Aquaculture – Definition, Types, Importance, Advantages

What is Aquaculture?

• Aquaculture is the practice of farming aquatic organisms such as fish, crustaceans, mollusks, and aquatic plants in controlled environments. It serves as an essential alternative to capture fishery, which involves harvesting fish from the wild, mainly from marine environments. With growing concerns over the sustainability of capture fishery, aquaculture has become an increasingly popular method to meet global demand for fish and other aquatic products. It is sometimes referred to as “underwater agriculture” due to its systematic and controlled approach to farming aquatic species.
• The need for aquaculture has arisen due to the limitations of capture fisheries. Marine resources, once thought to be abundant and endless, have seen significant depletion. Additionally, a large portion of the fish caught from the oceans is used for industrial purposes, not directly consumed by humans. This shift has necessitated the exploration of alternatives to meet the rising global demand for protein-rich food sources. Aquaculture, with its ability to grow fish and other aquatic species under controlled conditions, presents a sustainable and scalable solution.
• Globally, aquaculture has witnessed substantial growth in response to declining wild fish stocks. China leads the world in aquaculture production, contributing 62% of global output in 2008, with 32.7 million tonnes of fish, crustaceans, and mollusks. Other major producers include India, Vietnam, Indonesia, Thailand, and Bangladesh. Carps represent the most commonly farmed species, accounting for 39% of global production. Other significant species groups include tilapias, shrimps, prawns, oysters, and salmons. Among these, white leg shrimp generated the highest commercial value in 2008, followed by Atlantic salmon and various carp species.
• India, with its vast maritime resources and biodiversity, plays a key role in global aquaculture. It houses more than 10% of the world’s fish biodiversity and has made considerable advancements in the farming of freshwater fish and shrimp. Although research and development have been conducted in areas like mollusk culture, seaweed farming, and the cultivation of marine species such as seabass, these sectors have not yet scaled up commercially. Bridging the production gap between India and leading aquaculture nations like China requires better utilization of its diverse marine resources and expansive coastline, which holds great potential for future aquaculture expansion.

Definition of Aquaculture

Aquaculture is the farming of aquatic organisms, such as fish, shellfish, and aquatic plants, under controlled conditions to increase production for food, industry, and environmental restoration.

Characteristics of Aquaculture

Aquaculture is a highly productive practice with diverse benefits for agriculture, the environment, and the economy. Below are its key characteristics:

• High Productivity: Aquaculture yields higher productivity compared to traditional agriculture or veterinary practices.
• Integrated Farming: It can be profitably combined with agriculture, horticulture, or animal husbandry for enhanced output.
• Recycling: Efficient recycling of domestic and agricultural wastes, helping to protect the environment.
• Rural Development: It creates employment in rural areas, helping to reduce urban migration.
• Intensive Fish Culture: Aquaculture allows high-density fish farming (up to 200 fish/m³), yielding up to 25 tons/ha/year through water recirculation.
• Earning Foreign Exchange: Products like prawns, lobsters, and ornamental fish generated through aquaculture contribute significantly to foreign trade.
• Ranching: Fish hatcheries replenish wild fish populations, supporting capture fisheries and biodiversity.
• Replenishment of Coral Reefs: Artificial coral reefs help restore ecosystems that have been damaged.
• Leisure Activities: Activities such as sport fishing and public aquariums enhance recreational opportunities.
• Mariculture and Fisheries Enhancement: Mariculture supports coastal livelihoods and restores species like clams and trochus to depleted reefs.
• Agro-Industrial Development: Aquaculture fosters related industries such as fish product processing, seaweed culture, and pearl oyster farming.

Types of Aquaculture

Aquaculture, the farming of aquatic organisms, includes various types based on the species being cultivated and the environment in which they are grown. Each type of aquaculture has its unique processes and benefits, catering to different economic, ecological, and market needs. Below are the primary types of aquaculture:

