Doi:10.1016/s0025-326x(03)00107-3

Marine Pollution Bulletin 46 (2003) 806–815 Shrimp aquaculture development and the environment in the aez-Osuna a,*, A. Gracia b, F. Flores-Verdugo a, L.P. Lyle-Fritch c, R. Alonso-Rodrııguez d, A. Roque e, A.C. Ruiz-Fern a Unidad Academica Mazatlan, Instituto de Ciencias del Mar y Limnologııa, Universidad Nacional Autonoma Mexico, b Instituto de Ciencias del Mar y Limnologııa, UNAM, Apdo. Postal 70-305, Mexico D.F. 04510, Sinaloa, Mexico c Secretarııa del Medio Ambiente y Recursos Naturales, Apdo. Postal 1177, Mazatlan 82000, Sinaloa, Mexico d Posgrado en Uso, Manejo y Preservacion de los Recursos Naturales, Centro de Investigaciones Biologicas del Noroeste Sinaloa, Mexico e Unidad Mazatlan en Acuicultura y Manejo Ambiental, Centro de Investigacion y Desarrollo, Mazatlan, Sinaloa, Mexico Beginning in the middle of the 1980s, the Gulf of California ecoregion experienced a boom in shrimp aquaculture and became the second largest producer in the western hemisphere. The moderated, but continual development of shrimp farming, in conjunctionwith municipal and agriculture effluents has been accompanied by concern about: (a) depletion of fishing stocks, (b) reduction ofmangrove forest, (c) frequent harmful algal blooms in coastal waters and shrimp ponds, and (d) water quality deterioration. Wedemonstrate that environmental degradation resulted from a conjunction of factors including agriculture, untreated municipaleffluents, shrimp aquaculture, increasing number of fishermen, and an absence of an effective regulatory program. We recommendthe immediate implementation of an integrated coastal management program to protect the integrity of the coastal ecosystems andoperate upon the principle of environmental sustainability for the different economic activities including shrimp aquaculture.
Ó 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Shrimp aquaculture; Mangroves; Fisheries; Algal blooms; Water quality; Gulf of California The Gulf of California is a semi-enclosed sea on the Pacific coast of Mexico, one of the most biologically About 97% of shrimp aquaculture ponds in Mexico diverse regions in the world with approximately 6000 are located around in the Gulf of California at the states reported macrofaunal species (Hendrickx et al., 2002).
of Baja California, Baja California Sur, Sonora, Sinaloa This is a high productivity subtropical area with ap- and Nayarit. Since 1985, there has been an expansion in proximately 258,593 km2, which is situated between the shrimp aquaculture with the greatest increase in north- Baja Peninsula and mainland. The Gulf of California west Mexico so that this country has become the second region is characterized by the presence of approximately largest producer of farm-raised shrimp in the western 900 islands, 40 estuaries and lagoons. The Gulf of Cal- ifornia ecoregion defined by the World Wildlife Fund cerns about the possible effects of the installation of includes the ecologically important Marismas Nacio- shrimp facilities and pond effluents on coastal ecosys- nales (National Marsh) that lies south of the Gulf tems. This expansion, apparently without control, has proper. The Gulf and the adjacent ecosystems are pop- caused conflicts with other activities, such as traditional ulated with a multiplicity of marine mammals, birds, fisheries, agriculture and tourism.
reptiles and a wide variety of fish and shellfish. The re-gion supports fisheries, tourism, intensive agriculture,mining, and recently, shrimp aquaculture. These activi- ties and the presence of around 5 millions of inhabitants Corresponding author. Tel.: +669-9-852845; fax: +669-9-826133.
constitute a serious threat to the rich and complex bio- 0025-326X/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0025-326X(03)00107-3 aez-Osuna et al. / Marine Pollution Bulletin 46 (2003) 806–815 The wet ecosystems of the Gulf ecoregion comprises a is 23.5%. This ÔdeficitÕ (10,137 ton) is worth $65–135 great variety of habitats that include mangrove forests, salt-marshes, intertidal pools, swamps, freshwater innerlagoons, brackish and seawater systems, where there is arich and complex food chain. These habitats are im- 3. Development and characteristics of shrimp farming portant breeding ground for birds, fish, crustaceans, andmammals. Additionally, these ecosystems constitute SAGARPA/CONAPESCA (2002) report the total important fishery grounds and favorable conditions for area dedicated to shrimp farming is 52,648 ha, of which aquaculture; the lagoons provide nursery grounds for 51,059 ha (%97%) are located around the Gulf of Cali- postlarvae shrimp as well as for commercially important fornia; Baja California, 190 ha; Baja California Sur, 128 fish species.The whole Gulf of California ecoregion ha; Sonora, 9951 ha; Sinaloa, 37,390 ha; and Nayarit, contains substantial areas that have been considered suitable for shrimp farming; De la Lanza-Espino et al.
