Fishing Down the Value Chain: biodiversity and access regimes in freshwater fisheries - the case of Malawi.

Transcription

1 Fishing Down he Value Chain: biodiversiy and access regimes in freshwaer fisheries - he case of Malawi. Vicor Kasulo Faculy of Environmenal Sciences, Foresry Deparmen, Mzuzu Universiy, Malawi Charles Perrings Inernaional Insiue for Susainabiliy, Arizona Sae Universiy Absrac This paper considers he connecion beween he diversiy of cach in a muli-species fishery and he produciviy of he fishery under differen access regimes. A modified Gordon-Schaefer model is used o analyse he imporance of he level of diversiy in a fishery in open access and profi maximising regimes. The modified model, which includes boh environmenal and bioeconomic variables, is fied o daa from a gillne fishery in Lake Malawi. Pressure on socks is shown o be greaer a all levels of biodiversiy in open access han i is in profi maximising regimes. However, in a profi maximising regime boh cach and he produciviy of fishing effor is highes when here is a single markeed species. By conras, in an open access regime caches are maximised a higher levels of bioeconomic diversiy han in profi maximising regimes. Implicaions for policy are discussed. Key words Fisheries; biodiversiy; open access Address for correspondence: Charles Perrings Environmen Deparmen Universiy of York Heslingon York YO10 5DD UK cap8@york.ac.uk

2 1. Inroducion A long-held view of he developmen of fisheries is ha hey iniially exploi more abundan, more easily caugh species, and swich over ime o increasingly less abundan, less easily caugh species. Moreover, i is argued ha he rae a which less easily caugh species are subsiued for more easily caugh species is acceleraed in open access fisheries. A sudy of he mean rophic level of species groups repored in FAO global fisheries saisics has shown ha he succession has been from long-lived high rophic level piscivorous boom fish owards shor-lived low rophic level inverebraes and plankivorous pelagic fish (Pauly e al, 1998). There is less evidence on changes in he biodiversiy of freshwaer han marine fisheries. Noneheless, i is known ha he depleion of fish species has affeced he funcioning of freshwaer ecosysems in which he mos sensiive componens of food webs, energy flows and biogeochemical cycles are hose where he number of species carrying ou funcions is small (Schindler 1990). Pauly (1997) has argued srongly ha open access freshwaer aquaic sysems are paricularly hreaened by an influx of people displaced from oher pars of he economy. Recenly, he FAO has quesioned he degree o which he sae of African fisheries is deermined by he insiuional condiions under which fishing akes place, arguing ha changes in fish socks may be more heavily influenced by environmenal condiions han by fishery managemen (FAO, 003a, 003b, 004). The fishery invesigaed in his paper, in he souh wes arm of Lake Malawi,1 does no appear o bear his ou. The fishery has been exploied by radiional mehods for many years, and radiional fisheries sill accoun for he bulk of oupu. Modern regulaed commercial fishing sared in 1935 when purse seining was inroduced, bu i was no unil he inroducion of rawling in 1968 ha he commercial fishery became a significan indusry (Tweddle and Magasa, 1989). There is, however, sriking evidence of changes in he fishery since ha ime. An iniial repor on he fishery (Tarbi, 197) was followed by deailed invesigaions of changes ha had occurred as he fishery developed (Turner, 1977; Tweddle and Turner 1977). These sudies showed significan changes in he 1 The souh-wes arm of Lake Malawi is approximaely 50km long, 30 km across and reaches a deph of 100m in he cenre. Mos of he shoreline, and paricularly he souh coas is heavily reeded, backed by exensive marshes and small lagoons. The norh eas coas is rocky, and he norh wes coas has exensive sandy bays wih a few minor rocky oucrops. Three islands called he Maleris are an imporan feaure of his region and an inensive chilimira fishery operaes in heir viciniy. A major river, he Linhipe, flows ino he lake opposie he Maleri Islands (Tweddle e al., 1994).

