the eel fishery in lough neagh, northern ireland – an example of sustainable management?

The eel fishery in Lough Neagh, Northern Ireland –an example of sustainable management?

R . ROSELL

Department of Agriculture for Northern Ireland, Agriculture, Food and Environmental Sciences Division (Aquatic SystemsGroup), Newforge Lane, Belfast, UK

D . EVANS

Queens University of Belfast, Faculty of Agriculture and Food Science, Belfast, UK

M. ALLEN

Department of Agriculture for Northern Ireland, Biometrics Division, Belfast, UK

Abstract Lough Neagh produces over 500 t of grown eel annually and employs 300 people fishing yellow andsilver eel. Glass eel are transported upstream and stocked into the Lough. Since glass eel returns crashed in the1980s, additional glass eel seed has been purchased from other fisheries. The fishery now faces ecological, socialand economic pressures. Prices for the product have fallen; recruitment to the fishery has declined, and seed hasdecreased in availability and increased in price. Fishers are less inclined to take up the hard work required to makea living fishing eel and the fisher population is ageing. The European Commission has recognised the decline of eeland proposed emergency measures, which may further affect the viability of the fishery. The sustainability of thefishery is examined, based on the relationship between glass eel input and grown eel outputs over a period of45 years, set against increasing environmental, socio-economic, and natural resource pressures. Spawningescapement of silver eel is estimated by mark–recapture experiments.

KEYWORDS : Anguilla anguilla, eel, fishery management, stock recruitment.

Introduction

Lough Neagh (Fig. 1) is the largest freshwater lake inthe British Isles, with a surface area of about 400 km2

and a mean depth of 9 m. Its catchment drains 40% ofthe land area of Northern Ireland, through six majorand a number of minor affluent rivers, before eventu-ally flowing northward to the Atlantic Ocean throughthe River Bann. The eel, Anguilla anguilla (L.), fisheryin its current form originated in the 1960s, when theLough Neagh Fishermen’s Co-operative Society Ltd(LNFCS) was formed to acquire the total rights to alleel fishing in the lake and freshwater reaches of theout-flowing river. Prior to the formation of theLNFCS a number of separate owners controlled

different parts of the fishery and conflict between theinterests of local fishers and non-local owners madeholistic management difficult or impossible (Healy1913). The social and legal history of fishing, owner-ship of fishing rights and the acquisition of the total eelfishery right by the fishermen’s co-operative in the1960s and 1970s were described by several authors(Healy 1913; Donnelly 1986; Kennedy 1999). Thefishery management regime adopted by the LNFCS isdescribed in more detail by Kennedy (1999).

The single ownership of all elements of the eel fishingrights, from glass eel, yellow eel and silver eel makes thecurrent, perhaps unique, management system possible.This affords exploitation of yellow and silver eel inrelation to the history of glass eel supply, controlled

Correspondence: Robert Rosell, DANI, Agriculture, Food and Environmental Sciences Division, (Aquatic Systems Group), Newforge Lane,

Belfast BT9 5PX, UK (e-mail: [email protected])

Fisheries Management and Ecology, 2005, 12, 377–385

� 2005 Blackwell Publishing Ltd 377

through a combination of measures imposed by statelaw and additional restrictions on fishing operated bythe LNFCS. The long-term aim of the current man-agement regime is maximum sustainability of employ-ment for fishers. A key feature of the business being runas a co-operative is that revenue from silver eel fishingforms the basis of winter income support to fishers(who are shareholders in the total fishery) who fish foryellow eel in the summermonths. The silver eel revenuesalso pay for the stocking, and trap and transportactivity which maintains the level of the input stock.

