Thermoclines and winter carp

Malcolm,
An excellent article. I've tried to understand thermoclines from Walker's writing.

My questions to you are;
At what temperatures do you catch carp in winter? I suggest very little carp activity at temperatures as low as 4 degrees C. More like 10 degrees plus.

What depths are you fishing? Thermoclines are usually found at greater than 20 feet.

You're definitely onto something in that carp seem to find the warmest water and spend time there, and if temperatures are high enough, feed there. How they do this is hard to explain. Warmer water is less dense therefore easier to swim in?

Our winter carp man must be Jim Gibbinson, perhaps he will comment.

You can create a thermocline in your bath it just won't last very long.

Thermoclines have a limited impact on fishing as they don't last for any length of time. They only become relevant in very deep waters or during winter periods of prolonged high pressure with no wind.

Also, before the layers disperse the wind causes them to tilt so that the warm top layer (in summer) lies along the leeward bank. Which is one reason for fishing into the wind.

An interesting article, Malcolm.

As Malcolm and others have pointed out, a thermocline only occurs in very deep waters. Surface area is relevant, too, in that in a large, deep pit (or lake, reservoir or W.H.Y.)the thermocline will be located at shallower depth than in a small, deep pit - this is a consequence of wind-induced rotational flow.

In much shallower waters, there is thermal stratification, (as distinct from the presence of a thermocline) which other than when hydrogen bonding occurs, results in the warmest water being near the surface (subject to wind-tilting and/or mingling as a result of rotational flow.

The likelihood of there being a layer of water at a more-or-less constant 39.4C (as a consequence of hydrogen bonding)depends on depth and wind. In most waters, I imagine it would require a fairly prolonged period of extremely cold, still weather to create this effect - or a period of ice-cover.

The extent to which carp will move from one thermal layer to another in order to feed is an interesting question; my impression is that they are generally reluctant to do so. And it's not only temperature adjustment that might be necessary, but an equalising of pressure via the swim-bladder, too.

Thanks for the comments chaps!

Mark, I think your right in that carp won't feed at all below a certain temperature and, to a degree, will go into a kind of dormant state, and I also think this may vary between fish species. Exactly what that is though, I cannot say.

One large pit I know has depths up to 30 feet (rumoured to be deeper in places) and here the thermocline is normally found between approx 15ft and 25ft, but this is in the warmer months! In winter I've found a variation in temperatures at different depths, but obviously not to the same extent.

The point Jim makes re: their apparent reluctance to move from one thermal layer to another is very interesting, and emphasises the need to find the level at which they are comfortable when trying to catch them.

Would'nt the equalising of the pressure in the swim bladder be an automatic process though? Even at colder temperatures? So by temporarily venturing into another thermal layer for a nosh-up, the carp would not suffer at all!

Carp can equalise pressure in the swim bladder by means of ducts direct from the digestive tract - in effect by gulping or burping - so they are capable of making such adjustments in quite a short period of time; it's not instantaneous, though.

Perch and pike can only make such adjustments via diffusion from the blood, so the process takes much longer - which is why perch or pike caught in deep water can suffer distress. They may even die.

I'm not sure what the lowest temperature might be at which carp will feed (or CAN feed, which is another matter entirely). My rule of thumb is that all the time the water remains "bendy", we're in with a chance. The deciding factor on whether I will go fishing, therefore, becomes a matter of personal comfort (if a very cold wind is forecast, or heavy rain, I'll stay at home). Safety comes into it, too - I'll not go when the roads are dangerous due to ice or fog - although when I was younger and dafter I did!

In short, I've caught winter carp in all conditions in which I am prepared to fish: and that includes cat-ice in the margins and snow on the ground. Generally, though, I'm happiest when it's relatively benign and I can enjoy being by the waterside.

Sorry Malc, only just read this - superb and very interesting. I'll be picking your brains in Valdore. Keep em coming mate.

Brains? Moi?

I understand that thermoclines usually only exist in spring/summer/autumn in very deep lakes. The thermocline is a narrow layer of water where there is a rapid change in temperature from the top of the layer to the bottom of the layer - if you like, it's a thin sandwich filling between a warm surface layer and a cold bottom layer.

Water has a peculiar property - at temperature above 4 degrees C, warm water is less dense than cooler water, so the warmer water is in the upper level of the lake, the cooler water is in the lower level. If the lake is deep enough (I think its 20ft plus) there is further stratification of water layers, so there is the warm upper layer, then the thermocline, then the cold lower layer.

When the water temperature is 4 degs or below, its molecular structure changes and the coldest water floats to the top. That's why ice forms on the surface of the water.

**** Walker wrote about the subject in his book "Stillwater Angling". He made some revisions in later editions, adding that"it has been assumed that this phenomenon (of thermoclines)is a factor which anglers have to contend with in every sort of pond or lake. This in fact is not the case; it is only in quite large lakes and reservoirs having depths in excess of 15 or 20ft where a cold lower layer of water exists as late in the year as June. In shallower and smaller waters it has disappeared well before this time"

Nicely summarised, Keith. Spot on.

I think that maybe people are confusing fishing the thermocline, with fishing where the carp feel most comfortable.
People probably assume that this is dependant on temperature, when it is most likely much more a case of pressure (water, not angler).

The carp will sit where they feel most comfortable, if that is mid-water, then so be it.

Difficult to be certain what the "comfort zone" fators are as they relate to carp: temperature, water pressure, dissolved oxygen and food availability might all play their part. Can change through the day, too - I recall several weeks of catching margin fish in the 9-12ft band up to about 4.00pm (high summer), with post-4.00pm captures coming from the 12-15ft band (the water had an average depth of about 20ft). Whether fish moved deeper, or back up the slope to shallower water after dark I've no way of knowing because then, as now, I only fished during the saytime.

This matter of "vertical location", for want of a better phrase, is an interesting subject, and one that can be very important in that we can be fishing the correct swim but blank because we are fishing at the wrong depth.

PS. I realise that my foregoing comments are not directly relevant to this thread which is about winter fishing, but I thought it of sufficient interest to include it.

not totally relevant Jim, but probably the most important.

99% of carpers fish nailed to the deck or 2" above it, which is fine if the carp are that far below the surface, e.g. if the carp are on the bottom in a 6' deep swim, but what if your swim is 12'?
Providing it's clean gravel, then most will still put their bait on the bottom.