3 species composiion of caches as he rawl fishery inensified, wih larger cichlid species disappearing from he caches and smaller species increasing in abundance. The iniially abundan medium and large cichlid species, Lehrinops sridei and L. macracanhus, for example, were replaced by small cichlids such as Oopharynx argyrosoma, Pseudoropheus livingsonii and Lehrinops aurius. A decline in he large cafish Bagrus meriodionalis and Bahyclarias spp. was also noed (Banda e al., 1996). During his period he FAO (1976) used experimenal rawls o esimae oal fish biomass and o recommend maximum susainable yields (MSY) for each of seven fishing areas. These esimaes were used o specify oal allowable caches and o deermine he number of rawling licenses o be issued. Following he FAO (1976) sudy, he minimum legal rawl cod-end mesh size was increased from 5 o 38 mm. This was inended o reverse he decline in populaion of he larger cichlid species. However, no aemp was made o see if he hoped-for recovery of he large cichlid species had occurred unil 1989, when experimenal rawls were again used o esimae oal fish biomass and he species composiion of he cach. They showed ha species such as L. mylodon and L. macracanhus, which had declined subsanially in he 1970s, had become locally exinc. Oher large species such as Taeniolehrinops furcicauda, T. praeorbialis and Cenopharynx spp., had also declined. In he areas where mos rawling had aken place, he large and medium-sized benhic zooplankivores, large sedimen feeders and large piscivores had all declined. The sanding sock of small sedimen feeders and pelagic species had remained largely unchanged (Turner e al., 1995; Banda e al., 1996). A one-year moraorium on rawling in he souh-wes arm of he lake in 199/3 had a marked effec on boh fish biomass and species composiion, reurning composiion o ha in oher areas. In a follow-up sudy by Banda e al. (1996), no furher major changes in species composiion were deeced. This paper addresses one of he quesions raised by he FAO (003a, 003b) sudies: namely wha is he effec of fisheries managemen and access rules on he biodiversiy of he fishery. Tradiional fisheries in Malawi are of several ypes. The mos commonly used gear is he gillne, which accouns for over 40 percen of oal radiional caches of around 40,000 onnes per annum. In his secor, cach per uni effor in he souh wes arm of Lake Malawi showed a sharp decline from abou 0 kg per se in he mid 1950s o 5 kg per se in he early 1970s. The decline was largely accouned for by he disappearance of nchila (Labeo mesops) which had comprised 3

4 abou half of he cach in he 1950s (Walker, 1976). Since ha ime he species composiion of cach has coninued o change wih he percenage conribuion of ilapiines (Oreochromis spp) falling and he conribuion of usipa (Engraulicypris sardella) and haplochromines (kambuzi, uaka and chisawasawa) increasing (Munhali, 1997). We ask how boh he size and species composiion of caches is influenced by managemen and access regimes. We do no find he expeced relaion beween open access regimes and loss of biodiversiy. We do find ha he performance of he fishery under differen access regimes may be quie sensiive o he diversiy of fish socks. More paricularly, we find ha radiional open access regimes are associaed wih a higher diversiy of fish caches han regulaed access profimaximising regimes. We discuss he implicaions of his for he managemen of freshwaer fisheries in developing counries. The paper is presened in six secions. The following secion discusses Malawi s fisheries managemen and access regimes. This is followed in secion 3 by a presenaion of he mehodology used o derive resuls on he poenial impac of biodiversiy ha provide a esable se of hypoheses abou he behaviour of mulispecies fisheries under differen access regimes. Secions 4 gives empirical resuls for he case of he Malawi gillne fishery. Secions 5 and 6 hen use he resuls o draw conclusions abou he relaion beween biodiversiy and access regimes in his fishery.. Fisheries Managemen and Access Regimes in Lake Malawi Our discussion of fisheries access regimes uses Bromley s (1991) classificaion of naural resource regimes. Bromley disinguishes beween common propery and non-propery (open access) regimes. Under common propery regime a group of owners has a righ o exclude nonmembers and non-members have a duy o abide by he exclusion. On he oher hand individual members have boh righs and duies wih respec o use raes and mainenance of he resource. Under open access here is no defined group of users or owners and benefi sream is available o anyone. Thus individuals have a privilege bu no righ wih respec o use raes and mainenance of he resource. 4

