Osa Peninsula IMMA

Size in Square Kilometres

5 001 km2

Qualifying Species and Criteria

Humpback whale – Megaptera novaeangliae

[North Pacific – M. n. kuzira]

Criterion A; C (1)

[Southern Pacific – M. n. australis]

Criterion C (1)

Pantropical spotted dolphin – Stenella attenuata

[Coastal – S. a. graffmani]

Criterion C (2)

Common bottlenose dolphin – Tursiops truncatus 

Criterion C (2)

Spinner dolphin – Stenella longirostris

[Central America – S. l. centroamericana]

Criterion C (2)

Common dolphin – Delphinus delphis

Criterion C (2)

Marine Mammal Diversity 

Criterion D (2)

Orcinus orca, Steno bredanensis, Grampus griseus, Globicephala macrorhynchus, Lagenodelphis hosei, Physeter macrocephalus, Kogia sima, Ziphius cavirostris, Balaenoptera edeni, Balaenoptera acutorostrata

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The Osa Peninsula is a hot spot for cetacean diversity, providing habitat for over 17 cetacean species. The inshore waters of the IMMA serve as a critical reproductive and calving habitat for both southern and northern hemisphere populations of humpback whales (Megaptera novaeangliae). Semi-resident populations of false killer whales (Pseudorca crassidens) and killer whales (Orcinus orca) have been documented in the area. Photographic recaptures of these species in other parts of Costa Rica, as well as Panamá and Nicaragua, demonstrating connectivity, social stability and site-fidelity for over 10 years. Likewise, a semi-resident population of rough-toothed dolphins (Steno bredanensis) has been assessed through mark-recapture methods, showing individual dolphins with a high level of site-fidelity along foraging habitats within nearby shelf waters. The IMMA includes important cetacean habitat of three main categories: 1) continental shelf habitat for humpback whales, coastal pantropical spotted dolphins (Stenella attenuata graffmani), false killer whales, killer whales, common bottlenose dolphins (Tursiops truncatus), and rough-toothed dolphins; 2) oceanic depths for sperm whales (Physeter macrocephalus), pilot whales (Globicephala macrorhynchus), and other deep divers; and transitional habitat at the edge of the shelf-break, which is particularly important for offshore pantropical spotted dolphins (Stenella attenuata attenuata).

Description of Qualifying Criteria

Criterion A – Species or Population Vulnerability

North Pacific Humpback whales (Megaptera novaeangliae kuzira) that use the IMMA are part of the Central America distinct population segment (DPS), which is classified as ‘Endangered’ by the United States Endangered Species Act (81 FR 62260, September 8, 2016). The Central America DPS is one of 14 humpback whale DPS classifications around the world, and one of only four DPS listed as ‘Endangered’ (Bettridge et al., 2015). A DPS is made up of whales that share the same latitude breeding area but migrate seasonally to specific mid-to-high latitude feeding grounds that may differ among individuals (Bettridge, 2019). The Central America DPS is composed of whales that breed along the Pacific coast of Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama (Bettridge et al., 2015; Curtis et al., 2022). This DPS wintering area is understood to extend into southern Mexico (Wade, 2016; Curtis et al., 2022). The population estimate for the Central America DPS varies between 500-700 individuals depending on the mark-recapture method used (Calambokidis et al., 2008; Barlow et al., 2011; Wade, 2016). In comparison, the abundance of humpback whales off the United States West Coast, which includes some of the Central America DPS whales, is estimated to be approximately 5,000 individuals (Calambokidis & Barlow, 2020). Humpback whales from this DPS use this IMMA as a breeding ground during the Northern Hemisphere winter months, while Southern Hemisphere humpback whales (Megaptera novaeangliae australis) breed in the IMMA during the austral winter months (Felix et al., 2021; Palacios-Alfaro et al., 2012; Chereskin et al., 2019; Rasmussen et al., 2011; Pelayo-González et al., 2022).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

Humpback whales from both the southeast Pacific (Felix et al., 2021; Palacios-Alfaro et al., 2012; Chereskin et al., 2019) and northeast Pacific (Rasmussen et al., 2011; Pelayo-González et al., 2022) use this IMMA as a calving and reproductive habitat. The continental shelf areas of this IMMA provide habitat that is typical of humpback whale breeding habitat, with depths of less than 100 m and a slope less than 10% (Oviedo & Solis, 2008). Within this preferred habitat, behaviour associated with humpback whale breeding, such as singing (Chereskin et al., 2019) and competition involving groups of males are regularly documented. A significant proportion of documented humpback whale encounters in the Osa Peninsula during the austral breeding season between 2001 and 2006 were of mother-calf pairs (149 /208 total encounters) (CEIC, unpublished data). Mother-calf pairs also comprised over 50% of encounters with endangered northeast Pacific humpback whales (N=115) during the boreal breeding seasons between 2001 and 2006 (CEIC, unpublished data; Rasmussen et al., 2011).

