Ecological Footprint of Different Culture Modes of Penaeus vannamei in Northern China

Abstract

The rapid development of shrimp aquaculture has resulted in numerous ecological problems, thereby necessitating the assessment of its sustainable ecological development. This study employed the ecological footprint method to conduct a quantitative analysis of the environmental ramifications of two culture modes (pond and factory) of Penaeus vannamei. The analysis includes a horizontal comparison between two different modes and a vertical comparison among different aquaculture links of the same mode, with the objective of identifying the weak link in the aquaculture process. The results show that the ecological footprint per unit of profit of the factory culture mode was lower than that of the pond mode, while the ecological footprint per unit of output was higher in the former. Water resource consumption was identified as the primary component of the ecological footprint in both modes, accounting for over 70% of the total, followed by feed consumption. The higher energy consumption in the factory culture mode is ascribed to the operation of mass-production facilities. The feed conversion ratio in shrimp aquaculture requires improvement, as evidenced by a ratio of 1.05 in the pond mode and a higher ratio of 1.82 in the factory culture mode, indicating suboptimal feed utilization efficiency. In light of these conclusions, various measures and suggestions are put forth, including improving shrimp feed composition, implementing energy-saving measures, weighing production planning across different culture modes, and optimizing water resource utilization.

1. Introduction

As an important part of fisheries, the aquaculture industry plays an important role in food and nutrition requirements. In 2021, the output of aquaculture in China increased by 40.89% compared to 2010 [1], with a relatively high growth rate; however, its rapid development has also brought environmental problems, such as mangrove destruction and land salinization, which is caused by the transformation of agricultural land into aquaculture waters [2]. The report of the 20th National Congress of the Communist Party in China proposed new requirements for accelerating green transformation, promoting the priority of ecological sustainability, preservation, and intensive conservation for the future ecological protection of our environment [3]. As a major cultivar in the aquaculture industry, the culture of Penaeus vannamei must make efforts in this direction. Therefore, it is of great significance to evaluate the ecological sustainability of Penaeus vannamei culture, including the sustainable development of different aquaculture modes, for the modernization of Chinese fisheries. The concept of an ecological footprint was first proposed by the Canadian ecological economists Wackernagel and Rees [4], who represented the impact of human production activities on the environment in a specific area. The ecological footprint is a method that combines ecological and economic benefits to estimate the degree to which resources are sustainably used; it has been widely used in the assessment of the sustainable utilization of fishery resources at home and abroad. Peron et al. concluded that although mariculture activities can produce obvious economic benefits in the short term, they can affect the coupling of marine ecosystems in the long run. Therefore, a balance between ecological and economic benefits should be emphasized in aquaculture [5]. Kurnia et al. calculated the ecological footprint and biological capacity of fisheries in Jakarta Bay and found that the ecological footprint value was higher than the biological capacity value and was unsustainable [6]. Using different culture modes, Berg calculated the ecological footprint of tilapia cage culture in different regions, and the results showed that the ecological footprint of tilapia in Zimbabwe Lake Kariba was approximately 1000 times that of the other regions [7]. From the perspective of different fishery production methods, Tyedmers calculated the ecological footprint of caught and farmed salmon and found that caught salmon had a higher minimum and maximum footprint per ton than farmed salmon [8]. From the perspective of different fishing activity areas, Gyllenhammar et al. conducted an empirical study on the environmental effects of marine fishery activities in the Baltic Sea on multiple scales, such as aquaculture farms, local offshore waters, and international seas in offshore waters, and found that the ecological footprint of aquaculture farms was at a relatively high level [9]. On the ecological footprint of shrimp culture, Ofori et al. explored the relationship of the area changes between the Pambala–Chilaw lagoon complex and the Ihala Mahawewa mangrove and shrimp farms, and the results showed that current shrimp farming was unsustainable, and the mangrove ecosystem function would continue to decline if effective measures were not taken to regulate shrimp farming activities and mangrove restoration [10]. Tao et al. studied a compound pond recirculating the aquaculture system and concluded that the ecological and economic benefits of this aquaculture system were largely superior to the traditional pond culture mode and more in line with the requirements of sustainable development; however, the ecological footprint of the unit of output was not quantitatively analyzed [11]. Liu et al. calculated the ecological footprint and ecological footprint index of the two culture modes of Penaeus vannamei and found that environmental pressure in the intensive culture mode was lower than that of the semi-intensive culture mode. However, this research did not analyze feed, wastewater, or other items. The feed accounted for a high proportion of the input of the Penaeus vannamei culture; therefore, its ecological footprint also needs to be taken into account in the calculation [12]. It can be seen that the sustainable development of fisheries is an inevitable choice when reducing the environmental pressure of aquaculture in China, and the quantitative assessment of the environmental impact of different culture modes to explore ecologically sustainable culture modes is a necessary condition to achieve sustainable fisheries.