Due to the construction of a flood control anddrainage scheme in the River Bann in the 1930s, elverupstream migration is impeded by a set of sluices(replacing a natural fall) at the tidal limit of theestuary. Elver passes incorporating traps around thisobstruction allow elvers to be collected and transpor-ted to Lough Neagh, a practice which began in the1930s and, with one time gap, persists to the present.Records from this trap and transport operationprovide continuous annual data on elver immigrationsince 1959. There is no legal fishery for glass eel inNorthern Ireland other than specifically permittedactivity for stocking waters to which they wouldotherwise have restricted access. In addition to thenatural supply from the River Bann, the LNFCS has

purchased glass eel for stocking Lough Neagh on theEuropean market since 1984, when major declines innatural return of glass eel were noted in the Bann andat other European index sites. This policy has contin-ued, but the combination of natural local supply andpurchases has not always made up the input to theLNFCS’s annual target of 8 million elvers (equivalentto approximately 2700 kg). Glass eel fetch high prices,in excess of 900 € (£630 sterling) per kg of live glass eelbeing quoted in 2004/2005. These prices, because ofshortage of supply and demand from eel farms, nowthreaten to curtail the ability of the Lough Neagh co-op to purchase stocks.

Two main extraction fisheries for eel occur onLough Neagh. The Lough is fished between May andSeptember for yellow eel, the traditional means being along line of over one thousand hooks fished overnight.Hook baits include earthworms (Lumbricus spp.), fishfry captured in bait nets, pieces of fish flesh, and morerecently mealworms (various coleopteran larvae avail-able through the pet food trade). There is also draft netfishing, using an 80–100 m seine net with a cod-enddeployed from a boat in open water. The recentaddition of hydraulic net haulers to the draft net boatshas increased the ease of use of this formerly hand-hauled gear and permits many more hauls per day.Increases in effort through improved efficiency meas-ures, such as haulers, are to some extent compensatedfor by decreases in the number of active boats. Becauseof market forces and the ageing fisher population, boatnumbers have decreased to around 100–110 in 2004,from about 200 in 1985 (LNFCS, personal communi-cation).

Yellow eel fishery conservation measures in placeinclude daily quotas (a cap on the weight of eel whichthe LNFCS will buy from any one fisher), and methodrestrictions – only draft nets and long-lines arecurrently permitted. Fyke netting is not permitted, toensure that all catch can be marketed as day fresh.Trawling is not permitted because of the risk of over-exploitation and its incompatibility with long linefishing on the same fishing grounds. There is a 2-dayweekend cessation on the yellow eel fishery, applied bythe fishers� co-op in conjunction with state regulations.The LNFCS applies a minimum marketable gradinglength for yellow eel of 41 cm, well above the minimumlanding size of 30 cm prescribed in state legislation.

Emigrating silver eel are caught at two (formerlythree) fixed stations on the River Bann. Fixed meshstructures in the flow channel downstream migratingeel in to fixed Coghill nets lowered into the flow. Theseeel weirs must, by state law, maintain a free gap of10% of the river width at the deepest part of the main

100 km

RiverBann

LoughNeagh

Ireland

Figure 1. Location map.

R. ROSELL ET AL.378

� 2005 Blackwell Publishing Ltd, Fisheries Management and Ecology, 2005, 12, 377–385

flow, and are only fished at night. This fishery can befished with relatively (to yellow eel fishing) low levels ofeffort and provides a source of working capital to theLNFCS.The Lough Neagh catchment has a high proportion

of improved grassland managed as intensive pastur-eland, and as a result the Lough is in a hypeutrophicstate (Smith 1993; Foy, Smith, Jordan & Lennox 1995;Foy, Lennox & Gibson 2003). Because of its largefetches and windy climate, it is usually well mixed,preventing some of the potential deoxygenating effectsof enrichment (Wood, Andrew & Carter 2000). Thehigh productivity maintains very high standing cropsof chironomid larvae upon which eel feed heavily(Kennedy & Vickers 1993).

Materials and methods

Glass eel, yellow eel and silver eel data

The LNFCS supplied their data on glass eel trap/transport and purchases since 1959 and annual yellowand silver eel catches since 1964. These data wererecorded at the packing station at Toomebridge as eelare collected daily and exported to market.

Age profiling of the current fished eel population

Samples of eel were taken throughout 2003 to make upa bulked sample representative of the whole yellow andsilver fishing period. Length (mm), weight (g) and sexwere recorded. One total (ungraded) catch from bothlong-line and draft net methods were also screenedeach month of the active fishery (May to September),enabling measurement of fish below market size. Asub-sample of fish were aged from dried otoliths gluedto glass microscope slides, progressively ground using

a gradation of fine emery papers to a surface throughthe origin, and read by transmitted light on a binocularmicroscope.

