Aiming at a moving target, a slow hand fails! 75 years of fisheries management in Lake IJsselmeer (the Netherlands)

60 (2008) 21–31www.elsevier.com/locate/seares

Journal of Sea Research

Aiming at a moving target, a slow hand fails! 75 years of fisheriesmanagement in Lake IJsselmeer (the Netherlands)

J.J. de Leeuw a,⁎, W. Dekker a, A.D. Buijse b

a Wageningen IMARES, Institute for Marine Resources and Ecosystem Studies, P.O. Box 68, 1970 AB IJmuiden, the Netherlandsb Deltares, Department of Freshwater Ecology & Water Quality, P.O. Box 85467, 3508 AL Utrecht, the Netherlands

Received 20 October 2007; received in revised form 25 March 2008; accepted 28 March 2008Available online 12 April 2008

Abstract

Lake IJsselmeer is a former estuary in the Netherlands that has been cut off from the sea in 1932. Excessive fishing effort,ongoing declines in landings and low revenues indicate that 75 years of fishery have not been sustainable in terms of socio-economical and ecological stability or avoidance of over-exploitation, despite measures aiming at reductions in fishing effortthroughout the management history. We review the management history with a focus on how responsible fisheries managementdepends on time scales of management decisions, in comparison to time scales of fish population dynamics, and ecologicalchanges. Management actions to improve sustainability have been generally implemented with considerable delays and in smallsteps, to avoid short-term losses in revenues. These actions turned out to be insufficient, as their potential impact was bothinadequate and counteracted over time by technical advances in fisheries and by unforeseen ecological changes.© 2008 Elsevier B.V. All rights reserved.

Keywords: Sustainable fisheries; Over-exploitation; Ecological change; Management decisions; Effort reduction; Co-management

1. Introduction

Managing fisheries in a sustainable manner is notor-iously difficult, especially in complex, more or less open-access fishery systems (Charles, 2001; Caddy and Seij,2005; Hilborn et al., 2005; Beddington et al., 2007; FAO,2007). The complexity arises from (a) multiplicity inobjectives, fishing gears and fish species, (b) dynamics ofthe fish populations and the environment, and (c) socio-economic structures, which all act on different temporaland spatial scales (e.g.,Daan, 1997; Lane and Stephenson,1999; Welcomme, 1999; Orensanz et al., 2004; Caddyand Seij, 2005; Beddington et al., 2007). Such complex

⁎ Corresponding author. Tel.: +31 317 487096; fax: +31 317 487326.E-mail address: [email protected] (J.J. de Leeuw).

1385-1101/$ - see front matter © 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.seares.2008.03.005

systems are often over-exploited, which leads to unpre-dictable, and suboptimal, economic revenues and unstableecosystems (Beddington et al., 2007; Shertzer and Prager,2007). Examples of successful fisheries show thateffective governance in which an adaptive managementcan timely cope with ecological change and uncertaintiesis a prerequisite for sustainable exploitation (Caddy andSeij, 2005; Freon et al., 2005; Hilborn et al., 2005;Hilborn, 2007c).

We review 75 years of fishery management in LakeIJsselmeer, a former estuary (then called “Zuiderzee”) inthe Netherlands. The fish stocks of the lake have beenconsidered over-exploited ever since the area was closedoff from the sea in 1932 by a major dam (“Afsluitdijk”)and became a freshwater lake (Van Densen et al., 1990;Dekker, 1996). From the very beginning, the official

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http://dx.doi.org/10.1016/j.seares.2008.03.005

22 J.J. de Leeuw et al. / Journal of Sea Research 60 (2008) 21–31

national policy has been to reduce fishing effort in order toincrease individual income of fishers and to compensatefor envisaged losses owing to planned land reclamations(Zuiderzeewet 1918). Ecological changes and a shift insociety from a socio-economic towards a more ecosys-tem-based approach posed large challenges to managersto achieve sustainable exploitation. We focus on theimpact of time scales of management decisions, incomparison to time scales of fish population dynamics,and ecological changes on achieving this goal.

2. The ecological setting

Lake IJsselmeer (52°40′N 5°25′E) is a former estuaryin the delta of the River Rhine, that is fed by a lesserbranch, the River IJssel. It became a shallow freshwaterlake (mean depth 4 m with some gullies up to 8 m deep)shortly after the Afsluitdijk fenced off the marine in-fluence through the Wadden Sea in 1932 (Fig. 1). Thecreation of three polders during the 1930s to 1960sreduced the lake-surface area by more than 40% to about

Fig. 1. Map of Lake IJsselmeer and Lake Markermeer indicating years of conHoutribdijk) and polders. Stars indicate cormorant colonies (see Fig. 2).

