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

Improve Your Coarse Fishing (UK) - - Tactics -

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”

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