Billfish from the families Xiphiidae (swordfish) and Istiophoridae (marlins and sailfish) are large, often pelagic fishes that are highly migratory. Although some billfish have been the target of global commercial and sport fisheries for decades, prehistoric billfish foraging is relatively rare, but includes systematic swordfish (Xiphias gladius) and/or striped marlin (Kajikia audax) exploitation in the Santa Barbara Channel region of California, the Gulf of Maine, and the northern coast of Chile. While whole vertebrae, rostra, and other elements can often be identified to species, fragments of these, or other non-diagnostic elements such as fin ray spines, as well as modified bones, are difficult to determine to species-level beyond general identification as billfish or "large fish." We performed collagen fingerprinting on modern (n = 17) and archaeological (n = 30) billfish and large tuna (Scombridae) remains from museum collections and Chumash archaeological sites in California's Santa Barbara Channel region to test this method for determining the species of fragmentary remains. These data demonstrate that collagen fingerprinting can distinguish between the families Istiophoridae, Xiphiidae, and Scombridae, although distinguishing between species within Istiophoridae needs additional research. All but one of our archaeological specimens are from swordfish, with just one striped marlin, suggesting that the Chumash were likely encountering or targeting swordfish more frequently than other billfish species. Our study demonstrates that collagen fingerprinting is an important technique for documenting ancient billfish and other fisheries around the world.
