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Ocean & Coastal Management 73 (2013) 1e12

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Ocean & Coastal Management

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The impacts of shrimp farming on land use, employment andmigration in Tumbes, northern Peru

F. Mialhe a,*, Y. Gunnell b, C. Mering a

aDepartment of Geography, Université Paris Diderot 7, CNRS UMR 8586, 2 rue Valette, 75005 Paris, FrancebDepartment of Geography, Université de Lyon, CNRS UMR 5600 EVS, 86 rue Pasteur, 69365 Lyon Cedex 07, France

a r t i c l e i n f o

Article history:Available online 4 January 2013

* Corresponding author. Present address: DepartmeNamur, 61 rue de Bruxelles, 5000 Namur, Belgium. Te

E-mail addresses: francois.mialhe@fundp.ac(F. Mialhe).

0964-5691/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.ocecoaman.2012.12.014

a b s t r a c t

Export-oriented shrimp aquaculture appeared in the coastal landscape of Peru in the late 1970s. Its rapiddevelopment has entailed both positive and negative environmental and socioeconomic impacts acrossthe newly emerging shrimp farming territory of the Tumbes river delta. Here we combine ground sur-veys and interviews with remote sensing analysis of the transformed environment in order to charac-terize and quantify the nature, origin and scale of the environmental and social impacts caused by theintrusion of aquaculture. Results show that shrimp farming has encroached on several land cover cat-egories and converted 17% of the Peruvian mangrove. We provide an overview of the history and natureof those impacts. Minimum full-time equivalent employment, which occurred during a white-spotepidemic, was attained in 2001 with 439 full-time jobs; employment peaked in 2006, with 2660 full-time jobs. However, considering indirect benefits, remittances and the prevalence of part-time jobs,the population reliant on aquaculture probably exceeds 10,000. A geographical analysis of social net-works reveals how shrimp farming draws a sustained influx of population from the Andes and how itmodifies the interaction between population and the natural coastal environment. Recent sectorialimprovements towards achieving a more sustainable management of the coastal resources are analysed,and additional recommendations predicated on a more integrated approach are provided.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Among the diverse productions of aquaculture, shrimp farminghas received special scrutiny because of its negative environmentaland social impacts. Worldwide production of farmed shrimps hasincreased from less than 100,000 metric tons in 1980 to more than3.5 million metric tons in 2009 (FAO, 2012). Shrimps, as many othercrustacean organisms, are high value food commodities. Crusta-cean production accounted of late for only 9.5% of the global pro-duction in mass but for 23.1% in terms of value (FAO, 2010).Growing demand among developed countries and emergingeconomies, technological advances conducive to the intensificationof production, and the global decline in marine fish catches havebeen the main drivers behind this surge in shrimp farming (Biaoand Kaijin, 2007; Paul and Vogl, 2011). Aquaculture has also beenpromoted to alleviate poverty through the supply of direct and

nt of Geography, University ofl.: þ32 485 36 34 24..be, framialhe@hotmail.fr

All rights reserved.

indirect jobs, proteins and revenue (Hishamunda and Ridler, 2006;Asian Development Bank, 2004; Edwards, 2000; Heck et al., 2007).For example, several development projects conducted by multi-lateral agencies such as theWorld Bank and the Asian DevelopmentBank focused on aquaculture during the 1980s (Goss et al., 2000;Hall, 2004) and shrimp farming, a non-traditional export activity,benefited substantially from them. Shrimp farming has sincebecome a major source of export earnings for several SoutheastAsian countries (Hall, 2004).

The ensuing economic development was associated with bothpositive and negative impacts. In total, shrimp farming is estimatedto occupy between 1 and 1.5 million hectares along the world’scoastlines (Berlanga-Robles et al., 2011). Mangrove degradation, forexample, has largely been depicted as a major environmentalconsequence in American and Asian coastal areas. Almost half ofthe total mangrove land cover area has been depleted in the last 50years (Curran, 2002). Although several factors have led to man-grove destruction, shrimp farming is considered a major culprit(Valiela et al., 2001). Until recently, development of shrimp farms inmangrove ecosystems was not prohibited and even sometimesencouraged by national and local governments, who assessed thetraditional use of mangrove resources as inefficient (Stokstad, 2010;

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e122

Armitage, 2002). Other negative ecological (e.g. soil and waterpollution) and social impacts have arisen with the development ofthe aquaculture industry, such as social inequalities in food securityand resource allocation, and the marginalization of smaller scalefarmers (Bailey, 1988; Stonich, 1995). A major unforeseen impact isthat the development of aquaculture has failed to reduce thepressure on capture fisheries: instead of operating as a substitute ithas expanded the demand for fish protein by creating newmarkets(Curran, 2002).

A positive outcome of the activity is the jobmarket generated bythe farms, with opportunities for improving human livelihoods.Overall, global aquaculture production, including shrimp farms, isestimated toprovide a direct source of income to16.7millionpeopleand indirectly to another 6.8 million (Valderrama et al., 2010). Evensuch afigureprobably underestimates reality ifweconsider that justin Bangladesh 1.2 million people are directly involved in shrimpproduction and 4.8 million household members benefit from theindustry (Islam, 2008). However, according to some case studies inAsia (India, Philippines, Indonesia), shrimp farming appears to havebenefited mostly affluent and elite classes, and in some case haswidened the gap between rich and poor (Adduci, 2009; Hall, 2004;Armitage, 2002; Stonich, 1995). Among the poorer sections of so-ciety, some individuals have benefited from aquaculture, mainlythrough job opportunities in the commodity chain (Edwards, 2000).Many, however, such as in Ecuador and Honduras, have seena reduction of their livelihood options because of poor planning ofaquacultural activities and contempt from the ruling class towardstraditional resource management practices and local indigenouspopulations (Stonich, 1995; Hamilton, 2011). Privatization of theresource base that supports traditional livelihoods has caused somein- and out-migration of labour for economic reasons, with farmowners taking advantage of interregional or international wageinequalities and favouring non-local populations as an avoidancestrategy against local collective protest (Resurrección and Sajor,2010). In places such as the Philippines or Bangladesh, the devel-opment of shrimp farming has led to emigration because of envi-ronmental degradation (Primavera, 1997). However, through theremittances sent home by the migrants, aquaculture has alsorevealed a capacity to enhance the resilience of households in theiroriginal home territories by spreading economic risk and broad-ening economic opportunities. In Vietnam, remittances have alsoincreased inequalities among households in the communities oforigin (Adger et al., 2002). In Thailand, the development of inlandshrimp farming has also promoted migration into the continentalinterior (Flaherty and Vandergeest, 1998). In Indonesia, thegovernment-led transmigration of population from Java to Sumatra,Kalimantan and others islands has been critical in the developmentof shrimp farms outside Java, where shrimp diseases affects manyproduction units (Armitage, 2002; Hall, 2004). Shrimp farming hasalso generated some international migration. In Thailand, whereThais tend to avoid unskilledwork, the government has encouragedimmigration policies advantageous to shrimp farms. These nowemploy low- and semi-skilled workers from Laos and Burma(Resurrección and Sajor, 2010).

