THE EXOTIC SPECIES Litopenaeus vannamei ( BOONE , 1931 ) OCCURRENCE IN CANANEIA , IGUAPE AND ILHA COMPRIDA LAGOON ESTUARY COMPLEX

Exotic species are an exponential problem throughout the world, being one of the main causes of alterations both of the environment and of biodiversity. The introduction of exotic species is typically linked to activities of socioeconomic relevance. The consequences of such invasions have ecological, economic and sanitary components, and these components sometimes operate synergistically. The present study records the presence of Litopenaeus vannamei in several areas of Cananéia, Iguape and Ilha Comprida estuary. A total of 109 samples taken with a gerival net were examined to evaluate the presence of L. vannamei as a bycatch of fishing activities seeking Farfantepenaeus paulensis, F. brasiliensis and Litopenaeus schmitti, between March 2005 and December 2013. Sixty-four individuals of L. vannamei were captured the size and weight of the smallest and the largest specimens of which were, respectively: 1.68 and 6.30 cm and 26.70 and 31.78 g. The data give no indication that L. vannamei is proliferating in the region to the point of being considered an invasive species nor that it is causing economic problems.


INTRODUCTION
The introduction of exotic species in the aquatic environment can cause severe consequences such as the removal, predation and exclusion of native species by competition, as well as by hybridization (WILLIAMSON, 1996), creating an impact on the ecosystem and fisheries in general.Organisms that have been introduced into an environment where they do not occur naturally are considered exotic species.Studies of these species have accompanied mankind throughout history (ROSIQUE & BARBIERI, 1992).However, the problems caused by the invasion of exotic species are growing and starting to become a phenomenon with worldwide consequences (TAVARES, 2003).The high frequency of invasion is associated largely with human activities (BARBIERI et al., 2007) such as transport and accidental introduction via the ballast water of ships, or as a result of the escape of specimens from poorly planned and managed aquaculture activities.
According to TAVARES (2003), the consequences of the introduction of exotic species are commonly considered as ecological, health or socioeconomic problems.Often, according to the same author, these classifications have been shown to be unsatisfactory, either because the categories overlap, or because any consequences of an ecological order end up simultaneously having health and socioeconomic effects.
The introduction of exotic species can cause major impacts to the biota and the ecosystem as a whole.Examples such as the fish Gambusia holbrooki (GIRARD, 1859), which was introduced into Australia to control the incidence of a mosquito, has presented a large increase in its population and current studies show that it has been responsible for the extinction of several other species of fish both in Africa and Asia (HOWE et al., 1997).
In recent years, the interest of the scientific community has focused on the issue of the introduction of exotic species in terms of ecological and economic impacts arising from the invasion of various ecosystems (SILVA et al., 2002).However, the issue of biological invasion goes far beyond academic concern, becoming in some cases, a question of public health (HOWE et al., 1997).
The introduction of decapod crustaceans in areas in which they do not naturally occur has been cited in the scientific literature (MANTELATTO & GARCIA, 2001;MELO & CRIVELARO, 2002;SILVA et al., 2002;MAGALHÃES et al., 2005).RODRIGUES & SUAREZ (2001) have reported several cases of the dispersal of decapod crustaceans, both freshwater and marine, resulting from human activities.
The shrimp Litopenaeus vannamei (BOONE, 1931), native to the eastern Pacific, was brought to Rio Grande do Norte in 1981 for cultivation in nurseries (TAVARES & MENDONÇA, 1996), but did not produce good results for years.Only as from the early 90s did the species begin to show positive results, leading to its cultivation along almost the whole Brazilian coast.Marine shrimp farms are located mostly on the coast, often in mangrove areas.
Occasionally, during harvesting or due to the disruption of containment booms, unspecified quantities of individuals have ended up escaping from farm ponds and invading the natural environment (TAVARES, 2003).
L. vannamei was cultivated in excavated tanks in the estuarine lagoon complex of Cananeia, Iguape and Ilha Comprida until September 6, 2005.This fact has led to conflict between artisanal fishermen and recreational fisheries in the region, as the former (or latter?) used exotic species as live bait, leading to fishing competition with the native white shrimp (Litopenaeus schmitti, BURKENROAD, 1936).In addition, there is an imminent risk of transmitting diseases to native species of shrimp in the study area (BARBIERI & MELO, 2006).It is for these reasons that the present study seeks to report on the occurrence of Litopenaeus vannamei in the estuarine lagoon complex of Cananeia, Iguape and Ilha Comprida to make a critical assessment of the introduction of exotic species into the region and the need for greater control.

MATERIAL AND METHODS
In order to evaluate the use of L. vannamei for fishing for pink shrimp (Farfantepenaeus paulensis PÉREZ-FARFANTE, 1967 andF. brasiliensis LATREILLE, 1817) and white shrimp (Litopenaeus schmitti) as live bait in the region, 109 samples were taken with a type of fishing net called the Gerival (2 meter mouth by 2 meter depth) between March 2005 and December 2013, in the estuarine lagoon complex of Cananeia, Iguape and Ilha Comprida.Each sample consisted of three consecutive 45-minute hauls (bottom trawls: 500m), undertaken parallel to the shoreline, totaling 327 fishing operations during the period (109 samples x 3 consecutive hauls).Twelve sampling points were selected, two in Trapandé Bay (Andrade and Prainha) and ten in Mar Pequeno (localities Boa Vista, Piçarro, São Paulo Bagre, Pedrinhas, Ubatuba, Sítio Arthur, Subauma, Pedra do Farol, Agrossolar and Cocaia) (Figure 1).These locations are often used by artisanal fishermen for fishing native shrimp (F.paulensis, F. brasiliensis and L. schmitti).
The gerival is the fishing gear normally used to catch shrimp for use as live bait, it consists of a conical trawl net made of nylon mesh, kept near the bottom with the help of a lead fishing line at its largest opening (the mouth).The gerival is dragged with the tidal stream, catching the shrimp that rise by opening its mouth into the shape of a hood in which they are trapped.