5 In pre-colonial imes he Lake s resources of waer, fish and shores were under a common propery regime. Indeed, unil he end of he Firs World War he fishery was regulaed by family heads, village headmen and chiefs. The firs fishing regulaions were inroduced in These prohibied fishing by raps, weirs and poisoning and excluded foreign commercial fishers from operaing wihin wo miles of radiional fishing grounds. However, enforcemen of he regulaions was lax (Chirwa, 1996). A Fisheries Deparmen was esablished in 1946, and charged wih he responsibiliy for regulaing fishing and he fish-rade, for compiling fisheries saisics, and for conducing research. This implicily ransferred he conrol and ownership of he lake s resources from he communiies o cenral governmen. During he nex wo decades he Deparmen experimened wih differen ypes of fishing gear and boas, and proposed new fishing regulaions ha inroduced licenses for commercial fishers. However, enforcemen remained a problem due o he mobiliy of fishers and heir seasonal fishing pracices, and monioring remained weak (Chirwa, 1996). Afer independence, he Malawi governmen s policy on fisheries was o maximize susainable yield from socks ha could be economically exploied in naional waers. I also aimed a improving he efficiency of exploiaion, processing and markeing of he fish (OPC, 1971). These policies were refleced in he Fisheries Ac (1974), which auhorized he use of hree insrumens: licensing, gear resricions and closed seasons. Firs, licenses were required for commercial fishing, fishing vessels, rou fishing and fish rading. There was a provision in he Ac o limi he number of licenses for any class of fishing in Malawi. The aim was o preven he depleion of fish socks by limiing he number of licenses. Second, cerain fishing mehods were prohibied including he use of cerain nes, explosives and poison. Third, he Ac prohibied fishing during cerain specified periods, eiher wih respec o paricular areas of he counry or o Malawi as a whole. Policing of hese regulaions was unsuccessful due o lack of rained saff and parol equipmen, and he low level of penalies for non-compliance. Iniially, he Fisheries Deparmen was seen as a guardian of fish socks. More recenly he emphasis has shifed owards concern for he fishing communiy and consumers, and fish resources are seen more as a source of susainable benefis o boh. As elsewhere, he emphasis has shifed owards co-managemen designed o exploi local knowledge and skills (Bland and Donda, 1994). This is refleced in he Fisheries Conservaion and Managemen Ac (1997) ha 5

6 implemens he Naional Fisheries and Aquaculure Policy. The mos imporan feaure of he new Ac is he provision i makes for co-managemen hrough legally binding agreemens beween he governmen and recognized fisher associaions. Only fishing areas no subjec o a co-managemen agreemen coninue o be managed by he Fisheries Deparmen (EAD, 000). In summary, he fish resources of Lake Malawi were iniially managed as a radiional common propery resource unil governmen regulaions were inroduced. The inroducion of governmen conrol led o he disappearance of he common propery regime, since all naural waer bodies in Malawi and is resources became he propery of he sae. The Fisheries Deparmen as a governmen insiuion was given he mandae o conrol he fish indusry, bu was largely unsuccessful. In paricular regulaion of radiional fisheries was weak. In fac, since he inroducion of governmen regulaion, he radiional fishery can righly be considered as being an open-access regime. The inroducion of co-managemen regimes has reurned some auhoriy o fishing communiies, bu given ha socks are shared beween many communiies he reurn o each communiy depends on he acions of neighboring and disan communiies who fish he same socks (EAD, 000). 3. A modified Gordon-Schaefer model of a muli-species fishery To invesigae he relaion beween he diversiy of harves and he produciviy of a fishery regime, we use a modified Gordon-Schaefer model. Sock producion models of his ype have been criicized mosly because hey do no use biological informaion on naural moraliy, growh or age. Neverheless, hey are sill widely used and acceped paricularly in ropical lakes where biological parameers of caches are no easy o ge, and where he species concerned are numerous and shor-lived so ha aging is ofen difficul (Fréon e al., 1993). The modificaion o he Gordon-Schaefer includes boh he effec of he species diversiy of fish caches on yields, and he effec of environmenal condiions on he growh of fish socks. In his case we use a measure of waer polluion. In Lake Malawi, as in mos African lakes, waer polluion is an emerging problem ha needs close monioring. Increasing levels of biological oxygen demand leads o a reducion in fish produciviy hrough europhicaion and his reduces boh he food and habia available o some fish species (Boosma e al., 1999: Hecky e al., 6