Sub-criterion C2: Feeding Areas

The waters of the Osa Peninsula IMMA host critical foraging habitats for coastal pantropical spotted dolphins (Stenella attenuata graffmani), Central American spinner dolphins (Stenella longirostris centroamericana), common dolphins (Delphinus delphis), and deep diving teuthophagous odontocetes (CEIC, unpublished data). Coastal pantropical spotted dolphins were most commonly observed in neritic waters, without any significant variations due to seasonality. The most common behaviours observed were foraging and traveling (Dry Season 2001-2006: foraging=34%, traveling=42%, out of 653 encounters; Rainy Season 2001-2006: foraging=43%, traveling=41%, out of 515 encounters). Central American spinner dolphins were the third most abundant species off Osa Peninsula waters during surveys in 2001-2006. This subspecies is one of the two endemic forms occurring in the Eastern Tropical Pacific, S. l. centroamericana and S. l. orientalis (Perrin 1990, 2008b), with the former being more coastal and the latter highly pelagic (Perrin, 2008a). Habitat suitability modelling shows that coastal habits of S. l. centroamericana are concentrated in depths close to the 200 m. Central American spinner dolphins favour the upper limit of the neritic habitat in oligotrophic waters, where mesopelagic prey (lanternfish belonging to the family Myctophidae) would be encountered in considerable density. Common dolphins (Delphinus delphis) in the IMMA correspond with the central Eastern Tropical Pacific Stock, specifically to the “C” subpopulation. According to Fernandez & Oviedo (2009) and Daniel & Chivers (2006), this is the subpopulation that occurs closer to shore, in contrast to units “A” and “B” that occur in offshore waters of the central Eastern Tropical Pacific. Common dolphins in the IMMA are believed to focus on mesopelagic prey (lanternfish belonging to the family Myctophidae) off the continental shelf, where small-scale micro-upwelling linked to the shelf edge topography, would promote a stronger vertical migration of the Deep Scattering Layer to shallower waters. The coastal waters over the continental platform are also important feeding areas for false killer whales (Pseudorca crassidens), which have been documented to spend more than 37% of their time during observations in the IMMA engaged in feeding behaviour (n=1952 sightings), consuming over 11 species of pelagic and demersal bony fishes (Palacios-Alfaro et al., 2022).

Criterion D: Special Attributes

Sub-criterion D2: Diversity

The diversity of cetacean species in this area includes more than 17 types, including coastal pantropical spotted dolphins, common bottlenose dolphins (Tursiops truncatus), Central American spinner dolphins, common dolphins, rough-toothed dolphins, false killer whales, killer whales (Orcinus orca), Risso’s dolphins (Grampus griseus), short-finned pilot whales (Globicephala macrorhynchus), Fraser’s dolphins (Lagenodelphis hosei), sperm whales (Physeter macrocephalus), dwarf sperm whales (Kogia sima), Cuvier’s beaked whales (Ziphius cavirostris) and unidentified beaked whales (Mesoplodon spp.). In addition to the toothed whales mentioned above, the IMMA hosts balaenopterids such as migratory humpback whales from both the Southern and Northern Hemispheres, and rorqual whales like Bryde’s- (Balaenoptera edeni) and minke (Balaenoptera acutorostrata) whales (Palacios-Alfaro, unpublish data). False killer whales are considered transient in the IMMA. However, a high proportion of photographic recaptures within the IMMA over a period of 10 years shows the intensive use of this area as critical habitat. Their population size is small N=91.95; 95% CI: 89.22-94.76 with an estimated survival of 0.99 (Sánchez-Robledo et al., 2020). Re-sighting of highly distinctive individuals on different capture occasions are concentrated in the Osa Peninsula and Golfo Dulce. The lack of recaptures between false killer whales identified in Nicaragua vs Costa Rica (Pouplard et al., 2019), or southwestern Costa Rica vs Isla del Coco (Douglas et al., 2011), suggests that there may be discrete population units along a wider range extending the whole eastern tropical Pacific, among these, a population unit ranging over the Nicoya and Panama (CEIC, unpublished data).

