San Jorge Gulf IMMA

Criterion A – Species or Population Vulnerability

There are populations of both common bottlenose dolphins (Tursiops truncatus truncatus), and Lahille’s bottlenose dolphins (T. t. gephyreus) in the San Jorge Gulf (Golfo San Jorge), and it is probably the southern border for the later sub-species’ distributions (Fruet et al., 2014). Small groups of both subspecies are sighted regularly within the IMMA, and sporadically large groups of approximately 50 individuals (putative common bottlenose dolphins) are sighted with calves (Coscarella et al., 2021a). Lahille’s bottlenose dolphins are listed as Vulnerable by the IUCN (Vermeulen et al. 2019), but are not assigned to a category at the national level in Argentina. Although the common bottlenose at the international level is listed as Least Concern, at the national level in Argentina it is listed as Vulnerable.

The sei whale (Balaenoptera borealis) is listed as EN both by the IUCN (Cooke, 2018) and the Red List of Argentina (Hevia et al. 2019). These whales have increased their presence in the last ten years in the area, and still increase according to the sighting per unit effort presented in Coscarella et al. (2023). Their main activity in the IMMA is feeding, so it may be a previously unknown feeding ground for the species, particularly important since these behaviours are performed very close to the shore (Coscarella et al., 2022).

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations

There is a small population of Commerson’s dolphins (Cephalorhynchus commersonii) that are regularly sighted in the IMMA (Coscarella et al., 2021a; Mermoz, 1980). There is no abundance estimation available, but in recent aerial surveys more than 50 individuals were sighted (Coscarella, unpublished information). Commerson’s dolphins are sighted during the whole year from a land station in Punta Marqués, with highest sighting rates during the summer months (Coscarella, 2021a).

Sub-criterion B2: Aggregations

There are two rookeries of South American sea lions (Otaria byronia) (also known as Otaria flavescens in Argentina) present in the IMMA at Monte Loayza and Punta Marqués, with more than 12,000 individuals in total (Grandi et al. 2014; Páez et al. 2017).

There is a population of sei whales regularly present in the coastal zone of the area from October until July. A preliminary abundance estimation from aerial surveys conducted during the 2021-2022 season, estimated  706 sei whales were present in the area in November 2021,  and a total of 2776 in May 2022 (Coscarella et al., 2023).

The San Jorge Gulf IMMA also provides breeding habitat for dusky (Lagenorhynchus obscurus), Peale’s (Lagenorhynchus australis), Risso’s (Grampus griseus) and both bottlenose subspecies all of which have been sighted in groups including calves during the summer months (Coscarella et al., 2021).  The productive waters in this IMMA provide abundant food resources on which these species depend.

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

The IMMA hosts two South American sea lion rookeries, where pups are regularly documented. The main area of reproduction is Monte Loayza within the IMMA where 245 pups were recorded in 1995 and 1415 recorded in 2012 making this one of the biggest breeding areas for this species in southern Patagonia (Crespo et al., 2021; Grandi et al., 2014).

Sub-criterion C2: Feeding Areas

The San Jorge Gulf is a very rich area that provides prey for sea lions and all dolphin species.  It is likely to be the productive habitat and abundant food resources that attract such large numbers of marine mammals.

Coscarella & Riera (2022) reported that Sei whales devote 30% of their time budget to feeding, mainly on squat lobsters (Munida gregaria) in the area, very often near the coast. The estimate is obtained from the frequency this behavior is observed from a vantage point in the top of a cliff in the center of the area, particularly in Punta Marquès, where they can be observed very close to the shore (Coscarella et al. 2023)..

Humpback whales frequently feed on silversides near the coast (Riera et al. 2022).

Sub-criterion C3: Migration Routes

Several species of balaenopterids use the area for transit between feeding grounds in the Antarctic / sub-Antarctic and breeding grounds in the tropics, and many can be observed very close to the shore in Punta Marquès (Coscarella et al. 2023). The San Jorge Gulf is an important stop off point for the southern right whale during its migration (IWC, 2013, Coscarella et al., 2021; Iñíguez et al., 2010).

Criterion D: Special Attributes

Sub-criterion D1: Distinctiveness

Recently humpback whales have been reported feeding in the Punta Marqués Protected Area. The whales swim very close to the shore, and the feeding technique named natural barrier feeding, presented as a cultural trait, consists of the whale forcing prey against a barrier (a wave-cut platform) and then accelerating towards the prey using, generally, a lateral lunge-feeding approach to capture small fishes (Riera et al., 2022).

Sub-criterion D2: Diversity

This IMMA includes habitat that supports an important diversity of marine mammal species, both pinnipeds and cetaceans. Nineteen marine mammal species are sighted in the area, with 12 that are sighted more frequently, some during the whole year and others during a specific season every year. The rest of the species are sighted once or twice a year (Hevia et al. 2022; Coscarella et al. 2021a; Retana & Lewis, 2017; Iñíguez et al, 2010; Reyes, 2006).