It’s complicated: the relationship between humans and cod

Our relationship with cod hasn't always been plain sailing, and a new project led by a researcher at Trinity College Dublin wants to bring that history into focus.

Prof Poul Holm has secured a prestigious €2.5 million grant from the European Research Council to build a database of information, ranging from the DNA of fish remains excavated from human settlements to the details of ship and monastic logs and even restaurant menus. Why? To figure out how cod fisheries shaped human diets and practices in centuries past.

As a co-founder of the international Census of Marine Life’s History of Marine Animals Project (now the Oceans Past Initiative), Holm is no stranger to combining marine history and science, and he draws on an eclectic mix of data sources. “Anything that will tell us about what used to live in the sea is of interest,” he says.

Data sources include findings from archaeological excavations about what fish people ate. “[You can] dig into kitchen middens or the waste dumps and simply identify what types of fish are there, how many, what would be the calorific value and how it was cooked,” says Holm, who is professor of environmental history at Trinity. “And now we have DNA analysis too, which can tell us where that fish originally came from.”

Valuable clues and figures are also tucked away in written documents such as monastic records, ships logs, market ledgers and restaurant menus, which are mines of information about how widely fish species such as cod and herring were traded and consumed. And maps, too, are useful records of where fish were hauled, notes Holm. “Medieval and early modern maps tell us loads, both about where people fished and how early fishermen experienced the sea.”

Fisheries effects

While fish has been a staple in the European diet for centuries, the finer details of how cod’s availability and popularity waxed and waned still need to be teased out, says Holm. One major shift happens around 1050, when western Europeans apparently switched rapidly from eating freshwater fish to marine fish. “We don’t know for sure why that happened,” he says. “But it is clearly a big choice, and it’s something that will have been momentous for coastal communities.”

However, Holm's main focus for the ERC-funded project is on the later "fish revolution" in Europe, when cod comes into its own. One of the turning points was in 1497, when navigator John Cabot voyaged across the Atlantic and returned with tales of the Grand Banks, a series of submarine plateaus off Newfoundland where the waters teemed with fish.

“In a couple of decades you see people, particularly from southern Europe, going in droves to the Grand Banks, and there is an enormous increase in supplies, which drives down prices, but it is a supply of better-quality fish,” says Holm.

That glut of plentiful cod seems to have had knock-on effects, including perhaps some coastal communities being abandoned around 1600-1650.

“A number of excavations show that some villages were simply totally deserted, and possibly these people were outcompeted by this influx of cheap fish,” says Holm. “That is an indication of the globalising effects of the North Atlantic fisheries.”

The lure of such an easily traded commodity also had political repercussions, he says. “These fish resources were of value, so they drove interest among [monarchs] in exploiting and claiming sovereignty of the fish banks.”

Netting data 

Holm now wants to get a deeper understanding of fisheries and the effects of cod being traded during the medieval and early modern periods. To do this he will gather data from countries around Europe to compare their trends.

“We need a solid empirical basis,” he says. “And one of the outcomes of this project will be a web-based geographical information system, which will provide the public and the historians of the future with easy access to this kind of information.”

Another “intended consequence” of the project is to link data about the abundance of cod with climate change. “This project will for the first time provide the statistical evidence that will enable modellers to look into how climate and fish abundance may be related in the very long run,” says Holm.

“That will have a direct relevance to modern day marine management. We clearly need a much better understanding of the long-term effects of climate change, and that is where history becomes so important: it provides a lens into the past to help us better plan our future.”

READ THE SIGNS: 'OCEAN LITERACY' ON THE MENU

When you think of historical documents, restaurant menus probably don’t top the list, but they could tell us something about our track record of overfishing.

By analysing menus, Prof Poul Holm of Trinity College Dublin can see how we have overstressed some species, such as abalone and the European oyster, right off the table.

“Species that 100 years ago would be so superabundant that we would have them regularly have [disappeared] from menus as well as commercially extinct,” he says.

Even relatively recent changes are apparent if you know how to read the menu, he says. “If you look at menus from the 1980s, you would find that people were eating a lot of fish that was marketed under different names, but once you crack the code you see in the 1980s we begin to eat Patagonian toothfish and the orange roughy fish, which are sourced in the Southern Ocean and flown across the globe to restaurants. But within 10-20 years, these species, which were readily available in menus, suddenly disappear again, because they were being overfished.”

Holm would like to see restaurant menus offer information about species so consumers know more about what’s on their plates.

“We need more ocean literacy,” he says. “Our enjoyment of food should be coupled with better understanding of the impact of food practices. It’s not something that should just be for academic books; this information could also be on your typical menu.”