Southwest Atlantic Subtropical Continental Slope and Canyons System IMMA

Size in Square Kilometres

297 319 km2

Qualifying Species and Criteria

Sperm whale – Physeter macrocephalus

Criterion A; B (2); C (1, 2)

Long-finned pilot whale – Globicephala melas edwardii

Criterion C (1, 2)

Common bottlenose dolphin – Tursiops truncatus

C (1,2)

Atlantic Spotted dolphin – Stenella frontalis

Criterion C (1,2)

Common dolphin – Delphinus delphis

Criterion C (1,2)

Risso’s dolphins – Grampus griseus

Criterion C (1,2)

Killer whale – Orcinus orca

Criterion C (2)

Sei whale – Balaenoptera borealis

Criterion A

South American  fur seal – Arctocephalus australis

Criterion C (2)

Marine Mammal Diversity 

Criterion D (2)

Physeter macrocephalus, Globicephala melas edwardii, Tursiops truncatus, Stenella frontalis, Delphinus delphis, Grampus griseus, Orcinus orca, Orcinus orca, Balaenoptera borealis, Arctocephalus australis

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This IMMA ranges from the 200m to 3000m isobaths and from Santa Catarina State (ca. 27°S), southern Brazil, to Buenos Aires Province (ca. 38°S), northern Argentina. It is under the influence of the Brazil current, and subantarctic waters transported by the Falkland (Malvinas) currents as well as continental waters from the La Plata River and Patos Lagoon plumes, which form the subtropical shelf front.  Surface and subsurface upwelling events influence the productivity of the area that sustains a diverse array of cetacean species and is an important aggregation area for sperm whales (Physeter macrocephalus). At least eight cetacean and one pinniped species use the area regularly either throughout the year or seasonally for feeding and/or breeding purposes.

Description of Qualifying Criteria

Criterion A – Species or Population Vulnerability

Sperm whales (Physeter macrocephalus) and sei whales (Balaenoptera borealis) whales both occur throughout this IMMA and are, classified respectively as Vulnerable, under criterion A1d (Taylor et al., 2019), and Endangered, under criterion A1abd (Cooke, 2018) on the IUCN Red List. Sperm whales were intensively hunted in the area (e.g. Smith et al., 2012). Despite an IWC agreement to suspend hunting of sperm whales in international waters, commercial catches of sperm whales continued in northeastern Brazil between 1960 and 1967 (Ramos et al., 2001). Sei whale populations were also targeted by commercial whaling in their western South Atlantic breeding grounds as well as in their Southern Ocean feeding grounds. In Brazil, the sei whale was one of the main target species for coastal whaling operations (Williamson, 1975). It is estimated that about 4,700 sei whales were captured off the Brazilian coast between 1947 and 1974 (Zerbini et al., 1997). Currently, noise pollution from seismic prospecting, chemical contaminants, collision with vessels and incidental catches in high seas fisheries are among the potential threats for both species.

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

The IMMA encompasses a historical sperm whale hunting ground, and historical whaling data indicate the area’s longstanding importance for the species (Smith et al., 2012).  Combined data from Di Tullio et al. (2016) and Zerbini et al. (2004) indicate that sperm whales occur in the IMMA throughout the year.

Furthermore, sperm whales were the most frequently recorded species during ten ca. 35-day long dedicated ship-based cetacean line transect surveys conducted in the IMMA from 2009 and 2015. Sperm whale sightings represented approximately a third (n= 140) of all cetacean sightings identified to species level (n=344) (Di Tullio et al., 2016, Ecomega unpublished data). Sperm whale encounter rates were highest at depths over 1000m. This supports previous studies in the same area (Zerbini et al., 2004) showing that the continental slope is an important aggregation area for this species.

During austral autumn months fewer sperm whale sightings of larger mean group sizes were documented. Abundance estimates of this species within the IMMA varied from 271 (95% CI: 72 – 1021) in the autumn of 2010 to 1,253 (CI: 660 – 2378) in the spring of 2012 (Di Tullio, 2016).  Sperm whales were again the most frequently observed species during a recent ca. 35-day-long summer survey carried out in Feb-Mar 2023. In this survey, several new-born calves were documented.

