Research Finds We’re Eating Younger, Smaller Cod—and That Matters

That bag of cod fillets you pick up at the grocer comes from fish much likely much smaller and younger than its ancestors that were eaten by people in the distant past, according to a new study that includes a University of Maryland anthropologist.

In research published Wednesday in Science Advances, Associate Professor George Hambrecht and colleagues looked at the inner ear bones of cod collected and analyzed at 12 former fish production sites in Iceland dating from the second half of the 9th century through the 19th century. They found that cod from the 10^th to 12th centuries were, on average, 25% larger and up to three times older than the cod we see and eat today.

The history of cod stocks can be an important tool informing present-day management of the species to ensure it remains a viable food source. Decisions about how much cod fishing is globally permitted are based on what’s considered a “normal” or “baseline” cod population, but the definition of normal is based on data only 100-150 years old. This leads to a potentially inaccurate assessment of just how significantly the fish have shrunk over time, Hambrecht said.

“We can’t accurately determine the rate of change and impact on a fish population, or any other resource we are harvesting, without knowing what the state of a population was like before major human impacts,” he said. “Our project is measuring when we can see the first human impacts on Icelandic cod, as well as gathering data on what that population looked like before those human impacts.”

The research team—which includes experts from the University of Iceland, the University of Alaska, Northeastern University, Queens College, CUNY and more—also found that the noticeable changes in cod populations didn’t start when the Viking populations fished for the species in the 9th century, but only when demand for the fish from European markets began to rise in the 14th and 15th centuries. At that time, there were more cod deaths caused by fishing than by natural causes or environmental factors.

“This is an extremely important finding both for understanding the scope of historical fishing and for estimating the natural mortality rate of cod stocks, which is crucial for modern stock assessments. Until now, it has been impossible to verify what mortality rates were before fishing began," said Guðbjörg Ásta Ólafsdóttir, a biologist at the University of Iceland and co-author of the paper.

This study was supported by a $1,750,000 grant from the National Science Foundation, for which Hambrecht is the principal investigator. It is part of a larger movement in archaeology that is leveraging study of the past to help deal with problems of the present.

“Today, data from archaeological and historical sources can help us address new and novel problems in ways that we could not have anticipated when I first started excavating,” Hambrecht said.