Central Magellan Strait IMMA

Criterion A – Species or Population Vulnerability

The sei whale (Balaenoptera borealis) is classified as Endangered (EN) under IUCN Red List status although the most recent species assessment indicates that in 2023 (following a required delay) it can be down-listed to VU (Cooke, 2018). The species is designated as ‘Critically Endangered’ under law by the Chilean government (clasificacionespecies.mma.gob.cl). Sei whales were extensively exploited in the Southern Hemisphere (Aguayo-Lobo et al., 1998). The largest catches were made by Antarctic pelagic fleets, which hunted over 110,000 sei whales between 1960 and 1970 (Horwood, 2002). In Chilean waters, this baleen whale was the third highest whaling target between 1929 and 1979 (Aguayo-Lobo et al., 1998). In Chile, the conservation category was designated considering the IUCN A1 criterium, taking into account a reduction in population size of 84% in the southern hemisphere populations during the last three generations (considering a generation time of ~23 years) (Christiansen, 2006).

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations

Studies of Peale’s dolphins (Lagenorhynchus australis) within the Strait of Magellan in Chile indicate that populations remain year-round in specific areas close to shore (Viddi & Lescrauwaet, 2005). Land-based surveys on the west coast of the Strait of Magellan reported higher numbers of Peale’s dolphins near shore in summer than in winter. Higher concentrations of Peale’s dolphins have been observed during spring in the southern part of the Strait of Magellan, which is thought to be the preferred calving area of this population. Data from Hucke-Gaete et al. (2022) show a high number of sightings in the area. The population of Peale’s dolphins in the entire Magellen region in southern Chile is estimated to comprise around 2400 individuals (Gibbons et al., 2002). Observations of feeding combined with evidence of mating and calving indicate that a population of Peale’s dolphins is fulfilling all of its key life cycles within the IMMA. Behaviour associated with mating mostly occurred in late summer (February-March). During summer months, fission-fusion dynamics occurred, with small groups joining to other small groups to form larger groups in order to mate. The calving season seems to be concentrated during the spring occurring mainly between November and December, but with calves observed as early as October (Lescrauwaet, 1997). Based on 191 hours of survey effort, Viddi and Lescrauwaet (2005) reported that Peale’s dolphins were concentrated in a small part of their study area, which was strongly associated with kelp beds. Feeding was the most frequent behaviour observed, followed by traveling. The former behavioural state was observed principally inside and on the border of kelp beds, while traveling was observed mainly outside the beds. Kelp forests appear to be a fundamental element of preferred habitat for Peale’s dolphins in coastal ecosystems. Data of Peale’s dolphins feeding upon schools of Fuegian sprat (Sprattus fuegensis) and pejerrey (Austromenidia nigricans; Notothenia magellanica) were recorded between 1989 and 1995 by Lescrauwaet (1997).

Criterion C: Key Life Cycle Activities

Sub-criterion C2: Feeding Areas

Sei whale sightings and behaviour data collected in the area between 2004 and 2015 and a compilation of data from different sources, revealed a continuous presence of the species in the area (Acevedo et al., 2017; Hucke-Gaete et al., 2022). Observed behaviour included milling, traveling, and feeding. Milling (67.4%) and traveling (23.3%) behaviours were the most commonly seen behaviours. In During milling behaviour, the whales made random movements, with dives of 5 to 7 min followed by four or five blows at the surface in-between dives and sometimes defecation, suggesting foraging. In addition, during nine encounters classified as ‘milling’, feeding by seabirds (e.g., seagulls Laridae, black-browed albatrosses Thalassarche melanophris, and giant petrels Macronectes giganteus) was observed in the area where the whales were sighted. Lunge-feeding behaviour at the surface was observed on four occasions, and the prey observed on two occasions was Fuegian sprat (Sprattus fueguensis) (Acevedo et al., 2017).