Northeast of Santa Cruz Province IMMA

Criterion A – Species or Population Vulnerability

Chilean dolphins (Cephalorhynchus eutropia) have been recorded in this particular area of the Argentine coast, at Ría Deseado, more than 600 km north of the closest known population, which is located at the southern tip of the continent, closer to the species’ core range on the Pacific coast of South America. Although there is no abundance estimate available for the number of Chilean dolphins in this IMMA, available information suggests that since 2009, only three Chilean dolphins have been recorded in the Ría Deseado (Morgenthaler et al., 2014). This is a small resident population that is extremely vulnerable to local extirpation (Morgenthaler et al., 2014).  The species is listed as Near Threatened on the IUCN Red List of Threatened Species (Heinrich et al. 2017), but this population’s isolated status, and the entire species’ fragmented distribution and reliance on small pockets of coastal habitat that often brings it into contact with anthropogenic threats, mean that all necessary measures must be taken to protect it.

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations

Since 2009, three individual male Chilean dolphins have been recorded in the Ría Deseado (Morgenthaler et al., 2014).  These three photo-identified individuals were observed on multiple occasions between November 2009 and January 2012.  Morgenthaler et al. (2014) also describe observations of dolphins in the Ria Deseado area that could be Chilean dolphins, but were difficult to distinguish from sympatric Commerson’s dolphins (Cephalorhynchus commersonii) because their ventral surfaces were not visible. Furthermore, they describe possible hybrid individuals with characteristics of both Chilean and Commerson’s dolphins.  Given Chilean dolphins known limited home ranging patterns, and the very few, but repeated observations of known individuals in the same area, it is likely that the Ria Deseado hosts an isolated remnant population of Chilean dolphins in danger of local extirpation.

The presence of Commerson’s dolphins year-round suggests that the population is resident in the Ría Deseado estuary (Iñíguez & Tossenberger, 2007, Righi et al., 2013). Abundance has been estimated using photo-identification that successfully identified 26 resident individuals within the estuary (Iñíguez & Tossenberger, 2007). Another study carried out between 2002 and 2004, indicated that adult abundance was higher during spring (34 and 35 individuals in 2002 and 2003, respectively) and decreased during autumn (7 individuals) and winter (16 individuals) (Righi et al., 2013).

Mating and calving takes place during the austral spring and summer, between September and February at Ría Deseado (Iñíguez, 1991; Iñíguez & Tossenberger, 2007, Righi et al., 2014). Calves were present in the study area on 58 occasions (6.09% of total sightings) over 200 days of survey effort between 1986 and 1991 and 1994 and 1997 (Iñíguez & Tossenberger, 2007).

Commerson´s dolphins in the Ría Deseado display unique feeding behaviour in the IMMA, driving prey against anchored ships, piers, and beds of giant kelp (Macrocystis pyrifera) thereby reducing the number of potential escape routes for the fish (Iñíguez & Tossenberger, 2007).

The IMMA also hosts a permanent South American fur seal (Arctocephalus australis) rookery and accompanying feeding habitat. Aerial surveys and land observations conducted in January 1994, February 2020 and May 2011 estimated that between 300 and 500 individuals are present at Cabo Blanco, and the IMMA also encompasses their feeding habitat (Crespo et al., 2015).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

There are five South American sea lion (Otaria byronia) rookeries in the IMMA: Cabo Blanco, Roca Foca, Islote Lobos, Isla Blanca and Isla Pingüino (Grandi et al., 2015).  Aerial surveys conducted in January 2012 yielded an estimate of 146 individuals for Cabo Blanco, 61, including one pup, for Islote Lobos, 1707, including 31 pups, for Isla Blanca, and 591 for Isla Pingüino (Grandi et al., 2015). The presence of this species is recorded year-round in the region (Iñíguez, pers. comm.). The five rookeries present in this cIMMA represent about 9% of the total number of colonies in the province of Santa Cruz, with 2,505 individuals recorded in January 2012 (Grandi et al., 2015)

Criterion D: Special Attributes

Sub-criterion D1: Distinctiveness

The IMMA hosts the only known population of Chilean dolphins in Argentine Atlantic waters (Morgenthaler et al., 2014).  The population appears to be discontinuous with the rest of the species’ range, given that the nearest known population is 600km south of this IMMA.

There is evidence for reduced gene flow (at least of females as shown by mitochondrial DNA analysis) between Commerson’s dolphins in all of the sampling locations suggesting isolation and divergence of Commerson’s dolphin groups over relatively small geographic distances (Cipriano et al., 2011; Kraft et al., 2021). Therefore, the precautionary approach suggests that each sampling location (including Ría Deseado) should be considered as a candidate for separate management, with efforts made to identify and reduce potential threats even in the absence of evidence for existing threats (Cipriano et al., 2011; Kraft et al., 2021). Ongoing research of microsatellite markers indicates a similar pattern of differentiation among localities, and for Puerto Deseado signals of genetic intromission have been detected in the “grey morph” of Commerson’s dolphins, indicating some genetic flux with Chilean dolphin in the area (Coscarella, unpublished information).