1900 km2. In 1975, a dam cut off the southern part of thelake (Markermeer, ca. 700 km2), which became lessproductive in terms of primary production and fishproduction (Van Densen et al., 1990; Mous et al., 2003).Water retention time is ca. 6 months in the northern part(IJsselmeer) and 12 months in the southern part (Mar-kermeer). After a period of strong eutrophication in the1960s (phosphate load 7 g m− 2 yr− 1), nutrient reduc-tions in the 1980s led to a sharp drop in phosphateconcentrations (Fig. 2, data Rijkswaterstaat). A highabundance of small-sized fish, which was reinforced bystrong growth overfishing on piscivorous fish (speci-fically perch Perca fluviatilis and pikeperch Stizoste-dion lucioperca; Dekker, 1991, 1996), is attractive forfish-eating water birds. The population of cormorantsPhalacrocorax carbo strongly increased in the 1980s.A stepwise shift of the breeding colonies in the 1990stowards areas with higher fish densities in the northernpart (Fig. 1 and 2, data Rijkswaterstaat) was facilitatedby new breeding options created as a by-product ofnature-enhancement activities. An increase in the

struction of main dams separating water compartments (Afsluitdijk and

Fig. 2. Major environmental changes in IJsselmeer and Markermeer: A. Decline in lake area by embankments and construction of a dam (1976)splitting the lake in two compartments: IJsselmeer and Markermeer. B. Decline in phosphate levels since 1972. Note the immediate drop inMarkermeer after closure of the dam in 1976. C. Number of breeding pairs of cormorants showing northward shift in newly established colonies( Fig. 1). D. Climate change illustrated by increase of periods with water temperatures N20 °C in summer. Data from public monitoring informationcollected by Rijkswaterstaat, Lelystad.

23J.J. de Leeuw et al. / Journal of Sea Research 60 (2008) 21–31

occurrence of high water temperature (Fig. 2) mayhave enhanced shifts in fish communities from cold towarm water species. Especially smelt Osmerus eperla-

Fig. 3. Changes in biomass (cpue) of common fish species in IJsselmeer and M(eel: 3-m electro beam trawl since 1988, no earlier data). Biomass figuresspecies and do not reflect fish production (relatively high in small species li

nus, a small cold-water species and staple food ofpiscivorous fish and birds, showed a strong decline inrecent years (Fig. 3).

arkermeer from annual fish surveys (1966–2006) with 8-m beam trawlwere not corrected for (unknown) differences in catchability betweenke smelt). Data from IMARES.


3. Fish and fisheries

The productive waters of Lake IJsselmeer are exploitedby a multi-species fishery on the dominant fish species(Fig. 3), including small short-lived planktivorous species(smelt; life cycle 1–2 years), larger piscivores (perch andpikeperch; life cycle 4–7 years), benthivores (bream Ab-ramis brama, roach Rutilus rutilus, flounder Plathichtysflesus; life cycle 4–10 years) and long-lived, migratoryspecies (eel Anguilla anguilla; life cycle N10 years).

Eel is economically the most valuable fish (€ 10/kgstandardized to 2006 price level at the fish auction, nosignificant trend in price index since 1960s) and despitethe tenfold decline in yield during the last decades, it isstill the major source of income of the fisheries (Fig. 4). Itslife cycle is at least 10 years, but poorly understood asgrowth rates, migration rates and age of reproduction areextremely variable over the distribution area (Åström andDekker, 2007). Eel has been fished mainly with bottomtrawls until the ban on trawling in 1970, but large fykes (inthe shore zone), and summer fykes (in open water) aremostly being used now. Trawls and fykes are character-ized by having a considerable by-catch (N90% in weight)of especially young fish of other species (Mous et al.,2003). More labour-intensive gears targeting eel (~10%of the total eel landings) include eel boxes (since 1967)and baited hook-and-line while having minimal by-catches. After the dam was closed in 1932, the eel fisheryexpanded under the freshwater conditions during the1930s and 1940s, but reported catches were temporarilylower during World War II (Fig. 5). Since the 1950s,landings have declinedmore than tenfold, although cyclicdynamics with a period of roughly 8–12 years (Fig. 5)have obscured the ongoing decline for most of the time(Dekker, 2004a). The decline of the eel is observed at a

Fig. 4. Decline in number of fishing permits and economic yield (indexed to 21966 and 2006. Data from IMARES.