7 1999). Since mos polluion of he lake is due o run-off from agriculural areas, we ake of rainfall in he cachmen area of he souh-wes arm of Lake Malawi as a proxy for he level of polluion. This reflecs he fac ha annual yields of sedimens and nuriens deposied in he lake are highly, and posiively, correlaed wih rainfall in he cachmen. For example in he high rainfall year of 1997/98, deposiion of suspended sedimens from he souhern cachmen was nearly 50 percen greaer han in 1996/97 (Hecky e al., 1999). The use of rainfall figures also indirecly capures he impac of river discharges from Linhipe River, which is one of he larges riverine conribuors of nuriens and sedimens ino he lake (Mwichande e al., 1999). Mkanda and Barber (1999) have used rainfall energy derived from rainfall daa o develop a geographical informaion sysem (GIS) model for he predicion of soil loss, and sedimenaion in Lake Malawi. Biodiversiy is measured by an index of he species diversiy of he harves and is assumed o reduce he cach per uni effor. Two indices are used: an unweighed and a price-weighed Simpson s index. The unweighed Simpson s index of cach is: s Y i B =Σ (1) i=1 Y where Y represens he oal fish cach and Y i is he cach of he ih species. The price-weighed Simpson s biodiversiy index of cach is: s Pi Y i B = Σ () i=1 TR where P i is he uni price of species i, and TR is he marke value of he oal fish cach. The value of B is deermined by changes in marke condiions for differen species and of changes in species composiion overime due o naural causes and o fishing pressure. In boh he unweighed and weighed indices, a loss of biodiversiy is refleced in an increase in he value of An ideal measure of waer qualiy should have aken ino accoun he level of chlorophyll a, or he concenraion of nuriens and suspended sedimen levels in he surface mixed waer-layer of he lake. Unforunaely, his deailed informaion is no available on a long-erm basis. 7

8 he biodiversiy index, which ranges beween zero (as he number of species harvesed ends o infiniy) and one (if he number of species harvesed is one). If each species caugh has he same marke value, hen he bioeconomic Simpson s index of cach is he same as he unweighed index. If differen species have differen marke values, he impac of price weighing depends on he relaive abundance of more and less valued species. The economic biodiversiy index of a communiy dominaed by species of high (low) marke values will be greaer (less) han he corresponding ecological biodiversiy index of he same d B communiy. Tha is > (<)0 dp B >(<) B where B and B are he bioeconomic and biological diversiy indices respecively. Since he weighed biodiversiy index reflecs boh he economic scarciy and he relaive abundance of species, an ecologically dominan species will became more (less) dominan in he weighed index if i is more (less) valuable. The use of a weighed biodiversiy measure reflecs he fac ha consumers do no regard all species as equally valuable, and ha he differences beween species inform he decisions of boh fishers and regulaors. Empirically, he sequence of exploiaion is from more o less valued valued species (Boechler, 1996; Pauly e al., 1998), a phenomena we have called fishing down he value chain. By using hese biodiversiy indices, he model is able o capure imporan properies of muli-species fisheries wihou describing all he species ineracions. I does his by aggregaing he differen species involved and hen modeling he effec of he diversiy of hose species on he dynamics of he aggregaed fishery. In his way he effec of changes in biodiversiy wihin he fishery on produciviy is capured while mainaining he simpliciy of he Gordon-Schaefer model. The model is summarized as follows. Firs, suppressing ime subscrips, he growh and susainable yield funcions are: X & = rx(1 ew X/K) qbex (3) 8

9 Y = qkbe(1 ew qbe/r) (4) Where X denoes fish biomass, r is he inrinsic growh rae, W is he environmenal qualiy variable, e is a parameer ha gives he amoun by which a uni change in he environmenal variable depresses he naural growh rae of fish biomass, K is he maximum environmenal carrying capaciy, q is he cachabiliy coefficien, E is effor, and Y is harves. The implicaions of he model for he level of effor and sock size under differen access regimes are obained by solving for he opimal values of E and X under each access regime. Defining p o be he uni price of harvesed fish biomass, c o be he uni cos of effor, and δ o be he discoun rae, he resuls are summarized in Table 1. Table 1: Effor and sock size under differen access regimes Access regime Level of effor Sock size Open access r( 1 ew c pqbk ) K( 1 ew qbe r) Profi maximising qbξ ± where qb [( qbξ ) 8φq B θ ( φr( 1 ew ) c) )] 4φq B ξ = φ( θ + r( 1 ew )) c θ = δ + r( 1 ew ) MSY r( 1 ew ) K( 1 ew ) qb 1 c pqb oa ( δ + r( 1 ew ) qbeo ) ( δ + r( 1 ew ) bbe ) o The effec of a change in he species diversiy of cach under differen access regimes is hen obained by differeniaing he seady sae values of E and X under each access regime wih respec o B. The resuls are summarized in he following proposiion: If an increase in biodiversiy reduces he effeciveness of fishing effor hen, in a mulispecies fishery, he maximum susainable yield level of sock size is no affeced by changes in biodiversiy, bu he effor required o cach he MSY increases (decreases) as fish diversiy increases (decreases). In open access and profi maximising fisheries, an increase (decrease) in fish biodiversiy implies an increase (decrease) in sock size. However, he impac on he open 9