These impacts have been addressed in different ways bystakeholders of the shrimp farming sector. The wide spectrum ofsolutions reflects differences in diagnosis, in perception of theimpacts, but also divergent interests. For example, Béné (2005) hashighlighted a sharp opposition between a politicized discourserooted in political ecology, which promotes a holistic approachinvolving extensive and mixed farming systems, and a technocraticand market-oriented discourse which advocates intensive, closedsystems assorted with best management practices. Concepts andguidelines emanating from the prescriptions of Integrated CoastalManagement (Chua et al., 2006; Primavera, 2006) and Ecosystem-

Based Management, for example, strive to reconcile economicdevelopment and resource conservation objectives by reframingaquaculture through the lens of the ecosystem services narrative(Barbier et al., 2008). However, the successful conciliation of con-servation goals and development objectives at sites where shrimpfarms have become established still remains a largely unfulfilledideal (Barbier et al., 2008).

In South America, shrimp farming developed first in Ecuador in1969 (Twilley et al., 1999). In Peru, it began in the 1970s, initiallyunder the impulse of government-led experiments. The privatesector was first allowed to invest in shrimp farming in 1978 fol-lowing a shift in national policies towards liberal economic prin-ciples (National Institute of Natural Resources, or INRENA, 2007).That same year, the government allocated 6000 ha to aquaculture,mostly in saline areas on the inner fringes of mangrove swamps.Initially, the development of aquaculture was driven by a govern-ment-endorsed licence to exploit land resources, with the eco-nomic pattern broadly following an export-based system modelledon vent-for-surplus theory (Myint, 1958). Following the import-substitution model of industrialization, export-led growth modelsof development through non traditional export were supposed tostabilize the balance of payments and revitalize economic growthin many developing countries (Barham et al., 1992). This modelargues that export activities in the basic sector (export) create jobsin the non-basic sector through spillovers (Tiebout, 1956) and areparticularly well suited to small regions or cities that need toimport goods not produced locally (Malecki, 1997). In this per-spective, shrimp farming was a suitable candidate activity sincea number of advantageous conditions were locally available:unfarmed land, the proximity of Ecuadorian expertise, privatecapital, wild post-larvae in the local ecosystem, and an existingresearch unit in the local Fisheries department. The well-knowncollapse of Peruvian marine fisheries in 1972 due to anchovyoverfishing (e.g. Thorpe et al., 2000) also provided a perfect con-juncture for developing aquaculture in the Tumbes delta.

Based on a case study, this paper aims to assess some of theimpacts generated by ex nihilo shrimp farming in the coastal area ofTumbes, northernmost Peru. In this so far poorly documented re-gion, we first map the land cover and land use changes that haveoccurred through the development of aquaculture to unveil theenvironmental changes that have occurred at landscape level. Thenwe estimate the number of jobs created by the newly introducedshrimp farming system. Through an analysis of labour migration,we identify the determinants of population flow at the individual,household and regional levels and analyse the role of shrimpfarming in driving immigration. We finally connect those threeaspects to show how shrimp farming has shaped, and been shapedby, the interactions between society and the environment.

2. The study area

The study area is part of Tumbes Department, in the northerncoastal zone of Peru on the border with Ecuador (Fig. 1). Climate isinfluenced by the semi-arid conditions in the south, by the equa-torial climate in the north, and by El Niño events. The 180 km-longTumbes river is the main watercourse in the area (drainage area:5656 km2) and the only navigable river of the Pacific coast of Peru.It rises in Ecuador (Zaruma Mountains) and forms a delta in thestudy area. The river discharge regime is unimodal and peaks inMarch. The coastal area comprises a mosaic of various ecosystemssuch as mangrove (association of Rhizophora mangle, Lagunculariaracemosa, Conocarpus erectus and Avicennia germinans), dry forest,savanna and algarrobal (Prosopis pallida).

Among the provinces forming the Tumbes Department (popu-lation: 191,713), Tumbes province was the most populated in 2005

Fig. 1. Location of the study area.

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e12 3

(population: 139,073) (Instituto Nacional de Estadistica e Infor-mativa, or INEI, 2009). Between 1981 and 2005, the Departmentpopulation increased by 77% (83,649 inhabitants), the bulk of thisincrease (67%) affecting Tumbes alone.With a population density of225 km�2, the coastal area, which includes the La Cruz, Corrales,Tumbes, Papayal, Aguas Verdes, and Zarumilla provinces, is muchmore thickly populated than the hinterland (10 km�2). Given alsothat demographic fertility is greater in the hinterland, migrationhas been an important driver of this demographic imbalance.Alongside services and international trade with Ecuador, agri-culture is a major activity. Rice and banana are the twomains crops,both irrigated.

Peruvian shrimp production statistics (Fig. 2) exhibit high var-iability over time. The major disturbances to a steadily growingproduction were (i) El Niño in 1983 and 1997e1998, which causedflooding, clogging of waterways by sediment, mangrove depletion,and a critical reduction of wild post-larvae of Penaeus vannamei,Penaeus stylirostris and Penaeus californiensis in 1984; (ii) the

1980 1983 1986 1989 1992 1995 1998 2001 2004 2007 2010

Years

Farm

ed s

hrim

p pr

oduc

tion

(Mt)

020

0040

0060

0080

0010

000

1200

014

000

Fig. 2. Shrimp production in Tumbes between 1980 and 2006 Source: PeruvianDepartment of Fisheries.

occurrence of the seventh cholera pandemic in 1991; and (iii) anepidemic caused by an outbreak of white-spot syndrome (WSS) inAugust 1999.

