Understanding The Substrate

In South Africa the main substrates that we find in our dams can vary tremendously, with the opposite extremes being very muddy, soft soils to hard, rocky soils. Understanding the type of substrate you are fishing on is crucial for several reasons, the most obvious one being that certain fish species only occur over certain substrates, namely they are confined to that particular niche. This is often the case in the smaller bream and kurper species. Another reason is to be able to adequately prepare your fishing approach so that you can present your bait optimally and have an effective scent dispersal pattern. When deciding which area to fish noting what the bottom looks like is therefore one of the first important activities to carry out. Rocky substrates always surprise me by the number of carp that will feed over this substrate. That is despite the very soft mouths of these fish, which one would think are prone to being damaged when feeding in such a hard substrate. In one of my home dams, Darlington, large sections of the dam bottom are characterized by rock banks and fields of boulders with shale and mudstone being strewn everywhere with a small amount of shallow soil among the rocks. Yet despite this, these rocky areas holds some excellent carp fishing opportunities. Large expanses of rocky substrate, shown here at Darlington Dam in the Eastern Cape, can deliver surprisingly good carp fishing. Rocky substrates are very easy to use ground feed on, although in my experience fish will sometimes take quite a while to turn onto the baits. The bait is exposed, and scent travels very well. It is highly likely that carp feeding on rocky substrates are eating algae from the rock surfaces as well as waterfleas (Daphnia spp.), and the rock dwelling waterborne nymphs of various aquatic insects such as mayfly, damselfly, dragonfly, and caddis. Unless an external dirty or turbid water source feeds into the dam, most dams with a lot of rock on the bottom are clear, thus light penetration is often very good which encourages bottom weeds which in turn provides a breeding ground for a diversity of aquatic insect larvae. Although most of this article concerns carp, both Smallmouth and Largemouth Yellowfish thrive in rocky and gravelly bottoms. This is partly because it is the natural habitat preference of these stream dwellers, but also because clear water over these substrates allows them to hunt (in the case of the Largemouths) and find the small insect larvae such as caddis that hide under and on the sides of rocks. Rocks also influence the actual water chemistry in the way that they slowly dissolve and cause fluctuations in the water’s pH. Some kinds, such as limestone and shale, have high amounts of Calcium Carbonate which increases the pH and makes the water more basic. I have yet to test how this influences the deterioration of PVA mesh bags, but I am sure that it can influence this, particularly since the bait is resting right against this surface. A sure fact is that pH definitely influences plant growth in these waters. Fish can easily be lost when they wrap the line around large boulders standing in knee-deep water. When fishing on rocky substrates, particularly if the water is clear, you can be certain that fish can be extremely spooky. Using camouflaged clothing, particularly if you are fishing over short distances, can be a distinct advantage, and in addition minimizing your movement to avoid being spotted. Fish will often also tend to hold towards large underwater rock structures. I have had the opportunity to observe some of the behaviour of carp feeding on the rocky substrate of the Von Bach Dam in Namibia, and they seemed not to mind it at all. While fishing from a boat we saw several huge carp suspending over rocky outcrops in the dam and caught a number of these fish on artlure. Many fish were also digging and feeding actively in the gravel within the shallows, thus even though the mouth of carp is soft they are very capable of working this substrate. Sterkfontein Dam is another water with a large amount of rocky substrate but which does not adversely influence both carp and yellowfish who very actively patrol these areas. Yellowfish in particular favour these types of areas. One behavioural aspect of carp on rocky substrates is that they tend to suspend in mid-water a long distance above the bottom. Why this is so I am not sure, but it could certainly be that they are feeding on suspended Daphnia. Lifting baits off the bottom using baits such as floaties and pop – ups, is essential to broadcast their scent more effectively over a rocky substrate or boulder field. An important aspect to bear in mind is that carp feeding on rocky or boulder- strewn substrates cannot move long distances with their heads down while feeding simply because they would bump into the rocks all the time, so they cruise just for short distances, stop over a softer piece of substrate, feed vigorously and then move on. These fish actually spend a lot of time cruising at different depths above the bottom, which is where using a brightly coloured pop-up or floatie is a good tactic to attract the attention of cruising fish. This is one area in which a fishfinder can be invaluable to detect softer areas among the rockier parts of the bottom. All substrates vary in their degree of uniformity. One substrate which is the most non-uniform of all is definitely the rocky one. A graphical demonstration of this it to look at how uneven the bottom is of rivers, and to note that a dam with similar underlying geology is just a slower wearing version of that. Depending on the area of the dam you are fishing, rocks form large boulder outcrops, boulder fields, rock banks, interspersed with flatter areas of finer gravel. This is what gives them one distinct disadvantage, that of hanging up on the bottom. Good areas to fish for carp are always along deeper river courses that have been covered by the dam, but if these old courses are lined with rocky banks, they are near impossible to fish effectively. While constantly hanging up is incredibly frustrating, adapting your approach from bottom-hugging paste baits to using baits that rise above the ground such as floaties, pop-ups, oozers and bread punch can solve the problem. When fishing these conditions I typically switch to using only a single hook on a sliding Rietvlei or inline sliding trace as it not only lessens the chances of hooking up but also reduces the risk of losing a good fish.

Understanding The Substrate

Words: Dr. Gareth Coombs

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