European scale, especially in the synchronic drop since1980 in glass eel numbers entering continental waters(Moriarty and Dekker, 1997; Dekker, 2004a). The drop infishing yield has been observed already before 1980, andis found throughout Europe (Dekker, 2003), though not asintense as in Lake IJsselmeer (Dekker, 2004a).

The piscivorous perch and pikeperch are caught in amixed gillnet fishery (mainly 101–140 mm stretchedmesh). Until 1963 also two-boat seines were used. Bothspecies have a life cycle that is considerably shorter thaneel, and their numbers are regulated only by local dyna-mics. They become sexually mature after about 2 sum-mers. Pikeperch is fast-growing and enters the fisheryafter 2 years. The majority of commercial landings con-sists of 2–4 year old fish. Pikeperch is more expensivethan perch (€ 6/kg, versus€ 2.50/kg for perch). Perch isusually caught at an age of 4–5 years. Since the twospecies have very different growth characteristics, theoptimal mesh sizes of gillnets differ and therefore har-vesting rates are suboptimal (Buijse, 1992; Buijse et al.,1992). The considerable by-catch of diving water birdsposes a serious ecological problem (Van Eerden et al.,1999; Witteveen+Bos, 2003).

Landings of less valuable species (b€ 1/kg) oftenrepresent by-catches in fykes and gillnets (e.g., bream,roach, and flounder). In addition, a fyke fishery on smeltexists during the short spawning run in early spring, and alarge seine fishery on bream which are sold for stockingfish ponds for recreational fishery. The catch of the latter(live specimens) is largely unreported but has been esti-mated based on inquiries to seine fishers, at N1000 tonnesper year in the 1990s (thereby exceeding the combined eeland perch/pikeperch fishery by weight).

Bream and roach have been dominant species in theannual fish surveys in the 1970s and 1980s but their

006 prices) of commercial fishery on eel, pikeperch and perch between

1 The Ministry responsible for the fisheries has changed its nameover the years. Agriculture, Fisheries, Nature and Food Safety havebeen included in the name, reflecting changes in priority. For clarity,we refer to this as Ministry of Fisheries, although this did not alwaysconform to the official name.

Fig. 5. Landings of eel (A), and pikeperch and perch (B) from Lake IJsselmeer and Lake Markermeer and estimates of fishing effort. The number offishing permits declined since the 1940s. The number of fykes and eel boxes (A) and the number of gill nets (B) increased in the 1970s and 1980s(gear used, reconstructed from inquiries among fishers, Dekker, 1991) and declined stepwise since 1989 (total number of gear allowed, based on gearrestrictions and information of Fisheries Organization PO IJsselmeer). The increase in eel boxes around 1990 reflects a difference between actuallyused (before 1989) and maximum total number present (including extra boxes made prior to inventory and cap of numbers).


numbers have greatly diminished (Fig. 3). The smelt stockis in severe decline since the 1990s, which is possiblyrelated to increasing water temperatures and changes infood conditions. There has been no or only a limitedfishery on smelt since 2004. Ruffe Gymnocephalus cer-nuus is a benthivorous species and has been part of a trashfishery (as by-product of eel trawling) until 1970, but iscurrently of no commercial value. It is the only speciesthriving since the mid-1990s (Fig. 3).

The number of fishing companies has steadily de-creased since 1932 from ca. 1600 fishing companiesto less than 80 in 2006 (exact numbers are not avai-lable as only the number of registered fishing permitsis recorded, see below). The socio-economic positionof the remaining fishing companies has been rela-tively stable at a low level (around social minimum,Taal and De Wilde, 1997), but decreased since 1990(Fig. 4) and dependence on supplementary income(both from fishery on less-valued species like bream,

roach and flounder and from outside the fisheries) hasincreased.

4. The management system

In Lake IJsselmeer, the Ministry1 of Fisheries isresponsible for fishery management and the Ministry ofTransport, Public Works and Water Management forgeneral water management (e.g. quality) and infrastruc-ture. Even during the planning phase for the embankments(Zuiderzeewet 1918), long before the estuary was actuallycut off from the sea, its likely socio-economic conse-quence for the local fishers communities and thelikelihood of over-exploitation of the resources were


recognized. A subsidiary Law (Zuiderzee Steunwet 1925)foresaw the need for subsidies and support for alternativesources of income to reduce fishing activities, but specifictargets have never been set.

