Below the surface

Fish behaviour is on the change but autumn is one of the best seasons to be out on the bank

Autumn adaptation

Lengthening nights and a crispness in the morning air are sure signs that autumn is on its way and with it our rivers and lakes begin to change in readiness for the colder months that lay ahead.

One of the first changes that occurs is the dying back of weedbeds. Often this is caused by a lack of nutrients in the water caused by the plants using up what is available and the dry conditions ensuring that fresh supplies aren’t washed into the watercourse. this can lead to plants becoming spindly and weak as they strive to grow. eventually, the plants will overstretch themselves and start to break up, leaving clear patches where once the weed was lush and thick.

Similarly, the water will often turn crystal clear as the lack of nutrients reins in the division of algal cells and they too begin to age and die in large numbers. Clear water will often last until either the wind stirs up silt from the bottom of stillwaters, or rain brings extra water into rivers. these clear- water conditions can make fishing tricky, but the effect of wet and windy weather producing better fishing conditions will be heightened.

Extended feeding spells

Water temperatures will also begin to slowly fall as the weeks press on. Daytime air temperatures are likely to be falling, but the longer nights, with their cooler temperatures, also tend to have a knock- on effect. Despite the temperature becoming less optimal, oxygen levels will tend to increase which can lead to improved sport as the fish are able to feed for longer.

Fish also start to alter their behaviour as the conditions change. Young of the year fish, which have been frequenting the weedy shallows for the summer, will start to move into deeper water once the margins are no longer warmer than the main body of water. they will shoal up, as there is safety in numbers, and can often be found around

structure in vast numbers. Growth also stops as the water temperature declines and below a species- specific threshold it will stop altogether. Hopefully these small fish have grown large enough to endure the winter ahead.

Fish location

Adult fish tend not to have such a marked change in their habitat use, but some changes do occur. Often, they will start to feed more during daylight as conditions become more conducive. Many riverine species will start to move downstream towards deeper and slower water, where they overwinter. This tends to be a steady movement occurring over weeks and months, rather than all at once. With the prey fish moving downstream the predators also follow suit and, generally speaking, more fish will be found in deeper stretches of river than during the summer months.

Fish in lakes will also begin to move to deeper water. Whereas during the height of summer a lot of fish will be found in weedbeds, as the plants become less stable and more prone to being dislodged by strong winds, the fish will start to congregate on the weed edges instead. Once again, predators will be quick to follow suit and can often be found here too.

Why some species, such as tench, become much harder to catch as autumn marches on is poorly understood. While these are typically warm- water fish, the conditions are still suitable for them to be feeding. Perhaps they change their behaviour in a different manner to other species. Possibly moving into thicker vegetation, rather than moving out, making them difficult to target.

Natural food supplies

The numbers of larger invertebrates tends to decrease as the year goes on, but because most species live for several years this is not as marked a decline as we sometimes imagine. There is still plenty of natural food available, although it can become more difficult to get hold of. Hatches of emerging adult invertebrates will dwindle away and the larval stages may well spend more time hidden in the substrate, making them more difficult to catch. The diet of roach starts to become more dominated by plant material. This is probably a by- product of how they must feed, because they derive very little benefit from eating plants. Instead, it is probably that they are eating algae from the stems of plants because it contains a myriad of tiny invertebrates, which they swallow long with the green- stuff.

Species that are less adaptable in their diet may begin to struggle to find enough food. Bream, for example, may have to feed harder for longer to satisfy their appetite.

The coming weeks and months are a great time to be on the bank. Everywhere around us the cycle of the seasons continues as it has done for millennia. The fishing is also often at its very best, thanks to the adapting behaviour of the fish and the changing environment. It surely is a fantastic time to be on the bank.

“Oxygen levels will tend to increase which can lead to improved sport ”