OOS 21-6 - Archaeological investigations and amino acid stable isotope data reveal patterns of fishing across the food web on California's Channel Islands

Studies characterizing the historical flow of energy within pre-industrial environments and the long term dynamics of human fisheries can yield important insights for managing sustainable ecosystems. Here, we present bulk tissue, and amino acid δ13C data of fish remains from a late Holocene coastal archaeological site in the California Channel Islands and investigate historical marine food web dynamics and fisheries strategies. We show people fished in diverse marine habitats, including coastal rocky reefs and pelagic waters. However, over 50% of recovered fish remains came from 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 (i.e., ‘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 multivariate “fingerprinting” of archaeological fishes revealed that the pre-industrial coastal food web relied on basal resources from kelps and phytoplankton. Subsequent bootstrapping analyses showed ~80% of measured fish specimens were ‘specialists’, utilizing predominantly kelp- or phytoplankton-derived essential amino acids, whereas 20% of our measured fish likely used a combination. This coupling of benthic and pelagic energy sources suggests late Holocene coastal food webs in the region were in a stable configuration immediately prior to first European arrival. This stability likely contributed to sustaining densely populated local settlements, intensive fisheries, and high local faunal diversity. Our findings provide important pre-industrial data for marine ecosystems and illustrate the value in a compound-specific stable isotope approach to historical ecology and archaeology.