Changes in the foraging ecology of South American fur seals in the southwestern South Atlantic Ocean since the Middle Holocene

CARDONA, LUIS; SAPORITI, FABIANA; CRESPO, ENRIQUE ALBERTO; VALES, DAMIÁN GUSTAVO; ZANGRANDO, A.F.; BORELLA, FLORENCIA; GOODALL, NATALIE; OLIVEIRA, LARISSA ROSA DE

Valparaíso

Congreso; XVII Reunión de Trabajo de Expertos en Mamíferos Acuáticos de América del Sur y 11º Congreso SOLAMAC; 2016

During archaeological and historical times, humans have reduced the abundance of pinnipeds in such a way that the current ecological role of these predators may have changed dramatically. Stable nitrogen and carbon isotopes from bone collagen were used to reconstruct the foraging ecology of South American fur seals (Arctocephalus australis) since the Middle Holocene in the southwestern South Atlantic Ocean. Also, stable isotope ratios of carbon and nitrogen in zooarchaeological and modern mollusc shells were assessed to account for changes in the ecosystem baseline throughout time. Fur seals Inhabiting the Río de la Plata and surrounding areas 7000 years ago were depleted in 13C as compared with their modern counterparts (-15.9 ± 0.6? vs. -13.5 ± 0.8?) but differences in δ15N were not statistically significant (21.3 ± 1.9 ? vs. 20.5 ± 0.6?). Conversely, fur seals from northern and central Patagonia seem not to have changed diet since 2200 BP (average for the period: δ13C= -13.4 ± 0.5?, δ15N= 20.6 ± 1.1 ?) and the same was true for fur seals from Tierra del Fuego between 6400-4300 BP (average for the period: δ13C= -15.4 ± 0.5 ?, δ15N= 20.5 ± 0.5 ?). In contrast, isotopic ratios dropped in fur seals from Tierra del Fuego during the 19th century (δ13C= -17.2 ± 0.3 ?, δ15N= 18.6 ± 0.7 ?), coinciding with the decimation of the local population by commercial sealers and a major drop in marine primary productivity. Currently, fur seals from Tierra del Fuego forage at a lower trophic level than during most of the Middle Holocene (δ13C= -13.2 ± 0.7 ?, δ15N= 19.0 ± 1.6 ?). Present evidence does not support a significant impact of hunter-gatherer activities on the foraging ecology of fur seals. On the other hand, the large scale removal of fur seals and other species since the late 18th century may have modified their foraging habits, but the concurrence of environmental changes (e.g. Little Ice Age) preclude us to assess the actual impact of commercial sealing on the foraging ecology of this species.