Commerson’s Dolphin Habitat Network IMMA
Size in Square Kilometres
10 917 km2
Qualifying Species and Criteria
Commerson’s dolphin – Cephalorhynchus commersonii
Criterion B (1); D (1)
Lahille’s bottlenose dolphin – Tursiops truncatus gephyreus
Criterion A; B (1)
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Summary
This IMMA is a network of coastal habitats along the coast of Argentina, that are important for small resident populations of Commerson’s dolphins. The Commerson’s dolphins are patchily distributed and there is a high genetic distinctiveness among groups along the coast.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
Lahille’s bottlenose dolphin (Tursiops truncatus gephyreus): This subspecies has been recorded in the IMMA often in mixed groups, feeding and traveling together with common bottlenose dolphins (Tursiops truncatus truncatus) especially in the area of Bahía Engaño in the mouth of Chubut river (Vermeulen et al., 2017).
Criterion B: Distribution and Abundance
Sub-criterion B1: Small and Resident Populations
Commerson’s dolphin: At Bahía Engaño in the mouth of the Chubut River, the population is estimated to be around 350 individuals, most of which remain in the area all year round. There is a decrease in abundance of the species in that area that has been linked to an increase of Sea Surface Temperature during summer months (Coscarella, 2005; Coscarella el al 2010). In the area of Camarones, the estimate of Commerson’s dolphins is 239 individuals (Coscarella, 2005). At Bahía San Julián although there is no population estimation, there have been 95 Commerson’s dolphins photo-identified since 1996 (Iñíguez Bessega, unpublished data). For the rest of the areas in this network there are reports on the presence of dolphins, but no estimates of abundance are available.
In all the areas calves have been observed. In Bahía Engaño in the mouth of the Chubut river and in Bahía Camarones calves have been reported from September until March (Coscarella, 2005) and in Comodoro Rivadavia/ Rada Tilly from November until May (Coscarella unpublished information). The breeding season takes place during the austral spring and summer, between September and February (Iñíguez, 1991; Iñíguez & Tossenberger, 2007, Righi et al., 2014). Bahía San Julián is also a reproductive area for Commerson’s with at least 4 newborn Commerson’s every year (Iñíguez Bessega, unpublished data).
In every area Commmerson’s were observed chasing and hunting silversides (smelt or whitebait). Commerson’s dolphins are opportunistic feeders, exhibiting pelagic feeding strategies in northern Patagonia, at the northern end of its range. This species can change its foraging tactics by adapting to different habitats, including those with extreme tidal ranges (Koen-Alonso, 1999). They deploy different hunting techniques in each area. In Bahía Engaño and Camarones, dolphins use not only individual feeding but cooperative feeding (Coscarella et al., 2010). In Bahía San Julián, Commerson’s dolphins prey on silversides fish and squid (Iñíguez et al., 2000). At Ría Santa Cruz, diving showed a high frequency during the ebb tide, and could therefore be potentially related to a benthic foraging strategy (Loizaga de Castro et al., 2013). A diet study of Commerson’s dolphins at Tierra del Fuego (53º20’S, 68º30’W), showed the presence of benthic preys, indicating that this species feeds at or near the bottom (Bastida et al., 1988).
Lahilles Bottlenose dolphins – An abundance estimate for both subspecies of bottlenose dolphins combined, created a joint estimate from aerial surveys indicating a very small population of 34 individuals in the the area of Bahía Engaño in the mouth of Chubut river (CI 95% 22-51) (Coscarella et al. (2012).
Criterion D: Special Attributes
Sub-criterion D1: Distinctiveness
Commerson’s dolphins: There is evidence for reduced gene flow (at least of females as shown by mitochondrial DNA analysis) between all of the sampling locations and the suggestions for 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 discrete location within this IMMA network 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).
Supporting Information
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