Mark–recapture estimates of silver eel escapement

Batches of emigrating silver eel were purchased fromthe fishery, tagged with FLOYTM tags and releasedinto Lough Neagh in the autumn of 2003 and 2004.Recaptures were recorded by the staff in the packingstation and noted as captured in one of two sequentialweirs in the River Bann.

Factors influencing eel output

Cross spectral analysis was conducted to investigatethe relationship between the potential explanatoryvariables – natural glass eel input (kg); additionalpurchased glass eel input (kg); mean (August toNovember) water flow (106 m3 d)1) of the LowerRiver Bann; and mean (May to September) watertemperature (�C) of Lough Neagh at a depth of 10 m –and the response variables of yellow and silver eeloutput (kg). This initial screening of the data will formthe basis of developing a predictive model for yellowand silver eel outputs. Annual time series data wereavailable for natural and purchased input from 1960 to2004, mean water flow from 1970 to 2004, mean watertemperature from 1968 to 2004 and yellow and silvereel output from 1965 to 2004. The analysis was carriedout using the software package GenStat.

Results

Data gathered by the LNFCS are presented inFigure 2 (yellow and silver eel catches) and Figure 3(glass eel supply). Data were bulked annual marketed

year

0

200

400

600

800

1000

1200

Cat

ch (

ton

nes

)

1965

1968

1971

1974

1977

1980

1983

1986

1989

1992

1995

1998

2001

2004

Figure 2. Lough Neagh eel catches, 1964–2004, in tonnes. Yellow eel catch in open bars and silver eel catch in solid bars. Data courtesy of Lough

Neagh Fishermen’s Co-operative Society Ltd.

SUSTAINABLE MANAGEMENT OF THE LOUGH NEAGH EEL FISHERY 379


catch in the case of yellow and silver eel, and totalelver/glass eel trapped and transported upstream fromthe tidal head traps in the Bann estuary to LoughNeagh. Figure 3 also gives the quantities of glass eelpurchased on the international market and placed inLough Neagh annually by the LNFCS since the firstsevere decline in returning glass eel in 1983. Since theLNCFS took over the entire fishery in the early 1960s,there has been a slow downward trend in silver eelcatch, initially linked to increased output of yellow eeland a deliberate shift in effort from silver to yelloweel fishing. Since 1990 there has been a slow decline inthe catch of both yellow and silver eel. The quantity ofglass eels trapped and transported upstream were highduring a period of active transporting between 1936 to1946 and again from 1959 to 1983. After the pan-European recruitment crash of 1983, glass eel supplywas maintained by heavy stocking of non-local mater-ial up to 1989. From 1990 to 2004, both upstreamtransported natural and purchased glass eel inputs

were considerably reduced, averaging somewhat lessthan half that of the period from 1960 to 1990.

Ages for combined male and female yellow eel in theLough Neagh commercial eel fishery averaged15 years, range 6–24 years [Fig. 4 (yellow eel) andFig. 5 (silver eel)]. Average age for male silver eel was12 years (range 8–16 years) and female silver eelaveraged 17 years (range 14–28 years). The rangespread of ages in the fishery is considerable and willnaturally tend to smooth any input–output relation-ships. Growth rates (not shown) are approximatelylinear post-recruitment at about 7 cm and average2.65 cm yr)1.

Mark–recapture experiments to estimate silver eelescapement

Recaptures to the fishery of the release batches in both2003 and 2004 were 25% and 38% respectively(Table 1). The returns from 2003 included a small

0

2

4

6

8

10

12

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Age (years)

Freq

uenc

y in

sam

ple

(n =

75)

Figure 4. Ages of yellow eels in the Lough Neagh Fishery, 2003.

Year

0

2

4

6

8

10

12

Elv

ers

(ton

nes)

1936

1941

1946

1951

1956

1961

1966

1971

1976

1981

1986

1991

1996

2001

Figure 3. Natural and imported glass eel/elver supply to Lough Neagh, in tonnes – Natural supply in open bars, imports in solid bars. data courtesy

of Lough Neagh Fishermen’s Co-operative Society Ltd.

R. ROSELL ET AL.380


number of silver eel that appeared to revert to yellowafter tagging or delay migration, appearing in theyellow or silver eel catch the following year.