In this study, the ecological footprints of different culture modes in northern China were quantitatively analyzed to explore the ecological sustainability of Penaeus vannamei. Compared to previous studies, the representativeness of these samples was fully considered, and the sample size was increased on the basis of sample universality to better reflect the developmental status of the local shrimp industry. At the same time, this article separately compares the environmental impact and eco-economic benefits of different culture modes, which increases the accuracy of the research results and has important reference value for the government, relevant environmental management departments, and aquaculture practitioners.

2. Overview of Data Sources and Evaluation Methods

2.1. Data Sources and Culture Modes

2.1.1. Data Sources

Hebei Province and Shandong Province are the main producing areas of shrimp culture in northern China. In 2022, the modern agricultural industrial technology system conducted a field survey on the culture situation of Penaeus vannamei in these two regions in 2021 and obtained 84 samples in total, including 38 samples from Hebei Province and 46 samples from Shandong Province. From the perspective of culture modes, the pond culture and factory culture modes are the main culture modes in Hebei Province and Shandong Province, respectively, accounting for 89.47% in Hebei Province, and 86.96% in Shandong Province (

Table 1. Distribution of culture samples in different regions and different culture modes in northern China in 2021.

Region	Culture Mode	Quantity	Proportion (%)
Hebei	Pond	34	89.47
	Factory	4	10.53
	Total	38	100.00
Shandong	Pond	6	13.04
	Factory	40	86.96
	Total	46	100.00

).

2.1.2. Overview of Culture Modes

Considering that the ecological footprint component method can use some samples to represent the advantage of the overall situation [13], this study selected eight pond culture modes in Hebei Province and eight factory culture modes in Shandong to calculate the ecological footprints of the two modes. The sample selection was as follows:

(1)

Pond culture mode

The traditional pond culture mode is the main form of shrimp culture in Hebei Province, and in recent years, Penaeus vannamei culture in Tangshan City has become a pillar industry for local farmers to obtain rich and rural revitalization. A number of Penaeus vannamei culture bases have been established in Caofeidian, Fengnan, and other regions. In this study, eight shrimp farms in the Caofeidian District of Tangshan were selected as sample points for the pond culture mode. The culture area of the sample points was 7.53 × 10⁴ m². The average stocking density was 37.44 tail/m³, and the survival rate of the shrimp seedlings was 35.6%. Affected by climatic conditions, the pond mode casts seedlings in April to May every year, and the growth cycle of shrimp is approximately five months, so only one round of farming can be done per year. In order to cultivate a pond culture, it should be harvested irregularly and, at the same time, sold in bulk in order to obtain maximum profits.

(2)

Factory culture mode

Rizhao City, Binzhou City, and Weifang City are the main areas of shrimp culture in Shandong Province, among which Rizhao City was the earliest area to invoke a shrimp factory culture in China. In this study, eight farms in Donggang District, Rizhao City, were selected as sample points for the factory culture mode. The culture areas of the sample sites were 3000 m² or 3500 m². The average stocking density was 319.64 tail/m³, and the average survival rate of the shrimp seedlings was 72.6%. The growth cycle of shrimp is approximately four months, and there are 2 or 3 culture cycles per year. In the factory mode, cement ponds are built in greenhouses to carry out farming. By artificially regulating the farming environment, high-density farming is carried out in limited water bodies, and solar energy or other heat energy is used to control the breeding water temperature in the most suitable conditions for the growth of shrimp; therefore, the growth state of the shrimp can be optimized.

