Hundreds of thousands of pounds worth of fish have been lost – mostly from public or club waters – as mostly shallow lakes just haven’t had enough oxygen levels to cope with the long arctic conditions.
Even major fishery group CEMEX Angling lost prime and valuable carp at two venues..
For more on this story, read this week’s Angler’s Mail magazine, out today, Tuesday, January 11 for one week in all good newsagents and supermarkets.
And below we publish the full Angling Trust factsheet on how to prevent YOUR water losing fish under the ice…
Ice on Your Lake – What does it mean for your stock?
THIS is the third year when many of our lakes have been frozen over and snow covered for long periods. It may yet happen again before the spring of 2011 so be prepared.
Fish kills on many waters are inevitable after such prolonged cold weather and seem to be driven by the duration of the cold period, the depth of the water, sediment loads and the density of fish in the fishery.
Cold weather results in long periods of poor feeding and low growth in fish. They deplete their body reserves of important nutrients, even though they are at a very low metabolic rate because they are cold blooded and at the same temperature as the water. Lethargic fish will often stay at the same place within the lake and the water column and if they are settled on the bottom become targets for parasites and bugs.
The auto immune system in fish shuts down during long cold periods and is slow to recover as water temperature rise. Many of the bugs and pathogens which can damage fish are better adapted to lower temperatures than the fish and so get a head start on growth and activity before the fish as temperatures rise. It is during this lag period that fish are most at risk from diseases.
During the summer months there is plenty of natural food and anglers’ bait available to fish but these rapidly diminish as autumn sets in and fewer anglers are on the banks.
At this time, it is a good idea to start feeding the fish with good quality nutrient rich pellets. Little and often with increasing periods between feeding as temperatures drop, being careful not to overfeed. If the feed is uneaten it will rot off on the lake bed and lead to depleted oxygen levels which in turn will harm the fish.
As soon as a lake freezes over oxygen can no longer be absorbed by the water. The only oxygen available to the fish is already in the water column and the levels of this will reduce over time as fish, plants, sediment and invertebrates all make demands on it.
Light levels under the ice are very low so plants cannot contribute as they normally do and become net users of oxygen even though they are dormant.
If there are open areas and you see fish hanging around at the surface it could be an indicator of low oxygen levels in the rest of the lake. If you see them hanging around just under the ice it probably means the same.
Organic debris, comprising uneaten bait and ground bait, leaf litter, dead plankton, topsoil run-off and lake sediment makes demands on the oxygen in the water as well, so in the autumn you should concentrate on managing those aspects which you can control; removing leaf litter as best you can, removing fallen twigs and branches, preventing soil run-off, and in the spring treat sediment with Siltex (calcium carbonate) to activate the sediment during the warmer months and get the invertebrates working it to reduce volume.
Longer term management of “at risk” waters
WATERS at special risk will be shallow, less than 1.5 metres deep, have high sediment loads and high stock levels.
What to do? Monitor your fish and condition them for winter with additional good quality feed, consider using a probiotic feed during the autumn and early spring, remove sediment and leaf debris before the onset of winter, cut down overhanging vegetation on the southern and western shores.
Managing the vegetation has two benefits; it will reduce the leaf fall into the lake in the autumn and increase the wind action across the lake thus reducing the risk of freezing over and increasing the uptake of atmospheric oxygen by the water.
Try to maintain an ice free area in the fishery by using an air diffuser system to keep the water moving. Sub surface air diffusers will put oxygen into the water column even if the lake is ice bound. Splash aerators can super cool the water because they generate surface disturbance and can be liable to damage by frost and ice.
You don’t have to have an electricity supply any longer to power air diffusers as they are now available with solar power systems.
WHEN thick ice covers the lake, drop the water levels below it by a couple of inches.
That will create an air space and allow oxygen to be taken up through the water surface. It will also allow the poisonous gases created by the bio-system to escape.
Oxygen can be delivered chemically by injecting hydrogen peroxide into the water under the ice. This needs to be done by specialists so speak to your fishery manager, advisor or local EA fisheries team.
Ice breaking can work but you need to avoid causing shock waves, which can damage the fish in extreme circumstances, keep the ice free area open and make it as large as possible to have any real affect. Aeration solutions are a better way of managing the situation and you can find out more from Aquaculture Equipment.
Club or fishery members of the Angling Trust are eligible for a 10% discount on aerators at www.aquacultureequipment.co.uk or call Mark Stockton on 07715 007 964. Simply quote your membership number when you call.