The farming systems involve semi-intensive and intensivemonoculture of shrimps (P. vannamei). Post-larvae are produced inhatcheries mainly located in Ecuador (Evans and Tveteras, 2011)whereas formulated feed is produced nationally from forager fish.The stocking density of post-larvae varies from 15 m�2 for semi-intensive to >50 m�2 for intensive systems. Farms are large scale,many of them with a production area exceeding 50 ha. Yields insemi-intensive systems approximate 1 to 1.5$103 kg per cycle withtwo to three cycles per year, while intensive systems yield between5$103 and >10$103 kg per cycle. Farmers are now dramaticallyreducing intensive systems and have shifted towards semi-inten-sive systems following the recurrence of viral diseases. The absenceof a local market likely to absorb the production unfit for export hasprovided a further impetus for the farmers to abandon the inten-sive system, inwhich production costs remain very high (E. Mialhe,pers. comm. October 2012).

3. Methods

In order to assess the multidimensional nature of aquaculture-related impacts both in space and time, a specific methodologywas elaborated based on remote sensing and field work.

3.1. Mapping changes in land use

The assessment of environmental impacts at the landscape levelwas achieved through a multitemporal inventory of land resourcesobtained from a satellite image- and aerial photograph-basedanalysis of land use changes. Remote sensing is a convenient toolfor obtaining synoptic and repetitive information about the state ofland resources and then to assess the land use changes (Green et al.,1996; Rogan and Chen, 2004). A total of eight images were used inthis study: three Landsat MSS, one Landsat TM, one Landsat ETMþand three SPOT 5 (Table 1). Landsat images were acquired from theGlobal Land Cover Facility while SPOT images were acquiredthrough the ISIS program of the CNES (Centre National d’ÉtudesSpatiales). Aerial photographs were taken in 1962 by the Fuerzas

Table 2Image geometrical correction tests.

Image (with acquisition date) No. of groundcontrol points

RMSE

Landsat MSS (1977) 23 0.444064Landsat MSS (1982) 18 0.471381Landsat MSS (1983) 20 0.602474Landsat TM (1991) 20 0.499527Landsat ETMþ (2000) 17 0.246883Spot 5 (2003) 11 0.102056Spot 5 (2004) 15 0.074806

Table 1Imagery used in the study.

Source Date (years) Groundresolution (m)

Aerial photographs 1962Landsat MSS 1977, 1982,

198357

Landsat TM 1991 28.5Landsat ETMþ 2000 28.5SPOT 5 2003, 2004,

200710

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e124

Armadas del Peru. In total, the image data set covers a period of 45years.

Because misregistration can decrease the accuracy of diachronicmaps (Dai, 1998), geometric corrections were performed system-atically (Fig. 3). Given field investigations and in situ GPS data col-lection carried out in 2007, a SPOT 5 satellite image from 2007 wasselected as the reference image. All the other images were thus co-registered against the SPOT 5 using second-degree polynomialtransformation and nearest neighbour resampling. The root meansquare errors (RMSE) of the images are given in Table 2. Except forthe Landsat MSS image acquired in 1983, for which the low qualitydid not allow the same level of accuracy to be attained, all the RMSE

Fig. 3. Flow chart of the remote sensing procedure for land use change mapping.

values were suitable because below the recognized accuracythreshold of 0.5 (Hui et al., 2008).

The image classification procedure followed the steps indicatedin Fig. 3. Principal Component Analysis (PCA) is a multivariatestatistical technique based on an orthogonal transformationdesigned to convert possibly correlated spectral data into a (usuallysmaller) set of linearly uncorrelated variables called principalcomponents. PCA was first performed on each image in order toincrease radiometric contrasts and reduce redundancy betweenstrongly correlated channels (Chavez and Kwarteng, 1989; Eklundhand Singh, 1993; Lu and Weng, 2007; Campbell and Wynne, 2011).Components with the higher eigenvalues were then subjected to anunsupervised K-means classification, which has become a routineprocedure of unsupervised pixel classification (Lillesand et al.,2007). The number of user-defined classes varied from 15 for theLandsat to 25 for the SPOT 5 images. These classes were firstinterpreted and were then merged on the basis of a land covertypology elaborated from field investigations (Mialhe, 2010). Thetypology included the following classes: wetlands, water bodies,bare soil, mangrove, dry forest, mixed vegetation (including sav-anna and riparian forest). The sea was masked by segmenting thewater body classes. Because maps derived from remotely sensedimages can contain errors, e.g. due to preprocessing or inter-pretative techniques, classification accuracy was assessed using theKappa index, frequently used in remote sensing and derived froman error matrix (Story and Congalton, 1986; Foody, 2002, 2004).Kappa indices ranged here between 0.81 and 0.98. Aerial photo-graphs were visually interpreted using the same class typology asfor the satellite images. Finally, several change detectionmapswerecomputed using a post-classification method based on the indi-vidual land use maps (Singh, 1989).

3.2. Surveys

Field work was conducted to collect information aboutemployment in the aquaculture sector and labour migration. It wasconducted between April and June 2007. First-hand data werecollected through questionnaires and interviews with local stake-holders (government agents, farm operators, environmentalists)while second-hand data were compiled after visiting the appro-priate institutions (referenced whenever relevant hereafter in thetext).

The unbiased assessment of population involvement in specificactivities is not a simple task because employment can be informal,irregular or indirect. Here, quantitative estimates of employmentlevels relied on estimations of the labour force required at severalstages of the commodity chain: farms, conditioning plants, andinput salesmen. One of the three major conditioning plants wasvisited. Chief and section managers were questioned about theoperations conducted within the plant and about the labour forcerequired to perform each operation. Data was normalized by themass of shrimps processed in order to allow for interannual com-putations. Information about the same operations in other plants

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e12 5

confirmed these numerical estimations. The assessment of jobs inthe transformation chain is based on the following empiricalequation:

Ep ¼ ½ðpþ yÞ*xþ ðqþ sÞ*w�=z (1)

where Ep is the number of annual full-time jobs per plant, p is thetotal mass of shrimps produced (in 106 g), q is the mass of wholeshrimps destined for export (in 106 g, 10% of the production onaverage), s is the mass of unbeheaded shrimps (in 106 g), x is theaverage number of labourers involved in beheading operations(x ¼ 8$10�6 g), w the average number of people required forfreezing and conditioning operations (w ¼ 10$10�6 g), y the pro-portion of total production to be beheaded (y ¼ 0.9), and z thenumber of days worked by each employee (z ¼ 260).