RESULTS
During the harvesting, the three species of native shrimp in the region (F.brasiliensis, F. paulensis and L. schmitti), the exotic shrimp Litopenaeus vannamei (Table 1) and the accompanying characteristic fish fauna were captured.Although few individuals of L. vannamei (n = 64) were caught, this alien species was captured at all the sampling sites, which shows that the species is already quite widespread within the estuary (Table 1 and Figure 1).The average sizes and weights of the specimens found were: 14.32 (± 7.48) cm and 13.59 (± 5.92) g, respectively.The size and weight of the smallest and the largest specimens captured were: 1.68 to 6.30 cm and 26.70 to 31.78 g, respectively.The proportion of males to females was 55. 94%  Species introduced, such as L. vannamei, can bring parasites, bacteria and virus pathogens (such as white spot) with them, doing enormous damage to the native species (ROYO et al., 1999).The Japanese oyster Crassostrea gigas (THUNBERG, 1793) may have been the origin of the viral disease that decimated the population of native oysters Ostrea edulis (LINNAEUS, 1758) off the coast of Spain and France (BARBIERI, 1998).Whether accidental or deliberate, the introduction of L. vannamei may bring pathogens which affect other species by competing with native species Bol.Inst.Pesca, São Paulo, 42(2): 479-485, 2016 for the same habitat or food as well as possibly leading to genetic contamination, thus impacting the entire ecosystem involved.
L. vannamei, as well as other species, is affected by various diseases of viral origin.In 1995 over 95% of the stocks in southern Texas were decimated by TST viruses (Syndrome Taura Virus), and in 1996, the stocks of L. vannamei in Texas and South Carolina were again severely affected (JSA, 1997apud TAVARES & MENDONÇA, 2004).In Brazil, in February 2005, several farms in Santa Catarina which cultivated L. vannamei were affected by the White Spot Virus (White Spot Syndrome).According to TAVARES & MENDONÇA (2004), the introduction of exotic species will always involve the risk of contamination of native species by exotic pathogens.In the complex case of the estuarine lagoon of Cananeia, Iguape and Ilha Comprida, the contamination of native species may arise directly from nursery cultivation, whether in adults or infected larvae.
The estuarine lagoon complex of Cananeia, Iguape and Ilha Comprida is in an area of significant environmental interest, being considered by the IUCN (International Union for the Conservation of Nature) as the third estuary in the world in terms of primary productivity and as a nursery of Atlantic Ocean species.The region also includes the Biosphere Reserve of the Atlantic and contains many protected areas, such as the APA Federal Cananeia Iguape and Peruíbe, the APA State Ilha Comprida, the Ecological Station of Chauás, Parque Estadual da Ilha do Cardoso and Mandira Extractive Reserve.
The data of this present study give no indication that (as to whether?) L. vannamei is proliferating in the region to the point of being considered an invasive species and causing economic problems; they show, rather, that since 2008 no specimen has been caught in the estuary.If this species had achieved success in the environment to the point of reproducing, certainly we would be capturing it now, even if there were but few individuals in the estuary, but this has not occurred since 2008.
Whether accidental or deliberate, the introduction of exotic species can bring pathogens to other species, competition for the same resource or habitat with native species, in addition to genetic contamination, thus impacting the entire ecosystem involved (TAVARES, 2003).An important aspect in studies of ecology and population dynamics of invasive species is their relationship to the existing ecosystem.Invasive species always interact with the native species, either by predation or competition, resulting in local extinction (BYERS, 2002).Native and invasive species may compete for space or food, leading to extinctions, or invasive species can take advantage of a vacant niche and maintain a balance with a native one (APOLINÁRIO, 2002).However, to consider invasive species just as threats or pests, can only be a superficial reading of a larger ecological process.According to WILLIAMSON (1996), one of each ten species introduced by humans into a new environment becomes an invasive species, one in each ten invasive species succeeds in establishing itself, and one in each ten established species becomes a pest.Comparing this statement with our data, we may conclude that L. vannamei has not become a pest nor even succeeded in establishing itself in the estuarine lagoon complex of Cananeia, Iguape and Ilha Comprida.
The classic ecological view that large changes in natural populations would upset the balance of the planet has recently been changing in the light of new studies and definitions of terms, such as population balance (ACKEFORS, 1999, BARBIERI & MELLO, 2006, BARBIERI et al., 2007).

Table 1 -
to 44.06%.The Bol. Inst.Pesca, São Paulo, 42(2): 479-485, 2016 largest number of individuals captured occurred during October 2005 (Table 2) but in January, February and March 2006 no specimens were captured.In 2007, specimens were captured in February (3) and March (1).No specimens were captured during the period from 2008 to 2013.Number of individuals of the native and exotic shrimp species captured in Cananeia, Iguape and Ilha Comprida Estuarine Lagoon Complex.