The range size of farms in the Gulf of California re- (1993), estimated 236,000 ha of lowlands potentially gion vary from 4 to 1200 ha, with a mean estimated at available for the shrimp aquaculture for the Gulf of 150 ha. The pond size also is variable (<2 and 40 ha), 2– 15 ha being predominant. The more common manage- Shrimp aquaculture and its sustainability here has ment system in the region is the semi-intensive type become controversial. On one hand, traditional fish- which occurs in 89% of the farms, while intensive and ermen from open sea and coastal lagoons are con- extensive types comprise 2% and 9%, respectively. The fronting shrimp farmers due to coastal ecosystem mean stock density for intensive shrimp farms is 58 damages and the consequent decrease of fisheries yields.
postlarvae mÀ2 (PL mÀ2), for the semi-intensive 13 On the other hand, numerous farm owners and oper- PL mÀ2, and for extensive 7 PL mÀ2; 39% of the farms ators of shrimp farms report that catches of wild stocks blue shrimp (L. stylirostris), 37% stock white shrimp in both open and coastal systems have de- shrimp (L. vannamei) and 24% stock both shrimp species clined because of over-exploitation and contamina- (Lyle-Fritch et al., 2001). During 1999, in Sinaloa 74% tion of the coastal zone. Shrimp farm owners indicate of shrimp farms operated two cycles per year, and the that the develop of the shrimp farm have been poor rest only one. However, in 2001 and 2002 the tendency or moderate, due essentially to problems of land pos- has been to reduce the number of cycles per year due to session, lack of government stimulus, and increasing the decreased crops during cold months. The duration of the cycles fluctuates between 120 and 140 days de-pending on season, marketing demand, and diseases.
More details on the management and characteristics of shrimp ponds are summarized in Table 1.
The shrimp fishery in the Mexican Pacific is mainly supported by three species: Litopenaeus vannamei (white shrimp), Litopenaeus stylirostris (blue shrimp), Farfan-tepenaeus californiensis (brown shrimp), and to a lesser Legal aspects of mangrove conservation in Mexico extent Farfantepenaeus brevirostris (crystal shrimp) and are included in the regulation 059 of the Federal Law on Trachypenaeus pacificus (zebra shrimp). Fishing of the the Ecological Equilibrium (Anonymous, 1988); white first two species has reached critical situation, and cat- mangrove (Laguncularia racemosa), black mangrove ches of brown shrimp and crystal shrimp are at their (Avicennia germinans), and buttonwood (Conocarpus maximum sustainable yield (INP, 1998). Shrimp farm- erectus) are under special protection, and the red man- ing represents the only alternative for a substantive in- grove (Rhizophora mangle) is considered as a rare species. Despite legal efforts concerning mangrove con- In 2001, a total of 17,487 ton and 10,586 ton of servation, legislation on this matter is still deficient and shrimp were caught by the fleet from the coasts of Sin- aloa and Sonora, respectively (SAGARPA/CONAP- There is significant uncertainty about the total area of ESCA, 2002); which is 78.7% of the Mexican Pacific and mangroves in Mexico, and the magnitude of shrimp 48.8% of the total for Mexico. In the last two decades, aquaculture impact on these ecosystems is unknown.
