New Research Paints a Clearer Picture of Humans’ Impact on a Common Fish Species

ANTH researcher and colleagues looked at the inner ear bones of centuries-old cod fish to observe changes that coincide with increased fishing efforts 

According to new research published in Science Advances, the cod you eat today likely came from a fish much smaller and younger than its ancestors—and humans are at least partially to blame.

Looking at the inner ear bones of the centuries-old cod—collected and analyzed at 12 former fish production sites in Iceland that date back to the second half of the 9th century through to the 19th century—Department of Anthropology Associate Professor George Hambrecht and colleagues found that cod who lived during the 10th–12th centuries were, on average, 25% larger and up to three times older than the cod we see and eat today.

The significance of this finding stretches beyond your dollar not going as far as it would have for your predecessors. Decisions about how much cod fishing is globally permitted are based on what a “normal” or “baseline” cod population is, and present decisions about what’s “normal” are being made using data that is only 100-150 years old—a potentially inaccurate assessment of just how significantly the population has shrunk over time.

“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. 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,” Hambrecht explained.

The research team—which consists of 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 instead only when there were increased demands for the fish from European markets in the 14th and 15th centuries. At that time, there were more cod deaths caused by humans than there were deaths by natural causes, or related to any 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 named the Principal Investigator.

“This study is part of a much larger movement in archaeology that is mobilizing the past to help deal with the present,” said Hambrecht. “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.”

Photo by iStock

Published on Fri, Feb 7, 2025 - 5:56PM