Stocking Densities
Whilst fishing is a ‘natural’ pursuit it is often guided by ourhand in an attempt to improve the sport. This may be changing thespecies present or increasing the biomass of fish in the particularwater. The act of stocking a water however brings with itconservation and commercial considerations. Changing the biodiversityof a water can adversely affect those species already present and insome cases it will affect the newly introduced species.
The following documents look at the moralities and conservationissues as well as the practical issues surrounding the stocking ofcoarse fish and the affect of commercial pressures to ‘overstock’waters. These discussion documents have been prepared for the SACGand we would welcome your comments on them.
A THREAT TO THE SPORT?
By Keith Barker
Fishing is a natural pursuit. In essence it is the attempt tocapture wild creatures and return them unharmed to their environment- unless retained for consumption, as with trout and salmon. Withinthis attempt we deliberately restrict our approach and introducelimits as to the acceptability of our methods. Angling is not thesame as commercial fish gathering because the method, approach andphilosophy are different. We use rods rather than trawl nets orexplosives because removing the fish from the water by any possiblemeans is not an angling consideration. We angle for fish that havesome necessary part to play in the equation and which are not merelypegs or counters at our complete behest. We pursue fish that havesome ‘choice’ as to whether or not to accept our bait and which aredeceived by our presentational skills. Where would be the anglingskill, or fidelity to the generally accepted principles of the sport,if any bait, no matter how clumsily presented, was always taken by afish at every cast?
In most waters, historically, such readily caught fish have notbeen common but there is a steadily developing transformation takingplace – the ‘bagging-up’ lake. Sometimes such waters aredisparagingly referred to as ‘carp puddles’ or ‘muddy holes’ butcould such waters constitute a threat to the sport of angling? Ifsuch a threat does exist then it would be strangely ironic for theintent of such waters is to make anglers more successful. Successhere, of course, being measured solely in terms of how many fish canbe caught in any given time and how ‘easy’ they prove to be in thecatching.
The means to achieve angling success, in these terms, can readilybe explained. By overstocking any specific acreage of water, beyondwhat the water’s natural food stocks can sustain, the fish have nochoice but to become dependent on the food sources provided byanglers in the form of groundbait and hookbaits. Carp appear to bethe ideal fish for such a distortion of nature’s intent for they aregenerally quite hardy, cheap, grow rapidly and acquire a good size -all important considerations on a ‘bagging’ water, especially ifcompounded by the purposes of match angling.
We cannot refer to any objective and absolute reference withregard to such massively overstocked waters to determine whether ornot they contravene the fundamental tenets of the sport, but we canask questions about their existence. Whilst the ‘fish-a-chuck’mentality is evidently popular with many anglers (or such ‘bagging’waters would not exist), how should this be judged when set againstthe traditionally accepted view of angling being a worthy contestbetween angler and fish?
Angling is a hunting sport. It is fundamentally different,however, from the hunting that uses a gun, bow and arrow, spear orblow dart. In all forms of ‘missile’ hunting the hunter only requiresof the quarry that it be visible and within range. No furtherco-operation from the target is needed; the rest of the process beingthe domain of the hunter, dependent upon his/her skill and a degreeof luck perhaps. Most angling does not need sight of the quarry butit does need the proximity of the fish for the process to have anychance of success. Having, by one means or another, brought the fishclose to our angling trap we then have to rely upon the co-operationof the fish to complete a successful sequence leading to hooking.Angling skill manifests itself, thus far, in getting the fish near abait, presenting the bait in such a manner as to allay the fish’ssuspicion and in providing a bait attractive enough to be taken. Ifany one of the elements fails then the whole process fails. In theend, hooking success depends upon the fish. Anglers can prepare thecircumstances but the circle has to be completed by the fish. Beyondthis there is skill required in playing and landing the hooked fishbut this aspect is common to all waters, whether ‘natural’ or’bagging’.
In the past it has been a general belief that the degree ofuncertainty within this hooking process (and each of the elementsleading to it) has been what has made angling a sport which isuniquely different to other forms of hunting or commercial fishing.The question arises, however, as to where the pitting of wits existson a water where the fish cannot hide, either because of a lack ofspace or because they are in such extra-ordinary competition for foodthat they must forage more recklessly and less selectively thannature fitted them to do? There is an aspect of relativity here foranglers have, over many years, tampered with fish stocks in waters.At what point, though, does ‘acceptable’ fishery management (as in atraditional sense) stray into being an ‘unacceptable’ one thatsubjectively perverts angling from being a sport into being afish-getting exercise? Failing any other objective measure we need tolook to advice from science as to what constitutes a healthy andnatural environment for fish to live in. This means that, amongstother things, we need to heed advice on recommended stockingdensities. The closer we can approximate to nature’s levels, asmeasured by environmental scientists, then the more confident we canfeel that we are not straying too far from this facet of angling’sfundamental principles.