A dozen of grow-out farms were visited, ranging from extensiveto intensive and from medium to large-scale. Farm managers werequestioned about the labour force required for permanent andtemporary operations. External agents were also questioned abouttemporary work loads. The following information was sought:number of permanent workers for grow-out operations underdifferent production intensities (ranging from extensive to inten-sive), proportion of skilled workers, number of temporary workersand number of annual production cycles. Because numerical datagiven by farm managers were suitably convergent, an average ofreported figures was calculated. These numerical data were alsoconsistent with estimations made by Berger et al. (2004). For on-farm operations, separate functions were computed for perma-nent and temporary workers. Employees include both skilled(technical, administrative, secretarial) and unskilled workers (forgrow-out operations, security, monitoring), whereas the temporaryworkers are hired for harvesting and cleaning tasks. The empiricalformula for on-farm employees is:

Epf ¼ Q*F þM*SIþ N*I (2)

where Epf is the number of permanent workers on the farm, Q theaverage number of skilled jobs per farm, F the number of farms, Mthe number of permanent unskilled workers per hectare for semi-intensive and extensive farms (M ¼ 0.2), N the number of perma-nent unskilled workers per hectare for intensive farms (N ¼ 2), SIthe area of semi-intensive and extensive farms (in ha), and I thearea of intensive farms (in ha).

For temporary workers the function is:

Et ¼ A*B*V þ I*B*W (3)

where Et is the number of temporary workers, A is the total pro-duction area (in ha), B is the average number of cycles per year, V is

Table 3Land use changes detected by remote sensing methods.

Period Qualitative land use changes Quantita

Time-slicedevolution

1962e1977 Expansion of aquaculture Average1977e1991 Development of ponds Gained a

Coastline variation Accretion1991e2000 Interruption of aquaculture Developm2000e2003 Recovery of aquaculture w1000 h2003e2007 Continued recovery of

aquaculturew1000 h

Summary1962e2007 Expansion of agriculture Gained a

Coastal accretion w375 hasand spit

Development of fish ponds Mangrov

the number of workers needed per harvest and per hectare, W thenumber of workers needed to clean the intensive ponds after har-vesting operations, and I the area of intensive farms (in ha).

The total number of jobs was calculated from equation (4):

Ed ¼ Epf þ Epþ Etþ T þ U (4)

where Ed is the total number of jobs, T is the number of individualsworking in local services dedicated to aquaculture (such as foodand input supplies), and U is the estimated number of workersworking in undeclared farms. Other variables are as given inequations (1)e(3).

A questionnaire was submitted to unskilled workers (n ¼ 70)and served several purposes. Its aimwas to estimate the proportionof migrants among the unskilled worker population and to identifythe determinants of the migration at individual, household andcontextual levels. Because most farmworkers live most of the timeon the farm, surveys were carried out on the farm during the rest ofthe time. Six farms presenting a range of production intensitieswere surveyed. Respondents were selected randomly among theworkers, i.e. without indicating our intended focus on migrants.The questionnaire included a general section dedicated to allworkers and a special section concerning immigrant workers.

4. Results and discussion

4.1. Land cover and land use change

Land cover changes observed from the six diachronic land usemaps produced (see Supplementary Material for five of thesemaps) have been interpreted and summarized in Table 3. The mapsequence provides a detailed record of habitat depletion for each ofthe time slices indicated in Table 3. This table includes only non-seasonal changes, i.e. it does not consider phenological changesin the ecosystems or cropping systems. The successive main landuse changes are related to the development of agriculture, thedevelopment of shrimp farming and the variability of shrimp pro-duction. The main transformative process occurring in the studyarea during the second half of the 20th century has been thedestruction of natural habitat by agriculture and aquaculture.Agriculture first developed on fine-textured bare soil and man-grove in the delta and along the small river floodplains, and it waspromoted in this lowland environment by the introduction of high-yielding rice varieties and new irrigation schemes. Between 1977and 1991, the ponds appeared primarily on bare soil (which in-cludes beaches and saline soils with scattered halophytes, e.g.Distichlis spicata and Sesuvium portulacastrum), mainly on thelandward side of the mangrove belt. Mangrove and dry forest

tive estimate of impact

of 47 ha yr�1 gained at the expense of bare soil (526 ha) and mangrove (185 ha)t the expense of mangrove (600 ha), dry forest (500 ha) and bare soil (2000 ha)associated with channel avulsionent of bare soil at the expense of water bodies (w1800 ha)a of recovered ponds, scattered along the coasta of recovered ponds

t the expense of bare soil (1330 ha), dry forest (852 ha), savanna (853 ha)of new coastal sediment (i.e. w3 km of seaward progradation) near present day

e (w1000 ha), bare soil (1000 ha), savanna (1490 ha), dry forest (700 ha)

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e126

located on the mangrove fringes were first to be cleared. Somefarms, however, were also implanted as enclaves in the mangroveheartland. Although the bulk of the mangrove was converted toponds, some portions were also deforested for building the farmaccess roads and bridges (INRENA, 2007). El Niño (1997e1998) andthe WSS outbreak episode explain the reduction of areas underproductive aquaculture during the 1991e2000 decade. Estimatingthrough remote sensing alone the shrimp farming areas that tem-porarily halt production is a difficult task because of the difficulty indistinguishing between naturally bare soil and disused (i.e. driedup) ponds based on spectral signatures alone. However, a visualinspection of the maps in the Supplementary Information showsthat the total change (w1800 ha) correspondsmostly to a decline inpond use. During that same time interval, however, some newfarms also developed on bare soil (w500 ha). The area corre-sponding to ponds that recovered during the following period(2000e2007) is w2000 ha.

A more comprehensive account of the proportion of land coverconverted to ponds is best provided by the map of land use changebetween 1962 (estimated from aerial photography) and 2007(obtained from SPOT 5) (Fig. 4, see Supplementary Information fora colour version of Fig. 4). It reveals the contrast between the di-versity and heterogeneity of initial land cover types and the com-parative uniformity of present day land use as the delta becameprogressively converted to aquaculture. In total, the percentages oforiginal land cover that have been converted to shrimp farms be-tween the coastline and the pan-American highway are 16%, 18%,

Fig. 4. Changes in land us

14% and 28% for mangrove, bare soil, dry forest, and savanna,respectively. The absence of environmental and land use planningpolicy enforcement gave a free hand to indiscriminate aquaculturedevelopment, yielding a relatively anarchic spatial pattern of farmoccurrence. Depletion of the TumbesePiura dry forest, recognizedin this region as containing high rates of bird endemism (Best andKessler, 1995), raises conservation issues of international propor-tion. Like the Guayaquil flooded grasslands in adjacent Ecuador, thistropical and subtropical broadleaf woodland is listed as a remark-able terrestrial ecoregion by theWorldWide Fund for Nature and isreally a mosaic of many habitats, with at least 14 endangeredspecies and a catalogue of nearly 500 species of bird, mammal,batracian and reptile. The risk of desertification relating to theincrease of grassland savanna over woodland is another concern.

