Natural History Of The Meres – Part 2

I finished my last piece by saying the “Why” questions had gained in resonance with me. So in this piece I’d like to explore these in more detail and explain why I feel that the knowledge gained gave me a kind of edge in catching fish more consistently from Marbury and other meres I’ve fish over the last twenty odd years.

Phil’s first tench from Quoisley

The meres of the above region are natural lakes. That is, they were not formed by man, modified in some circumstances yes, but essentially created by a natural episode in the earth’s history, ie, the last glacial period (Ice Age). It is also known that they were all formed at or about the same time, 12 to 15 thousand years ago.

At the end of the last ice age, the earth started to warm up and the ice sheet retreated northwards. As it did so it left large blocks of ice in the hollows of the mere and other regions of the UK. The hollows probably forming because of the weight of epoch ice pressing down on the underlining bedrock. The geology of the mere region is, in the main, sandstone, with other harder rock material around it. Sandstone is one of the softer type of rock strata, therefore it compacts more easily and further than other harder types,thereby being more prone to making hollows. All rock stratas, after the compression of glacial ice, rebound upwards again over time, some types more fully than others.

Subsequently, the blocks of ice that were left in the hollows melted away and formed a lake (mere). It’s also most likely that Marbury, Quoisley and Bar meres, were at one time, not long after the last ice age, one huge lake that spanned several square miles.

Over the millennia since the ice sheet retreated, and the rebound occurred, there has also been the natural processes of succession (life, death and decay of plants and trees) at work. All of which have added many millions of tons of material. In effect this process along with the process of natural drying has raised the surrounding land somewhat, perhaps by as much as a metre. One non-natural factor that has undoubtedly had one of the greatest impacts on the surrounding land is drainage by man. This has greatly assisted the drying out process of the land.

Bar Mere

In the case of Marbury, Quoisley and Bar meres the impact of drainage by man is still evident today. All three meres have a ditching system that connects them to the wider area’s drainage system. If those ditches are allowed to become blocked by silting or over-vegetation, the meres’ level can increase by anything up to a metre. This can have an impact on fish, their spawning and future stock recruitment in several ways. If the water level is beyond what is the seasonal natural baseline there is the distinct possibility that they may spawn above that baseline. A warm dry spring could leave the eggs high and dry before they hatch, due to receding water levels. The most catastrophic event that can befall gravid and ready to spawn fish is ditching work, carried out during or just after spawning, as the level can go down by as much as a metre in two to three days. Marbury, however, is a slightly different case, as it is the deepest of the three named meres, with a lot of its surface area being between 4 – 8 metres deep. Subsequently, a sustained metre increase of water may not permit the water-body to warm up sufficiently over the spring, for spawning to take place at all that year.

As the meres have evolved over the last 12 – 15 thousand years they have gained in some circumstances their own unique characteristics and ecology. I’ll address the characteristics first, as these are the most relevant I think to consistent catches. On the larger and deeper meres of 3m plus, all have at least one shelf and some have two. The shelf, or shelves, are most pronounced on the windward bank. The reasons for this are several fold. On larger waters the wind speed picks up to greater velocities because of the larger distances it can travel, resulting in bigger swells. Which in turn are a destructive eroding force on the windward bank. The swash (rebound of the water back into the mere) carries the eroded sediment out, where it attempts to settle out of suspension on the natural mere sides. However, at the same time this is happening, there are also incoming waves that are attempting to drag the sediment back by virtue of their orbitals.

Figure 1

Orbitals are rotating decreasing circles of water stacked up on top of one another, created by wind action on the water (see Fig. 1. & 2.) As each stack reaches shallow water they start to drag along the bed of the mere, which slows the stack down, causing it to distort. As the largest orbital reaches the bed it forms what we know as a breaking wave. It is this breaking wave that is the destructive eroding force on the bank. In big winter storms the orbital stacks can go down 7-10 feet. The average stack in modest blows is about 3 – 5ft.

Now you know why, when fishing at an angle to a big wind, your line and end tackle can be moved about. This effect on large shallow lakes (5 – 8ft) is greatly magnified and worse, as the orbitals may already be dragging on the bottom of the lake in such conditions. Conversely, on deeper lakes, it is only as they reach the shallower water that they have an impact on your line and tackle.

On meres that are reed-fringed, the impact of wave erosion is far less, as the wave energy is dissipated by them before it gets to the bank.

The culmination of the above actions is that you normally get the first shelf at a depth of 5 – 7ft. The water in this region of the mere is the warmest in the whole water-body during the summer, therefore the largest concentrations of aquatic life are going to be found there. Furthermore, it is most likely that the fish will be there as well.

Figure 2

This knowledge of shelves and food supply I used to devastating effect on Marbury when fishing for the tench. The norm on the mere followed a similar pattern each year, as it does on many waters. From the start of the season and for the next 2 – 3 weeks the tench could be caught quite easily as they were grouped up getting ready for spawning (known as Duffer’s Fortnight). However, after they’d spawned they vanished and few anglers could catch them. With the knowledge of where, and at what distance the shelf was in each swim, and it did vary greatly from swim to swim, I could, and did catch tench almost every trip during the summer, once I’d sussed it out.

The tench on Marbury were very obliging as they feed during the day and rarely at night. This meant I could bait the second shelf for bream and fish at night for them. The bream, it must be said, were also obliging in this respect, as they rarely fed after 10. 30 in the morning. It was also interesting to note, I never caught many tench on the bream shelf, which was in 14 -16 ft of water. Strangely, I never once caught a bream of the tench shelf.

The final question that needs answering is “How was the second 14 -16 ft shelf created?” After giving this question a great deal of thought, I came up with the possibility that at some point in the geological past, the mere’s water level had been a lot lower than it is now, and the same process that created today’s first shelf had created that one as well.

A double from a Cheshire mere

It must be remembered that five – eight thousand years ago, Britain was a far different place than it is today. The whole of the three counties Cheshire, Shropshire and Staffordshire) were heavily forested, and trees during the growing season can take up vast quantities of water. For example, it is known that deciduous trees can pump up to 80 gallons of water an hour. A forest the size of the one that covered the area at that time would also act as a sponge during the winter through the rich humus layer that covered the forest floor.

The mere probably started to increase in size when man started to fell the forest for agricultural use. As the forest slowly disappeared the subsequent generations of farmers would have had to install drainage systems on the surrounding land to keep them dry for the crops they were growing. It is also likely that the historical drainage system was channelled into the mere. Whilst this section may seem at odds with the opening glacial/geological section, it is wholly consistent with environmental change over such a time period.

Next week in the final Part 3 – The Ecology of the Meres.