1. Algaculture
   • This form of aquaculture involves the cultivation of algae.
   • It primarily focuses on microalgae, also known as phytoplankton or planktonic algae.
   • Microalgae, commonly referred to as seaweed, are often not cultivated on a large scale due to their specific environmental needs. Instead, they are typically harvested from natural ocean habitats.
   • Algaculture contributes to industries such as food supplements, biofuels, and pharmaceuticals.
2. Fish Farming
   • Fish farming is the most widely practiced form of aquaculture.
   • It involves the commercial raising of fish in controlled environments like tanks or enclosures, primarily for food production.
   • Common species raised include salmon, catfish, tilapia, cod, carp, and trout.
   • As wild fish stocks face depletion due to overfishing, fish farming offers a sustainable alternative to meet the growing demand for fish protein in global markets.
3. Freshwater Prawn Farming
   • This type of aquaculture focuses on raising freshwater prawns or shrimp for human consumption.
   • It is designed as a commercial activity to supply markets with high-quality, farm-raised freshwater prawns, providing an alternative to marine shrimp farming.
4. Integrated Multi-Trophic Aquaculture (IMTA)
   • IMTA is a sustainable practice where waste from one species becomes an input, such as food or fertilizer, for another species.
   • This method combines species like fish or shrimp (food producers) with seaweed (inorganic extractors) and shellfish (organic extractors), creating balanced ecosystems.
   • IMTA contributes to environmental sustainability, economic diversification, and social acceptability by reducing waste and improving resource efficiency.
5. Mariculture
   • Mariculture refers to the farming of marine organisms in the ocean or enclosed sections of the sea.
   • It includes the cultivation of marine fish, prawns, oysters, and other species in saltwater ponds.
   • Besides food, mariculture also produces non-food products like fish meal, nutrient agar, cultured pearls, and even ingredients for cosmetics.
6. Shrimp Farming
   • Shrimp farming is dedicated to cultivating marine shrimp for human consumption.
   • About 75% of the world’s farmed shrimp comes from Asia, with China and Thailand being the largest producers.
   • Latin America also plays a significant role, with Brazil leading in shrimp production. Thailand is the primary exporter of farmed shrimp globally.
7. Whaling (Cultural and Economic Context)
   • Though not strictly classified under fish farming, whaling contributes significantly to the economies of some large fishing nations.
   • Approximately two-thirds of whales are captured in the southern oceans, while the remaining third is harvested from the North Pacific and North Atlantic.
   • Whaling is still important in countries such as South Africa, South America, and Australia, accounting for around 10% of global whaling.

Why is aquaculture important?

Below are the reasons why aquaculture is important:

1. Rich Protein Source: Fish produced through aquaculture is a high-quality source of protein, often containing more protein than chicken or pork, making it an essential component of a nutritious diet.
2. Meeting Growing Demand: As the global population continues to grow, the demand for fish is also rising. Natural fish stocks from oceans and ponds cannot sustainably meet this demand, and aquaculture helps fill the gap between the demand and supply of fish.
3. Sustainable Food Production: Aquaculture offers a sustainable method for food production by reducing the pressure on wild fish populations. It helps prevent overfishing and contributes to the long-term sustainability of aquatic ecosystems.
4. Diversification of Agricultural Income: For farmers, aquaculture is a valuable tool to diversify their income. By integrating fish farming into existing agricultural practices, farmers can generate additional revenue streams, enhancing economic stability.
5. Lower Greenhouse Gas Emissions: Compared to traditional livestock farming, aquaculture has a lower carbon footprint. The production of fish requires less land and produces fewer greenhouse gas emissions, making it an environmentally friendly alternative.
6. Potential for Integrated Farming: Integrated fish farming, such as combining fish farming with paddy crops, has great potential in countries like India. This practice optimizes land use and improves productivity without depleting natural resources.
7. Integration with Poultry Farming: Aquaculture can also be integrated with poultry farming, creating a mutually beneficial system where the waste from poultry serves as a nutrient source for fish farming, further enhancing resource efficiency.
8. Horticultural and Agricultural Potential: Aquaculture land offers opportunities for combining fish farming with horticulture and agriculture, providing further avenues for maximizing land productivity and supporting diverse farming practices.