shrimp catches in Sinaloa and Sonora have declined However, on a regional scale, there is evidence of significantly, from an average annual catch of 24,316 ton mangrove destruction in Sinaloa and Nayarit. The and 15,718 ton, respectively, during the 1980s, to 17,587 Federal Agency of Environmental Protection, PROF- ton and 11,012 ton, respectively, for the 1990s (Fig. 1), EPA (Procuradurııa Federal de Protecci i.e. a reduction of 28–30%. When global shrimp catch in considers that Sinaloa has problems of shrimp fishing the entire Gulf of California is examined, the reduction during the prohibited season as well as of mangrove aez-Osuna et al. / Marine Pollution Bulletin 46 (2003) 806–815 Fig. 1. Gulf of California ecoregion. Localization of zones with major density of shrimp farms (shadow areas). Tendency of the shrimp catch (filledcircles) and shrimp farming (unfilled circles) production from the Gulf of California ecoregion (Â103 ton/y) by state and globally during the 1980–2001 period (Baja California and Baja California Sur have an catch and shrimp farming <710 ton/y) (data from SAGARPA/CONAPESCA, 2002).
deforestation for shrimp farm construction. In terms of Berlanga-Robles (1999) observed that drying lagoons in vegetation coverage, the degree of mangrove deteriora- the Huizache-Caimanero system (Sinaloa), caused a tion in Mexico is not as evident as in other countries.
20% loss of water surface from 1973 to 1997 and an Growth of shrimp aquaculture has been moderate and increase of the adjacent seasonal salt pans. The authors mostly concentrated in seasonal flood plains.
considered that the impact to the system was a conse- Despite discrepancies with mangrove extension, sev- quence of a reduction of deciduous tropical forest for eral authors have agreed that Sinaloa and Nayarit are agricultural purposes, and a 50% decrease of mangrove among the four states with more mangrove surface in forests was observed between 1973 and 1997. In addition the country (Flores-Verdugo et al., 1992; Tovilla, 1994).
to the elevated rate of mangrove deforestation (1.9% per Tovilla (1994) estimated an area of 153,409 ha in Nay- year), mangrove coverage in this zone is scarce and with arit, and 74,539 ha in Sinaloa; these regions with a patchy distribution that aggravates an unstable con- Campeche (117,000 ha) and Chiapas (70,000 ha) com- dition. Carrera and de la Fuente (2001) report that in prise more than 60% of the national mangrove forest Marismas-Nacionales (Nayarit) about 1456 ha of wet- lands have been replaced by shrimp farm ponds.
In Sinaloa, development of shrimp aquaculture and Though digital images of mangrove impact by aqua- other anthropogenic activities was studied, in order to culture have been made in Mexico and have demon- assess their impact on mangrove and salt marsh eco- strated a non-significant perturbation, such estimations systems as well as on the surrounding terrestrial eco- determine vegetal coverage and not forest structure in systems. In Ceuta lagoon (Sinaloa), Alonso-P terms of density and basal area. Agraz-Hern observed changes of land use mainly by agriculture (1999) found that in Estero de Urııas (Sinaloa) mangrove (141% increase from 1984 to 1999) but no mangrove density around shrimp farms has decreased 50% in damage by aquaculture was detected. Ruiz-Luna and comparison with mangrove located elsewhere. In the aez-Osuna et al. / Marine Pollution Bulletin 46 (2003) 806–815 Table 1Characteristics of the shrimp ponds at the Gulf of California ecoregion a Generally polyethylene.
b Number of postlarvae per m2.
c Dry feed added/wet weight of shrimp harvested.
Gulf of California ecoregion mangrove forests are dis- interrupt seasonal streams and tidal channels affect- tributed in narrow fringes of less than 30 m width, such ing mangroves by altering fresh water availability mangroves border tidal channels that escape image and the flooding periods. Such events are particularly resolution (e.g. 80 Â 80) of some satellites as well as the critical in semiarid regions of the continental margin scales (>1:30,000) of some aerial photographs or maps.
of the Gulf of California and might induce mortality Such mangroves are particularly sensitive to changes in of vast mangrove zones, particularly those species hydrological patterns due to their marginal distribution, under environmental stress. Levees of roads to and are easily displaced by a variety of human activities shrimp farms and fishing sites pose a similar hazard and natural events. Nevertheless and despite their lim- to mangroves when they alter tidal channels. Pump- ited distribution, in dry and semidry regions they are key ing operations for water exchange in shrimp farms ecosystems as feeding grounds and rest areas for mi- can cause significant changes in the hydrodynamic gratory birds and as an additional energy supply for patterns of coastal lagoons. Additionally, an artifi- trophic chains of adjacent terrestrial ecosystems (Flores- cial rise of water levels in ponds enhances saline in- In southern Sinaloa, Ruiz-Luna and Hernandez- (b) Hypersalinity. Water evaporation in shrimp ponds Cornejo (1999) showed that 4 of 19 shrimp farms have has been estimated to increase 50% in comparison replaced mangroves. Most shrimp farms in Sinaloa are to natural wetlands (Twilley, 1991). With this high located in the central and northern regions where it is evaporation rate, discharges of hypersaline waters possible to find shrimp ponds that interrupt the natural to the adjacent estuarine system are significant.