The encroachment of aquaculture on bare soil (whether dry orwet) has also impacted natural drainage because this type of landcover mostly corresponds to creeks in the intertidal zone. Asa consequence, the mangrove ecosystems that depend on the ebband flow of water in the creeks have been affected (INRENA, 2007).The construction of canals by farmers has also increased floodhazard in built-up areas. The impacts are thus not limited to theconverted areas but also have off-site effects. Shrimp-farm efflu-ents, which diffuse to the surrounding water bodies, usually dam-age both flora and fauna (Gräslund and Bengtsson, 2001; Pàez-Osuna, 2001). Evidence of such impacts on the local flora andfauna would require a purpose-designed ecological investigation,but previous studies have already highlighted a link between the

e from 1962 to 2007.

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e12 7

development of shrimp farming and the reduction of fish catchesand crab populations (e.g. Cardisoma crassum) within the Tumbesmangrove area (INRENA, 2007; McClennen, 2004).

Deforestedmangrovebetween1962 and2007 ismapped in Fig. 5(see Supplementary Information for a colour version of Fig. 5). Itreveals that 1228ha ofmangrove havebeendestroyed, afigure closeto official data (1278e1294 ha) but less than claimed by environ-mentalists (3000e4500 ha) for that same time period. Depletionrepresents about one sixth of the total mangrove area. The creationin 1988 of a 2972 hamangrove sanctuary, unique in Peru and furtherrecognized as a Ramsar site (wetlandof international importance) in1997, was a direct consequence of aquaculture development. It hasbeen effective in the limitation of encroachment by aquaculturewithin the limits of the sanctuary but much less in its buffer area,which comprises patches of dry forest and salt marsh and wasdesigned to reduce extractive activities such as logging. Conversionof forested land to aquaculture had a direct impact on natural re-sources andon the level of ecological goods and services (Sathirathaiand Barbier, 2001). The extension of aquaculture at the expense ofmangrove habitat raises questions of sustainability because themangrove habitat supplies natural resources and ecosystem ser-vices of direct utilitarian value to shrimp farmers (post-larvae,nutrient cycling). Because fish, molluscs and crustaceans thatdepend on the mangrove habitat are routinely harvested by small-scale fisherfolk and collectors (INRENA, 2007), the reduction inmangrove land cover has also negatively affected livelihoods.

Avulsion of the main Tumbes channel causing migration of theriver mouth has occurred several times as a consequence of Niño-related floods. Fig. 5 maps the shoreline variations between 1962and 2007 resulting from the beach erosion and accretion processesin response to Niño events. Because of the limited number ofshrimp farms pumping Tumbes river water, the impact of flowextraction on river discharge is deemed limited and thus has notplayed a key role in the observed shoreline variation. Some farms,however, have suffered the consequences of shoreline variations,with several farms located near the beaches having ceased to

Pu

Pu

Puert

N

N

NPa

Pa

Pa

Fig. 5. Mangrove depleted by aquaculture betwee

operate the more exposed ponds. Others farms have plantedmangrove vegetation in the hope of stabilizing the shoreline. Thereis no evidence of newly developed farms since 2007 in the studyarea. However, some new farms have appeared to the back of thebeach in the southern part of Tumbes Department. These new in-stallations have caused detectable losses of dry forest.

4.2. Employment in the shrimp farming sector

Peru lacks official statistics about employment in the shrimpfarming sector (Evans and Tveteras, 2011). Based on our own data,Fig. 6 shows the evolution of total employment between 1980 and2006. Employment after 2006 was not computed because infor-mation about surface areas under semi-intensive and intensivefarming is scarce. A minimum was attained in 2001 (in the middleof the WSS epidemic) with 439 full-time jobs, and the peak wasreached in 2006, with 2660 full-time jobs. This is consistent withthe estimation of 1130e2260 permanent employees given by Evansand Tveteras (2011). Our estimate does not take into account thepost-larvae collectors (larveros) who used to work along the bea-ches and tidal channels until this activity was definitively banned in2000. Most of themwere previously in farming and came from theAndean provinces during the shrimp boom (Peña-Ruiz, pers.comm., April 2007). According to the INEI (2009), there were 4000larveros in 1997 and only 300 in 2002. Approximately 70% of themstayed in Tumbes after the ban (Peña-Ruiz, pers. comm., April2007). On-farm permanent work is the most important source ofjobs before temporary work on farms and in conditioning plants.The number of jobs has undergone important changes, with somebooms in 1986e1988, 1993e1997 and 2002e2006 and some bustsin 1990e1991 and 1998e2001. While busts are mostly related toenvironmental shocks and viral outbreaks, booms are related toeconomic incentives and technological innovation.

A more accurate estimate of the people directly or indirectlydependant on aquaculture requires family members to be includedbecause wages are locally shared with household members or sent

erto Pizarro

erto Pizarro

o Pizarro

0 5 10 sretemolik5,2

0 5 10 sretemolik5,2

0 5 10 sretemolik5,2

1962 / 1991

1991 / 2007

cific Ocean

cific Ocean

cific Ocean

Recession

Progradation

Rivers

Land mass

Recession

Progradation

Rivers

Land mass

Depleted mangrove

Land mass

n 1962 and 2007, with shoreline variations.

1980 1985 1990 1995 2000 2005

010

0020

0030

0040

00

Years

Full−

time

jobs

TotalFarm − permanent

Farm − temporaryConditioning plant

Undeclared farms

PL shortage

El Niño

Cholera

WSSV

Intensification

Fig. 6. Full-time jobs in the local shrimp commodity chain.

1 The currency rate exchange between US dollar and Peruvian sol in April 2007was: 1 USD ¼ 3.06 soles.

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e128

to the family by single migrants. Based on a conservative estimateof three beneficiaries per household, a minimum population of8000 is thus estimated to depend on aquacultural wages. This fig-ure is based on the hypothesis of full-time employment in thesector, but given that most of the workers are employed on a part-time basis, the estimated population reliant on aquaculture is likelyto exceed 10,000. This figure is less, however, than the estimate of20,000 by Berger (2002).