Types of Aquaculture Practices

A. Depending on Hydrobiological Features

Aquaculture practices are categorized based on hydrobiological features, particularly salinity levels. These categories include freshwater, brackish water, metahaline, and mariculture. Each type is characterized by distinct methodologies and species targeted for cultivation. The following points provide an overview of each aquaculture type and its associated practices:

1. Freshwater Aquaculture
   • This type focuses on the cultivation of economically significant aquatic organisms in freshwater systems such as ponds and tanks. Various practices include:
     • Composite Fish Culture: Involves raising compatible species with different feeding habits together to optimize resource use and increase yields.
     • Monosex Culture: Cultivation of a single sex of a species to enhance growth and yield, often leading to more efficient production.
     • Monospecies Culture: Centers on the farming of a single fish species, simplifying management and production practices.
     • Jeol Fish Culture: Utilizes shallow water bodies with low oxygen levels for cultivating air-breathing fish like Channa and Clarias.
     • Predator-Prey Culture: Combines predator fish (e.g., murrels) with prey species (e.g., tilapia) to create balanced ecosystems in shallow waters.
     • Culture in Temple Tanks: Uses stagnated temple tanks for cultivating species such as common carp and tilapia, making use of otherwise unused water resources.
     • Culture in Irrigation Tanks: Irrigation tanks with inlet and outlet systems are used for raising major carp species, enhancing agricultural productivity.
     • Raceway Culture: Involves a system of earthen or cemented tanks that maintain a continuous flow of water, mimicking stream conditions.
     • Sewage-Fed Fish Culture: Employs treated sewage water rich in nutrients to promote fish growth, capitalizing on the natural nutrient cycling.
     • Fish Culture in Recirculating Systems: In water-scarce areas, water is continuously circulated through filters to maintain quality, facilitating sustainable production.
     • Ornamental Fish Culture: Focuses on high-demand aquarium species such as guppies and goldfish for the international ornamental fish market.
     • Culture of Larvivorous Fishes: Raises fish like Gambusia to control mosquito populations, contributing to public health.
     • Integrated Fish Farming: Combines fish cultivation with agricultural crops or livestock, maximizing land use and economic returns.
     • Culture of Sport Fishes: Cold-water species like trout are cultivated in high-altitude regions for recreational fishing purposes.
     • Culture of Plankton and Other Fish Food Organisms: Involves mass culturing protein-rich organisms essential for feeding larval finfish and shellfish.
2. Brackish Water Aquaculture
   • This practice leverages areas with mixed salinity, ideal for a variety of organisms. Cultivation methods include:
     • Culture in Tidal Ponds: Utilizes tidal movements to provide natural water exchange and nutrient influx for species such as milkfish and prawns.
     • Pen and Cage Culture: Involves using pens or cages for farming fish and crustaceans, allowing for controlled environments while utilizing natural conditions.
     • Rack, Raft, or Rope Culture: Primarily used for shellfish such as oysters, these methods promote efficient growth in high-density environments.
     • Mangrove Crab Culture: Involves the farming of Scylla serrata in shallow brackish waters using bamboo cages, combining habitat conservation with aquaculture.
3. Mariculture
   • With extensive coastal and open sea areas, mariculture focuses on marine organisms:
     • Floating Cage Systems: Used for cultivating finfish, prawns, and lobsters, providing a sustainable method for marine aquaculture.
     • Racks, Rafts, and Ropes: Employed for shellfish farming, particularly mussels and pearl oysters, maximizing space utilization in marine environments.
     • Seaweed Cultivation: Involves using nets or webbings to farm various types of seaweeds, contributing to food, pharmaceuticals, and biofuels.
4. Metahaline Culture
   • This practice utilizes salt pans during off-seasons for salt production:
     • Brine Shrimp Culture: Artemia salina is cultivated in highly saline conditions, providing a rich source of live food for finfish and shellfish.
     • Cysts Production: The dormant eggs of Artemia, formed under unfavorable conditions, can be harvested for export, offering significant economic benefits.

B. Depending on Motive of Farming

Aquaculture practices can be categorized based on the motive of farming, primarily driven by economic and commercial considerations. The classification typically includes extensive, intensive, and semi-intensive fish culture, each varying in terms of management effort, investment, and yield.