10 access and profi maximising levels of effor depends on he level of biodiversiy. For small numbers of species an increase (decrease) in fish biodiversiy implies an increase (decrease) in effor levels. As he number of species rises, he effec on effor levels reverses, and an increase (decrease) in fish biodiversiy implies a decrease (increase) in effor. Tha biodiversiy has no impac on MSY is an arefac of he way i has been modelled. In freshwaer fisheries where species have been inroduced, here is some evidence of an increase in oal fish biomass over some ime horizon despie a reducion in he number of species. The Lake Vicoria fishery in Eas Africa is an example. The inroducion of he Nile Perch ino his fishery was associaed wih he loss of some 00 haplochromine cyclids, bu a significan increase in oal fish biomass (Kasulo, 000; Perrings 000). Where species are merely deleed from an exising fishery, however, he evidence is less clear. I has been assumed here ha biodiversiy does no affec he produciviy of he fishery, bu does affec he effeciveness of fishing effor. The impac of he bieconomic diversiy of he cach on effor levels depends on parameer values. For low levels of biodiversiy (B close o 1), he addiion of a markeed species increases he opimal level of effor. As he number of species increases, however, he effec of an addiional species on opimal effor falls, evenually becoming negaive. If he diversiy of species had no implicaions for eiher he value of harves or for he growh of fish socks, he opimal sraegy would be o reduce he number of species o one. From an ecological perspecive, eliminaion of all species and all rophic levels bar one would effecively desroy he sysem, bu simplificaion of a fishery o he poin where he number of arge species is reduced o one is no uncommon. I has o be noed ha he value-adjused or bioeconomic diversiy index used in he model measures he diversiy of cach weighed by he economic value of he species involved. Indeed, in he empirical case invesigaed in his paper i measures he diversiy of species weighed by heir marke value. In mos cases he aggregae value of he cach is no independen of he diversiy of species in ha cach. The value of he aggregae cach increases over a leas some range of biodiversiy. This has implicaions for he fishery response o any change in environmenal condiions. 10

11 4. Esimaion of he modified Gordon-Schaefer model The modified aggregae Gordon-Schaefer model is applied o he gillne fishery of he souh wes arm of Lake Malawi. We firs esimae he parameers of he model, and hen use hese parameers o esimae he open access, MSY and opimal soluions of he gillne fishery. They are also used in he invesigaion of he biodiversiy-produciviy relaionship, which analyses he impac of changes in biodiversiy on open access and opimal soluions. The parameers of he model are esimaed using daa on fish cach and price per species, fishing effor, cos of effor, and rainfall as a proxy for he level of waer polluion. The period of sudy is beween 1976 and Daa on rainfall is colleced by he Meeorological Deparmen and is available from he Malawi Naional Saisical Yearbook. Daa on fish cach and price per species and fishing effor were obained from he Malawi Fisheries Deparmen. No daa are regularly colleced on he cos of effor because i is very difficul o cos fishing effor in a radiional fishery (FAO, 1993). The cos of effor is herefore calculaed on he assumpion ha rens are dissipaed due o near open access condiion. The following wo equaions were esimaed: * * r * * ln Xˆ = r - q Eˆ - Uˆ - rew + μ (5) qk * * r * * ln X = r - q E - U - rew + μ (6) qk where * * Uˆ ˆ = ; Uˆ X * -1 * ( Eˆ -1+ Eˆ ) Eˆ = ; * Uˆ +Uˆ -1 Uˆ = ; W W = +W * -1. * * U X = ; * U -1 * ( E-1+ E ) E = ; Eˆ = E * B ; * U U = +U -1 ; Y Uˆ = ; E B E = E* B Y U = E B. 11

