WHERE HAVE ALL THE FISH GONE?
A decline in a once-productive venue may be down to the natural cycle of life although misfortune and human intervention may also be to blame
AQUESTION that comes up all the time is: “Why is it that a once prolific fishery now appears to be a shadow of its former self?” While this often refers to river venues, it can just as easily apply to natural stillwaters and although it is perhaps the most fundamental question that we anglers can ask, it is also one of the most complex to answer. Let’s break this question down into some of its key components. One piece of this jigsaw, and one that has been little studied, is the question how does the number of fish in a venue relate to the quality of sport? Obviously, this will depend upon how catchable the fish are. Are they hungry? Are there areas where they cannot be fished for? Do they mainly feed at night? All of these factors will vary and it would only be useful to look at this over a period of time, perhaps years, to determine the relationship between catches and fish present. Catch data is a very underused, and it can certainly give an indication of how a fishery is perceived. It can, though, be biased. If anglers stop visiting a stretch of river because it is perceived to be in decline then it might be impossible to gain enough information. Fish populations are never static, either in space or time. Fish will move around and in some years there will be more catchable fish than in others. What if, for example, the bulk of 100 chub migrate upstream to a different river stretch? The fishing is going to go rapidly downhill, but there probably isn’t a lot that can be done about it. On small stillwaters the situation is likely to be different. Those fish aren’t able to go anywhere so if catches tail-off over time it is possible that the fish population may be waning. This could be mitigated by stocking, as long as it is clear that the fish have died and that there is no underlying problem with the fishery. This brings us to temporal (time) changes in fish populations. Fish don’t live forever, but they can live for many years, often much longer than we expect. Roach may live into their teens, whereas bream, tench and barbel can live for 30 years or more. Of all coarse fish, carp can be the longest lived, with some fish having almost reached pensionable age! It may take young fish many years to reach a catchable size, however. Have you ever wondered why it is rare to catch a barbel or tench weighing less than a pound in a natural
fishery? The young of both of these species have a specific diet and habitat preference, which makes them extremely difficult to catch on conventional gear. The fish may be five years old or more before they start to show up in catches. Small roach, however, can reach a catchable size in a year. Very often, the fish that we catch are mainly from just one or two successful years of spawning. Individual fish lay hundreds of thousands of eggs so when conditions for their early survival are good the year-class can be very strong. Yet, these delicate tiny fish need conditions to be just right, and so a flood in mid-summer, a long, cold winter or a cool summer can lead to few surviving. So we start fishing our stretch of river when the chub fishing is already good and the fish, averaging a couple of pounds, could already be 10 years old. Over time the fishing changes, becoming a little harder but the fish get bigger. Rather than catching bags of fish, the norm becomes just a couple, and we have to fish into dark to catch them. This is okay because now they are five-pounders and worth the effort. Then, 10 years have flown by and ‘suddenly’ the chub are no more. What has actually happened is that one strong year class has gradually aged, grown larger, but each year some have died off, until eventually the population is so low that the chances of catching even one fish are slim. With luck, at some point the remaining chub will spawn successfully and the next strong year class will start to come through. There could well be several years between the peak of one year class and the next getting to a catchable size. Alternatively, the decreasing chub population may leave more food for young dace so, over time, the fishery switches to a different species. So, fish populations are never static and there are many reasons why the fishing changes. These changes may occur relatively slowly over decades, and superimposed on the natural fluctuations in fish numbers might be human-induced changes such as habitat removal for flood defence, pollution, siltation and other factors. On the face of it, wanting a fishery to remain on top form year after year is something that we all wish for, but given the complexity of fish populations is something that is never seen in natural fisheries. Change, often over years, happens, and it is rarely possible to turn the clock back.
“Often, the fish we catch are from one or two successful years of spawning”