The management approach for the lake has beenderived from the open-access fishery characterizing theformer Zuiderzee. Up until today, the fishing rights aresolely owned by the State and the fishery is dominated bythe competition between licensed fishers. Since 1932,national authorities regulated the number of fishing per-mits (until 1996 equating the number of fishing vessels)through license agreements. The ministry has furtherregulated fishing practices (1963) and introduced variousrestrictions on gear types, mesh sizes, minimum legalsizes, fishing time, and fishing areas (see Table 1 foroverview of main management decisions). In 1988, rep-resentatives from fishery organizations, researchers andwater managers (but not from the ministry responsible forfishery management) proposed a management plan thatset targets for drastic effort reductions to enhance thesocio-economic position of the fishery. In addition, a co-management system was proposed to increase the in-volvement of stakeholders inmanagement responsibilities(Visserijschap, 1988). A committee for fishery manage-ment has been established since 1997, but nationalauthorities governed the ultimate responsibilities, and aproper co-management system has not yet been imple-mented. The fishery organization (PO IJsselmeer) maypropose effort restrictions (on days fishing and gear use) in“annual fish plans”, which are then subjected to the licenseagreements of the national authorities and the Europeanpolicy frameworks. External driving forces influencingmanagement decisions include conflicting interests withsports fisheries (e.g., both targeting pikeperch), integralwater management directives influencing nutrient levelsand possibly fish production, and nature conservationissues related to both birds (food reservation, by-catch ingillnets, unsolved issues regarding fish-eating cormor-ants) and fish (by-catch of salmonids from reintroductionprogrammes). New European legislation on water qualityand ecological status (EU Water Framework Directive)and protection of vulnerable habitats and birds (EU Birdsand Habitats Directive) are in the implementation phaseand will further reduce the ecological boundaries forfishing activities in the near future.

5. History of fisheries management

The developments in eel fisheries and gillnet fishe-ries on perch and pikeperch are taken here to illustratethe history of 75 years of fisheries management of LakeIJsselmeer.

For the eel, the increase in the local stock after 1932 ledto increased catches, despite restrictions on fishing season,engine power, and increases in mesh size (Fig. 5, Table 1).Fishery organizations, researchers and national authorities,however, considered the eel stock at risk for over-ex-ploitation (Bossaers, 1987). During World War II regu-lations restricted fishing at night and large areas wereclosed, but an increase in the number of vessels wasstimulated to increase food production. The realised netdecrease in fishing effort led only to a short-term postwarincrease in revenues (Bossaers, 1987). After the restric-tions on fishing time and engine power were largely liftedin the 1950s, Deelder and De Veen (1958) identifiedextreme overfishing of eel based on the length distributionof the catches and decreasing revenues and stressed theneed for drastic effort reductions. In the 1960s, the trawlfishery for eel was also found to interfere with the gillnetfisheries on perch and pikeperch through a large by-catchof pre-recruit percids (Deelder, 1963), which led to acomplete ban on eel trawl fishery in 1970. An increasingnumber of fykes replaced the trawling (Fig. 5). Thesegears, however, also generated a substantial by-catch of(young) target and non-target species (Mous et al., 2003).With the unregulated increase in fykes, the overfishing ofeel and by-catch of young perch and pikeperch persisted,and fish stocks declined further. Moreover, liberalizationofmarketing obligations resulted in a considerable fractionof unreported landings (estimated at about 15%,Nagtegaaland Snel, 1984), thereby increasing uncertainties inlanding statistics and stock development. In 1988, thecommittee of commercial and recreational fishery repre-sentatives and researchers jointly proposed targets forsustainable exploitation and suggested drastic effortreductions by 75% to reverse the ongoing decline in re-venues since the 1950s. From 1989 onwards, effort re-ductions have been carried out that depended on nationalgovernmental financial incentives to cease fishing (buyoutof fishing enterprises and/or gears). Initially, a reduction ofonly 40% was implemented, to avoid a major loss ofincome for the fishing communities. However, this re-duction included surplus nets (i.e. gear that was counted inthe inventory of the mid-1980s but not actually in use) andthe actual reduction has been less than envisaged. Furtherreductions have been carried out in 1997, 2002 and 2005.

