Especies

© Ilustration by Uku Gorter in Encyclopedia of Marine Mammals 3ra Edition

Dusky dolphin

Scientific name: Lagenorhynchus obscurus

      Dusky dolphin has a wide distribution in the Argentinean sea and it is considered a frequent species. It inhabits cold-temperate waters, in coastal and platform habitats. In the Southwestern South Atlantic it can be found from La Lucila del Mar, Buenos Aires (36°19’S) south to Tierra del Fuego. There are also most recent records of the species around Falkland (Malvinas) Islands.

      Dusky dolphin feeds mainly on anchovy, squid, hake and other pelagic fish. It main predator is the Orca (Orcinus orca) although there have been reports of predation by sharks.

     Maximum age, recorded from growth bands in teeth, is 36 years old. Females are sexually mature at 6 to 7 years old, and have their first calf at 7 or 8 years old. They give birth to a calf every two or three years, during spring and summer. Calves at birth are about 80 cm (2.6 ft) and 9 kg (20 lb).   

       Population size was estimated in 1995 for the coastal Patagonian area comprised between Punta Ninfas (-42°58', -64°19') and Cabo Blanco (-47°12’, -65°44'), and resulted in 6,628 individuals (range 4,039 – 10,877; 0.508 ind/km2. Another estimation made during 2004-2095 between Isla Escondida (-43º 50’, -65º 20’) and Punta Bermeja (-41º 10’, -63º 00’) resulted in about 13,500 individuals. Recently, small scale estimation methods have been employed resulting in 0.7 ind/km2 in an area of 1,550 km2 within Golfo San Matías; and around 450 in the Península Valdés gulfs.

      Mortality in dusky dolphins could have been critic during the 80’s when the number of captured dolphins could have surpassed maximum sustainable numbers. Currently, there are reports of dolphin bycatch, especially in pelagic nets for anchovy fishery.

distribucion oscuro2.jpg

Map showing the worldwide distribution of dusky dolphin.

       

     In the Golfo Nuevo, dusky dolphins suffer from the effects of whale and dolphin watching activities. There are evidences of short-term impact, measured as changes in behavior of the groups. These changes, mainly on feeding behavior might implicate in energetic costs for dolphins. Thus, reducing individual survival rate and reproductive capacity or may be associated with changes in distribution.
     Nowadays, this species does not fall into any of the criteria defining the threatened category in the IUCN (International Union for Conservation of Nature) Red List for Endangered species. Thus, the species is classified as Least Concern both at national and international level. 

Foto: Alejandro Carribero
Foto: LAMAMA
Foto: LAMAMA
Foto: LAMAMA
Foto: LAMAMA
Foto: LAMAMA

 

 

References

 

- ALAFARO-SHIGUIETO, J., CRESPO, E., ELWEN, S., LUNDQUIST, D. & MANGEL, J. 2019. Lagenorhynchus obscurus (amended version of 2019 assessment). The IUCN Red List of Threatened Species 2019: e.T11146A160698904. https://dx.doi.org/10.2305/IUCN.UK.2019-1. RLTS.T11146A160698904.en

- CIPRIANO, F. W. 1992. Behaviour and occurrence patterns, feeding ecology, and life history of dusky dolphins (Lagenorhynchus obscurus) off Kaikoura, New Zealand. Doc. Thesis, University of Arizona, Tucson, AZ. 216pp.

- COSCARELLA, M. A, G. BELLAZZI, M. L. GAFFET, M. BERZANO, & M. DEGRATI. 2015. Technique used by killer whales (Orcinus orca) when hunting for dolphins in Patagonia, Argentina. Aquatic Mammals 41:192–197.

- CRESPI-ABRIL, A. C., N. A. GARCÍA, E. A. CRESPO, & M. A. COSCARELLA. 2003. Consumption of marine mammals by broadnose sevengill shark Notorynchus cepedianus in the northern and central Patagonian Shelf. Latin American Journal of Aquatic Mammals 2:101–107.