distribution of mangroves. This is evidence that man- Consequently, the increased salinity is particularly groves are being displaced by shrimp farm facilities. In critical for mangroves, especially for white man- the state of Nayarit, and particularly in San Blas, ma- grove (L. racemosa) which has a high affinity for ture mangrove ecosystems have been destroyed during fresh-estuarine waters (Kovacs, 2000). An elevation construction of shrimp ponds. The implications and of interstitial salinity can induce mangrove mortality magnitude of the damage are still unknown.
The main indirect impacts from shrimp aquaculture (c) Eutrophication. Though eutrophication has a minor on mangroves in the Gulf of California region were: effect on mangroves, communities that live attachedto their roots suffer changes in their structure and (a) Changes in the hydrological pattern. Shrimp pond le- distribution. Phytoplankton and macroalgal blooms vees change the pattern of runoff and sometimes they develop in tidal channels and lagoon systems. When aez-Osuna et al. / Marine Pollution Bulletin 46 (2003) 806–815 excessive growth of macroalgae occurs, they are natural wetlands inside aquaculture facilities. Aquacul- transported by tidal currents toward mangroves ture facilities should include ponds with filtrating or- and affect colonization processes by seedlings and ganisms (bivalves) and ponds with mangroves or other propagules. When macroalgae accumulate on man- aquatic macrophytes for water reuse.
grove seedlings, they block sunlight and increasethe contact surface, facilitating tidal flows which re-move propagules and seedlings from the soil.
5. Wild postlarvae and the shrimp fisheries In general, though mangrove impact by shrimp When larvae laboratories are not available or in short aquaculture in the Gulf of California region, is not as supply, a common source of postlarvae is direct ex- high as in other regions of Latin America and Asia, an traction from the wild. It is generally thought among integrated management plan for every hydrological farmers that these postlarvae are more resistant because basin is necessary in order to regulate all the activities.
they survive better and wild seeds also have a relatively lower cost than larvae from laboratories. However, wild propose the following ecological criteria as mitigating postlarvae supply is subject to spawning seasonal fluc- measures of mangrove impact: (a) Shrimp farm facilities should be developed, preferentially, in non-vegetated On the other hand postlarvae exploitation from the seasonal flood plains; (b) Infrastructure development environment poses a additional pressure on the shrimp should be based on studies of hydrological capacity, resource. One view is that the effect is negligible since flora distribution and buffer zones. Such infrastructure larval mortality is naturally high. In order to assess the should have only one road, one input stream, one impact of larvae extraction on shrimp populations, drainage channel for the several shrimp farms and Gracia (1989a,b) analyzed simulation models based on treatment systems for residual water; (c) About 30% or population parameters of white shrimp. The results more, of the farm surface should be kept in its original showed that the impact of larvae extraction was variable condition as a buffer zone between the farm and the depending on the stage of shrimp. There is a small im- agriculture lands in order to avoid saline intrusion, be- pact when extraction takes place at the first stages and tween farms so flooding are avoided and have a free increases exponentially in later stages, mainly in juvenile runoff from upper lands to the adjacent lagoon and from stages. Natural mortality is a critical factor too. Ac- the farm and the mangroves to avoid the border effect in cording to the analysis, postlarvae extraction has less the mangrove forest structure and as a potential zone for effect when organisms are caught in the coastal zone colonization; (d) Reestablish the runoff pattern toward close to the estuaries or coastal lagoons during shrimp mangroves by channels surrounding ponds. Mangrove reforestation on channel sides avoid erosion. Roads Once the organisms are established in the nursery should have culverts to allow tidal flows and terrestrial areas, the negative effect has an exponential increase; as a consequence, larvae extraction during the first juvenile To limit eutrophication: (i) shrimp farms should be stages can produce a high impact on shrimp populations restricted to non-vegetated seasonal flood plains and not and hence on total production. Fishing of small juveniles exceed 10% of the adjacent lagoon surface until the produces growth overfishing (Gracia, 1995, 1997a,b), hydrological capacity for removing nutrients without and the overall result is a decrease in total production.
