Fishing associations in Lower Saxony see many fish species threatened by global warming. "The effects of climate change on the fish are diverse," says Jens Salva, biologist from the fishing association in the Weser-Ems state fishing association. It has been a gradual process that has been going on for years. The water levels in the smaller rivers are problematic. In the past, there was a heavier runoff in small streams in summer and the groundwater level was higher. "Many small streams now dry up in summer because there isn't enough rain. Where there's no water, there's no fish," says Salva.
Trout, for example, need colder water temperatures. They can be found in streams that are cool in summer. But if the discharges are only low in the dry summers, the water heats up faster. "Warm water binds less oxygen and the oxygen content drops. This means stress for the fish, they migrate, become ill or die," explains the fish and aquatic biologist.
The bank areas of many standing water bodies and meadow ditches were also becoming increasingly dry, often as early as spring. This is where the fish swim to reproduce. They can no longer do that, and that has an impact on the populations. The available space for fish in shallow water is becoming less. "The number of fish deaths is growing. We are called more often by member associations or municipalities because fish are on the water surface, breathing heavily," reports Salva.
In river and lake fishing, the composition of the species changes, explains Steffen Göckemeyer, fishing advisor to the Lower Saxony State Fishing Association. Warm-water species such as European catfish benefit from the increased water temperatures, while cold-water species such as trout are disadvantaged. Fish losses due to feeding damage are increasing.
The carp pond economy is initially favored by mild winters, the growth phases of the carp are longer, says Göckemeyer. But here, too, summers that are too warm in connection with little precipitation lead to water shortages and low oxygen levels in the water. There would be emergency fishing, otherwise the animals would die. As a result of the reduced precipitation in spring, not all ponds of a fish farm would be dammed up and used.
The state fishing associations are increasingly taking care of the renaturation of water bodies. There are a number of projects. "For example, we create tributaries on large rivers such as the Ems or shallow water zones. And we take care of the rerouting of streams," says Salva. This means that streams that have been straightened are looped again.
The fish and water biologist demands that politicians do more for the rivers. The aim is to keep the water in the area. It starts with the smallest of ditches. The water must remain in the ground and must not be drained off as quickly as has been the case for decades.
Lower Saxony State Fishing Association Fishing Association in the Weser-Ems State Fishing Association e.V.