The w10,000 jobs can be differentiated according to whetherthey are contract-based or not, to wage levels, working conditions,security levels, and variability in time. In Tumbes, the workingpopulation represents 54% of the total (INEI, 2009). On that basis,the proportion of the working population employed in the aqua-culture commodity chain reached a maximum of 4% in the early1990s. This estimation does not consider indirect employmentcreated through the local expenditure of wages, e.g. on trans-portation, food, accommodation, retail, construction, or leisure. Italso excludes activity losses (small-scale farming and livestock) indry forest areas due to land conversion.

4.3. Shrimp farming and migration

From the set of unskilled workers we interviewed, 81% of themare internal migrants, all male andmostly young. An overwhelmingproportion of the migrants comes from Piura Department (87%),which is the adjacent province to the south, 7% from Lima, 2% fromCuzco, 2% from La Libertad and 2% from Cajamarca (Table 4 andFig. 7). Geographic proximity is evidently a cause in immigrantprovenance: Piura is the only Peruvian region contiguous withTumbes, with the two respective provincial capitalsw300 km apartby road. The bulk of migrants from the Piura region come from itsrural and mountainous eastern provinces. These consist of deepvalleys exposed to floods and soil erosion with small, low-productivity farms (Rubio, 2007). Biophysical and agriculture-related structural factors thus appear to be major constraints oneconomic prosperity. This is confirmed by poverty and extremepoverty indices, which are based on household level income andexpenditure (INEI, 2009) and are nationally much higher in themountainous provincesd respectively 72% and 39%d in the Andescompared to 45% and 5% in the coastal areas (INEI, 2009). In TumbesDepartment the extreme poverty index is 7.4%. The advantages ofTumbes are linked to factors already mentioned such as interna-tional trade and the production of export commodities such as rice,banana and shrimp. The main migration stream, therefore, isclearly from rural and mountainous to urban and coastal areas.

The threemainmotives given by themigrants for emigrating areeconomic: they expect to improve their standard of living, finda job, and support the household (Table 4). These all arise from pushfactors. Push factors, which can either be environmental, economicor social, are unfavourable conditions that prevail in the place oforigin; conversely, pull factors are attractive conditions that prevailin the place of destination (Lee, 1966). In the last several years,agriculture in Piura has been adversely affected by El Niño anom-alies and by an absence of effective agricultural policies. Together,these have further marginalized farmers who were already vul-nerable to agrarian problems (Rubio, 2007). Pull factors are relatedto needs in the labour market and to the presence of relatives oracquaintances. The availability of jobs in shrimp farming ranksthird among the list of pull factors, with 22% of migrants choosingTumbes because of the aquaculture industry (Table 4). These factorsare linked to the existence of social networks, i.e. links betweenindividuals from the same community or kinship group, regardlessof their current place of residence, thus including prior migrants(Massey, 1990). The existence of these social networks, where in-formation about economic opportunities is intensively exchanged,explains why the migrants have chosen Tumbes and why almosthalf of them were aware of job opportunities in shrimp farmingbefore leaving Piura. Social capital, i.e. the network together withthe information or resources shared among individuals, thus con-tributes to the emergence of migration as a livelihood strategy byproviding a direction to potential migrants. Social capital completesthe pushepull paradigm, which successfully explained the differ-ence between places of origin and destination but failed to explainwhy and how people move to a place with qualities similar to thoseof other places (Curran, 2002).

The members of the social networks also support the migrantsduring the initial job seeking stages: earlier migrants succeed insecuring jobs on their farm for new migrants by virtue of themutual trust that has already had a chance to grow between themand the shrimp farmmanager. Several data confirm that statement:our survey indicated that 97% of the workers had obtained theirjobs through their social networks and that 80% of them hada relative already working in shrimp farming. As a result, everyfarm includes several clusters of workers coming from the samegeographical area or from the same kinship group, thus confirmingthe more widely recognized importance of social capital in migra-tion patterns (Portes, 1995; Gray, 2009). The presence of prior mi-grants within the social network fuels the influx of new migrantsbecause the latter are informed of opportunity costs and are pro-vided with appropriate material reassurances (Curran, 2002).

A majority of migrants (68.5%) send remittances to their family.On average, farmworkers send 40% of their wages to their families,i.e. 231 soles1 for an average monthly salary of 573 soles. Thesesavings are declared to be mostly invested in the services sector inthe province of origin, such as grocery retailing or automobilerepair, or are used for basic household needs. Although this aspectwould require a more detailed analysis, previous studies in Andeancountries and in Asia have shown that remittances and returnmigration sometimes reduce social resilience and increase in-equalities between individuals and households within and be-tween home villages because wealth is not redistributed (Adgeret al., 2002; Lipton, 1980). One of the consequences of these mi-grations is the evolution of the gender ratio in Tumbes Department,which has increased from 106 males for 100 females in 1993 to112:100 in 2005 (INEI, 2009). In 1993, considering just the morerecent migrants, the ratio even reached 135:100 (INEI, 2009). This

Table 4Characteristics of migrant population based on field surveys (n ¼ 57).

Variables (various units) Results

Former region of residence (%) Piura (87), Lima (7), Cuzco (2), Cajamarca (2), La Libertad (2)Time already spent in Tumbes (years)Average 6.6Standard deviation 6.3

Main reason for migration (%) Improve standard of living (53), Find a job (51), Help thehousehold (45), Exerce the present position (11), Live withrelatives (7)

Reason for choosing Tumbes (%) More working opportunities (66), Known resident person (35),Shrimp farming (22)

Awareness of shrimp farming jobsbefore leaving (%)

No (54), Yes (46)

Decision to migrate (%) Personal (90), Household (10)Migration participants (%) Alone (64), With family members (26), Other (10)First job after arrival (%) Shrimp farming (67), Agriculture (10), Manufacturing (2),

Services (21)Access to present job in shrimp

farming (%)Through friend (54), Through relative (43)

Remittances sent home (%) Yes (68.5), No (31.5)Average monthly remittances (pesos) 231Average proportion of wage remitted

(%)40

Estimated future duration of stay inTumbes (%)

Forever (20), 5 more years (9), From 1 to 5 years (22),Less than 1 year (14), Do not know (35)

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e12 9

imbalance has begun to pose serious local demographic challengesinvolving fertility and household renewal issues.