eutrophication is known; (ii) In zones with agriculture, According to the author, total biomass reduction is discharge channels from shrimp ponds and agricultural higher as juveniles are younger; such fishing pressure lands should be connected into a single channel that poses risks to the optimal exploitation and the repro- carries wastes directly to the open sea, without contact ductive potential of shrimp populations.
with coastal lagoons, estuaries or bays. The aim of this Simulation analyses indicate that larvae extraction arrangement is to integrate agriculture and aquaculture has an impact on shrimp populations; the degree of the activities with ecological and economical functions of impact depends on the fishing effort and the age of coastal ecosystems into a single management plan. Ap- specimens. The effect on shrimp populations is propor- parently, the most suitable solution to avoid coastal tional to the number of larvae that are extracted for eutrophication is the dilution of waste discharge into the farming purposes; however, it could be minimal if ex- open sea (though not advisable for pesticides and other traction was carried out during the stages of high mor- substances that are not degraded); (iii) Use of adjacent tality incidence, i.e. before larvae enter breeding areas to mangroves as biofilters. The capacity of mangroves to settle. Shrimp exploitation during this stage is based on remove nutrients has been estimated as 2–3 ha of man- the strategy of minimal loss due to natural mortality grove needed per one ha of semi-intensive shrimp ponds (Watt, 1968). From this approach, the result would be (Robertson and Phillips, 1995). For certain zones man- that organisms that would die from natural mortality grove capacity is overloaded; (iv) Construction of semi aez-Osuna et al. / Marine Pollution Bulletin 46 (2003) 806–815 The application of this should consider several fea- would take place at postlarvae age where the impact on tures of shrimp populations related to biotic and abiotic the fishery is minimal. Moreover, postlarvae distribution components of natural mortality, reproductive strategies patterns offshore, and nursery ground immigration be- and any effects of accumulated mortality throughout havior, make it unlikely. Postlarvae distribution is not shrimp life cycle. An accurate estimation of the natural homogenous in time and space and it is known that they mortality is a basic requirement (Gracia, 1995), and a concentrate near lagoon and estuary inlets. Also, im- bias in the estimation of this parameter has important migration mechanisms are based on tidal movements consequences in fisheries management (Gracia, 1989b).
combined with postlarvae vertical migration. Postlarvae In the case of postlarvae and juvenile stages the prob- can remain near the bottom to avoid being carried off- lem is more complicated as reliable estimations of nat- shore when the tidal current is offshore and move higher ural mortality are scarce, so this parameter is considered in the water column during the opposite direction to to be high (without considering the effect of migra- enter estuaries and coastal lagoons (Macias-Regalado, tion). According to Alvarez et al. (1987) juvenile mi- 2001). However, as in the above case, further observa- gration in a given area can bias mortality by around tions are needed to give a sound opinion about a pos- 25%. When this bias is not considered, it could influence sible effect derived from pumping water on the fisheries calculations on shrimp extraction and management Nowadays, larvae extraction in Mexico is legal through regulation on their exploitation exist. Rules are 6. Harmful algal blooms and shrimp farming contemplated within Shrimp Mexican Official Norm(Norma Oficial Mexicana de Camar Most species of microalgae and many algal blooms and comprises shrimp species in Mexican waters; Sec- are beneficial for aquaculture; they provide a small but tion 4.4 refers to regulation applicable to shrimp species essential part of food indirectly to the rest of the food in their natural environment (larvae and postlarvae chain in the shrimp ponds. Under favorable environ- stages) that are currently used for the development of mental conditions, some microalgae species produce aquatic activities. Among these rules are: larva and harmful algae blooms (HABs) that can damage shrimp postlarvae catching can be authorized in (a) beach by consuming the oxygen in the water or producing fronts, with the exception of those beaches next to zones of water exchange between the sea and lagoon systems shrimp farms from some areas of the Gulf of California, and bays; (b) zones with temporal flooding; and (c) the observed effects were morbidity, mortality and a zones where shrimp larvae and postlarvae have little delay in the growth of shrimp