The spring nocturnal habits of tench.

Conservation, Research and Venue Development 3 replies 0 votes 71 views

In March - April it is common to hear reports of tench being caught at night by carp anglers. Tench anglers, who decide to fish into the first hour or so of darkness, are often rewarded with a fish  after a blank day. So what drives this early season behaviour ?

If you search around you will find lots of academic references to tench being a nocturnal species and even in one paper "a strictly nocturnal" species. Personally I think there are two things going on here. The first is that the scientists running a study, although they may have an interest in a particular fish species, it doesn't necessarily mean at the level of the angler and we shouldn't even assume they have significant knowledge of the biology and habits of the fish, especially not in alien environments such as gravel pits. Scientific test species are often chosen for convenience, the authors may not have even basic knowledge of the life style of that species. So when they need to describe their chosen species in a paper they may simply look for a few references elsewhere, If they find a reference to that species being nocturnal they will repeat it, not knowing any better, and so on. So the initial (and wrong) source reference gets repeated and after time, without checking, it becomes common to see tench called nocturnal.

There are lots of examples of how something gets repeated so often people begin to believe it to be true. This phenomenon has even got a name - the illusionary truth effect.  

Now of course young (small) tench may habitually be nocturnal, simply because it's safer for them. There are many predators of small tench and most of them are active at dawn and dusk especially so it's not surprising small tench take cover at these times, which is also one of the reasons we rarely catch the smallest fish. 

The second is that for purely practical reasons laboratory based experiments are often undertaken on small, immature fish, which we know behave differently to fish of the size we target. 

There is one paper that looks specifically at feeding and movement habits of tench and they came to the conclusion that tench were indeed nocturnal and fed at night. But like many studies they only used small fish, in fact fish of only around 90g and because these fish were shown to preferentially feed at night they fell into the trap of assuming all tench did so, thus reinforcing the widely held view - falsely.

However whilst we know not all tench are nocturnal (and not all the time), what drives this seasonal behaviour, on some waters ? We know on some waters, in winter, tench will certainly slow down levels of activity and will seek shelter in dying weed beds and other cover and simply lay up barely moving or feeding, although they may well have a short feeding spell if it's particularly mild. But generally not. If the fish are relying on natural food there's very little around, but the situation maybe different if there are anglers introducing feed through the colder months. Generally the chosen food of tench, largely invertebrates, are more active at dusk, though the night and into dawn and less active during the day. So on a purely "natural" diet they have the best opportunity to feed when light levels drop and their prey is active. Where the fishes normal diet is supplemented by anglers feed the situation may be different.

This doesn't explain what happens at the other end of the season, post spawning,  when the fish can appear to become much harder to catch, but that's for another time. 


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