Factors influencing eel output

When investigating the relationship between eel outputand natural input and additional purchased inputusing cross-spectral analysis, peak lag parameters of 15and 17 years were used for yellow and silver eel(respectively), whilst a lag of zero was used for bothmean water flow and temperature. This was to focus

the procedure around the lags that are thought to bebiologically meaningful.

The impulse response results for yellow eelshowed lags at 18 years for natural input and alsoa strong, although not significant, lag at 8 years(Fig. 7a). For silver eel there were strong, althoughnot significant, lags at 8 and 17 years for natural input(Fig. 8a). The other potential explanatory variableseither displayed no significant lags or significant lagsthat were not biologically meaningful (Figs 7b–d &8b–d).

The changing sex ratio of silver eel in Lough Neagh

Parsons, Vickers & Warden (1977) and Kennedy &Vickers (1993) noted that the sex ratio of Lough Neaghsilver eel tended to shift towards production of malesfollowing capture of glass eel in the estuary andtransporting these 40 km upstream to the Lough. Thesilver eel sex ratio is now biased towards the female(60–70% in 2003/2004) (Fig. 6).

Discussion

Sustainability of the present fishery

The most important question over the Lough Neagheel fishery is whether or not it is sustainable. Theprinciples applied to management of the fishery aim to

Table 1. Mark–recapture of silver eel 2003 and 2004

Date

Number tagged and

released to Lough Neagh

Recaptures:

Weir 1

Recaptures:

Weir 2

Recaptures following

season

Total

recaptures

Maximum escapement

estimate (%)

16 October 2003 189 33 7 7 47 75

4 November 2004 838 302 15 N/A 317 62

0

10

20

30

40

50

60

70

80

90

100

Per

cent

mal

e

1920 1930 1940 1950 1960 1970 1980 1990 2000 2010Year

Figure 6. Sex ratios in silver eel catches in Lough Neagh (percent male

by number in the emigrant population) in relation to elver trap and

transport operations. Solid horizontal bars are periods of active trans-

port.

0

2

4

6

8

10

12

14

Age (years)6 8 10 12 14 16 18 20 22 24 26 28 30

Freq

uenc

y

Figure 5. Ages of silver eels (50 males, open bars, 50 females, solid bars) in the Lough Neagh Fishery, 2003.



maintain employment at maximum levels while pre-serving the fishery for future generations. Thisapproach is exemplified by the immediate response ofthe LNFCS in purchasing glass eel from elsewhere forstocking Lough Neagh in 1984, after only 1 year offailure in the natural supply. This response was at thetime highly precautionary given the natural range ofages in eel fisheries (Figs 4 & 5). With hindsight, giventhe continuance of low natural supplies of glass eelsince 1983, it was the correct response.

Current model projections suggest that, as a resultof the stocking undertaken from 1984 to 1989,catches will be maintained to about 2006. Theremay be problems to be faced when the entirety of thefished stock derives from the low stocking levels ofpost-1989 (Fig. 3). Given the range of ages in thefishery, it is unlikely that the catches will see a sharpfall in any 1 year, rather a decline from 2005/2006onward. Current complications to modelling outputsinclude the unknown relative survival of imported vslocally upstream transported glass eel, and theimportance of a small residual natural upstreammigration to Lough Neagh.

However, there are several factors complicating thisanalysis, including some major externalities. Yellow

eel fishing activity is declining, because of low marketprices, an ageing fishing population, and physicallyeasier and more lucrative sources of employment forfishers. Prices for grown eel remain under pressurefrom aquaculture and this pressure is likely to remainfor the foreseeable future. At the same time, demandfrom European and Asian aquaculture business forincreasingly scarce glass eel recruits threatens to drivethe price of stock beyond the means of managed wildeel fisheries. This factor will persist unless a means isfound for artificially reproducing eel in captivity.Boat numbers actively fishing Lough Neagh foryellow eel have fallen from 200 or more boats to100–110 over a period of about 20 years. While someof this reduction in effort has been compensated forby the advent of mechanically assisted gear handling,part of the recent decline in yellow eel, and hencetotal output is because of reduced effort. The adventof hydraulically assisted haulers for the draft nets haschanged the balance between draft net and linefishers, with a probable positive effect in reducinglosses of undersized eel from long lines. The dailyquota applied per boat remains at 42 kg of eel andhas not increased with declining numbers of activeboats. While it is difficult to obtain accurate data, it