12 Y represens he aggregae fish cach, E is he level of fishing effor 3 and U is he cach per uni effor. W is an environmenal variable and μ is he error erm. The annual level of fish biodiversiy is measured by B. The weighed biodiversiy index is represened by B. Thus, Equaion 5 uses he unweighed biodiversiy index while Equaion 6 uses he price-weighed biodiversiy index. The dependen variable for he equaions is an index of relaive change in fish biomass. The parameers o be esimaed are; r, he inrinsic growh rae, q he cachabiliy coefficien, K he environmenal carrying capaciy, and e he parameer ha relaes how much a uni of he environmen variable W reduces he relaive growh of fish biomass. Regression resuls for Equaions 5 and 6, correced for auocorrelaion using a Prais-Winsen ransformaion, are repored in Table. Table Regression resuls correced for auocorrelaion. Equaion R Q r/qk re R F Saisic DW Saisic (3.3150) (-3.46) (.750) (-4.06) (3.3330) (-4.3) (.3140) (-4.434) Figures in parenheses are -saisics For equaion 5, all parameer esimaes wih he unweighed biodiversiy index are saisically significan a he 5 percen level, and he model explains 66 of he variaion in fish biomass. The corresponding F-saisic is also significan. Addiion of he weighed bioeconomic diversiy index (equaion 6) furher improves he significance of he esimaed parameers, and he goodness of fi. The model now explains 74 percen of he variaion in fish biomass. 3 For he gillne fishery, effor is expressed in number of ses of 91m (sreched lengh) ne per year. 1

13 5. Biodiversiy in he fishery Now consider he imporance of biodiversiy. Since we wish o relae biodiversiy o he srucure of propery righs and he regulaory regimes in he fishery, we firs consider he open access, MSY and profi maximising oucomes in he absence of a bioeconomic diversiy index. The correced parameer esimaes from Equaion 6 are r = , q = , K = , and e = These parameers are used o calculae he open access, MSY and opimal soluions, assuming B = 1. The resuls are repored in Table 3. The price of oupu is se a he average beach price for fish in 1997, MK56.14 per onne 4. Cos per uni effor is again se a he average for he fishery over he same year, K1.70. Polluion is proxied by rainfall. This akes he form W n =W /W av where W n is he normalised index, W is he amoun of rainfall in year and W av is he average rainfall. Since he value of B ranges beween 1, where only one species is markeed, and 1/s, where s species are markeed, he assumpion ha B = 1 implies ha for his exercise we are ignoring he impac of changes in he markeed value of differen species. Tha is, we are reaing he fishery as if i was a single species fishery. Table 3 Esimaes of cach, effor and sock levels for open access, MSY and profi maximising exploiaion in he single species fishery. Variable Open Access MSY Profi maximising Acual Average Cach (Y) Effor (E) Sock (X) These resuls are ypical of single species Gordon-Schaefer fisheries models wheher in freshwaer or marine fisheries (Conrad and Adu-Asamoah, 1986; Gallasegui, 1983). The open access soluion produces he lowes cach level associaed wih he highes level of effor. The MSY soluion gives he highes level of cach and he profi maximising soluion gives he lowes level of effor. Figures for he acual average indicae over-exploiaion by comparison wih he single species fishery, since he average cach is higher han he MSY cach and he average effor is above he MSY effor level. Since MSY does no change wih he biodiversiy 4 MK = Malawi Kwacha, he local currency in Malawi. 13

14 index he overexploiaion is no an arefac of he choice of B = 1. Indeed i is widely recognised ha he fishery was overexploied during he period analysed, The bioeconomic index capures he effec of marke valuaion of harves. The unweighed Simpson s index of may be a reasonable approximaion of a bioeconomic index in a subsisence fishery in which here is no by-cach, and all species are consumed. The weighed index reflecs he fac ha demand is higher for some species han ohers, and ha his influences which species are argeed by fishers. Lower bioeconomic diversiy implies ha fewer species are commercially valuable, and/or ha fewer species are argeed by fishers. Since mos fisheries in Lake Malawi, including he gillne fishery, are marke-driven, he weighed index is he appropriae measure of he diversiy of cach. The unweighed and weighed biodiversiy indices for he fishery over he period are shown in Figure 1. Two feaures are worh noing. The firs is ha he weighed index is generally higher han he unweighed index someimes very much higher. Fishers focus on he mos highly valued species. The second is ha he period divides ino wo. During he firs en years boh indices are increasing in value indicaing ha he diversiy of cach was falling. I was also quie volaile, indicaing ha he range of species caugh varied sharply from year o year. During he second en years he rend was reversed. Boh indices fell indicaing ha he diversiy of cach was rising slighly. The variance in boh indices also declined. (Figure 1 here) During he firs period he fishery was becoming dominaed by he high value chambo following he collapse of nchila socks in he 1970s. During he second period, as chambo socks hemselves came under increasing pressure, emphasis swiched o oher less highly valued bu more diverse socks of usipa (Engraulicypris sardella) and haplochromines (kambuzi, uaka and chisawasawa). Fishing down he value chain ironically increased he bioeconomic diversiy of cach. We are ineresed in he linkage beween hese measures of biodiversiy and he insiuional and echnological characerisics of he fishery. In a Malawian conex he open access case 14

