The Øresund Aquarium: “Ridiculous amount of juvenile cod this year”

Published on January 11, 2023

Studies conducted by The Øresund Aquarium show that there is a record number of juvenile cod in Øresund, meanwhile the cod populations in Danish waters in general is close to collapse.

Due to the massive decline in the Baltic Sea cod stocks, a total stop of targeted cod fishing was introduced in 2022 during its spawning period from January 15th to March 30th and for the rest of the year anglers were only allowed to catch a maximum of one cod a day. Investigations conducted by Øresundsakvariet show that the stronger protection of cod means that the number of cod fry and small cod has exploded in Öresund.

In Øresund there has been a ban on trawling since 1932 and it is the only Danish sea area with a healthy and strong cod population. But since the cod stocks in both Kattegatt and the Baltic Sea just north and south of Öresund, are threatened, the fishing restrictions of 2022 also applied to fishing in Öresund. This meant that the large spawning cod in Öresund were protected for the first time ever during their spawning period last winter, according to Øresundsakvariet.

– Over the past 25 years I have not seen as many cod fry in Øresund as this year. We continuously examine the fish population throughout the year by pulling a brood seine net carefully through the eel grass, which acts as nurseries for fish fry such as cod fry. We have done this for over 20 years and were happy when we caught 4-5 cod fry per draft. This year we caught an average of a minimum of 10 times as many,  said Jens Peder Jeppesen, marine biologist and head of the Øresund Aquarium.

– In addition to studies with waders on the coastal bottom environments, we have also continuously studied the coastal seabed over the summer and autumn via night snorkelling with powerful underwater lights and have been delighted to see so many cod fry. In fact, in many eelgrass beds from Copenhagen and up to the north of Helsingør, we have seen more cod fry than we have ever observed before.

– In the Øresund, the cod have an undisturbed seabed with plenty of food and hiding places, and when they arrived at the spawning grounds this winter they were not caught this year, but instead were able to spawn in peace and reproduce the stock, says the aquarium manager.

That there were several large spawning cod in Øresund this winter was confirmed by National Institute of Aquatic Resources, DTU Aqua, at their briefing in June. They reported that during their trips in the first quarter of 2022, a large amount of cod over 45 cm had been registered in Öresund, as well as many medium-sized cod. This indicates that a combination of a trawl-free seabed and a regulation of fishing works when we have to restore the pressured cod population, according to Jens Peder Jeppesen.

– The cod population has far better opportunities to grow in sea areas without bottom trawling. Because when the seabed is repeatedly disturbed by bottom trawling, sea nature and habitats for benthic animals and fish are destroyed. At the same time, the bottom trawl fishery has a large by-catch of e.g. smaller cod that do not survive, he says.