This should not be taken to be a plea for an end to fish stockingnor for an end to the use of groundbait and baits that supplementnatural foodstuffs in lakes. Yet whenever we have a situation wherebya fish has little choice (either because of hunger, competition orboth) but to take any bait an angler cares to use then we have, Iwould suggest, crossed into the realms of the unsporting.
How could such ‘bagging’ lakes be a threat to angling? They couldlead to an ongoing neglect of rivers that, by their nature, cannot beoverstocked in the same way small ponds and lakes may be. Not onlymight this lead to a decline in angling skill but it could lead toangling clubs giving up their leases on more naturally balancedwaters where the fishing is relatively more demanding and,consequently, underused by anglers. Likewise the same kind of problemcould affect ‘natural’ ponds and lakes where some degree of skillwould still be required to catch fish. It might be argued that ifsuch easy fishing is what anglers want then this is the way thatthings should proceed; part of an inevitable development that catersfor angling’s current and future prospects, wishes and values. Iwould argue that such a development really would be a shortcut to thedemise of angling in the form we have known it hitherto. Tackleresearch would cease effectively and the broad scope of anglingknowledge and experience would atrophy. Boredom and the lack ofchallenge would mean that fishing would become the home of transientparticipants with no significant roots in, or commitment to, thesport. Angling then would be as profound and meaningful as pluckingmagnetic ducks out of a bucket with a cane at the fairground.
Long before this had happened, angling would have lost the basicsympathy that it enjoys amongst non-anglers. Most non-anglers havesome concept of the spirit and sportsmanship that animates anglers.The vision of the lone fanatic, sitting stoically in the rain whilstwaiting for a bite, might be rather simplistic but it does epitomisewhat most people think about angling. Angling at its best is, to mosta noble pursuit because it exhibits virtues that we still value as asociety. If anglers lose this fundamental vision and the sportbecomes just another extension of the get-it-quick outlook on life,where fish are only an incidental commodity, then where wouldangling’s justification or value be – to non-anglers or, indeed, toanglers themselves?
COARSE FISH STOCKING DENSITIES
Guidance notes prepared by Dr Bruno Broughton, FisheriesManagement Consultant.
General Principles
In most productive, stillwater fisheries in Britain, where waterdepths generally are less than about 12-15 feet, it has beendiscovered that the weight of fish which can be supported per unitarea (or fish standing crop) is usually between 250-600lb/acre. Insome coarse fisheries where common (including mirror) carp arepresent in large numbers, the standing crop can exceed 750lb/acre.This information has been obtained as a result of fish populationsurveys, fish rescues on stillwaters which have been de-watered, anddirect counts following total fish kills.
The standing crop is governed by the fishery’s biologicalproductivity, and, this is influenced by water quality, the availableplant nutrients, etc. Providing light can penetrate through thewater, the depth of the fishery and the volume of water are of lesssignificance because the production of natural food items (chieflyaquatic invertebrate) is governed by the area of hard surfaces withinthe fishery – the bed, margins, submerged leaves of aquaticvegetation, etc. The water column supports few invertebrates otherthan small, planktonic animals invertebrates and free-swimming forms,notably Daphnia and similar species.
The figures cited above reflect the ‘natural’ situation, wherefish are reliant on plant and invertebrate food items. However, onmost fisheries anglers’ baits contribute to the diet of fish,enabling the communities to attain larger sizes. On heavily fishedstill waters, where anglers baits and groundbait make a significantcontribution to the diet of fish, fish standing crop figures of 900-1,000lb/acre and more are not unusual.
Carp
Where there is a substantial carp population, these fish competeadversely with other, non-carp species for the supplies ofinvertebrate food. In this situation, carp will ‘out-compete’ otherspecies, which may eventually become emaciated and gradually die outas a result of outbreaks of stress-induced diseases and parasites. Atmany other fisheries, this competition does not begin to becomeimportant until carp comprise a significant proportion (often atleast 40-50 percent) of the total fish biomass. Note, however, thatthis finding does not apply to crucian carp, which for this purposecan be classed as non-carp species.
This competition rarely affects small fish, which rely on aplanktonic diet that carp do not share. However, in order to growlarger than about six or seven inches, species such as bream androach must alter their diet to include larger, bottom dwellinginvertebrates. In coloured, heavily stocked carp fisheries, there maybe large numbers of small, non-carp fish but few of their parents; inclear water fisheries, where the young fish may fail to survive,there may be relatively few non-carp fish of any size.