For pikeperch and perch, length and age structures ofcommercial landings and population assessment modelsshowed that both species have been subject to severegrowth overfishing, the more so for pikeperch than forperch. Younger life stages (by-catch of trawl and fykes)as well as older life stages (gillnets) showed extremelyhigh fishing mortalities (Willemsen, 1977; Buijse et al.,1992; Dekker, 1991, 1996), and stocks usually become

Table 1Overview of main fisheries management goals, proposed measures, and realised measures in IJsselmeer and Markermeer

Year Main observations andresearch findings

Management goal Operational measure Realised measure/effect

1918/1925 Reduction fisheries (polderswill reduce fishing area)+higher income

Zuiderzeewet (1918)/Zuiderzee Steunwet1925 (license reduction,subsidies)

Ongoing decline in fishingpermits and regulations(see below)

1932–1940 Marine fishery replaced byfreshwater fishery, eelconsidered over-exploiteddespite stock increase

Reduce fisheries on eeland reduce interferencetrawl (eel) and gillnet(perch, pikeperch) fishery

Effort limitation Ban on 2 trawl types(1932). Limitation onengine power(b20 hp, 1934).Reduction in fishingtime. Closed areas fortrawl fishing

Increase minimumlegal size and mesh size

Minimum legal sizeeel 25 to 28 cm (1937),mesh size gillnetspikeperch 95 mm

1940–1945 Compensate foodshortage WWII

Increase fishingenterprises

20% increase vessels,no engine powerlimitationsLarge closed areas andreduced fishing time(war regulations;released after 1945)

1958 Overfishing eel (Deelder &de Veen, 1958)

Effort limitation Limit on engine powerReduction trawlfishing time

1963 By-catch of eeltrawling (Deelder, 1963)

Regulate fishery practices ‘Visserijwet’(Fishery Law)

Formulation of rulesfor fishing conditionsand practicesBan on seining andtrawling for pikeperch

1963–1970 Reduce interaction trawland gillnet fishery andrecreational angling

Reduction by-catchin eel fishery

Ban on trawl fishery(1970); trawlsreplaced by increasingnumber of fykes andeel boxes

Reduce pikeperchoverfishing

Gillnet mesh sizesincreased to 101 mm

1974 Liberalization End of obligatorylanding registration

Increase in non-reported landings

1977 Overfishing perch andpikeperch(Willemsen, 1977)

1984–1986 By-catch fykenetting for eel( Willemsen, 1985)

Regulate fishery Effort limitation Inventory and capnumbers of eel fykes;

Decline in eel recruitment(EIFAC, 1985)

Regulation fishingseasons and legalsizes

1988 Gear numbers stronglyincrease (Dekker, 1991)

Reformulatingfishery management(reduce overfishing)

75% effort reductionproposed

Stepwise reductionover next decades

(continued on next page)


depleted halfway during the fishing season. The lowrevenues from the perch and pikeperch fishery in the1960s contributed to the ban on two-boat seine fisheryin 1963 and on the eel trawl fishery in 1970. The

immediate reduction in by-catch mortality of youngpercids since 1970 resulted in a fourfold increase incommercial catches of the gillnet fishery 1 to 3 yearslater (Fig. 5). This finding is corroborated by model

Table 1 (continued)

Year Main observations andresearch findings

Management goal Operational measure Realised measure/effect

1989–1992 Extreme overfishing ofeel, perch and pikeperch(annual reports Neth. Inst.Fish. Research)

Effort reduction(gear + time)

40% reduction of capnumbers fykes1984/1986

Inventory and capnumbers of eel boxesand gill netsRestriction on number ofsmelt fykes

Minimum legal size foreel too low (Dekker, 1990)

Increase minimumlegal size eel(from 28 to 32 cm)

(Not until now)

1997–2001 By-catch of birds in gillnets (Van Eerden et al.,1999)

Co-management Fish plan (effort reduction50% in gear and time);transferable fishing rights

20% reduction eel gear

2001–2002 Eel stock in decline, allover Europe(Dekker, 2004a,b)

Food reservation andreduction by-catch(agreement for birdsand fishes)

Reduction gillnets(by-catch diving water birds).Fish plan effort reduction

20% reduction gillnets

2004–2005 Fish plan effort reduction 38% Effort reduction(fykes 42%, eel boxes7%, gillnet 14%, licences85 to 72)