Although the majority of the population is employed on a per-manent basis, immigrants and locals do not occupy the same jobson the farms (Table 5). Locals obtain the better paid jobs in main-tenance and management. Furthermore, skilled jobs (not surveyedhere) are dominated by locals with higher educational status. Theseadvantages secure positions with higher income and fewer work-ing hours. For immigrants, the relatively lower condition isexpressed by a greater willingness to change jobs. Work in shrimp

Tumbes

Zarumilla

Contralmirante villar

PiuraMorropon

Sechura

H

Ayacaba

Ferrenaf

B

0 25 50

N

Pacific Ocean

Pacific Ocean

Tumbes department

A

EC

Fig. 7. Geographic origin and number of

farming is a transitional activity for the immigrants, who spendmuch less average time in this occupation than the non-migrants(4.6 against 8.8 years, respectively). The future of immigrants af-ter having left shrimp farming needs to be thoroughly investigatedbut local informants declared that they either chose to stay (thenworking in the services or fisheries sector, or as seafood collectors),returned to their homestead, or emigrated to Ecuador or tosouthern Peru. These are common situations but they were dra-matically intensified during the El Niño and WSS events. Thepopulation involved in resource extraction from the mangrove

uacabamba

e

Pacasmayo

Huamanga

C

A

C

75 100 kilometers

ECUADOR

Pacific Ocean

Lima

Piura department

B

PERU

UADOR

Nber of shrimp farm workers per district of origin

123 - 4

6 - 7912

Department

Province

shrimp farm workers interviewed.

Table 5Socio-economic profiles of immigrants and locals.

Variable (various units) Immigrant(n ¼ 57)

Local(n ¼ 13)

Average age (years) 31 33Time spent in shrimp

farming (years)4.6 8.8

Life cycle status (%)Single 58 31Married 21 61Cohabiting 21 8

Average number ofchildren

1.2 1.5

Education level (%)Primary 30 31Secondary 65 38Further/Higher 5 31

Previous job (%)Primary sector 46 31Manufacturing 6 23Services 40 38Other 8 8

Contract type (%)Permanent 87 92Temporary 13 8

Present work onfarma (%)Production 51 38.5Security 29 15Maintenance 10 38.5Management 4 8Ancillaryb 6 0

Weekly hours (h) 61 53Mean wage (pesos) 573 682Willingness to change

jobs (%)Yes (78) Yes (42)No (22) No (58)

a Production encompasses activities dedicated to the grow-out of farmedshrimps: feeding, fertilizing, pond cleaning, harvest. Security refers to guarding thefarms against intruders. Maintenance includes themaintenance of thematerial usedin production such as pumps or aerators. Management refers to decision makingwith regard to buying the inputs, to the daily operation of the farm, and to timing ofthe harvest.

b On-farm ancillary work involves activities such as cooking and cleaning thebuildings.

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e1210

sanctuary, for example, consists predominantly (65%) of migrantsmainly originating from Piura department (Ayabaca, Huancabambaand Morropon provinces) (INRENA, 2007).

Overall, immigrants are deemed to play an important role in theeconomic viability of Tumbes shrimp farms because of the lowerlabour costs compared to wage expectations among the localpopulation. This is important because reducing the cost of labour isa major target among shrimp farm owners in order to remaincompetitive. The clustering of relatives and acquaintances at farmlevel also strengthens trust between shrimp farmers and workers.For the migrants, the advantages of a job on a shrimp farm arelinked to the contractual engagement in which they find securityeven though the contract can be easily broken. Shrimp farms alsoprovide a job soon upon arrival, thus reducing the costs of migra-tion. Consequently, even though shrimp farming as a pull factorremains weaker than the push factors previously mentioned, therise of aquaculture has evidently contributed to an influx of labourfacilitated by the information provided by prior migrants aboutemployment opportunities in Tumbes.

4.4. Shrimp farming, society and the environment in Tumbes

4.4.1. Existing environmental safeguards and outstanding issuesThe previous sections have provided some insights into land use

change, employment in the shrimp farming sector, and internalmigratory flows towards Tumbes. Together, those insights illuminate

how shrimp farming in Peru has redefined the interactions betweenpopulation and the environment. Through its dual process ofextensification and intensification, and also its relatively volatileproductivity determined by environmental and market factors,shrimp farming has shaped the natural and social environmentsthrough its unprecedented use and degradation of natural resourcesaswell as by its requirements in terms of labour. Shrimp farming hasalso suffered under the impacts of its own externalities such as thepollution of canals by effluents. During the recent intensification ofthe industry, labour requirements grew and attractivity to migrantslikewise increased. Further integration of these immigrants into thelocal economy poses an ecological threat from the moment theychoose to exploit natural resources, but can alsobebeneficial to localsbecause immigrants are more willing to occupy the low-wage jobs.Due to increasing population in the coastal area, growing inequalitiesbetween skilled and unskilled workers and the competing uses ofnatural resources between various stakeholders have led on somefarms to acts of sabotage, arson and theft. Conflicts have opposedshrimp farmers to inhabitants of Puerto Pizarro who live on the pe-riphery of the shrimp farms.

The principles of Integrated Coastal Management have neverbeen implemented in the Tumbes region. Most of the policies thatrule the use of natural resources are sectorial and concern isolatedsegments of the territory. Conservation-oriented managementinitiatives were nonetheless adopted to tackle the depletion ofnatural resources, the most important policies dedicated to theconservation of coastal ecosystems having been promulgated in1978 (protection of channels, mangrove and dry forest) and 1988(creation of the mangrove sanctuary and its buffer zone). Thesanctuary was created because of the growth of shrimp ponds inthe biodiversity-rich coastal habitats. The enforcement of rulesdedicated to curbing shrimp farm encroachment on the sanctuarylimits has proved to be more effective than in the sanctuary’s bufferzone. Shrimp farm implantation has continued in the buffer zone,which is an area where conservation practices and more sustain-able activities should have prevailed.

