Prolonged dry weather can have a detrimental affect on both River and Stillwater Fisheries. When we get a long period without normal levels or rainfall a decrease in water levels can often lead to low dissolved oxygen levels which can put fish at risk, especially during warm weather and where there is a lot of weed growth. Understanding how fish are affected by this is key to running a fishery so we have worked with both the Institute of Fisheries Management and the Environment Agency to put together this short guide.
Know what’s happening with your fishery
One of the key things for any fishery or club who have waters is to plan ahead. It’s essential to prepare for low rainfall and hot conditions rather than suddenly having to react when those conditions occur. It might seem like an obvious thing to say, but it’s really important that you actually know what’s happening at your fishery particularly with regards to water temperatures and dissolved oxygen (DO) levels, so make sure you are regularly checking DO levels. Remember as a result of photosynthesis, water plants and weed produces oxygen during the day, but then actually use up oxygen in the water during the night. This means that in warm conditions, oxygen levels will be at their lowest at first light so this is a good time to take a reading, as it tells you the lowest your DO will get under normal circumstances. As well as decreasing oxygen levels, rising temperatures will cause stress to your fish stocks directly, reducing resilience of fish to other problems and to diseases and parasites.
You also need to be very much on the watch for algal blooms as these can lead to big changes in oxygen levels over a short period of time. It’s also key to be aware of how densely your fishery is stocked, the more crowded the fish are, the more impact low water and hot temperatures will have.
Make sure you have aeration available and know how to use it
If you start to be concerned about reducing DO levels then that’s when it time to use aeration. This could be as simple as having water pumps that can be used for moving water around to specialist aeration equipment such as paddlewheels. Having some aeration equipment is one thing, but do you have enough staff or volunteers trained to use it ? Has it been serviced and tested prior to being needed ? Do you and the rest of your team know how to safely deploy it ? and do you have a plan as to where the best place in the fishery is to use it ? Using some aeration equipment in shallow, silty areas may make things worse as it will kick up large amounts of suspended silt into the water and possibly release other chemicals trapped in the silt. In some emergency circumstances you may be able to call upon the help of your local Environment Agency Fisheries team for additional support with aeration, but if you plan well, this shouldn’t be necessary. The equipment itself needn’t cost a fortune, if your club or fishery is an Angling Trust member then you get 10% off aeration devices from Aquaculture Equipment Ltd. The Environment Agency have made a great video on how to make a cheap Venturi aerator with easy to source components. You can watch the video on YouTube here.
If you had planned to stock fish and conditions are no longer favourable, it is best to delay. Not only will the new fish need to acclimatise to a new fishery, the increased stocking density will also put more pressure on existing stocks.
Let Nature Help
The key to helping river and stillwater fisheries remain more resilient during low water and hot conditions is to let nature help. Avoid too much weed cutting as weed will help river levels and provides shelter and shade for fish and invertebrates. Weed cutting will also disturb the silt and cause further problems. If you do cut weed, avoid piling it on the bankside as the run-off can further reduce dissolved oxygen. Don’t be quick to remove bankside vegetation as this will also provide valuable shelter and shade during warm weather. Sometimes there will be pressure from anglers to cut back overhanging trees and in-river woody debris, but not only does this provide shade, it also provides cover from predators. Fish stocks can be at greater risk from predation by fish eating birds and mammals during low flows, so it pays to leave the cover in place. If you do remove it to make fishing easier, you may very well find that the fish move away to find cover and you will be left with a barren stretch with very few fish to catch.
Fish care by anglers has improved hugely in the last 30 years and now it is rare to see anglers mishandling fish, but it’s worth reminding those that fish your waters that extra care needs to be taken during low water/high temperature conditions. If you have a high number of anglers fishing a relatively small stillwater, it may be a good idea to introduce bait limits. If anglers introduce large amounts of bait, not all of it will be eaten and it will cause more issues as that bait breaks down. Why not include a link to our Blog about How Do Water Temperatures Affect Fish and Fishing on your website to keep anglers informed. Consider asking anglers to refrain from using keepnets and encourage anglers to unhook fish without removing them from the water where it is safe to do so. This is particularly important for species such as barbel, trout and salmon. Because Salmon may already be exhausted from their trip up-river and may be heavy with spawn it is key that anglers who fish for them are aware of best practice guidelines for playing, unhooking and returning fish. This excellent video illustrates these principles very well.
We would like to thank both the Environment Agency and The Institute of Fisheries Management in the creation of this guide.