- CRESPO, E. A. ET AL. 1997. Distribution and school size of dusk dolphins Lagenorhynchus obscurus (Gray, 1828) in the Southwestern South Atlantic ocean. International Whaling Commission 47:693–698.

- CURCIO, N. (2019). Distribución y uso del hábitat de dos especies de delfines simpátricos en Golfo San Matías: relaciones con los factores abióticos y la disponibilidad de presas. PhD Thesis. Universidad Nacional de Buenos Aires, Argentina.

- DANS, S. L. 1999. Ecología poblacional del delfín oscuro Lagenorhynchus obscurus (Gray, 1828) en el litoral patagónico, Atlántico Sudoccidental. Tesis de Doctorado. Universidad de Buenos Aires, Buenos Aires, Argentina.

- DANS, S. L., M. KOEN ALONSO, S. N. PEDRAZA, & E. A. CRESPO. 2003. Incidental catch of dolphins in trawling fisheries off Patagonia, Argentina: can populations persist? Ecological Applications 13:754–762.

- DANS, S. L., E. A. CRESPO, S. N. PEDRAZA, & M. KOEN ALONSO. 1997. Notes on the reproductive biology of female dusky dolphins (Lagenorhynchus obscurus) off the patagonian coast. Marine Mammal Science 13:303–307.

- DANS, S. L., M. DEGRATI, S. N. PEDRAZA, & E. A. CRESPO. 2012. Tour boats effects on dolphins behavior: a sensitivity analysis applied to Markov chains. Conservation Biology 26:708–716.

- DEGRATI, M., DELLABIANCA, N.A., GARCÍA, N.A., LOIZAGA DE CASTRO, R., MANDIOLA, A. & ROMERO, M.A. (2019). Lagenorhynchus obscurus. En: SAyDS–SAREM (eds.) Categorización 2019 de los mamíferos de Argentina según su riesgo de extinción. Lista Roja de los mamíferos de Argentina. Versión digital: http://cma.sarem.org.ar.

- DEGRATI, M., LOIZAGA, L., COSCARELLA, M.A., SUEYRO, N., CRESPO, E.A. & DANS, S.L. 2020. Integrating multiple techniques to estimate population size of an impacted dusky dolphin’s population in Patagonia, Argentina. Frontiers in Marine Science (en prensa).

- KOEN ALONSO, M., E.A. CRESPO, N.A. GARCÍA, S.N. PEDRAZA Y M.A. COSCARELLA. 1998. Diet of dusky dolphins, Lagenorhynchus obscurus, in waters off Patagonia, Argentina. Fishery Bulletin, 96:336-374.

- LOIZAGA DE CASTRO, R., F. SAPORITI, D. G. VALES, N. A. CARDONA, & E. A. CRESPO 2017. Using stable isotopes to assess whether two sympatric dolphin species share trophic resources. Marine Mammal Science 33:1235–1244.

- LOIZAGA DE CASTRO, R., F. SAPORITI, D. G. VALES, N. A. GARCÍA, L. CARDONA, & E. A. CRESPO. 2015. Feeding ecology of dusky dolphins Lagenorhynchus obscurus: evidence from stable isotopes. Journal of Mammalogy 97:310–320.

- ROMERO, M. A., S. L. DANS, G. SVENDSEN, R. GONZÁLEZ, & E. A. CRESPO. 2012. Feeding habits of two sympatric dolphin species off North Patagonia, Argentina. Marine Mammal Science 28:364–377.

- SCHIAVINI, A., S. N. PEDRAZA, E. A. CRESPO, R. GONZÁLEZ, & S. L. DANS. 1999. Abundance of dusky dolphins (Lagenorhynchus obscurus) off north and central Patagonia, Argentina, in spring and a comparison with incidental catch in fisheries. Marine Mammal Science 15:828–840.

- WEIR, C. R., & A. BLACK. 2018. Records of the dusky dolphin (Lagenorhynchus obscurus) in the Falkland Islands, including associations with Peale’s dolphin (L. australis). Marine Biodiversity Records 11:1–18.