that turn into an eco- From the above statement, the general concern on In Mexico, many of the most important ports and how increased shrimp farming could affect renovation of coastal towns are beginning to show symptoms of eu- the shrimp population is relevant. Current Mexican trophication. Red tides are common in the Gulf of legislation to control impacts are useful; however, key California, and especially frequent in: Kino Bay, aspects to consider are the observance of fishing areas Guaymas Bay, Angel de la Guarda Island, Yavaros and avoidance of extraction of benthic postlarvae. In this sense, the maximum size for collection (20 mm) should be smaller because at this size postlarvae have thetic ciliate Mesodinium rubrum causes most red tides and their presence has been associated with upwelling, Another aspect that deserves attention is related to the side effects of postlarvae extraction on other com- toxic species found in 94 red tides studied in the Gulf of ponents of planktonic communities. No studies on California were the dinoflagellates Gymnodinium caten- plankton bycatch exist. However, the lack of informa- atum and Gonyaulax polyedra ( ¼ Lingulolidium polye- tion makes it difficult to give a sound opinion based on During 1989–1991 several studies in two shrimp farms Another concern related to shrimp aquaculture and from northern and southern Sinaloa found algae that fisheries has appeared; fishermen claim that pumping are considered to be harmful or toxic for shrimp water transfers postlarvae to shrimp ponds causing an additional impact on wild shrimp populations and 2002a). The most abundant specimens were cyanobac- consequently on shrimp landings. Considering the teria Anabaena spp., Anabaenopsis elenkinii and Oscill- number of farms and the amount of water pumped, it is atoria limnetica; they colonize superficial waters and obvious that some postlarvae could be carried into the block light penetration that results in eutrophic condi- ponds; however, there is no scientific evidence that this tions at the bottom of the ponds. Also, some dinofla- activity is affecting shrimp fisheries. First, this extraction gellates frequently observed are Prorocentrum minimum, aez-Osuna et al. / Marine Pollution Bulletin 46 (2003) 806–815 Gymnodinium spp., Gyrodinium spp. and Protoperidi- isms can be as symptomatic carriers of a pathogen which nium trochoideum ( ¼ Scripssiella trochoidea). P. mini- under normal conditions does not express itself.
mum is considered a toxic species whose abundance is The bacterial communities present in ponds are sus- promoted by humic acids and inadequate fertilization ceptible to fluctuations and interactions from physico- ees-Altamirano et al., 1994). Other studies con- chemical factors (pH, temperature, dissolved oxygen, ducted in three shrimp farms in Sinaloa during 1990– etc.). A correct feeding regime and also the generation of 1993 found that Synechocystis diplococcus, a non-toxic good algal blooms are important to maintain the water cyanobacteria, was frequently observed. Algal bloom quality and the balance of the bacterial communities, duration ranged from 1 to 10 days; dominant species since they are the main source of organic matter for the were the cyanobacteria A. elenkinii, Schizothrix calcicola system. An excess of organic matter in the system can and Anabaena aequalis, and the dinoflagellates P. mini- induce an accelerated development of the bacterial mum, Gymnodinium incoloratum, Gyrodinium spirale and communities in the pond. This high organic matter and other species of the genus Gyrodinium (Cort bacteria present cause a higher demand of oxygen in the pond bottom, which affect negatively the shrimp popu- were considered to be responsible for algal blooms: inadequate fertilization, excretion of substances that A number of infectious diseases have been described promote growth of microalgae and environmental con- in farmed shrimp. In the Gulf of California ecoregion, ditions. In one farm, shrimp weight was lowered because the most common parasitic diseases are ‘‘cotton of a S. calcicola bloom associated with strong rains.
shrimp’’, caused by microsporidea, and gregarines, of Water effluents from shrimp farms, in addition to which 3 genera affect shrimp, Nematopsis, Cephabolus municipal, agricultural and industrial wastewater, are and Paraophioidina. Several fungi have also been found discharged directly to coastal waters from the Gulf of to be shrimp pathogens, some more common in larval California; such discharges are not subjected to previous stages and others in juvenile and adult stages. The most treatment. Knowledge of how shrimp pond effluent common genus found in larvae is Lagenidium, while in affects coastal waters, and how it affects aquaculture juveniles and adults, Fusarium causes more problems.
