DROUGHT MEDIA BRIEF
MB MG Date / Dyddiad: July 2018
How does drought affect fish?
Extended periods of dry weather can have a severe impact on the health and wellbeing of fish stocks, leading to low water levels in rivers and some lakes and ponds resulting in less water for fish to live in, which in turn causes overcrowding and vulnerability to disease and predators.
Hot, bright weather also increases the risk of algal blooms, which can lead to less oxygen in the water, which in turn causes fish to die.
It is hard to predict the long-term implications of drought on fish, but the overall affect can be significant. Fish numbers fluctuate naturally with varying environmental conditions, however fish populations are robust and have survived severe droughts in the past but may take a long time to recover fully.
Which types of fish are most affected?
Certain types of fish (for example, coarse fish, carp, tench and roach) are more resilient than others, but severe drought will affect all fish.
Salmon, trout and grayling are typically the most vulnerable to low river flows, low levels, high temperatures and water quality, which may prevent them from reaching traditional spawning areas and affect their overall success.
Reduced river levels can affect the amount of living space for young fish. During hot weather, young fish are also particularly vulnerable to losses caused by low oxygen levels.
How will drought affect salmon and trout?
An extended period of drought may reduce salmon and trout numbers in any river. Both depend on good water flows in rivers to help them complete their life cycle.
As flows decline they may find it difficult to swim over weirs and other obstructions due to shallow water.
Salmon and trout are also very sensitive to good water quality and this can decline naturally as temperatures rise and algal blooms take hold in the bright conditions. Slower movement of the rivers can also lead to less oxygen entering the water, further worsening the situation.
I have seen dead fish. Is it because of the drought?
Low flow conditions may be to blame especially if temperatures are high, leading to less oxygen in the water, or if the water level has dropped and the fish are over-crowded. However, some small streams and ponds naturally recede in the summer, so drought may not be a factor. And like all animals, fish may also die from old age, disease, breeding difficulties or a polluted environment.
Signs of distress include: fish staying in one place near the surface of the water and appearing to gasp for air; swimming very slowly in large groups; obvious over-crowding. Dead fish are easy to spot, as they often float on the surface of the water.
Can I still fish in a drought?
It’s usually OK to fish during a drought, but anglers and fishery managers should pay careful attention to how the fish are behaving. If the fish exhibit unusual behaviour then please don’t fish. Fishery managers should consider restricting the use of keep nets and ground baiting during the hottest periods of a drought.
For many salmon and trout anglers, a water temperature 21°C (70°F) has become a round figure that represents the “don’t fish” limit.
NRW is calling on all fishermen to practice catch and release. Remember – all people fishing on C&R principles should:
- • Keep fish in the water at all times – air exposure should be limited to less than 20 seconds
- • Only use methods that are commensurate with good catch and release principles, – barbless hooks and no trebles to facilitate ease of unhooking and returning the fish
- • Ensure the fish has recovered before allowing it to swim away
What is Natural Resources Wales fish rescue policy?
Protecting Wales’ rivers and the wildlife that relies on them is one of the most important jobs that we do.
In certain situations, like large pollution incidents, we can attempt to rescue fish that are at risk of being killed, however this isn’t usually the case when it comes to extreme low flows and high temperatures.
Attempting to move fish has minimal effect on how many fish are killed during a drought as many die from the additional stress of being caught and moved. Bigger fish can usually be successfully moved but the smaller streams in question are usually only home to smaller fish that wouldn’t survive and moving any surviving fish to larger rivers can lead to overpopulation and strain existing fish populations.
We will take a case by case approach to incidents and assess all the potential benefits against the risks.