On the status of Atlantic cod in the Oslofjord

There are serious concerns about the status of the Atlantic cod ( Gadus morhua ) in the Oslofjord region. However, quantitative estimates of the cod biomass are scarce. Typically, analysis of juvenile fish has been used to assess the state of the cod, and datasets that contain recruited individuals tend to be limited. We here quantify the biomass, with an estimate of uncertainty, over the last 25 years based on a large dataset of commercial landings. By accounting for the number of boat-landing events, we can account for the variation in effort over this period. Our analysis indicates that cod biomass has been reduced by more than 80% from a peak in 2004-2005 to 2018. After 2018, the biomass was further reduced below 10% of the previous levels, but these estimates are more uncertain. Given large public interest and a recent decision to close large areas in the Oslofjord for fishing, our results are highly topical and can serve as a baseline for further investigations into why the cod has collapsed in this area, as well as a contrast to potential future recovery.