activities is just beginning. In Sinaloa, winter-spring Around 20 viruses have been reported to affect cul- red tides have occurred along the coast leading to red- tured and wild shrimp (Lightner and Redman, 1998).
tides episode within shrimp ponds. Toxicity studies The most important ones have been White Spot Syn- drome virus, Infectious Hypodermic Haematopoietic Necrosis virus and Taura Syndrome virus. It is impor- vealed toxicity below permissible limits (>80 MU g tant to keep in mind that shrimp are potentially very oyster tissue) for human consumption of shellfish, susceptible to environmental contamination, mainly due consequently, it is necessary to evaluate if this toxicity to insecticides due to their close phylogenetic relation- is enough to provoke death of shrimp in larvae and ship with insects, so water quality problems lead to disease outbreaks. In the case of bacterial diseases, vi- The main problem for sustainability of shrimp cul- briosis is most frequent disease, both in larviculture and ture in Sinaloa is the maintenance of good water quality growout. Vibriosis can be defined as an infection caused in the adjacent coastal region. The difficulty assessing by bacteria belonging to the genus Vibrio. In larval the impact of its discharges on receiving water bodies systems, bacteria have been considered the biggest cause rises from a lack of communication among farms, sci- of mortality. However, it is important to emphasize that entific and governmental authorities and the lack of up to now, diseases reported in larviculture are caused long-term. More details on the phytoplankton and by opportunistic bacteria, which affect larvae when they HABs on the situation in the Gulf of California ecore- are weakened by an environmental factor. In fact, most gion are given in Alonso-Rodrııguez and P Vibrio species have been associated with diseased shrimp, however this does not imply that they are themain cause of disease, but that due to their opportu-nistic behavior, they proliferate inside weakened shrimp.
Historically, Vibrio parahaemolyticus, V. alginolyticus,V. vulnificus and Listonella damsela have caused prob- The link between diseases and water quality seems to lems in growout ponds, whereas V. harveyi and V.
be more and more obvious. Stress caused by sub-opti- splendidus have caused problems in larviculture. How- mal environmental conditions induces adverse organism ever these species have also been found in the haemol- responses. Although aquatic organisms may seem heal- ymph and hepatopancreas of healthy juveniles of L.
thy during and immediately after a period of stress, a disease outbreak or a chronic mortality event may de- In a survey of 23 shrimp farms in Sinaloa during 2002 velop in the stressed population. Many of these organ- aez-Osuna et al. / Marine Pollution Bulletin 46 (2003) 806–815 that 18 of 23 farms suffered one or more diseases, the most frequent being caused by gregarines (13 of 23),white spot virus (10 of 23) and vibriosis (7 of 23). The Despite its importance, little is known about the water WSSV was detected in the Gulf of California region quality in coastal areas of the Gulf of California; how- from 1999, and in conjunction with vibriosis cause the ever, there are two identified issues of major concern: pesticides and nutrient overload related to agricultural Often bacterial diseases are treated using antibiotics.
runoff and raw municipal sewage discharges. There is an To evaluate the impact of their use the first thing to important development of intensive agriculture border- know is the patterns of use of the antibiotics. Another ing the eastern coast of the Gulf of California, with factor to take into account is the hydrology of the area approximately 1,728,868 ha of irrigated lands (Anony- and water physicochemical conditions. Theoretically, mous, 1994), distributed in the valleys Mexicali, Yaqui, the final destination of antibiotics applied in aquaculture can be non-target organisms, water, suspended solids amounts of fertilizers and pesticides are applied. In a and sediments. When antibiotics are present in the water previous study carried out in the Pacific coast of Mexico column, they can select for resistant bacteria. The main aez-Osuna et al., 1998, 2002) using bivalve mollusks as effect that antibiotics have on the suspended solids in the biomonitors, it was found that in lagoons of Altata- water column is that they reduce the number of bacteria adhered to these solids, reducing the feed availability to are surrounded by agricultural lands, the soft tissue of the meio and macrofauna which feed on them (Weston, oyster Crassostrea corteziensis had concentrations of up 1996). Antibiotics also contribute to the selection of to 216 lg gÀ1 of Cu and 655 ng gÀ1 of PCBs, respec- resistant bacteria. Concerning the presence of antibiotics tively. From 22 organochlorine compounds detected in in the sediments, these may affect, for example, their this study, the pesticide most frequently found and microbial capacity to reduce sulfate, increasing the which exhibited the highest concentrations was HCB, which can be used alone or in combination with other Antibiotic resistance poses several risks. The trans- fungicides in mixed protectants for seeds, or which can ference of resistance genes directly to bacteria that infect be present as an impurity of the synthesis of other sev- humans can also happen, with a consequent increment eral herbicides and pesticides. High HCB concentrations in the incidence of infections caused by resistant were found in oysters from those regions bordered by pathogens, leading to an increment in therapeutic failure extensive agricultural lands: Yavaros (911 ng gÀ1) and In clinical terms, there is wide evidence that fish Nutrient over-enrichment is another pervasive con- bacterial strains resistant to antibiotics developed due to tributor to the degradation of the coastal ecosystems in the use of those antibiotics in fish disease control.