15 corresponds o a poorly regulaed fishery in which rens are exhaused. The profi maximising case corresponds o a fishery subjec o well-defined propery righs in which marginal revenues and marginal coss are equaed. Since he persisence of an unregulaed fishery is jus as much a policy choice as he inroducion of regulaed fishery, we ask wheher here is a connecion beween he diversiy of harves and he srucure of he indusry. Recall ha our proposiion holds ha in boh open access and profi maximising fisheries, an increase in he bioeconomic diversiy of cach implies an increase in he size of he fish sock, bu ha he impac on he opimal level of effor in each case depends on he parameers of he model. For B close o 1, an increase in he bioeconomic diversiy of cach implies an increase in sock size. As he number of species rises, he effec on opimal sock size reverses, and an increase (decrease) in fish biodiversiy implies a decrease (increase) in sock size. To invesigae he diversiy-produciviy link in he fishery, we consider he relaionship beween biodiversiy, fish socks and cach under boh open access and profi maximising rules using he same daa se. Specifically we calculae he sensiiviy of he open access and profi maximising soluions o variaion in he bioeconomic diversiy of cach. Boh cos per uni effor and he discoun rae are held consan. Moreover, because we are ineresed in changes in relaive prices only, he average landed price of fish is also held consan. The resuls are used o fi relaionships beween biodiversiy, fish socks, effor levels and cach under boh an open access regime (Figure ) and a profi maximising regime (Figure 3). This enables us o ge some idea of he relaive performance of he wo fishery regimes a differen levels of cach diversiy, holding oher characerisics of he fishery consan. While fishers have some capaciy o deermine he level of cach diversiy hrough, for example, choice of fishing gear, cach diversiy is largely driven by (a) he diversiy of fish socks and (b) marke condiions, boh of which are given. Figure indicaes he prediced level of effor, sock size and harves for he open access fishery. I shows ha fish socks would be prediced o decline as he bioeconomic diversiy index rises (i.e. as bioeconomic diversiy falls). If he bioeconomic diversiy of cach were high, boh effor and cach would be prediced o increase as diversiy falls. The sock size, on he oher hand, would be prediced o decrease. If he bioeconomic diversiy of cach were low, effor would be prediced o increase as bioeconomic diversiy falls, bu boh sock and cach would be prediced 15

16 o decline. The mean bioeconomic diversiy index for he gillne fishery in Lake Malawi is shown as a poin of reference. (Figure here) Figure 3 shows he same daa for a profi maximising fishery. As in he open access case, sock size would be prediced o decline monoonically as he bioeconomic diversiy of cach declines. However, boh effor and cach would be prediced o rise monoonically. Indeed, boh cach and he produciviy of effor would be expeced o be highes when he bioeconomic diversiy index is 1- here is a single markeed species. (Figure 3 here) Noe ha boh figures reflec he parameer values of he paricular fishery being evaluaed, and he relaion beween insiuional condiions, biodiversiy and produciviy may be quie differen in differen fisheries. In he Lake Vicoria fishery, for example, he inroducion of he Nile Perch had a srongly negaive effec on he biodiversiy of harves, bu a srongly posiive effec on sock size. Neverheless, we believe ha our findings would hold in many radiional fisheries. Consider he relaive performance of he fishery in each of he wo saes. Gordon s (1954) observaion - ha any increase in produciviy will resul in a posiive ren ha will arac new enrans holds here. Thus, under open access all he poenial benefis of a fall in bioeconomic diversiy are dissipaed. Furhermore, he increase in produciviy of fishing effor as biodiversiy declines is offse by he seep decline in fish socks resuling from free enry o he fishery. The resul is ha fish socks under open access are lower a all levels of bioeconomic diversiy han is he case in a profi maximising regime. However, i is also clear ha he relaive efficiency of he wo saes is relaed o he diversiy of cach. For B = 1 a profi maximising regime clearly dominaes an open access regime. As B falls, however, he performance gap beween he wo regimes closes, and for B below he mean bioeconomic diversiy index esimaed for he Lake Malawi fishery, an open access regime yields higher levels of prediced harves and higher cach per uni effor han a profi maximising 16