2007 EU plan eel Regulation eel (In prep)

Management measures were reconstructed from published and unpublished records of the Ministry of Fisheries and Fisheries Organisations POIJsselmeer and Productschap Vis.


predictions showing major responses within 1–2 (pike-perch) to 2–4 (perch) years (Buijse, 1992). The sub-sequent sharp increase in number of fykes, with theirhigh by-catches of young fish, the considerable increasein number of gillnets employed in the 1970s and 1980sand technical advances (larger engine-powered vessels,gillnets of cotton replaced by multi-filament nylon(around 1960) and mono-filament nylon around 1980),more than compensated for the decline in the number offishing companies and resulted again in extreme over-exploitation (fishing mortality rates FN2; Willemsen,1977; Buijse et al., 1992, 1994; Dekker, 1991, 1996)and landings declined accordingly over the next twodecades (Fig. 5). Effort reductions of 75% have beenrepeatedly proposed for the gillnet fishery in the 1970s,1980s and 1990s, by researchers and angling organiza-tions. In 1989, the first inventory of the number ofgillnets present in the different enterprises was carriedout (Dekker, 1991), followed by a reduction in themaximum allowance on a license agreement. The gapbetween the actual usage before 1989 and the maximumallowance after 1990, was only gradually identified. In2001, the Bird Protection Agency and the fishery orga-nization agreed on a further reduction in the number ofnets, to reduce the by-catch of thousands of diving

waterbirds (Van Eerden et al., 1999; Witteveen+Bos,2003). As a consequence of a shift in the fishery fromMarkermeer to IJsselmeer in the late 1990s, followed bythe reduction in number of gillnets in 2002, a short-termincrease in pikeperch catches has been noticed. How-ever, this increase proved to be unsustainable and re-venues dropped again in recent years.

6. Aiming at a moving target

Since the creation of the lake in 1932, both the politicaland the environmental scene have changed considerably.The long-term management goals have been phrased dif-ferently over time, from stressing a socio-economic im-provement of a reduced number of fishing companies afterthe construction of dams and polders (Zuiderzeewet 1918)to a multi-species approach (conflicting interests of eel,perch and pikeperch fishery through by-catch problems)and subsequently to a more ecosystem-based approach inwhich the fishery should impose minimal ecological im-pacts (nature conservation of salmonids and birds conflict-ing with by-catches in fykes and gillnets; regulating thesmelt fishery in the context of food reservation for birds).Therefore, management goals gradually shifted fromfisheries that should be (1) socio-economical sustainable


to (2) sustainable in terms of biological production, and(3) to ecological sustainable exploitation, a shift thatnicely follows similar developments elsewhere in marineand inland fisheries over the 20th century (e.g.,Welcomme, 1999; Freon et al., 2005; Quinn and Collie,2005; Hilborn, 2007a). The levels of sustainable fishingeffort decrease with these goals for socio-economic, bio-logical, and ecological sustainability, respectively (e.g.,Quinn and Collie, 2005; Beddington et al., 2007; Hilborn,2007a). In fact, this means that over time the fisheriesmanagement targets for sustainable exploitation were setat increasingly lower thresholds of acceptance of over-exploitation, although targets were only defined on aconceptual level, and never quantified exactly.

Fish stocks have not only been affected by exploita-tion, but have also been influenced by ecosystem changes.The lake surface has been reduced stepwise through landreclamation projects, while fish production has alsosuffered from the dam splitting off the Markermeersince 1975 (Mous et al., 2003). In the 1970s and 1980s,pollution with various toxic substances (heavy metals,PCBs, etc.) and changes in eutrophication (increase sinceWorld War II, but greatly reduced since the 1980s) mighthave affected fish production too (Mous et al., 2003;Dekker, 2004b). The booming cormorant population inthe 1980s and 1990s has led to a higher natural mortalityfor fish stocks, and is now considered a fearsome com-petitor by the fishers. The rise in water temperaturesprobably contributed to a lower production of smelt andconsequently might affect the food base for perch andpikeperch.

Together, the political decisions to allow less inter-ference with the ecosystem and the changes in theecosystem imply a shrinking niche for commercial ex-ploitation, increasing the need to reduce fishing effortsbeyond the targets that would correspond to contem-porary management goals at various points in time.

