Hot Weather : Fish Suffer

Conservation of fish stocks during extended hot weather.

As you are well aware the weather of late has been exceptionally warm, and is forecast to remain unchanged for the coming weeks. The result of this is the low water levels and the increase in the weed growth in the river system.

While we all love to go fishing, we must try to limit any potential negative impact on fish stocks caused through angling. Therefore, we would urge our members and the wider angling community to seriously consider the possible risks to fish health from the current extended period of hot weather and its effect on reducing dissolved oxygen (D.O.) in our rivers to potentially, dangerously low levels.

Water has a specific level for D.O. (dissolved oxygen) it can hold. This level can be affected by several factors including water temperature, atmospheric pressure, salinity, aquatic vegetation etc. Given our current weather it is water temperature that is causing concern as at higher temperatures D.O. will fall considerably.

We must also remember that in rivers with substantial aquatic vegetation there is a daily cycle as plants photosynthesise which causes falls in D.O. during the night.

British rivers usually carry good levels of D.O. because of our temperate climate. While some of our native freshwater species like Salmonoids have evolved to require these higher levels of D.O. than other species, in these conditions these fish can have difficulty recovering from being caught at low D.O. levels.

This is because at low D.O. levels fish can’t quickly replenish Oxygen in their bloodstream. Given this we must be responsible and ensure that D.O. levels are suitable for not just the fishes everyday survival but for their full recovery after being caught by an angler.

As we see water temperatures pushing beyond 20°C the margin of safety between the minimum D.O. requirements for full recovery of these species and the level available in the water is dramatically reduced and the physical exertion of the fight can lead to fish mortalities even after appearing to be recovered and swimming away.

Therefore, we would ask all our fellow anglers to please be aware and fully consider this if you are planning fishing for these types of fish, and whether it may be best for fish safety and conservation to avoid the risk until such time as we get a significant change in the weather conditions.

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