2.1.3. Comparison and Analysis of Two Culture Modes

The factory mode does not need to consume a large amount of land, and its culture area is much smaller than that of the pond mode. As shown in

Table 2. Comparison of the input of two culture modes.

Culture Mode	Culture Area (m2)	Shrimp Seedling (Million Tails)	Stocking Density (Tails/m³)	Feed (t)	Labor (People)	Water (m³)	Electricity (kW·h)
Pond	7.53 × 104	5.66	37.44	35.25	2.00	2.26 × 105	58,952.84
Factory	3125.00	1.93	319.64	30.03	2.10	1.25 × 105	111,111.13

, the stocking density of the factory culture mode is approximately eight times that of the pond mode, which reflects its characteristics of using modern technology to achieve ultra-high-density shrimp farming. Compared to the pond mode, this culture mode is influenced less by natural conditions and can choose the seedling time flexibly; therefore, the survival rate of the shrimp seedlings is higher. The number of shrimp seedlings in the pond culture is 5.66 million, higher than that in the factory culture (1.93 million). However, the growth cycle of the shrimp in the pond culture is longer, the growth rate of the shrimp is relatively slow, and the amount of feed is relatively small. It can be seen that the difference in feed consumption between the two culture modes is not too large, and the pond mode uses about 5 tons more than the latter. From the absolute values of water and electricity consumption, we can see that the water consumption of the pond mode exceeds that of the factory mode, which is related to the large size of the culture mode. Under factory farming conditions, a large amount of feed is used daily. The oxygen demand per unit of area of shrimp is higher, and a large number of oxygenators are needed to continuously oxygenate the shrimp. Simultaneously, the mass-production equipment consumes electricity, which is also the reason behind the higher energy consumption in the factory culture mode.

2.2. Evaluation Methods and Index Selection

2.2.1. Process of Factor Transformation

To calculate the ecological footprint, the consumption of various resources needs to be converted into the corresponding bio-productive land area in a certain proportion through the yield and equilibrium factors, that is, the unit of global hectares [14]. This yield factor reflects the relative productivity of the average hectare in the world alongside the country with a specific land type, while the equilibrium factor reflects the relative productivity of the average hectare in the world with different land types (

Table 3. Yield and equilibrium factors for different land types.

Items	Cultivated Land	Forest Land	Pasture	Construction Land	Water	Energy Land
Yield factor	1.95	1.18	0.81	1.95	1.00	-
Equilibrium factor	1.74	1.41	0.44	1.74	0.35	1.41

Note(s): These yield factors come from the global footprint network [15], and the equilibrium factors come from Liu et al. [16].

).

2.2.2. Basic Calculation Formula of Ecological Footprint

The conversion process of the ecological footprint refers to the conversion process from the material to the land area, and its calculation formula is as follows:

$$\mathrm{EF}={\displaystyle \sum {\mathrm{A}}_{\mathrm{i}}}\times {\mathrm{e}}_{\mathrm{i}}\times {\mathrm{y}}_{\mathrm{i}}={\displaystyle \sum \left({\mathrm{C}}_{\mathrm{i}}÷{\mathrm{P}}_{\mathrm{i}}\right)}\times {\mathrm{e}}_{\mathrm{i}}\times {\mathrm{y}}_{\mathrm{i}}(\mathrm{i}=1,2,3\dots )$$

where EF is the total ecological footprint occupied by aquaculture, C_i is the consumption of item i, P_i is the average productivity of the corresponding bio-productive land for item i’s consumption, A_i is the area of bio-productive land occupied by the consumption item i, e_i is the equilibrium factor of consumption item i of the corresponding bio-productive land production, and y_i is the yield factor of the consumption item i produced by the corresponding bio-productive land.