7. A slow hand fails

Awareness of (high risks of) over-exploitation of theIJsselmeer fish stocks and its socio-economic conse-quences have played a major role throughout the historyof Lake IJsselmeer fisheries. Although the lack ofessential information (complete catch statistics and ef-fort monitoring) has hampered the evaluation of stockdynamics and of the effect of management decisions tosome extent, the ecology of the lake, the biology of thefish and the development of the fishery (including thesocio-economic aspects) have been well-studied andcommunicated frequently with the authorities and fish-eries organizations over decades (Deelder and De Veen,

1958; Deelder, 1963, 1965; Willemsen, 1977, 1985;Visserijschap, 1988; Van Densen et al., 1990; Buijse,1992; Dekker, 1990, 1991, 1996, 2004a; Taal and DeWilde, 1997).

Among the many management measures carried out(Table 1), the ban on the eel trawl has shown to be themost effective for the perch and pikeperch fishery. Apotential effect on eel stock recovery has been muchmore difficult to assess. The long life cycle of the eel, itscross-border panmictic population dynamics and cyclicpatterns in landing statistics in combination with therapid replacement of trawls by fykes obscured any clearcause–effect relationships of the temporarily achievedeffort reduction. However, the failure to prevent a re-newed increase in fishing effort after the ban on trawlingmeans that a unique opportunity to actually achieve themanagement goals, was completely lost. Because therewas no clear effort monitoring and effort reductions(caps) were carried out stepwise (mainly between 1997and 2005), it remains unclear what effort reduction hasactually been achieved. Obviously, however, effectiveeffort reductions only commenced 20–30 years after theban on the eel trawl, incurring 15–25 years of unwantedrise in effort and over-exploitation.

The prolonged period of extremely high fishing mor-talities has put the potential recovery of eel at great risks.Recent model studies demonstrate that stock recovery ofeel may take many decades, even if drastic effort reduct-ions (on a European scale!) would be carried out (Åströmand Dekker, 2007). Especially in long-lived species withslow potential recovery rates, sustained periods of over-exploitation may result in severe economic losses andgreatly increase the risks of stock depletion or collapse(Buijse et al., 1994; Daan, 1997; Orensanz et al., 2004;Caddy and Seij, 2005; Hilborn et al., 2005; Mullon et al.,2005; Beddington et al., 2007; Shertzer and Prager, 2007).The delay and slow, stepwise implementation of effortreductions were motivated by strong incentives to avoidshort-term declines in income for fishers, even thoughrevenues were expected to increase again with less fishingeffort after a recovery phase. However, given the highrates of exploitation, the small steps in effort reductionincrease the potential recovery time. As a consequence,fishers do not experience a reward on their effort re-ductions on the short-term and loose the incentive tocooperate on achieving sustainable exploitation at lowereffort levels (Hilborn et al., 2005; Hilborn, 2007b).Developments towards more ecological sustainable fish-ing levels and a probably lower fish production owing toecological changes further increase uncertainty about fu-ture fishing revenues and mid-term or long-term increasesin revenues may not be guaranteed. Under these


conditions, there is little base for co-management and self-regulation towards responsible fisheries (cf.; Hilborn et al.,2005). Instead, high operational costs and low revenuesinevitably drive fishermen out of business, or force them toreduce their effort, through buyouts of entire enterprises bythe government or by spending less time fishing, andshifting their activities to other sources of income. Thissituation aggravated the relationship between fishers andgovernment. The slow response to prevent excessive fish-ing levels since the 1970s can therefore be considered afailure to achieve biological, socio-economical and poli-tical sustainability.

Our review of the history of fisheries management onLake IJsselmeer focused primarily on the dynamics of thefish stocks, the shifting ecological settings, and the res-ponses of managers and fishers. This relates to currentissues on good governance of fisheries taking into accountsocio-economics, legal and political aspects (FAO, 1995;Kooiman et al., 2005). Amongst the criteria for goodgovernance, responsiveness ensures that all stakeholdersare servedwithin a reasonable timeframe, balancing short-term needs against long-term losses. The timeframe of thisresponsiveness criterion is severely restricted by the bio-logical characteristics of the stocks and ecosystems, andshifting political objectives. A slow hand, as observed inthemanagement of Lake IJsselmeer, serves only the short-term interests of fishers and managers, but impedes stockrecovery and increases the long-term losses.

References

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Documents

Aiming at a moving target, a slow hand fails! 75 years of fisheries management in Lake IJsselmeer (the Netherlands)