1. Extensive Fish Culture
   • This form of fish farming is carried out in large water bodies such as ponds and beels, where minimal effort is made to enhance or manage the system. Key characteristics include:
     • Low Management: The environment is left largely natural, with little intervention for improving water quality, stocking densities, or feeding regimes.
     • Modest Yield: Fish rely predominantly on natural food sources available in the ecosystem, resulting in modest production levels.
     • Low Investment: The cost of maintenance is minimal since there is no significant input for artificial feeding or water management, making it cost-effective but less profitable.
     • Natural Balance: Since the culture system is largely unmanaged, it relies heavily on ecological balance to sustain fish populations.
2. Intensive Fish Culture
   • This practice aims to maximize fish production within a controlled and managed environment. Characteristics include:
     • High Management: Intensive fish culture requires rigorous management of water quality, feeding, and stocking densities to ensure optimal growth conditions.
     • Artificial Feeding: Fish are provided with artificial feed in addition to natural food sources, greatly enhancing growth rates and overall yield.
     • High Yield: The production from intensive systems can exceed 6000 kg/ha/year, making it the most productive form of aquaculture.
     • High Investment and Profit: Although the initial cost of setup and maintenance is high, the returns far exceed the expenses, ensuring a significant profit margin for commercial fish farming.
     • Maximized Use of Resources: Intensive systems are designed to achieve maximum production from minimal water resources, making them highly efficient.
3. Semi-Intensive Fish Culture
   • As a middle ground between extensive and intensive systems, semi-intensive fish culture balances investment, management, and yield. It has the following features:
     • Moderate Management: Some management is required, including supplemental feeding and occasional water quality checks, but not as intensive as fully managed systems.
     • Intermediate Yield: The yield is higher than extensive systems but lower than intensive systems, offering a moderate production output.
     • Moderate Investment and Profit: While the costs are higher than extensive farming, they are lower than intensive systems, making it suitable for farmers seeking a balance between input and returns.
     • Risk Mitigation: Semi-intensive systems reduce the risks associated with full reliance on natural systems or the higher costs of intensive systems, offering a stable and reliable production method.

C. Depending on Special Operational Techniques

Aquaculture practices can also be classified based on the special operational techniques employed to manage fish culture. These methods offer distinct advantages and are designed to maximize the use of aquatic environments while addressing specific challenges. Two primary techniques used in fish farming include cage culture and pen culture, each with its own distinct operational approach and characteristics.

1. Cage Culture
   • Cage culture involves containing fish in specific sections of water, such as rivers or large reservoirs, using cages made from various materials like galvanized steel frames with nylon mesh or bamboo structures. The key features include:
     • Types of Cages:
       • Floating cages
       • Fixed cages
       • Submerged cages
       • Movable cages
     • Monoculture: This technique is commonly used for monoculture, where only one species is cultivated in a cage.
     • Applications: Cage culture is especially useful for utilizing waste waters, such as swamps or derelict water bodies. In India, it has proven effective for cultivating air-breathing fish species like Clarias, Heteropneustes, Anabas, and Channa.
     Advantages of Cage Culture:
     1. Efficient use of water resources.
     2. Economical water management.
     3. Daily monitoring and handling of fish are made easy.
     4. Reduces fish mortality.
     5. Simplifies the control of predators, competitors, and parasites.
     6. Harvesting is easier and more complete.
     7. Easy disease control and isolation of diseased fish.
     8. Lower initial investment compared to some other techniques.
     Limitations of Cage Culture:
     1. High risk of theft.
     2. Insufficient water renewal for removing metabolites.
     3. Requires high dissolved oxygen levels.
     4. Fouling agents like snails can accumulate on the cage mesh, requiring regular cleaning.
     5. Uneaten food and fish waste can negatively affect water quality.
2. Pen Culture
   • Pen culture refers to the confinement of fish in an enclosure created within natural water bodies like bays, estuaries, rivers, lakes, or reservoirs. These enclosures are often built using natural barriers and are commonly seen in narrow channels or coves to minimize costs and maximize efficiency.
     • Types of Enclosures:
       • Bamboo scaffolding used in places like the Philippines and China.
       • Floating net enclosures used for culturing species like tilapia and milkfish.
       • Single-layered pens of nylon webbing.
       • Double-layered pens that serve as nurseries for fish and prawn seed.
     • Structural Design: Pens are relatively small, typically between 2 and 7 hectares, although larger enclosures up to 120 hectares can be found in places like Japan. The pen depth needs to exceed one meter, even at low tide.
     • Water Barriers: Barriers are often constructed from stones, sand, soil, or concrete, and include screens to prevent fish from escaping. Sites with continuous water flow may have barriers upstream and downstream to maintain water circulation.
     Advantages of Pen Culture:
     1. Continuous water flow enhances oxygen supply and food availability, improving fish growth.
     2. Higher growth rates due to reduced energy expenditure on movement and feeding.
     3. Provides employment opportunities for local communities, especially in coastal areas.
     4. Regular water flow flushes out harmful metabolites, reducing fish mortality.
     Limitations of Pen Culture:
     1. Vulnerable to unfavorable weather, which may damage pens or flood the sites.
     2. Subject to pollution, particularly from events like algal blooms (e.g., Dinoflagellates).
     3. Biofouling by organisms like barnacles and algae may damage the pen structures.
     4. Terrestrial insects can invade exposed portions of the pen, causing structural damage.
     5. Nylon-webbed enclosures can be damaged by crabs.
     6. Predatory fish may enter the pen, posing a threat to fish stock and prawns.
     7. Abundant seaweed around the pen may lower oxygen levels, especially when it decays and releases hydrogen sulfide.