2.2.3. Index Selection

Based on the modern agricultural industrial technology system, the primary production data for the two modes were obtained. The selected sample points were the designated survey points of the modern agricultural industrial technology system, and the breeding technology of the sample point farms was in the middle and high levels of the industry. Based on the particularity of the aquaculture process and considering that the accounting index should fully reflect the component input in the process of the shrimp culture, seven components, including the floor area, culture area, feed consumption, labor, water consumption, electricity consumption, and wastewater, were selected as the input indices for the ecological footprint calculation of Penaeus vannamei. The ecological footprint per unit of yield was used to determine the environmental cost of producing one ton of Penaeus vannamei in each culture mode, which was used as the basis for the assessment of the environmental impact of shrimp farming. The ecological footprint per unit of profit was used to evaluate the number of natural resources that were consumed by each culture mode to produce CNY 10,000 of economic profit, which was used as the basis for the assessment of the comprehensive ecological economic benefits of shrimp farming.

The ecological footprint of each component was calculated as follows:

(1)

Feed: The main raw materials of the compound feed of Penaeus vannamei were 48% fish meal and shrimp shell meal, 15% wheat meal, 18% soybean meal, and 7% peanut meal (

Table 4. Feed composition and unit of the ecological footprint.

Composition and Proportion	Unit of Ecological Footprint (ghm2/t)
Fish meal and shrimp shell meal, 48%	2.115
Wheat meal, 15%	0.861
Soybean meal, 18%	2.061
Peanut, 7%	1.623
Result of calculation	1.629

Note(s): State Statistics Bureau.

). These five raw materials accounted for approximately 90% of the compound feed of Penaeus vannamei; their ecological footprint was used to represent the ecological footprint of the shrimp feed. The ecological footprints of the fish meal and shrimp shell meal were calculated based on the average output of aquatic products in China [1]. In 2021, the average output of aquatic products was 2454.29 kg/hm², and the area of the water required per ton of aquatic product was 0.407 hm², which could be translated into 2.115 ghm² globally. In 2019, the yield per unit of area of Chinese wheat was 5630.40 kg/hm². The cultivated land needed per ton of wheat was 0.178 hm², which could be converted into 0.603 ghm² in global hectares. Yang et al. concluded that the flour yield of domestic high-quality wheat was 70% [17]; that is, one ton of flour required 1.429 tons of wheat to be produced. This indicates that the ecological footprint of one ton of flour was 0.861 ghm². Simultaneously, according to the oil yields of soybeans and peanuts, the soybean meal and peanut meal were converted into the yields of soybeans and peanuts. The ecological footprint of one ton of shrimp feed was 1.629 ghm² after weighing.

(2)

Labor: Labor cost is a part of the input in aquaculture; therefore, the ecological footprint of labor cost should be taken into account. According to the Global Footprint Network, China’s per capita ecological footprint in 2018 was 3.80 ghm². This standard was used in this study to calculate the ecological footprint of shrimp farms.

(3)

Water footprint: Based on research data from the World Resources Institute, Huang et al. calculated that the water production per unit of area was 2.95 × 10⁵ m³/km² in China and the equilibrium factor of Chinese water resources was 5.19. According to the Global Footprint Network, the water resource yield factor in China in 2018 was 1.00, and it could be concluded that the ecological footprint required per cubic meter of water resources in China was 0.176 × 10⁻² ghm² [18]. In the pond mode, water change was not carried out in the whole process, and the water depth of the pond was approximately 1.5–1.8 m in the early stage of aquaculture, which was adjusted continuously with shrimp growth. The factory mode adopted a large-flow farming method throughout the entire cycle. The water was changed every two days for the first 30 days, with an average water change of approximately 25% each time, 40% daily for 30–60 days, and approximately 80% daily after 60 days.

(4)

Electricity: Xie calculated the ecological footprint of energy and found that the ecological footprint occupied by 1 kW·h of thermal power was 6.117 × 10⁻⁵ hm² of forest land and 5.134 × 10⁻⁵ hm² of pasture, and 1 kW·h of hydro-power was 2.145 × 10⁻⁶ hm² of cultivated land [19]. According to Zeng’s research [20], the proportions of hydro-power and thermal power in China are 21.59% and 78.41%, respectively. It can be concluded that the ecological footprint occupied by consuming 1 kW·h could be converted into a global hectare of 9.572 × 10⁻⁵ ghm² if the power in China was 0.463 × 10⁻⁶ hm² of cultivated land, 4.796 × 10⁻⁵ hm² of the forest, and 4.026 × 10⁻⁵ hm² of pasture.