–15

–10

–5

0

5

10

15

20

–20 –15 –10 –5 0 5 10 15 20LAG

IRF

–40

–30

–20

–10

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30

40

–20 –15 –10 –5 0 5 10 15 20

LAG

IRF

–20000

–10000

0

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–30000

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30000

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IRF

(a)

(c) (d)

(b)

Figure 7. Impulse response estimates between yellow eel and (a) natural glass eel input, (b) Additional purchased input, (c) water flow and (d) water

temperature. NB dashed lines denote 90% levels.

R. ROSELL ET AL.382


would appear that catch-per-unit-effort in the yelloweel fishery is, for the present, being maintained, andthat most boats achieve their daily quota in the peakfishing months.

Influence of ageing methods on estimation oflifespan of Lough Neagh eel

Previous work (Anonymous 1969) based on burningand cracking of otoliths suggested emigration of malesilver eel at 10–13 years, and females at 17 years.These tally with current work based on grinding andpolishing, of males emigrating at an average age of12 years and females at 15–20 years. These estimatesof age also match with peak statistical relationshipsin the input to output time series, with significantcorrelations at 18 years between glass eel inputmeasure and total catch. This lends support to theaccuracy of estimates of ages of eel in the fishery.These ages, along with currently measured growthrates averaging 2.65 cm yr)1, are similar togrowth parameters in the neighbouring Erne lakesystem (Matthews, Evans, Rosell, Moriarty & Marsh2001).

Implications of current levels of escapement ofsilver eel

The current catch of silver eel has beenmeasured at 25%(2003) and 38% (2004) based on mark–recaptureexperiments. These experiments measure recapture,not absolute escapement in a highly variable silver eelfishery. Difficulties, as with all mark–recapture experi-ments, include unknown losses from the study (forexample by illegal fishing). To date, only one tag (from aDutch eel processor) has been returned from outside theLNFCS.Tag lossdoesnot appear tobeamajorproblem,the FloyTM anchor tags retaining at almost 100% intank holding trials. The two active silver eel weirs in theRiver Bann are of similar construction, but vary in theireffectiveness. The first, at Toome, is situated near theoutflow of Lough Neagh, and fishes most effectively atmoderate flows. The second, some 10 km downstream,typically catches fewer eel and fishes best at low flows,generally taking fewer fish than the first (LNFCS,personal communication). Very high river flows makeall silver eel fishing difficult, and river levelsmay overtopthe deflecting structures and lead to high escapement.The regulated nature of the flow is also a source of

–8

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25000

–20 –15 –10 –5 0 5 10 15 20

LAG

IRF

(a)

(c) (d)

(b)

Figure 8. Impulse response estimates between silver eel and (a) natural glass eel input, (b) Additional purchased input, (c) water flow and (d) water

temperature. Dashed lines denote 90% levels.



variability – Lough Neagh is maintained by the Nor-thern Ireland Rivers Agency within level limits imposedby statute, to prevent flooding of land and maintaindrinkingwater supplies.This leads toa tendency for flowsto rise and fall dramatically as the sluice gate systems areoperated.Aneed to drain or retainwater during the silvereel migration will inevitably exert control over the runtiming of silver eel. The tagging experiments of 2003and 2004 imply overall estimated escapement levels ofthe order of 120–200 t annually, i.e. equivalent to some-what more than the current silver eel fishery catch. Thisequates to approximately 2.5–3.5 kg of silver eel ha)1 ofproductive area, a relatively high figure (Moriarty &Dekker 1997) for the latitude of Lough Neagh.