Role of water quality in aquaculture

Water quality is crucial in aquaculture, significantly affecting fish health, growth, and overall production efficiency. Here are some key roles of water quality in aquaculture:

1. Dissolved Oxygen Levels: Adequate oxygen is essential for fish respiration. Low levels can lead to stress, reduced growth, and even mortality.
2. Temperature Control: Different species have specific temperature requirements. Water temperature affects metabolic rates, growth, and reproduction. Sudden changes can stress fish.
3. pH Levels: The pH level affects nutrient availability and microbial activity. Most fish thrive in a neutral pH range (6.5 to 8.5), and extreme pH levels can cause stress and health issues.
4. Ammonia and Nitrite Concentrations: Toxicity from ammonia and nitrites can harm fish. Regular monitoring and management of these compounds are essential to prevent toxic build-up.
5. Nutrient Levels: The presence of nutrients (like nitrogen and phosphorus) can influence algae growth. Excessive nutrients can lead to harmful algal blooms, which reduce oxygen levels and produce toxins.
6. Salinity: For brackish and marine aquaculture, salinity levels must be suitable for the species being cultured. Incorrect salinity can cause osmotic stress and mortality.
7. Turbidity: High turbidity can limit light penetration, affecting plant growth and thus the overall ecosystem balance. It can also stress fish and hinder feeding.
8. Pathogen and Parasite Management: Good water quality reduces the risk of disease outbreaks. Poor water quality can stress fish, making them more susceptible to pathogens.
9. Water Exchange and Filtration: Proper water exchange and filtration systems help maintain optimal water quality by removing waste products and replenishing essential nutrients.
10. Biological Balance: Maintaining a balance of beneficial bacteria helps with the nitrogen cycle and overall ecosystem health, which is vital for the success of aquaculture systems.

Different levels of aquaculture

Aquaculture, the cultivation of aquatic organisms, can be classified into various levels based on operational intensity, capital investment, and management practices. Each level presents distinct operational characteristics, stocking densities, and production outputs, influencing the overall efficiency and sustainability of fish farming. The classification includes extensive, semi-intensive, intensive, modified extensive, and super-intensive aquaculture.