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

This IMMA is an incredibly productive marine area that provides food resources that aggregate a number of marine mammal species (and other megafauna groups) and provide a nutritional base and appropriate habitat for activities associated with reproduction.  During ten ca. 35-day long dedicated ship-based cetacean line transect surveys conducted in the IMMA from 2009 and 2015, calves were regularly present in observed groups of the following species:  sperm whales (10.2% of all sightings – n=176), common dolphins (Delphinus delphis37% of all sightings, n=38), common bottlenose (Tursiops truncatus41.5% of all sightings, n=41), Atlantic spotted dolphins (Stenella frontalis48% of all sightings, n=46), Risso’s dolphins (Grampus griseus20% of all sightings, n=10)  and long-finned pilot whales(Globicephala melas edwardii39% of all sightings, n=18)  (Lima et al., 2021, Ecomega unpublished data).

During recent surveys conducted in the IMMA sperm whales were the most frequently sighted species on the continental slope area and many groups with new-born calves were observed, especially in the austral summer (Di Tullio, 2016, Ecomega unpublished data).

Sub-criterion C2: Feeding Areas

The productive waters of this IMMA support a large biomass of both pelagic and demersal species of fish and cephalopods (e.g. Haimovici et al., 2004, 2009, 2014) which in turn are part of the food web involving cetaceans, pinnipeds and other large pelagic predators that occur in the area (Santos and Haimovici, 2000, 2001, 2002). Skin samples of ten species of free-ranging odontocetes sampled in the IMMA were used to conduct an analysis of Carbon (C) and Nitrogen (N) isotopic composition revealed the trophic structure and habitat of cetaceans and their prey. The results indicate that this IMMA is an important feeding area for several species (Troina et al., 2020a,b, 2021) that occupy different trophic positions. For example, sperm whales occupy one of the highest trophic positions followed by the long-finned pilot whale, and both species feed mainly on oceanic prey. Species occupying lower trophic positions and feeding in waters of the shelf break include common dolphins, common bottlenose dolphins and Atlantic spotted dolphins, followed by killer whales (Orcinus orca) (Troina et al., 2020a,b, 2021). These data provide indirect, but robust indications of the importance of the shelf-break and continental slope for these (and certainly other non-analysed) species.

Criterion D: Special Attributes

Sub-criterion D2: Diversity

At least sixteen species of marine mammal have been documented in this IMMA (e.g. Di Tullio et al., 2016; Passadore et al., 2008, Uruguayan unpublished data). Nine of those were frequently recorded and met at least one of the criteria to be included as qualifying species in this IMMA. The habitat appears to be especially important for sperm whales and sei whales and several small and mid-sized delphinids, such as Atlantic spotted dolphins, short beaked common dolphins, bottlenose dolphins, long-finned pilot whales, and Risso’s dolphins (Grampus griseus) that regularly use the area throughout the year for both feeding and breeding purposes.  The area also hosts South American fur seals for feeding (e.g. Zerbini et al., 2004; Di Tullio et al., 2016; Franco-Trecu et al., 2021; de Lima et al., 2022; Ecomega upublished data; Uruguay unpublished data).

Small delphinids show latitudinal and in-offshore gradients as well as seasonal variation in distribution patterns within the IMMA, which could indicate habitat partitioning between some species (Di Tullio et al., 2016). For instance, common dolphin’s density decreased in areas beyond the 250m isobath where the presence of Atlantic Spotted dolphin increased (Di Tullio et al., 2016). The common bottlenose dolphin and Long-finned pilot whale were observed forming mixed groups and at depths of ~500m within this IMMA (Di Tullio et al., 2016). The density of Risso’s dolphin increased in waters deeper than 600m (Di Tullio et al., 2016).

Other species are less frequently recorded in this IMMA include striped (Stenella coeruleoalba) and spinner (Stenella longirostris) dolphins; common (Balaenoptera acutorostrata) and Antarctic (Balaenoptera bonaerensis) minke whales, and humpback whales (Megaptera novaeangliae).

Supporting Information

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Bugoni, L., Mancini, P.L., Monteiro, D.S., Nascimento, L., Neves, T.S. 2008a. Seabird bycatch in the Brazilian pelagic longline fishery and a review of capture rates in the southwestern Atlantic Ocean. Endangered Species Research. 5:137-147. 

Bugoni, L., Neves, T.S., Leite-Jr., N.O. Carvalho, D., Sales, G., Furness, R.W. et al. 2008b. Potential bycatch of seabirds and turtles in hook-and-line fisheries of the Itaipava Fleet, Brazil. Fisheries Research, 90: 217-224.