Sex ratios in the Lough Neagh silver eel catch

The work by earlier authors (Parsons et al. 1977)demonstrating the link between silver eel sex ratio andupstream transport led to the conclusion that sex ratiocould be phenotypically determined by populationdensity, higher densities as a result of transport andstocking producing more males in the silver eel runs.Other possible conclusions, for instance that geneticallypredetermined males might not migrate upstream nat-urally, could not be ruled out. Now that upstreamtransport and stocking of glass eel has continuedannually since 1959, but at lower stock input levels since1989 (Fig. 3), silver eel are once again predominantlyfemale (Fig. 6). This implies that sex ratio in LoughNeagh is indeed primarily determined by stock density,and that at inputs of 75–100 g ha)1 of annual recruit-ment the stock will produce more males than females,with female output being the norm at 50 g ha)1 or less.The dominance of older females in the current stock alsoindicates that mortality in the yellow eel fishery duringthe growing phase is probably at acceptable levels fromaconservation standpoint. Overfishing would tend tocrop females differentially due to their longer residencetime in fresh water, as occurs in more intensive fisheries,such as the Isselmeer in TheNetherlands (Dekker 2004).

The European dimension

The declining returns of glass eel to Europe as a wholehave given rise to major concerns over the sustainabil-ity of European eel fisheries without effective manage-ment in place (Moriarty & Dekker 1997; Dekker 2002,2004, 2005; ICES 2003, 2004; Russell & Potter 2003;Starkie 2003). Only recently have European eel stocksbeen viewed as requiring anything other than localisedmanagement. Concern has been growing over thepopulation as a whole over the past decade (Moriarty

1999; Fontenelle, Briand & Feunteun 2001; Briand,Fatin, Fontenelle & Feunteun 2003; Dekker 2005).Moriarty (1999) highlighted under-supply of glass eel,compared with previous recruitment, to the full rangeof European eel growing habitats. Recent internationalworking groups (ICES 2003, 2004; Russell & Potter2003) continue to reinforce this advice and it nowappears that without proactive management, stocksmay continue to fall. Russell & Potter (2003) furtherargued the need for a series of management referencepoints and targets against which the status of theoverall European population can be assessed. Starkie(2003) listed the possible causes of population declineas all or a combination of overexploitation, oceano-graphic or climate change, freshwater habitat reductionor degradation, pollution and parasitism. Whatever thecauses of decline, emigrating spawners recruited togrowing areas before the severe recruitment decline ofthe 1980s are being replaced at ever lower numbers. TheEuropean Commission has picked up this concern andis considering measures to address effort control in eelfisheries as a short-term emergency measure while astock recovery plan is calling for specific action tocurtail silver eel fishing (Anonymous 2003).

Internationally imposed conservation measures willundoubtedly pose problems for the LNFCS, to a greaterdegree than to fisheries organised on a purely commer-cial basis. Should measures focus on silver eel alone, atfirst sight perhaps a logical action, the whole economicbasis of the fishery could be undermined.Removal of therevenues to the fishers from silver eel fishing couldremove the funding for stocking and glass eel trap andtransport operations, with the long-term result thatLough Neagh could yield fewer spawners to sea than itdoes in its current managed state. This paradox demon-strates the efficacy of the current system and its potentialas a model for wild eel fisheries elsewhere. LoughNeaghis as yet free of some of the impacts affecting othersystems, such as hydropower stations, but has been andis impacted by declining water quality in the form ofnutrient enrichment, the effects of land drainage, andregulated flows. The Japanese eel parasite Anguillicolacrassus, Kuwatiara, Niimi & Itagaki (see Kirk 2003 forreview) has reached Lough Neagh within the past5 years and is still increasing in prevalence (Evans andRosell, personal observation). Despite the many goodpractices adopted in local management, without aninternationally co-ordinated management plan capableof delivering stock-wide recovery and improving theoverall supply of recruits and spawners, the future of eelfishing in Lough Neagh is likely to be one of slowlydeclining returns. However, should international meas-ures succeed in stabilising glass eel supplies and as long

R. ROSELL ET AL.384


as markets for grown eel continue, Lough Neagh willcontinue to produce eel for consumption and supportemployment for eel fishers for the foreseeable future.

Acknowledgments

The authors wish to thank the Lough Neagh Fisher-men’s Co-operative Society Ltd and individual LoughNeagh fishermen for allowing access to boats andprocessing facilities, for supplying samples and histor-ical data, and for their keen interest in the work. TheDepartment of Culture, Arts and Leisure for NorthernIreland, Inland Fisheries Branch, provided financialsupport to D. Evans. Prof Granville Tunnicliffe-Wilson provided advice in using and interpreting theGenStat time series procedures.

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the eel fishery in lough neagh, northern ireland – an example of sustainable management?

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