Most coarse fish have a ‘growing span’ of 12-15 years, after whichthey usually die within a few years. Carp are the main exception, andit is known that they can undergo an extended, non-growing, old agephase of their lives. This enables them to live to ages of 30 yearsin many fisheries, and considerably longer in some situations.
For the majority of coarse fish, the fry which survive during thefirst summer of their lives suffer extensive mortalities in thefollowing winter. The mortality rate tends to be less if the fishhave enjoyed a prolonged period of good summer feeding – notablyduring hot summer weather in fisheries where there is a rich ‘soup’of small planktonic animals.
However, young carp are far more susceptible to wintermortalities. There are total winter kills of first-year carp in mostfisheries, for reasons which are not fully understood. This is whythe number of carp in some fisheries can remain constant for manyyears.
Pike
The deliberate creation of pike fisheries is not particularly easybecause – as a rule of thumb – a stable pike fishery will support apike to prey weight ratio 1:10. It follows that (i) good pikefisheries occur only where there are ample supplies of prey for thepike (i.e. good ‘mixed’ fisheries), and (ii) a good pike fishery mayneed to be 10 times the size of a specimen carp fishery to producecomparable sport.
The transfer of pike inevitably fails unless they have access tosufficient quantities of suitable-sized prey (or they are fed on deadfish). Pike ‘rescued’ from trout fisheries are notoriously vulnerableto premature mortalities, usually within a few months of theirtransfer. Likewise, the introduction of specimen sized pike from’donor’ coarse fisheries often fails. In both cases, the pike seemunable to adjust to their new environment, becoming so emaciatedduring the spring and summer months following their release that theydie sometimes as a consequence of disease.
The release of large-only pike into fisheries where the species isabsent almost always leads to the death of these fish: pike of10-12lb are exclusively female, and in the absence of male pike theyare unable to shed their spawn. Unlike other coarse fish, pike cannotreabsorb their eggs, and will therefore die.
New Lakes
Reasonably shallow, productive, new lakes should be capable ofsupporting – say – 450-600lb/acre of fish by natural means. If theybecome fished intensively, this figure might increase to 800lb ormore as a consequence of the introduction of anglers’ baits andgroundbait on which fish will feed.
An initial stock density of about 250-400lb/acre is appropriate,although this could be enacted through a phased stocking programmespanning several months. This measure should provide scope for thegrowth to larger sizes of the stocked individuals, as well as thesurvival and growth of their offspring.
Fish communities of these orders of magnitude reflect those whichcan develop naturally given the presence of mature fish, adequatespawning sites, spawning success and the subsequent survival andgrowth of their offspring. However, fisheries are able to supportgreater quantities of fish where the fish stocks have been enhancedby introductions.
Over-Stocking
The introduction of unnaturally large quantities of fish intoenclosed waters is a common management ploy which can produce ‘easy’fishing and excellent sport for anglers. However, if anglingintensity is low on such fisheries, the fish will have access torestricted quantities of natural food items and the fish communityoften declines in time through the gradual emaciation and eventualdeath of fish.
Where angling intensity is extremely high, the introduction ofanglers’ bait and groundbait may be sufficient to supplement the dietof the fish, enabling the long-term survival of an unnaturally largefish community. Such fisheries usually occur where common (includingmirror) carp dominate the fish community or comprise the entirestock. The fish standing crop may be maintained in his way at1,200lb/acre or more.
In exceptional circumstances a fish standing crop of1,600-2,000lb+/acre may be achievable. in such cases, though, theremay well be fish mortalities during periods when environmentalconditions are particularly adverse – especially during prolongedheat waves or severe winter weather, when the dissolved oxygen mayfall to critically low concentrations.
Moreover, the fish present in heavily-stocked fisheries aresusceptible to outbreaks of stress-induced diseases and parasiticinfections which sometimes cause substantial mortalities.
The net effect is that the fish community falls to or below thenatural ‘carrying capacity’ of the fishery. Not infrequently, thisstimulates the fishery owner or tenant to restock with additionalfish, and where these introductions are significant this perpetuatesa cycle of:-
overstocking – excellent initial catches – fish mortalities – poorsport – repeat overstocking – good sport again …
These general notes must be used for guidance only. They wereprepared by:
Dr Bruno Broughton B.Sc. (Hons), Ph.D., M.I.F.M.
Fisheries Management Consultant
Trenchard
Lower Bromstead Road
Moreton
Newport
Shropshire TFLO 9DQ.
Tel: 01952 691515; Fax: 01952 691316