Pacheco-Polanco et al. (2011) documented the occurrence of the inshore and offshore ecotypes of T. truncatus in Osa Peninsula and Golfo Dulce respectively. Oviedo et al. (2015) described the distribution of each ecotype. The distribution of offshore bottlenose dolphins in Osa Peninsula is primarily associated with depth; during the dry season bottlenose dolphin distribution is better predicted by depths close to the 200m bathymetric contour. During the rainy season this shifts to depths of less than 200m. Distance to the 200m isobaths is the second-best predictor of the ecological niche of T. truncatus in the IMMA (Oviedo et al. 2019). A semi-resident population of rough-toothed dolphins in the IMMA has been assessed through mark-recapture methods, showing individual dolphins with a high level of site fidelity along foraging habitat centered within shelf waters (CEIC, unpublished data). Short-finned pilot whales, Risso’s dolphins, Cuvier’s beaked whales, sperm whales and dwarf sperm whales constitute a community of teuthophagous odontocetes in the IMMA. Sperm whales have also recently been documented through both acoustic and observational evidence along the shelf edge off Osa Peninsula. Beaked whales, including Cuvier’s beaked whales un-identified members Mesoplodon family are also associated with depths beyond 1500 m in the IMMA (May Collado et al., 2005).

Finally, behavioural observations of pilot- and dwarf sperm whales in the IMMA include resting episodes after foraging dives, while most of the encounters of Cuvier’s beaked whales involve travelling from one foraging spot to another. The latter observations support the incidence of important foraging ground along the shelf edge off the Osa Peninsula, which would explain the habitat use of these deep diver species beyond neritic waters (CEIC, unpublished data).

Supporting Information

Castro-Azofeifa, C. 2020. Sightings of Orcinus orca (Linnaeus, 1758) (Cetartiodactyla: Odontoceti: Delphinidae) in the Costa Rican Pacific (1990-2020). Revista de Ciencias Marinas y Costeras REVMAR, 13(2), pp. 29 – 47.

Chereskin, E., Beck, L., Gamboa-Poveda, M., Palacios-Alfaro, J.D., Monge-Arias, R., Chase, A.R., Coven, B.M., Guzman, A.G. McManus, N.W., Neuhaus, A.P., O’Halloran, R., Rosen, S.G. and L. J. May-Collado. 2019. Song structure and singing activity of two separate humpback whales populations wintering off the coast of Caño Island in Costa Rica. Journal Acoustical Society of America, 146, pp. 509 – 515

Danil, K. and Chivers S J. 2006. Habitat-based spatial and temporal variability in life history characteristics of female common dolphins Delphinus delphis in the eastern tropical Pacific. Marine Ecology Progress Series, 318, pp. 277-286.

Douglas AB, Garita-Alpizar F, Acevedo-Gutierrez A, Baird RW, and Calambokidis J. 2011. False killer whales show fidelity to Costa Rican waters. In: Abstracts of the 19th Biennial Conference on the Biology of Marine Mammals, Tampa, FL, USA. 27 November- 2 December; 2011. 82pp. (Society for Marine Mammalogy: Anacortes, WA, USA.)

Felix, F., Acevedo, J., Aguayo-Lobo, A. and I. C., Avila. 2021. Humpback whale breeding stock g: updated population estimate based on photo-id matches between breeding and feeding areas. International Whaling Commission, Report No SC/68C/ASI/02

Fernández, M. and Oviedo L. 2009. Distribution and abundance of Delphinus delphis off the southern Pacific Coast of Costa Rica. International Whaling Commission, Report No. IWC/61/SC/SM9.

Herra-Miranda, D. 2016. Uso de hábitat del delfín dientes rugosos en el Pacífico Sur de Costa Rica (Habitat use of rough-tooth dolphins in the Southern Pacific of Costa Rica). Oral Presentation to the III Scientific Congress on Marine Science –Universidad Marítima Internacional de Panamá (UMIP).

Lizano, O. 2008. Dinámica de aguas alrededor de la Isla del Coco, Costa Rica. Revista de Biología Tropical, 56, pp. 31-48

May-Collado L., Gerrodette T., Calambokidis J., Rasmussen K., and Sereg I. 2005. Patterns of cetacean distribution in the Pacific Exclusive Economic Zone of Costa Rica based on data collected from 1979-2001. Revista de Biología Tropical, 53(1-2), pp. 249 – 263.

Morales-Ramirez, A., Acuña-Gonzales, J., Lizano, O., Alfaro, E. and Gómez, E. 2015. Rasgos oceanográficos en el Golfo Dulce, Pacífico de Costa Rica: una revisión para la toma de decisiones en conservación marina. Revista de Biología Tropical, 63(1), pp. 131-160.

Oviedo, L., and Solís, M. 2008. Underwater topography determines critical breeding habitat for humpback whales near Osa Peninsula, Costa Rica: Implications for Marine Protected Areas. Revista de Biología Tropical, 56, pp. 591 – 602. Available at: doi: 10.15517/rbt.v56i2.5610.

