Longtime Danish fisherman Kalle Jacobsen has been forced to sell his fishing boat and retire after six decades at sea, as unprecedented levels of oxygen depletion devastate marine life and Denmark’s coastal fisheries. The two main factors for this environmental collapse are nutrient pollution and climate change, leaving the once rich waters of Kattegat nearly dead.
A Lifetime on the Water Comes to an End
Kalle Jacobsen has spent 61 years making a living from the sea around Hundested, a harbor town in northern Denmark. Over that time, he has witnessed many highs and lows in the fishing industry. But today, he is facing a reckoning unlike anything he has seen before. The once-rich waters of the Kattegat are now nearly lifeless, battered by rising levels of oxygen depletion that suffocate fish and other marine animals.
Jacobsen, 75, has reluctantly put his beloved fishing boat “Charlotte” – named after his daughter – up for sale. After more than 20 years navigating the vessel, he is stepping back, unable to continue a profession that has become economically and ecologically impossible. For Jacobsen, this is far more than a career ending; it is the loss of his life’s identity.
Oxygen Depletion Reaches 23-Year High
The driving force behind Jacobsen’s retirement isn’t age or changing regulations, it’s the water itself. A new report from the Department of Ecoscience at Aarhus University reveals that oxygen depletion, or “hypoxia,” in Danish coastal waters is now at its worst level in 23 years. Without sufficient oxygen in the water, fish, mussels, and even bottom-dwelling worms cannot survive.
Oxygen levels are particularly low in the southern Kattegat, exactly where Jacobsen has fished for the bulk of his career. The situation is even more dire in northern Øresund near the island of Hven, where the last professional fisherman in Helsingør, Søren Jacobsen, is fighting the same battle. Around 17,000 square kilometers of coastal seabed in Danish waters are now affected by oxygen depletion, according to the report.
Root Causes to Denmark’s Coastal Fisheries Crisis: Agriculture and Climate
Two main factors are fuelling this environmental collapse: nutrient pollution and climate change. Large volumes of nitrogen and phosphorus enter the water through agricultural runoff, wastewater, and natural processes. These nutrients promote algae growth, which eventually dies, sinks, and decomposes, consuming oxygen in the process.
At the same time, rising global temperatures are playing a significant role. Warmer waters hold less oxygen, and higher temperatures increase the decomposition rate of algae, making matters worse. Scientists from Aarhus University warn that the combination of excess nutrients and warming seas is a lethal one for marine ecosystems.
Toxic Fallout on the Seabed
The consequences of declining oxygen go beyond the immediate loss of fish. Prolonged oxygen depletion causes the seabed to release toxic hydrogen sulfide gas. This compound is deadly to marine organisms and makes it even harder for life to return once oxygen conditions improve. Creatures that cannot relocate, like clams, sea worms, and some fish, simply die, and larger predators have no food left to sustain themselves.
Denmark’s Coastal Fisheries: A Dying Trade
These ecological changes are also shaking the foundations of Denmark’s coastal fisheries and traditional fishing industry. For a country with a long maritime history, the decline of coastal fisheries symbolizes more than economic hardship, it signals cultural loss.
Søren Jacobsen, who operates in Øresund, had hoped his son would one day take over the family business. Now, he’s uncertain whether that dream can live on. If the current trend continues, entire generations of Danish coastal fishermen could soon vanish.
Denmark currently has fewer than 2,000 registered full-time fishermen, down from over 10,000 in the 1980s. The environmental crisis adds further pressure to the already shrinking sector of Denmark’s coastal fisheries, which has also faced reduced quotas, stricter regulations, and competition from larger commercial fleets.
Uncertain Future
Marine scientists warn that reversing the oxygen depletion crisis will take significant and sustained efforts. Reducing nutrient outflows from agriculture and improving wastewater treatment infrastructure are vital steps. Additionally, addressing the root causes of climate change remains essential for preventing further decline.
Yet, for fishermen like Kalle and Søren Jacobsen, those solutions may come too late. Their way of life, shaped by salty winds and early mornings at sea, is fading along with the vibrant underwater ecosystems that once sustained them.
The ocean has long been the soul of Denmark’s coastal communities, but today, in too many places, it is silent.
