Status, population trend and population structure of South American fur seals Arctocephalus australis in Southwestern Atlantic waters.

CRESPO, E.A., A.C.M. SCHIAVINI, L.R. OLIVEIRA, N.A. GARCIA & J.S. MORGANTE

Istanbul, Turkey

Congreso; 23rd. ANNUAL CONFERENCE OF THE EUROPEAN CETACEAN SOCIETY..; 2009

The South American fur seals were severely depleted during the XVIII century. The objective of this work was updating information on distribution, abundance, population trend, population genetic structure and potential migratory paths along the Southwestern Atlantic. Distribution in Argentina includes: Mar del Plata (Buenos Aires), Isla Escondida, Isla Arce, Isla Rasa and Cabo dos Bahías (Chubut), Cabo Blanco and Islote del Cabo (Santa Cruz), seven rookeries in Staten Island and islets of the Beagle Channel (Tierra del Fuego). Censuses were carried out in rookeries from Isla Escondida to Staten Island from 1996 to 2007. The largest concentration is found in Chubut where numbers range from 4500 to 15500 depending on the season of the year.  On Staten Island 4500 seals are found. Pups were recorded at Isla Escondida (200-300), Isla Rasa (30) and 5 rookeries at Staten Island (around 1000). Skin samples (n=65) were taken from Southern Brazil (=Uruguay) (n=27), Mar del Plata (n=9), Puerto Madryn (n=5), Chubut Islands (n=24) and Tierra del Fuego (n=1) in order to evaluate population structure and expansion through mtDNA analysis. While in Uruguay the rate of increase is around 10% annually since the cease of exploitation in 1991, in northern Patagonia is close to 8%. From year to year an increasing number of fur seals are recorded in northern Patagonia, indicating seasonal migrations north–south. mtDNA analysis indicated no population subdivisions (Φst: -0.0292, Fst: -0.00716) along the Southwestern Atlantic and also detected a rapid population expansion from a small effective size in the fur seals from Uruguay (Fu’s Fs: -10.85149, P<0.0001) and Chubut Islands´ (Fu’s Fs: -6.58459, P<0.001). These results support the hypothesis that migration among breeding colonies sustains an ancient gene flow that results in a single Atlantic population for the species.