Slack enforcement encourages over-harvesting of aquatic or-ganisms within the sanctuary boundaries by individual collectors,who also ignore best practice rules such as a restriction of har-vesting activities during the spawning season. The ban in 2000 onwild post-larvae collection along the beaches and tidal channels,which was designed to prevent the intrusion of virus-bearing lar-vae into the production ponds, positively contributed to a reductionof industry-related environmental impacts not just because it hel-ped to restore the importance of post-larvae in the food chain, butalso because the post-larvae harvesting was carried out using fine-meshed netting, a practice which entailed unsustainable by-catchof other aquatic organisms. The management of natural resourceswithin the sanctuary was also devolved to the local communityafter 1999 through the creation of a Management Committee,which includes ordinary citizens, representatives of the shrimpindustry, academic institutions and some small-scale farmers andfisherfolk. The purpose of the Committee is to ensure the sustain-able use of natural resources within the sanctuary and in its bufferzone. On the ground, dialogue remains limited but some progresshas occurred through the constitution of action groups dedicated topromoting tourism in the sanctuary. A recent collaborative projecthas been successfully developed by shrimp farmers, NGOs and theSERNANP (Servicio Nacional de Areas Nacionales Protegidas) forthe production of spats of Anadara tuberculosis, a local and over-exploited mollusc, with a particular focus on genetic diversity anddisease prevention. Overall, the management policies still remainexceedingly sectorial, i.e. do not take sufficient account of the di-versity of coastal activities and their interactions. Their scope is alsolimited in that they do not consider the entire coastal zone as an

F. Mialhe et al. / Ocean & Coastal Management 73 (2013) 1e12 11

integrated system. Finally, they remain largely ineffective becausethe existing regulatory framework lacks the appropriate resourcesfor enforcement.

Environmental regulations dedicated to controlling the effluentsreleased by shrimp farms were introduced in 1994. All new farmswere forced to carry out an environmental impact assessment (EIA)by a certified agency, and farms above 50 ha were required to pro-duce an EIA declaration every six months. However, local officialsopenly admit that farms do not comply with the rules. Encroach-ments and the absence of EIA compliance point to a connivancebetween the shrimp industry, politicians and environmental agencyemployees, both at local and national level. In addition to giving theindustry an opportunity to be competitive in the internationalmarketplace, the numerous fiscal advantages granted to the in-dustry are also interpreted as a consequence of cronyism.

Among the more positive recent developments, the strongreduction of antibiotics and substitution by native probiotics iso-lated from the wild shrimp microbiota is a welcome noteworthy (E.Mialhe, pers. comm. October 2012). The methodology for shrimpvirus diagnosis based on molecular tools also promises a decreaseof viral outbreaks into the environment, subsequently decreasingimpacts on wild shrimp populations.

Local officials also recognize the existence of many unautho-rized farms, particularly in the more remote areas. Some of themwere visited during the course of this study. These illegal farmsmaintain a tacit agreement with authorized farms to sell theirproduce to the conditioning plants, which require the farmers to bedeclared. This informal system is well known but the willingness orresources to police it remain elusive.

4.4.2. Outlook for the futureThe findings brought into focus by this study provide a basis for

formulating a few recommendations towards an improvement ofcoastal management in Tumbes. Although the perspective adoptedhere has been restricted to shrimp farming and does not, therefore,authorize prescriptions relevant to all aspects of Integrated CoastalManagement, considerations regarding land use planning, socialwelfare and local governance would suggest the following prior-ities: (i) stricter urban planning in the vicinity of existing ponds inorder to limit the total length of direct contact between residentialland use and ponds; (ii) a moratorium on habitat fragmentationthrough stronger enforcement of existing resource harvesting pol-icies; (iii) a regeneration of forest habitats and a restoration of baresoil areas (beaches, salt marshes); (iv) improved design of canals forboth water intake and effluents. (v) Better monitoring of immigrantlabour should alsohelp to anticipate the increase in local demand forgoods and services. Migrant workers would also gain from a stricterenforcement of labour laws, which would not only improve theireconomic status and working conditions but could also limit theurge to engage unsustainably in the harvesting of wild species.

The setting up of the Management Committee in 1999 remainsa landmark among the more innovative governance schemes in theregion. Other frameworks conducive to dialogue between the dif-ferent agencies involved in shrimp farming are called for, one beingcross-border cooperation with Ecuador. This perspective wouldallow watershed-scale integrated planning, particularly given thatgold mining activity in the Ecuadorian part of the Tumbes rivercatchment has been releasing inorganic mercury and sodium cya-nide in the water, which raises concerns for the shrimp productionin the coastal areas (Guimaraes et al., 2011).

5. Conclusion

This case study has analysed some impacts triggered by thedevelopment of shrimp farming in northern Peru. Since the first

appearance of ponds in the late 1970s, shrimp farming has expe-rienced severe upsets due to external environmental factors such asEl Niño and world market instabilities, but also to internal mis-management. The growth of aquaculture has also induced socialand economic changes: shrimp farming has created a labour mar-ket draining migrants from poorer mountainous regions. In addi-tion to the attraction exerted by shrimp farming, social capital wasalso found to be a major driver of migration. The production chainrelies on a diversity of segmented labour tasks. Shrimp farming wasestimated to support the livelihoods of 10,000 individuals con-tributing to the local economy, but a more thorough diagnosiswould also require accounting for livelihoods that were destroyedor stifled by the development of commercial aquaculture. Byremote sensing analysis we quantified and qualified the areas overwhich aquaculture-related land use has expanded. As in othercontexts throughout the Tropics, aquaculture has expanded at theexpense of mangrove but the intensity with which this has occur-red must be put into perspective because aquaculture has alsodeveloped over land cover categories initially detected as bare soil,dry forest, and savanna. A moratorium on the destruction of relictmangroves has been in place since 1988 through enforcement ofa habitat conservation policy. Recent history reveals several adap-tations of the local socialeecological system such as the adoption ofnew management practices and an intensification of productionsystems. By providing a quantitative account of changes in land use,farmed shrimp production, labour markets and a qualitativeassessment of migratory flows, this case study contributes to theongoing global debate on the processes and policies best adapted toattaining sustainability in resource allocation and management. Itpromotes a holistic perspective on the impacts of shrimp farmingon the socioeconomic and natural environments at the local andregional levels, with global ramifications and feedbacks relating toworld markets and to epidemiological and climatic hazards.

Acknowledgements

The authors acknowledge the Isis program, Centre Nationald’Etudes Spatiales (CNES), for providing SPOT 5 images at a nego-tiated price. Three anonymous reviewers contributed helpfulcomments, resulting in a more balanced treatment of the manyissues and specialisms that we have attempted to combine here ina cross-disciplinary synthesis.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ocecoaman.2012.12.014.

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