Mild or cold winters, what's best for fisheries?
A curious colleague put this question to me the other day. It got me thinking, which at my age is never a bad thing.
Keeping people fishing
It’s always a good idea to have as many people as possible out fishing. The wider fisheries community doesn’t always shout about the economic value our sport brings to the nation, especially in rural areas. Fishing in cold snowy conditions or on iced up fisheries is for the brave or perhaps the foolish. More people are likely to keep on fishing in a mild winter. Consider our licensees at fisheries like Drayton, Earlswood, Boddington etc. Relying as the bailiffs do on anglers visiting the fishery for their livelihood, a mild spell, especially if it coincides with the Christmas and New Year period can produce a useful income boost at a difficult time of year. I feel sure that anyone whose livelihood depends on the tackle trade feels the same way, preferring a mild winter over a cold, frosty one.
Rivers versus canals
Mild winters are pretty much always accompanied by rain, more often than not somewhat too much of it for comfort. Rivers can be out of bounds for fishing for days, weeks or maybe even months at a time. This is where the nation’s canal network really comes into its own. Unless there are exceptional rainfall conditions when the canal is literally washed away, canals are pretty much always fishable. Rarely do water levels fluctuate and the worst that can happens is the canal becomes very coloured. I have lost count of the number of winter leagues scheduled for river venues that have been moved to the canal following flood conditions.
Keeping cormorants at bay
It has been said that you are not a proper fisheries manager until you have spent 100 consecutive mornings at a fishery scaring cormorants. My personal record was 107 mornings in a row at Boddington back in 2000. I slept like a log on that 108th morning. As my colleague Carl Nichols and licensee John Collins are currently discovering, it’s a tiring business, cormorant scaring. I can image Carl is keeping his fingers crossed for some below zero temperatures and ice cover in the vicinity of Earlswood. Still, it will be worth it in the end.
Dangers of ice cover
I touched on the issue of ice cover in a previous blog. Several weeks of ice cover, especially on heavily stocked shallow stillwaters can lead to big trouble. Levels of dissolved oxygen can drop and levels of carbon dioxide build up. Shortage of oxygen can I believe lead to an increase in ammonia concentrations. The nitrifying bacteria that convert ammonium ions to nitrate ions need a supply of oxygen. Touch wood and maybe I am tempting fate but I have never experienced a problem of this nature on a Trust reservoir, perhaps due to the large size of the waterbody for the average size of the reservoir fisheries in our portfolio must be at least 30 acres
Managing a portfolio of reservoir fisheries with fluctuating water levels brings with it its own unique challenges. Most reservoirs are operational and levels fall each year as the water is used to feed the canal network. Take Boddington Reservoir as an example. With average winter rainfall, it refills four or five times over but in a dry winter it may not even fill up at all. I recall one occasion, I think the winter 1997/1998 when Drayton failed to refill. Luckily the following summer was wetter than average which saved the day.
Fish are cold blooded, having the same temperature as the water in which they swim. Temperate fish have evolved to undergo an annual period of low activity so a cold winter might be better for fish health. One of the worst scenarios for some fish species are fluctuating spring temperatures. Carp may become spawn bound and if the cannot be shed then septicaemia may set in, leading to fish deaths.
Completing the winter fisheries management Programme
Much of the Trust's fisheries management work is undertaken in the October to April period. The ideal conditions for some activity such as canal fish rescues would be cold but not freezing. Once ice cover sets in fisheries management tends to grind to a halt. Some of our work such as fish harvesting and translocation is more efficient when temperatures rise slightly. The reason for this relates to the position of fish in the water column and how they subsequently respond to electrofishing. When they are moribund there is a tendency for them to sink rather than float to the surface.
For many fish species, more than 99% of the fry fail to survive beyond the end of their first winter. In simplistic terms, there is insufficient food available and so most succumb.
In theory warmer winters, accompanied by reasonable light intensities should lead to higher food production and hence better fry survival. I was in Worcester just a few days ago. The New Road cricket ground, home of the legendary Basil D’Oliveira was a metre under water and the Severn a raging torrent. I sometimes wonder how any small fish ever manage to survive in these conditions.
Indeed, many do inevitably get washed out to sea as estuary netsmen often record coarse fish in their catches. However, some fry do always survive in nooks and crannies away from the main flow. And elvers, the young eels about to enter their fourth year of life are now entering the Severn estuary and migrate upriver. They can do this much more easily when the flow of the river is high.
Last date edited: 22 February 2016
About this blog
The team undertake a diverse range of work including looking after the Trust's £40 million worth of fish stocks, managing agreements with over 250 different angling clubs and helping more people, especially youngsters, take up angling on the canal. Follow this blog to keep updated with the thoughts and work of the team.See more blogs from this author