White Legged Shrimp : Friend or foe? | Sunday Observer

White Legged Shrimp : Friend or foe?

An ecosystem is an interaction of trees, rivers, soil, air, sunlight, bacteria and higher animals, it is where these living and non living components jointly facilitate nutrient cycles and energy flows.The community of living organisms within an ecosystem is vital to the flow of these energy and nutrient cycles. Some scientists refer to the entire planet as a single ecosystem interconnected by nutrient cycles and energy flows. Distortion of the living organisms within an ecosystem would result in disruption to the nutrient cycles and energy flows within that particular ecosystem. This distortion can come in the form of the introduction of an alien species to the existing ecosystem.

Recently, certain information has reached the Sunday Observer that a foreign shrimp species, native to Pacific regions of Central and South America, is to be introduced to Sri Lanka.

The underlying reasons behind the move

This species, named Pacific White Legged Shrimp (Litopenaeus vannamei) is going to be introduced by National Aquaculture Development Authority (NAQDA) for shrimp farming. The reasons for selecting this particular species is stated as salt tolerance and high growth rate, says Environmentalist and Attorney at Law, Jagath Gunawardana.

The current shrimp species used for aquaculture, known as tiger shrimp (Penaeus monodon), is not tolerant of high salt concentrations found in the brackish water ecosystems.

“However, the white shrimp is known to compete with P. monodon, the local species grown for the purpose of aquaculture. In addition, more and more countries have come to realize the potential risk of importing this species for aquaculture,” he says.

National Aquaculture Development Authority, Director General, Nimal Chandraratne admitted that there are plans on importing L. vannamei to enhance aquaculture in Sri Lanka. According to him, the reasons behind the selection of this particular species lie in its ability to tolerate broad salinity range, on its disease resistance and the high production per unit area in comparison to P. monodon. Chandraratne says L. vannamei is imported on a large scale for the purpose of aquaculture throughout the world.

Potential threats to environment

Gunawardana says, both India and Thailand have published academic papers on the negative trends observed in the behaviour of L. vannamei. This literature states, L. Vannamei has the potential to be either a competitor or a predator of P. monodon as per the trend observed, and that L. vannamei carries infectious diseases.

In the publication, Preliminary risk assessment of Pacific white leg shrimp (L. vannamei) introduced to Thailand for aquaculture (2013) by Senanan et al, it is stated, a high occurrence of Taura Syndrome Virus (TSV), has been detected in sub-adult P. L. vannamei caught from the river. TSV is an alien pathogen carried by L. vannamei.

The publication also states that L. vannamei consumed the same diet types in similar proportions as P. monodon. Stomach content analysis indicated that L. vannamei can utilize food resources available in the Bangpakong River and these resources were shared between L. vannamei and local shrimp species including P. monodon.

Therefore, concerns have been raised on the decision to introduce L. Vannamei which has a bad track record of disease, in addition to the establishment of the species in the natural habitats, which would have an adverse effect in the whole ecosystem.

“ The parties involved in importing this species, that is, whether NAQDA would be involved in the process or whether private business owners involved in aquaculture industry would be importing the species directly, is not specified. Also, this species would have to be imported continuously, unless they are capable of breeding here,”he says.

According to Gunawardana, the need for regular import of L. vannamei is subject to concern and it is too pre mature to study their ability to breed under local conditions.

“The main concern with importing is the transfer of diseases to our country, with each shipment. Also, the validity of the host country’s certification indicating that these species are disease free is debatable.

Therefore, testing for diseases is a tedious process and needs a streamlined mechanism, since random sampling would not be valid in this case. Any transfer of diseases would be a cost to the environment,” he says.

University of Wayamba, Department of Aquaculture and Fisheries, Senior Lecturer, Dr Sevvandi Jayakody agreed that importing L. vannamei for aquaculture is a concern since L. vannamei is known to carry infectious diseases.

“This is an exotic species to the Indian Ocean and new pathogens and new diseases would be introduced to the country with this species. One such disease is the white fecal matter syndrome, which is not found in P. monodon. Studies have already proven that this disease causes the death of the shrimp and is also likely to be contracted by all crustaceans,” she says.

Senanan et al, states that L. vannamei has escaped from farms to the Bangpakong River and the numbers of L. vannamei sampled in the river is positively correlated with the location and area of shrimp ponds. Via remote sensing and a geographic information system (GIS) used to estimate location and total area of shrimp ponds (active, inactive, and abandoned ponds) in the Bangpakong River watershed, it was found that most ponds were located within 5 km of the river.

