Pre-industrial ecology and foraging behavior of swordfish Xiphias gladius in the eastern North Pacific

Abstract

The historical ecology and foraging behavior of many apex marine predators are poorly known. This includes highly mobile pelagic species such as billfish (Xiphiidae and Istiophoridae), which have long held cultural significance for coastal peoples. In California’s Santa Barbara Channel Region, Chumash people have hunted billfish for >2000 yr, providing a deep historical record of these species. We present bulk tissue δ13C and δ15N data for 15 Late Holocene archaeological swordfish Xiphias gladius and 1 striped marlin Kajikia audax previously identified to species through collagen fingerprinting. When compared to data sets of modern northeastern Pacific and archaeological Gulf of Maine swordfish, we identified significant overlap in the isotopic values of modern and archaeological swordfish from the Pacific, indicating that pre-industrial swordfish were reliant on food webs of the North Pacific Subtropical Gyre and the California Current System. We also identified differences in the isotopic composition of swordfish captured by island vs. mainland communities, with swordfish remains from mainland sites having lower and more variable δ13C values, potentially indicating different source populations. The isotopic range of swordfish from California archaeological sites was much broader than those from the Gulf of Maine, suggesting a wider range of habitats used by Pacific swordfish. Our results provide important pre-industrial data for an apex marine predator.