Mortality drives production dynamics of Atlantic cod through 1100 years of commercial fishing

Most edible fish species have been fished for centuries or millennia,
leaving little record or understanding of their population responses prior
to human impact, and thus no baseline for population conservation. Here,
we reconstruct the population dynamics of Atlantic cod, one of the world’s
most harvested fish species, from the pristine state during the Viking era
through more than 1100 years of fishing. Analysis of cod otoliths
recovered during archaeological excavations of Icelandic fish processing
sites revealed that cod in the 10th to 12th centuries were 25% larger and
up to 300% older than modern, despite slower density-dependent growth
rates attributed to the 6-fold increase in abundance. Fishing mortality
came to dominate a time-invariant natural mortality rate and other
population characteristics after the 14th century, with minimal evidence
of environmental effects at the century scale. Despite the absence of
catch records and surveys, biological reference points based on pristine
fish populations are now possible where otolith collections are available.