the Gulf of California. The degree of nutrient impact However, the differences among methodologies em- varies among the coastal bodies, depending on factors ployed by different diagnostic laboratories often mask including shallowness, high stratification or long resi- these changes. Lastly, the isolated strains represent dence times. Agriculture, shrimp farms and human only a fraction of the existing bacteria in the system, the wastes, are the main land-based nutrient sources of the one capable of growing in the culture media being used. Perhaps induced changes are much bigger than agriculture as the dominant one, with an estimated an- they are thought to be. In Sinaloa, it was found (Lyle- nual input of 26,119 ton of P and 49,356 ton of N de- rived only from Sinaloa and Sonora. There are around 5 farms use food incorporating antibiotics; oxytetracy- million inhabitants around the gulf; only a very few of cline being the most applied (67%). Other antibiotics the coastal cities have sewage treatment plants and most supplied are enrofloxacin, norfloxacin, florafenicol and of them have been designed to simply reduce the amount of solids and organic matter content in the waste waters.
During 2002, rules were established that include re- Assuming that (a) the nutrient load associated with quirements and measures to control disease outbreaks municipal sources is 1.4 g P dayÀ1 and 6 g N dayÀ1 per and for the use and application of antibiotics (Norma person and (b) the drainage area has the capacity to Oficial Mexicana NOM-EM-05-PESC-2002). Among reduce this load by self-depuration by 25% for P and these rules are: Section 4.11 refers to role of the sani- aez-Osuna et al., 1998), the estimated an- tary agency to determine the procedure required for nual input from municipal sources would be around the harvest when diseases are confirmed. Section 4.13, prohibits use chloramphenicol and furazolidone Shrimp farm water supply can be achieved either by (nitrofurans) in shrimp farming. Section 4.14 prohi- open seawater structures or through small natural bits treatment with antibiotics 30 days before the har- channels (‘‘esteros’’) that connect the shrimp facility with an estuary or a coastal lagoon, as frequently occur aez-Osuna et al. / Marine Pollution Bulletin 46 (2003) 806–815 in Sinaloa and Nayarit. Pond water is continuously ex- orquez-Tapia, L., 1992. Programa de Ordenamiento Ecol changed (3–20%) and drained through an effluent ditch para el desarrollo acuııcola de la regi that, later on, brings back the waste water to the coastal aficas con Actividades Productivas Prioritarias. OEA. De- aez-Osuna et al., 1997). Considering a scenario partamento de Desarrollo Regional y Medio Ambiente, SEDESOL with approximately 26,050 ha of shrimp farms in oper- aez-Osuna et al. (1999) estimated a load of 834 Carrera, E., de la Fuente, G., 2001. Inventario y Clasificaci ton P/y and 2900 ton N/y. Considering a scenario of 51,059 ha (SAGARPA/CONAPESCA, 2002) for the on, G., Lugo, A.E., Pool, D.J., Morris, G., 1978. Mangrove of entire region around the Gulf of California, and con- arid environments in Puerto Rico and adjacent islands. Biotropica sidering previous assumptions, it is estimated that a load of 1600 ton P/y and 5700 ton N/y, is input, which rep- ees-Altamirano, R., Alonso-Rodrııguez, R., 1997. Mareas rojas resents an amount comparable to municipal loads but significantly less than agricultural discharge.
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