Oviedo, L., Herra-Miranda, D. and J.D. Pacheco-Polanco. 2014. The identification of the Central-American spinner dolphin’s critical habitat off Osa Peninsula‚ Costa Rica. In: Abstracts of XVI Reunión de Trabajo de Especialistas en Mamíferos Acuáticos de América del Sur y X Congreso SOLAMAC. Cartagena Colombia 01 al 05 de diciembre 2014. pp. 858 pp.

Oviedo, L., Pacheco Polanco J.D., and D. Herra-Miranda. 2015. Monitoreo de Cetáceos en las Áreas de Uso Múltiple Golfo de Nicoya y Pacífico Sur 2014-2015. Reporte Final de Consultoría Proyecto Golfos SINAC-BID-Marviva, pp. 154.

Oviedo, L., Herra-Miranda, D., Pacheco-Polanco, J.D., Figgener, C., Marquez-Artavia, A., Quirós Pereira, W. and Iñiguez., M. 2015. Diversidad de cetáceos en el paisaje marino-costeros de Golfo Dulce, Península de Osa, Costa Rica. Revista de Biología Tropical, 63(2), pp. 395 – 406. [In Spanish].

Oviedo, L., Fernández, M., Pacheco-Polanco, J.D. and D. Herra-Miranda. 2019. Spatial analysis on the occurrence of inshore and offshore bottlenose dolphins (Tursiops truncatus) in Osa Peninsula waters and Golfo Dulce. Journal of Cetacean Research Management, 20, pp. 1-11

Palacios-Alfaro, J. D., Martinez-Fernandez, D., Sanchez-Godinez, C., and Venegas, R. 2012. “Distribution and behavior of humpback whale (Megaptera novaeangliae Borowski, 1781) (Breeding BSG), in southern Pacific of Costa Rica,” International Whaling Commission, Report No. SC/64/SEP16.

Palacios-Alfaro, J. D., M. Gamboa, D. Martínez-Fernández, A. L. Rodriguez-Tinoco and C. Sanchez-Godinez, 2022. Orca Orcinus orca (Linneaus, 1758) and False killer whale Pseudorca crassidens (Owen, 1846) in Osa, Puntarenas, Costa Rica: behavior, temporal and spatial distribution. Poster Presented at the 24th Biennial Conference on the Biology of Marine Mammals, Palm Beach, USA. August 1-5, 2022

Pelayo-González L, Herra-Miranda D, Pacheco-Polanco JD, Guzmán HM, Goodman, S. and Oviedo, L. 2022. Decreases in encounter rate of endangered northeast Pacific humpback whales in Southern Costa Rica: Possible changes in migration pattern due to warming events. Front. Mar. Sci. 9:927276. doi: 10.3389/fmars.2022.927276

Perrin W. F. 1990. Subspecies of Stenella longirostris (Mammalia: Cetacea: Delphinidae). Proc. Biol Soc. Wash, 103(2), pp. 453-463.

Perrin W. F. 2008. Spinner dolphin Stenella longirostris. In Perrin W.F., Wursig B. and Thewissen J.G.M, eds. Encyclopaedia of Marine Mammals, 2nd edn. pp. 1100-1103. San Diego: Academic Press.

Pouplard, E., Oviedo, L. Herra-Miranda, D., Sanchez-Robledo, E. and J. De Weerdt 2019. Occurrence and distribution of False killer whales (Pseudorca crassidens) in Central America. In: Abstracts of the World Marine Mammals Conference, Barcelona, Spain. 09-12 December; 2019.

Rasmussen, K., Calambokidis, J., and Steiger, G.H. 2011. Distribution and migratory destinations of humpback whales off the Pacific coast of Central America during the boreal winters of 1996-2003. Marine Mammals Science, 28(3), pp. 267 – 279. Available at: doi: 10.1111/j.1748-7692.2011.00529.x

Rodríguez-Fonseca, J. 2001. Diversidad y distribución de los cetáceos de Costa Rica (Cetacea: Delphinidae Physeteridae, Ziphiidae y Balaenopteridae). Revista de Biología Tropical, 49, pp. 135-143.

Sánchez-Robledo, E., Oviedo, L., Herra-Miranda, D., Pacheco-Polanco J.D., Goodman, S., and H. Guzmán. 2020. The Abundance of False Killer Whales, Pseudorca crassidens (Artiodactyla: Delphinidae) in costal waters of Golfo Dulce and Osa Peninsula, Costa Rica. Revista de Biología Ambiental, 68(2), pp. 1-10.


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