Since the middle Holocene, human activity has influenced the marine communities of Tierra del Fuego. How has population and diet of Southern Fur seals (Arctocephalus australis) changed in Holocene Tierra del Fuego due to human and climate impacts? What implications do these changes have for the marine ecosystem? The effects of climate and human activity on an ecosystem are compared between Holocene and historic food webs, by measuring changes in food chain length and fluctuation in Otariid niche. Stable carbon and nitrogen stable isotopes measured from archaeological A. australis collagen are used to identify differences in habitat preference and trophic level between individuals of different life history stages from a middle Holocene archaeological site and compared to potential dietary components.
Results/Conclusions
The 160 measured A. australis individuals vary in δ13C from -15.5‰ to -11.1‰ and in δ15N from 20.3‰ to 16.0‰, while potential prey items are limited in δ13C from -13.7‰ to -9.6‰ and in δ15N from 18.3‰ and 14.0‰. The broad carbon range in A. australis relative to potential prey items, known species of kelp forest habitat, suggests offshore feeding preference for almost half of A. australis individuals. A. australis pups show an expected higher trophic position from adult females while yearlings and juveniles express a bimodal distribution between offshore and nearshore diets and habitats. Sub-adult and adults show the broadest range in values, with females being limited to -18.5‰ in δ15N and under, suggesting males had access to higher trophic level prey in various habitats while females may have preferred to feed near rookeries. These middle Holocene individuals are significantly lower in δ13C values when compared to modern prey items, suggesting that significant hunting of Otariids in the mid-20th century and the resulting population declines effectively removed a top-down predatory pressure in marine Tierra del Fuego and ultimately reduced food change length.