(5)

Wastewater: Considering the different culture modes, this study calculated the ecological footprint of wastewater from a pond and factory, respectively. According to the characteristics of pond culture wastewater, the chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) were selected as the accounting items of water pollution. In the research by Bai et al., water pollution was transformed into the ecological footprint of aquatic products, with currency as the medium, with the introduction of the unit cost per pollutant treatment and unit price per aquatic product [21]. Li et al. found that the COD content and ammonia nitrogen content in the effluent from shrimp culture ponds were 2.21 × 10⁻³ kg/m³ and 6.19 × 10⁻⁵ kg/m³, respectively [22]. The ecological footprint per ton of pond culture wastewater was 4.445 × 10⁻⁵ ghm² based on the total output value of the fishery and the total output of aquatic products. In the factory mode, the ecological footprint of wastewater was transformed into an energy ecological footprint using the energy consumption data from sewage treatment plants. According to a study by Chu et al., the average ton of waterpower consumption in China is 0.325 kW·h/m³ [23], and the ecological footprint of one ton of wastewater is 3.111 × 10⁻⁵ ghm².

3. Results

3.1. Analysis of Ecological Footprint Components of Shrimp Culture

The ecological footprint components of the Penaeus vannamei culture and the consumption of various resources are listed in

Table 5. Analysis of ecological footprint components in shrimp culture.

Items	Consumption		Resource Type
	Pond	Factory
Floor area (m2)	100.00	1875.20	Construction land
Culture area (m2)	7.53 × 104	3125.00	Cultivated land, waters
Feed consumption (t)	35.25	30.03	Cultivated land
Labor	2.00	2.10	Food, water, energy
Water (m³)	2.26 × 105	1.25 × 105	Water
Electricity (kW·h)	5.90 × 104	1.11 × 105	Cultivated land, forest land, pasture
Wastewater (m³)	1.50 × 105	1.25 × 105	Energy land

. The ecological footprint of the breeding process belongs to the following six types of land resources: the floor area included the total area of the shrimp farm, except for the culture area, which could be attributed to construction land. The culture area included the pond area and water resource land, which belong to cultivated land and water. In the shrimp feed, wheat was the main raw material, which could be classified as cultivated land, while some other raw materials were mostly the waste or by-products of other products, whose ecological footprint was calculated in the main product and could be ignored. According to Xie et al. [19], the ecological footprint accounting process considers the energy involved in cultivated land, forestland, and pasture. The wastewater discharged during the breeding process of Penaeus vannamei was processed and converted into energy, and this part of the consumption could be attributed to energy from the land.

3.2. Accounting Results of Ecological Footprint of Shrimp Culture

The ecological footprint of each component and its proportions are listed in

Table 6. Accounting results of ecological footprints.

Items	Unit EF	Pond		Factory
		EF (ghm2)	Proportion (%)	EF (ghm2)	Proportion (%)
Floor area	3.393 ghm2/hm2	0.034	0.00	0.636	0.22
Culture area	3.393 ghm2/hm2	25.550	5.15	1.060	0.37
Feed consumption	1.629 ghm2/t	57.422	11.58	48.919	17.00
Labor	3.800 ghm2/person/year	3.167	0.64	2.660	0.92
Water	0.176 × 10−2 ghm2/m³	397.339	80.14	220.00	76.44
Electricity	9.572 × 10−5 ghm2/kW·h	5.643	1.14	10.636	3.70
Wastewater	4.445 × 10−5 ghm2/m³	6.668	1.35
Wastewater	3.111 × 10−5 ghm2/m³			3.889	1.35
Total		495.82	100.00	287.80	100.00

