Archaeological and stable isotope data reveal patterns of fishing across the food web on California’s Channel Islands

Abstract

How do human communities integrate within food webs? Studies characterizing the historical flow of energy among people and local environments can yield important insights into managing sustainable ecosystems. Here, we combine zooarchaeological, bulk tissue, and compound-specific stable isotope data from late Holocene Santa Rosa Island to investigate the ecological role of people within a southern California nearshore marine ecosystem. We show people foraged in diverse marine habitats, including kelp forests and pelagic waters, and consumed a wide range of species. However, zooarchaeological results reveal >50% of recovered fish remains came from presumed kelp forest carnivores of mid-trophic level (3.0–4.0) such as surfperches and rockfishes. Local fishing strategies thus did not involve the preferential removal of large-bodied, high trophic level species – a pattern known as “fishing down the food web” which has been documented in modern commercial fisheries and results in the collapse of marine ecosystems. Essential amino acid δ13C analysis revealed that the historical fish community relied on basal resources from kelps and phytoplankton. This coupling of benthic and pelagic energy sources suggests late Holocene coastal food webs in the region were in a relatively stable configuration immediately prior to first European arrival. This stability likely contributed to sustaining densely populated Chumash settlements, intensive fisheries, and high local faunal diversity. Our findings provide important pre-industrial data for marine ecosystems and document some of the mechanisms behind the intensive, yet sustainable long-term fisheries of the Island Chumash.