Otarie a criniere

The South American Sea Lion is the most abundant marine mammal occurring along the southern part of South America (Cappozzo 2002). The population of the coast of Uruguay consists of two main reproductive colonies, Isla Lobos (35º01’S) and Cabo Polonio (34º24’S), and is estimated to be about 12,000-13,000 individuals (1,200-2,675 pups born per year; Páez 2006, Pedraza et al. 2012, Franco-Trecu 2015). On the northern coast of Argentina, there are only four haulouts (about 2,500 individuals), while the Patagonian region has both reproductive and non-reproductive colonies (about 120,700 individuals). An additional 7,500 animals are found in the Falkland Islands (Crespo et al. 2012). Baylis et al. (2015) reported a minimum estimate of 4,443 pups born at the Falklands in 2014. The Chilean population is estimated to be approximately 197,000 animals (Venegas et al. 2001, Bartheld et al. 2008, Sepúlveda et al. 2011, Oliva et al. 2012, Contreras et al. 2014). There are at least 105,000 individuals in Peru (IMARPE 2013), and no more than 200 on the Brazilian coast (Sanfelice et al. 1999, Pavanato et al. 2013). Therefore, the total global population is approximated to be at least 445,000 individuals.

South American Sea Lion numbers are increasing in northern Patagonia, in the Rio Negro (41º03’S) and northern Chubut (43º34’S) provinces, at 5.7-6% per year (Dans et al. 2003a, Grandi 2010). In central Patagonia, in the central (43º57’S) and southern Chubut (45º23’S) province, they are also increasing at 6% annually (Reyes et al. 1999, Reyes 2004). In Chile between 15°56’S and 48°40’S, the population increased from 137,000 to 197,000 in 7 years (Oliva et al. 2012, Contreras et al. 2014). The population trend in the Magallanes Region is unknown. On the other hand, abundance has been decreasing in Uruguay. Negative trends for all sex and age classes of the breeding population were reported by Páez (2006) as -1.4% per year for adult males, -2.1% for adult females, and -4.5% for pups. Results from population modeling by Paez (2006) showed a 2% per year decline for total population size and a 3% decline in birth rates. This coincides with recent findings from Franco-Trecu (2015) that estimated a -2% (CI -1.1% to -2.5%) decline in pup production using pup count data from 1956-2013. Although the reasons for the population decline in Uruguay are still unknown, it is suspected that it could be related to interactions with fishing activities (Crespo et al. 2012, Riet-Sapriza et al. 2013) and with the long-term effect of harvest (Franco-Trecu 2015). The cumulative effects of population extractions, including pup harvesting (~50,000) and zoo and aquaria sales (144 young males and 285 young females), not only reduced the local population size, but also could have disrupted its social structure to the point where Allee effects could be limiting the post-harvesting population recovery at Isla de Lobos (Franco-Trecu et al. 2015). In southern Patagonia, in the Santa Cruz (46º01’S) and Tierra del Fuego (54º88’S) Provinces, the trend is unknown because data are insufficient to estimate a rate of change (Schiavini et al. 2004); however, the current numbers are clearly less than the estimates reported in the late 1940s. Sealing activities, performed mainly at northern Patagonia and at Tierra del Fuego, are likely responsible for the depletion (Schiavini et al. 2004). At the Falkland Islands there was a 95% decline in the population from >380,000 animals to <30,000 (from 80,555 pups in the mid 1930s to 5,506 pups in 1965; Hamilton 1939, Strange 1979). The number of pups estimated in 2014 for the Falkland Islands was 6% of the number estimated in 1930s (Baylis et al. 2015). Different hypotheses have been proposed to explain the decline, include commercial sealing and environmental change (Strange 1979, Thompson et al. 2002, Baylis et al. 2015). However, the trend has been positive since 1990; with an 8.5% annual increase from 1990 to 1995, and a 3.8% annual increase between 1995 and 2003 (Crespo et al. 2012).

South American Sea Lion population trends along the Chilean coast are not homogenous. In northern Chile the populations are increasing (Barthled et al. 2008, Oliva et al. 2012) whereas the trend is unknown for central and southern Chile (Sepúlveda et al. 2011).

Due to the 1997-98 El Niño Southern Oscillation (ENSO), the Peruvian population of South American Sea Lions declined from about 144,087 animals in December 1997 to 27,991 in December 1998, a reduction of 81% (Arias-Schreiber and Rivas 1998, Arias-Schreiber 1998). This was probably due to a combined effect of mortality and dispersal from historically surveyed breeding and haul out sites. After this dramatic reduction, there was a recovery of 76.3%, with an estimated 118,220 individuals by 2006 (IMARPE 2006). The recovery of the population of Sea Lions on the coast of Peru is due to improved reproductive levels as a consequence of an increase in food availability as well as migration from the colonies in northern Chile (Oliveira et al. 2012). However, the stronger and more frequent ENSOs that appear to be occurring along the Peruvian coast may put the population in Peru at greater risk (Soto et al. 2004).

The majority of subpopulations in the southwestern Atlantic Ocean are increasing, although the trends are not homogeneous. However, in contrast to what is observed on the Peruvian Pacific coast, the population sizes do not show large inter-annual fluctuations (Crespo et al. 2012). In Chile, the population is increasing steadily (Oliva  pers. comm).