17 regime (Figure 4). The implicaion is ha for a fishery characerised by high levels of bioeconomic diversiy of harves, i is no obvious ha a commercial (profi maximising) fishery dominaes an radiional (open access) fishery. (Figure 4 here) 6. Discussion Wha are he inferences o be drawn from his? The bioeconomic diversiy measure used in his paper capures he effec of a change boh in he relaive abundance of markeed species, and in he relaive prices of hose species. If an increase in he bioeconomic diversiy of cach reduces he effeciveness of fishing effor, as his paper shows ha i does in he Lake Malawi fisheries, here will be greaer pressure on low diversiy han on high diversiy sysems in boh open access and profi maximising regimes. As one would expec, he pressure on socks is greaer a all levels of biodiversiy in open access han i is in profi maximising regimes. However, he relaive performance of he fishery under each regime ype varies wih he diversiy of cach. In he relaively biodiversiy rich fishery of he souh wes arm of Lake Malawi, a radiional poorly regulaed gillne fishery (open access) yields higher caches and cach per uni effor han a profi maximising fishery based on he same echnology and fishing he same se of socks. There is less of an efficiency cos o he persisence of radiional open access regimes in his case, and less of an incenive o simplify he fishery. This is a leas consisen wih he general evidence on freshwaer fisheries where radiional open access regimes have ypically been less selecive in he se of harvesed species han profi-maximising regimes. This does seem o have imporan implicaions for he managemen of fisheries in Malawi, and poenially in oher developing counries. The main poin is ha i is no obvious ha he inroducion of a regime based on he esablishmen of clearly defined access righs will offer a significan produciviy advanages over radiional open access regimes in he Malawian fishery, and poenially elsewhere. More imporanly, if biodiversiy conservaion in fisheries is an objecive, hen he differences in performance of he fishery under differen access regimes should a leas promp invesigaion of he biodiversiy implicaions of a regime change. Finally, we emphasise ha our findings are based on a single fishery. Since he Malawian fisheries share many of he same 17

18 characerisics as oher muli-species freshwaer fisheries in Africa and elsewhere, however, we hink i likely ha replicaion of he sudy would confirm a leas he general relaion beween propery righs, diversiy of cach and produciviy idenified here. Finally, o reurn o he findings of he FAO (003a, 003b and 004) sudies on freshwaer fisheries in Africa, while i is clear ha year on year flucuaions in caches of paricular species are indeed driven by environmenal condiions, he argeing of species has hisorically had a significan impac on he relaive abundance of hose species. The commercial exincion of nchila (Labeo mesops) is a case in poin, as is he decline in chambo (Oreochromis spp.). A characerisic feaure of radiional fisheries in Lake Malawi, which has persised in he parially regulaed gillne fishery sudied in his paper, is he non-specificiy of caches. For ha reason such radiional fisheries perform relaively beer han mono-specific commercial fisheries in highly diverse ecosysems, where by-cach imposes a cos disadvanage on he laer. 18

19 Figure 1: The biodiversiy and bioeconomic diversiy indices for cach in he gillne fishery of he S.E. arm of Lake Malawi BD Index BED Index Figure : The effec of bioeconomic diversiy of cach on sock size, effor and cach in an open access fishery Cach (onnes), effor/ BED Index Bioeconomic diversiy index Cach Effor Sock Sock (onnes) 19

20 Figure 3: The effec of bioeconomic diversiy of cach on sock size, effor and cach in a profi maximising fishery Cach (onnes), effor/ BED Index Bioeconomic diversiy index Cach Effor Sock Sock (onnes) Figure 4: The relaion beween bioeconomic diversiy of harves on cach and cach per uni effor in open access and profi maximising fisheries Cach (onnes) BED Index Cach per uni effor Bioeconomic diversiy index OA Cach P Cach OA CPUE P CPUE 0

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