The Global Fish Trade Boomed 800 Years Ago, Bones Suggest

Researchers have traced the international fish trade all the back to the medieval period of London history, finding that the city's fish supply was suddenly globalized in the early 13th century, practically overnight, by international imports.

According to a new study published in the peer-reviewed journal Antiquity, ancient cod bones found in 95 different excavations in and around the city of London suggest that the global fish trade exploded around 800 years ago.

Analyzing these bones for date and origin, researchers from University College London (UCL), Cambridge, and the University of Central Lancashire (UCLan) were able to identify a sudden change in the prevalence of imported fish.

"It's a truly remarkable shift. We had expected a gradual increase in imports as demand grew along with the city's medieval population - thought to have quadrupled between AD 1100 and AD 1300," lead author Dr David Orton of UCL said in a statement. "But this is something else: evidence for locally caught cod drops off suddenly when the imports come in."

According to the study, the researchers determined the organ of different layers of fish bone based on both chemical analysis and simple observation. Headless bones, the researchers explain, often mean that they were shipped from distant waters, as Cod were traditionally decapitated as part of the preservation process for long-distance transport. Local fish, however, were disposed of with their heads on. To support this theory, the researchers also chemically analyzed sample vertebrate from the different groups, matching biochemical signature with bones of fish from likely sources.

According to the study, the shift to headless vertebrate bones was rapid and extensive in London, indicating a boom in the international fish trade.

"This discovery clarifies an important rapid shift in the demand for distant food resources of one of Europe's major centres," wrote co-author James Barrett of Cambridge. "It shows us that local fishing could no longer keep up with this demand, that London's ecological footprint was increasingly extensive and that growing trade connections were making the world a smaller place."

While it remains unclear how exactly the global fishing trade impacted local fishing industries, the researchers claim that these findings can help historians better understand the development of international trade in general prior to the Black Death's devastating impact on Europe.

The study was published in Antiquity.