in northern Santa Cruz province and Tierra del Fuego. Around the Falklands (Malvinas) and Kerguelen Islands, as well as off mainland Argentina, Commerson’s Dolphins are often seen swimming in or at the edges of kelp beds. They sometimes move very close to shore, even inside the breakers. However, they are also observed occasionally offshore in waters deeper than 50 m.
South American Commerson's Dolphins appear to be opportunistic, feeding on various pelagic and bentho-pelagic species of fish, cephalopods, crustaceans, and benthic invertebrates in coastal waters but also on pelagic schooling fish in more open areas (Riccialdelli et al. 2013). In the Kerguelen Islands, they seem to have a more restricted diet, consisting mostly of semi-pelagic fishes (e.g. Champsocephalus gunnari) and to some extent benthic fishes (Robineau and Duhamel 1984). Feeding behaviour and group size depend on the habitat type. Group size may reach one hundred individuals when the dolphins are feeding on schooling pelagic fish. When they are feeding in tidal areas in front of small rivers, in kelp forests and in waters influenced by river discharge, they are more typically alone or in small groups (Iñíguez and Tossenberger 2007, Coscarella et al. 2010, Loizaga de Castro et al. 2013).
|Continuing decline in area, extent and/or quality of habitat:||No|
|Use and Trade:||
The dolphins (Commerson’s and others) in Beagle Channel, the Magallanes region, and southern Tierra del Fuego were harpooned for crab bait from the 1970s until at least the early 1990s. The scale of this killing was great enough to cause reduced abundance of dolphins by the late 1980s although according to Lescrauwaet and Gibbons (1994) and Goodall et al. (1997), there was some evidence suggesting that the scale of this exploitation had declined, due in part to the fact that legal bait was more readily available and in part to measures taken by Chilean government agencies (Lescrauwaet and Gibbons 1994, Reeves et al. 2003).Small numbers of Commerson’s Dolphins were live-captured in Argentina and Chile and exported to Japan, Germany and the United States during the late 1970s and 1980s (Goodall 1994).
Until the late 1990s, various species of small cetaceans, mainly Commerson's Dolphins and Peale's Dolphins (Lagenorhynchus australis), were harpooned and used as bait in the fisheries for Southern King Crab (Centolla; Lithodes santolla) and False King Crab (Centollón; Paralomis granulosa) in both Argentina and Chile (Lescrauwaet and Gibbons 1994). Because the Centolla was overfished in the Magellan region, fishing effort shifted to the Centollón, which was exploited principally farther west in the channels. Commerson's Dolphins were generally not found there but were relatively abundant in the eastern part of the Strait. In Argentina, the crab fishery operates in the Beagle Channel, where there are relatively few Commerson's Dolphins.
Commerson’s Dolphin is the cetacean most frequently taken in fishing nets off southern South America, perhaps due to its coastal distribution which overlaps with trammel and artisanal gillnet fisheries (e.g., Iñíguez et al. 2003). It is taken most often in fairly large-mesh nets. Although the scale of the bycatch is unknown, at least 5-30 died each year in nets set perpendicular to the shore in eastern Tierra del Fuego alone during the 1980s and early 1990s (Goodall 1994) and this remains the case (according to Dellabianca’s examination of the R. Natalie P. Goodall database in Ushuiaia, July 2017). They are also taken in this type of fishing in the Argentine provinces north of Tierra del Fuego and in the eastern Strait of Magellan and Bahia Inútil in Chile. Commerson’s Dolphins are also killed at least occasionally in midwater trawl nets on the Argentine shelf (Crespo et al. 1997, 2000). The bycatch in Chubut Province in Hake and shrimp fisheries was estimated as 25 to 170 individuals per year, mostly females, in the 1990s and early 2000s (Dans et al. 2003). With banning of nighttime pelagic trawling and the replacement of pelagic trawlers with twin-beam trawlers, the level of bycatch of Commerson’s Dolphins may now be nearer the low end of that range (Crespo et al. 2007).
Incidental mortality in gillnets was calculated as almost 180 animals for the fishing season 1999-2000 in a small area of Santa Cruz Province, southern Argentina (Iñíguez et al. 2003). Although this figure should be interpreted with a certain degree of caution, given that it is based on extrapolation from a small area, continued gillnet bycatch of Commerson’s Dolphins in this area (M. Iñíguez, unpubl. data) remains a concern.
The species is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES) and also the Convention on Migratory Species (CMS).
Although Commerson’s Dolphins may have been seriously affected by the illegal deliberate take for bait in the Chilean crab fishery, the pressure on them in the southern part of their range apparently was reduced beginning in the late 1980s. However, in various parts of their range, incidental mortality in gillnets and other fishing gear continues and represents an ongoing threat (Dans et al. 2003, Iñíguez et al. 2003). Although the magnitude of this threat is undocumented, the similarity between Commerson’s Dolphins and Hector’s Dolphins (Cephalorhynchus hectori; currently listed as Endangered on the Red List) in their habitat preference and vulnerability to gillnets raises concern about the potential for depletion wherever gillnet fisheries and Commerson’s Dolphins overlap. Gillnet mortality, in particular, should be monitored and investigated in more detail but even better documentation of the extent of spatial and temporal overlap between fisheries and dolphins would be useful for assessing the degree of threat to the species as a whole, and to demographically independent subpopulations. In 2016, the government of Argentina adopted a National Action Plan to mitigate mortality of marine mammals in fisheries.
Further research is needed to provide current abundance estimates for a larger proportion of the species’ total range, and more up-to-date, quantitative information on human-caused mortality. This latter should include an update on the illegal killing of Commerson’s Dolphins for use in King Crab fisheries in southern Chile. Better information is also urgently needed on the status of the Kerguelen subspecies population of Commerson’s Dolphins at the scale of the whole Kerguelen Plateau.
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|Citation:||Crespo, E., Olavarria, C., Dellabianca, N., Iñíguez, M., Ridoux, V. & Reeves, R. 2017. Cephalorhynchus commersonii. The IUCN Red List of Threatened Species 2017: e.T4159A50351788.Downloaded on 23 June 2018.|
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