Cooke, J.G. 2018. Balaenoptera borealis. The IUCN Red List of Threatened Species 2018: e.T2475A130482064. Accessed on 08 December 2022.

Dalla Rosa, L., Secchi, E.R., 2007. ‘Killer whale (Orcinus orca) interactions with the tuna and swordfish longline fishery off southern and south-eastern Brazil: a comparison with shark interactions’. Journal of Marine and Biological Association. U. K., 87:135–140.

de Lima, R. C., Franco-Trecu, V., Carrasco, T. S., Inchausti, P., Secchi, E. R., Botta, S. (2022). Segregation of diets by sex and individual in South American fur seals. Aquatic Ecology, 1-17.

Di Tullio, J.C. 2016. ‘Uso do Habitat por Cetáceos no Sul e Sudeste do Brasil’. Doctoral Thesis. Universidade Federal do Rio Grande, Rio Grande, Brazil. 149pp.

Di Tullio, J.C., Gandra, T.B.R., Zerbini, A.N., Secchi, E.R. 2016. ‘Diversity and distribution patterns of cetaceans in the subtropical southwestern Atlantic outer continental shelf and slope’. PLoS One, 11 (5), e0155841.

Franco-Trecu, V., Naya, D. E., Inchausti, P. (2021). Fur Seal Trophic Ecology in Uruguay. In Ethology and Behavioral Ecology of Otariids and the Odobenid (pp. 635-642). Cham: Springer International Publishing.

Haimovici, M., Martins, A.S., Figueiredo, J.L., Vieira, P.C. 1994. ‘Demersal bony fish of the outer shelf and  slope of southern Brazil Subtropical Convergence Ecosystem’. Marine Ecology Progress Series, 108:59–77.

Haimovici, M., Fischer, L.G., Rossi-Wongtschowski, C.L.D.B., Bernardes, R.A., Santos, R.A. 2009. ‘Biomass and fishing potential yield of demersal resources from the outer shelf and  slope of southern Brazil’. Latin American Journal of Aquatic Research, 37(3):395–408.

Haimovici, M., Santos, R.A., Bainy, M.C.R.S., Fischer, L.G., Cardoso, L.G. 2014. ‘Abundance, distribution and population dynamics of the shortfin squid Illex argentinus in Southeastern and Southern Brazil’. Fish Research, 152:1–12.

Lima, R.C., Di Tullio, J.C., Secchi, E.R., Castro, F.R., Troina, G.C. 2021. ‘Delphinid Mixed-Species Associations in the Oceanic Waters of the Western South Atlantic’. Aquatic Mammals, 47(1):53-62.

Möller, O.O. Jr, Piola, A.R., Freitas, A.C., Campos, E.J.D. 2008. ‘The effects of river discharge and seasonal winds on the shelf off southeastern South America’. Cont Shelf Res. 2008; 28:1607–1624.

Muelbert, J.H., Acha, M., Mianzan, H., Guerrero, R., Reta, R., Braga ES, et al. 2008. ‘Biological, physical and chemical properties at the Subtropical Shelf Front Zone in the SW Atlantic Continental Shelf’. Continental Shelf Research, 28:1662–1673.

Passadore, C., Domingo, A., Szephegyi, M., and Secchi, E. R. 2012. Influence of environmental and longline fishing operational variables on the presence of killer whales (Orcinus orca) in Southwestern Atlantic. Journal of the Marine Biological Association of the United Kingdom, 1–10. doi:10.1017/ S002531541200166X.

Passadore, C., Domingo, A., Secchi, E. R. 2015. Analysis of marine mammal bycatch in the Uruguayan pelagic longline fishery operating in the Southwestern Atlantic Ocean. ICES Journal of Marine Science 2015 Vol. 72 Issue 5 Pages 1637-1652. DOI: 10.1093/icesjms/fsu250.

Passadore, C., Szephegyi, M., and Domingo, A. 2008. Presencia de mamíferos marinos y captura incidental en la flota uruguaya de palangre pelágico (1998–2007). Collective Volume of Scientific Papers ICCAT, 62: 1851–1857.

Piola, A.R., Möller, O.O., Guerrero, R.A., Campos, E.J.D. 2008. ‘Variability of the subtropical shelf front off eastern South America: winter 2003 and summer 2004’. Continental Shelf Research, 28:1639–1648.