1. Extensive Level
   • Characterized by low stocking densities, extensive aquaculture typically uses about 5,000 carp fry or 5,000 to 10,000 shrimp post-larvae per hectare.
   • Feeding: This level does not involve supplemental feeding; instead, it relies on natural food sources stimulated through fertilization to enhance growth.
   • Pond Size: Ponds generally exceed two hectares in area.
   • Water Management: Water replacement is minimal for carp culture, while shrimp culture requires tidal flushing, allowing fresh water to enter during high tides and old water to exit during low tides.
   • Production Yield: Expected yields are relatively low, averaging less than 0.5 tons per hectare annually for shrimp and 1 to 3 tons per hectare for carp.
2. Modified Extensive Level
   • This intermediate system lies between extensive and semi-intensive aquaculture, with pond sizes ranging from 1 to 2 hectares.
   • Stocking Density: Moderate stocking densities of 30,000 to 40,000 shrimp post-larvae or 5,000 to 7,500 carp fingerlings per hectare are used.
   • Feeding and Fertilization: Organic and inorganic fertilizers are applied monthly, alongside low to moderate amounts of supplementary feed.
   • Water Management: Water replacement occurs every two to three months for carp culture and bi-weekly for shrimp culture, at a rate of 10% to 20%.
   • Production Yield: Production averages around 1 ton per hectare for shrimp and 4 to 5 tons per hectare for carp.
3. Semi-Intensive Level
   • Utilizing medium-sized ponds of approximately 0.5 hectares, semi-intensive aquaculture features higher stocking densities than the extensive level, with 50,000 to 100,000 shrimp post-larvae or 10,000 carp fingerlings per hectare.
   • Feeding: Moderate amounts of supplemental feeding are provided to enhance growth.
   • Water Management: Water replacement is conducted once or twice monthly for carp and once or twice weekly for shrimp, typically at 10% to 20%.
   • Production Yield: Average yields reach about 1.5 tons per hectare for shrimp and 5 to 7 tons per hectare for carp.
4. Intensive Level
   • Intensive aquaculture is marked by high stocking densities, utilizing small ponds around 0.2 hectares.
   • Stocking Density: The density of culture organisms can range from 300,000 to 500,000 shrimp post-larvae or 20,000 to 25,000 carp fingerlings per hectare.
   • Feeding: This system is highly dependent on formulated feeds, with fish fed regularly, sometimes as frequently as three to six times daily.
   • Water Management: Daily water replacement is critical, occurring at a rate of approximately 25% to 30%.
   • Production Yield: Intensive systems can produce significantly higher yields, averaging 8 to 10 tons per hectare for shrimp and 12 to 15 tons per hectare for carp.
5. Super-Intensive Level
   • This highly advanced form of aquaculture relies on almost continuous water flow, necessitating daily water exchanges.
   • Infrastructure: Super-intensive systems are often housed in cement tanks, fiberglass tanks, or raceways, equipped with high-efficiency biological filters for water recirculation.
   • Tank Size and Stocking Density: Tank sizes range from 50 to 100 cubic meters, with stocking densities of 800,000 to 1,000,000 shrimp post-larvae or 40,000 to 50,000 carp fingerlings per hectare.
   • Feeding: High-quality formulated feeds are used, delivered through demand feeders.
   • Monitoring: Regular water quality checks are performed using electronic devices.
   • Production Yield: Yields can be exceptionally high, with shrimp culture producing 10 to 12 tons per hectare and carp culture yielding 15 to 20 tons per hectare.

Advantages of aquaculture

Below are the key advantages:

• High-Quality Protein Source: Aquaculture produces fish that are rich in high-quality protein, making it a vital source of essential nutrients, including healthy omega-3 fatty acids.
• Sustainable Fish Production: As wild fish stocks decline, the future of fish production depends largely on aquaculture. It offers a sustainable method for meeting the increasing demand for seafood without depleting natural fish populations.
• Affordable Food Source: Due to its ability to produce fish at lower costs compared to capture fisheries, aquaculture makes seafood more affordable, even for lower-income populations, ensuring access to nutritious food.
• Pollutant-Free Fish: Farmed fish are often safer than wild-caught fish, as they are raised in controlled environments free from pollutants such as heavy metals, pesticides, and other environmental contaminants.
• Food Security for a Growing Population: Aquaculture supports global food security by producing a stable and predictable supply of fish, helping to feed the world’s rapidly growing population.
• Increased Employment Opportunities: The expansion of aquaculture creates jobs in rural and coastal areas, from fish farming to processing and marketing, boosting local economies and improving livelihoods.

Disadvantages of aquaculture

Below are the main disadvantages:

• Impact on Local Flora and Fauna: The infrastructure required for aquaculture, such as fish farms and ponds, can disrupt local ecosystems, including wetlands and mangroves. This habitat destruction affects the biodiversity of these areas, leading to the loss of important plant and animal species.
• Effluent Discharge: Untreated wastewater from aquaculture operations often contains a high organic load, including excess feed, fish waste, and chemicals. When discharged into surrounding water bodies, it can cause eutrophication, leading to harmful algal blooms and oxygen depletion, which negatively affects local aquatic ecosystems.
• Introduction of Exotic Species: The farming of non-native or exotic species can introduce new pathogens to the local environment. These foreign species might carry diseases that native species are not resistant to, potentially leading to widespread infections and ecological imbalance.
• Disease and Parasite Transmission: Captive fish in aquaculture systems often live in crowded conditions, making them more susceptible to diseases and parasites. These infections can be transferred from farmed fish to wild populations, threatening the health of natural fish stocks and biodiversity in surrounding areas.