Risk assessments and guidelines

Senanan et al, further states that while aquaculture promises economic and social benefits, aquaculture escapees can pose ecological risks to the receiving aquatic environments. Some ecological impacts, such as reducing aquatic biodiversity or spreading alien pathogens, may undermine the sustainability of aquaculture and small-scale fisheries. By incorporating science-driven ecological risk assessment prior to new introductions, and integrating a risk monitoring program, it may be possible to prevent such undesirable outcomes.

Gunawardena says, according to National Policy on Invasive Alien Species, under the risk assessment guidelines, it requests reporting on a risk management system in order to mitigate potential adverse effects.

However, Biodiversity Secretariat, Director, Padma Abeykoon said, when NAQDA was informed by them to carry out risk assessment under National Policy on Invasive Alien species, NAQDA responded saying, this is not the first time this species is being imported. “They say, they have imported and produced a reasonable stock in the Puttalam region in the past. Since this is the second time they are importing this species, they do not have to carry out risk assessment, unless they are going to farm in an area other than Puttalam,” she says. Abeykoon further said, the Environment Impact Assessment (EIA) must be conducted prior to the large scale farming project and NAQDA has been requested to carry out an EIA. “Also, NAQDA informed us that this is an intensive farming system using a covered tank and that eggs will not be released into the ecosystem,” she said.

Chandraratne acknowledged that trials with vannamei has been conducted in Puttalam earlier, and were successful. He said, an Import Risk Assessment (IRA) has been conducted on L. vannamei which has been relatively successful. He says, the species would be introduced to the Mannar and Batticaloa area, under the precautions recommended by the IRA. As a result, only the brood stock of L. vannamei would be introduced and this would be a specific pathogen free stock.

“We have requested a quarantine facility to be built under budgetary allocations this year. Therefore, imported L. vannamei would be quarantined for any infectious diseases they carry and then be stocked in a bio secure hatchery, initially. Then, L. vannamei would be transferred to a bio secure farm, where water used in the farming process would be re- circulated without being released outside.”

The Department of Fisheries and Aquatic Resources, Director General, Christy Lal Fernando said, they are the body responsible for issuing approvals for importing invasive aquatic species to the country and that permission has already been granted to import L. vannamei.

According to Section 37 of Flora and Fauna Protection Ordinance, no import of wild animal is permitted except under the permit issued by the Department of Wildlife Conservation.

As per information received via anonymous sources, DWC has not yet given permission to import this species. Authorities from the DWC were not available for comment.

Environment impact of aquaculture

Dr Jayakody says, P. monodon, despite being native to the Indian Ocean region, carries diseases. Also, the release of water from P. monodon farms, containing fecal matter intact with pathogens, to the natural ecosystem resulted in its disruption.

“The incidence of white spot syndrome which is virulent was high in P. monodon farms. In consequence, large scale farmers who already profited by the venture abandoned their farms, causing loss of livelihood for their employees.

The farming was subsequently taken up by the workers who did not have adequate knowledge or guidance by NAQDA. This contributed to the complete transformation of Mundala lagoon, as a result of water that was released from these farms,” she says.

Therefore, Dr Jayakody says, there is a pressing need for a cost- benefit analysis to be carried out on the aquaculture industry. “There needs to be a calculation of percentage of mangroves, salt marshes and other coastal vegetation sacrificed for aquaculture. Biodiversity in the Puttalam district has been lost to future generations due to shrimp farming. Now there will be new aquaculture projects in the Mannar and Batticaloa regions, where pristine mangroves are to be found. Therefore, it is important to know whether we have lost a billion to gain a million,” she says.

However, Chandraratne insists, there are no abandoned Shrimp farms in the Puttalam region, and all the farms in the area are currently functioning. He says, there is a crop calendar with a fallow period, according to which the farms function. He further says, the mangroves along the Dutch canal are rehabilitated and there is a thriving mangrove population in the area right now.

“Also, we won’t be touching the mangroves belt and patches of mangroves found inland in Wedithalathivu, Mannar area. The aquaculture park will be developed under a blue green concept,” he says.

Throughout the history of mankind, environment has paid the price of industrial expansion. Many economic policy making bodies have recognized the importance of preserving biodiversity, and hence that of ecosystem assessment. While economical development is important for the betterment of living standards of humans, it is important to ensure irreversible damage is not caused to the environment, in the process. 

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