Piola, A.R., Campos, E.J.D., Möller, O.O., Charo, M., Martinez, C. 2000. ‘Subtropical Shelf Front off eastern South America’. Journal of Geometry and Physics, 105: 2156–2202.

Madureira, L.S.P., Vasconcelos, M.C., Weigert, S.C., Habiaga, R.P., Pinho, M.P., Ferreira, C.S., et al. 2005. ‘Distribuição, Abundância e interações ambientais de espécies pelágicas na região sudeste–sul do Brasil, entre o Cabo de São Tomé (RJ) e o Chuí (RS)’. In: Madureira LSP, Rossi-Wongtschowski CLDB editors. Prospecção de recursos pesqueiros pelágicos na Zona Econômica Exclusiva da região sudeste e sul do Brasil: hidroacústica e biomassas. Série Documentos Revizee: Score Sul. Instituto Oceanográfico– Usp. São Paulo. 2005; 144p. Available: programa-revizee-s%C3%A9rie-de-documentos.

Ramos, R.M.A, Siciliano, S., Borobia, M., Zerbini, A.N., Pizzorno, J.L.A., Fragoso, A.B. L. et al. 2001. A note on strandings and age of sperm whales (Physeter macrocephalus) on the Brazilian coast. Journal of Cetacean Research and Management 3 (3): 321-327.

Santos, R.A., Haimovici, M. 2000. ‘The Argentine short-finned Illex argentinus in the food webs of the southern Brazil’. Sarsia 85:49–60.

Santos, R.A., Haimovici, M. 2001. ‘Cephalopods in the diet of marine mammals stranded or incidentally caught along the southeastern and southern Brazil (21–34°S)’. Fish Research, 52:99–112.

Santos, R.A., Haimovici, M. 2002. ‘Cephalopods in the trophic relations off southern Brazil’. Bulletin of Marine Sciences, 71: 753–770.

Secchi, E.R., Vaske, T., 1998. ‘Killer whale (Orcinus orca) sightings and depredation on tuna and swordfish longline catches in southern Brazil’. Aquatic Mammals, 24, 117–122.

Secretariat of the Convention on Biological Diversity 2014. Ecologically or Biologically Significant Marine Areas (EBSAs): Special places in the world’s oceans. Volume 2: Wider Caribbean and Western Mid-Atlantic Region. 86 pages.

Smith, T.D., Reeves, R.R., Josephson, E.A., Lund, J.N. 2012. ‘Spatial and seasonal distribution of American whaling and whales in the age of sail’. PLoS ONE 7(4): e34905. doi:10.1371/journal.pone.0034905

Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L. 2019. ‘Physeter macrocephalus (amended version of 2008 assessment)’. The IUCN Red List of Threatened Species 2019: e.T41755A160983555. Accessed on 08 December 2022.

Troina, G.C., Dehairs, F., Botta, S., Di Tullio, J.C., Elskens, M., Secchi, E.R., 2020a. ‘Skin δ13C and δ15N reveal spatial and temporal patterns of habitat and resource use by free-ranging odontocetes from the southwestern Atlantic Ocean’. Marine Biology, 2020:167-186.

Troina, G.C., Dehairs, F., Botta, S., Di Tullio, J.C., Elskens, M., Secchi, E.R., 2020b. ‘Zooplankton-based δ13C and δ15N isoscapes from the outer continental shelf and slope in the subtropical western South Atlantic’. Deep-Sea Research. part I, 159:103235.

Troina, G.C., Riekenberg, P., van der Meer, M.T., Botta, S., Dehairs, F., Secchi. E.R. 2021 ‘Combining isotopic analysis of bulk-skin and individual amino acids to investigate the trophic position and foraging areas of multiple cetacean species in the western South Atlantic’. Environmental Research, 111610.

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Zerbini, A. N., Secchi, E.R., Bassoi, M., Dalla Rosa, L., Higa, A., Sousa, L., et al. 2004. ‘Distribução e abundância relativa de cetáceos na Zona Econômica Exclusiva da região sudeste-sul do Brasil. Série de Documentos Revizee-Score Sul. pp40. programa-revizee-s%C3%A9rie-de-documentos.

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Zerbini, A.N., Andriolo, A., Heide-Jorgensen, M.P., Pizzorno, J.L., Maia, Y.G., VanBlaricom, G.R., et al. 2006. ‘Satellite- monitored movements of humpback whales Megaptera novaeangliae in the southwest Atlantic Ocean’. Marine Ecology Progress Series, 313: 295–304.


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