. The ecological footprints of the two culture modes were 495.82 ghm² (pond) and 287.80 ghm² (factory), respectively, and the absolute ecological footprint of the pond culture mode was relatively high. In the pond mode, the top three ecological footprints accounted for the highest proportions of water consumption, feed consumption, and culture area, whereas in the factory mode, the top three accounted for the highest proportions of water consumption, feed consumption, and electricity consumption. In these two modes, the ecological footprint of the floor area accounted for a relatively low proportion, indicating that most of the farms covered the culture area. The proportion of the culture area in the pond mode was 5.15%, whereas that in the factory mode was only 0.37%. Compared to the pond mode, the factory mode did not occupy a large amount of land and mainly used advanced technology and equipment to achieve ultra-high-density intensive farming needs. There was little difference in the level of labor input between these two modes; the ecological footprint of labor consumption in the pond mode was relatively high due to its longer culture cycle. It is worth noting that the Global Footprint Network shows that China’s per capita ecological footprint increased to 3.80 ghm² in 2018. According to the study of Shi et al., from 1991 to 2013, China’s per capita ecological footprint increased from 0.992 ghm² to 2.419 ghm², an increase of 144% [24]. This indicates that the growth rate of resource consumption in China is always at a high level. However, in 2018, China’s per capita ecological carrying capacity was only 0.9 ghm²; that is to say, China’s per capita ecological deficit was as high as 2.9 ghm², which also shows that people have ignored the protection of the environment and resources while rapidly developing the economy. This also reminds us that we should rationally use ecological resources and improve resource utilization efficiency while developing the shrimp aquaculture industry.

3.3. Comparative Analysis of Ecological Footprint Occupancy per Unit of Output

The ecological footprint per unit of output refers to the ecological footprint consumed to produce one ton of shrimp. The higher the value, the greater the negative impact on the environment under the same production conditions. The ecological footprint per unit of profit refers to the size of the ecological footprint for every CNY 10,000 of economic profit. The lower the value, the higher the ecological economic benefits of farming.

Table 7. Ecological footprint occupied per unit of output for the two culture modes.

Culture Mode	Total Production (kg)	Net Profit (CNY)	Net Profit per Unit of Output (CNY/kg)	EF per Unit of Output (ghm2/t)	EF per Unit of Profit (ghm2/10,000 CNY)
Pond	33,531.25	179,823.75	7.81	14.79	27.57
Factory	16,562.50	454,555.47	13.54	17.38	6.33

shows the ecological footprint per unit of output for the two culture modes. The ecological footprint per ton of shrimp produced by the factory mode was 17.38 ghm², which is higher than that of the pond mode, indicating that the factory mode causes higher environmental costs at the same yield level. According to the preliminary analysis, the reason for this result is that the ecological footprint of each component in the factory mode is larger, especially the consumption of water resources, which leads to an improvement in the ecological footprint level of the factory mode. At the same time, the factory mode pursues an off-season price advantage, avoiding the peak harvest of shrimp in order to obtain the maximum profits; therefore, the advantages of this mode are eventually reflected in the economic benefits. The net profit per unit of output of the factory mode was 13.54 CNY/kg, about 1.5 times that of the pond mode, showing obvious advantages in economic benefits. Moreover, as is shown in Figure 1, the ecological footprint per CNY 10,000 of profit was 6.33 ghm², which is lower than the 27.57 ghm² of the pond mode, indicating that a greater economic value is created by using the ecological footprint per unit. However, this also indicates that the factory mode does not fully consider the impact on the environment when using modern technology to pursue high-output benefits, resulting in the phenomenon of high economic benefits and low ecological benefits.

There was no obvious correlation between the ecological footprint per unit of output and the profit of the two culture modes. Although the factory mode could produce more economic profits under units of ecological footprint consumption, its output of shrimp per ton had a greater negative impact on the environment. The ecological footprint per unit of output of the pond mode was slightly lower than that of the other mode, but the ecological footprint required to generate a unit of economic profit was much higher than that of the factory mode. Thus, the two culture modes demonstrate great room for improvement in their degree of consumption in nature and degree of resource utilization.

4. Analysis and Discussion

4.1. Water Consumption Has the Largest Proportion of Ecological Footprint

Water consumption accounted for 80.14% of the ecological footprint of the pond mode and 76.44% in the factory mode (Figure 2 and Figure 3), both of which were the highest proportions. The average proportion of water consumption was highly consistent with the proportion of each sample. The traditional pond mode did not require a large amount of water change; however, its farming scale was generally large, and the overall water consumption increased while under the factory mode. A large amount of aquaculture waste was generated every day, which seriously affected the quality of aquaculture water. In the late stages of aquaculture, a large amount of water needed to be changed almost every day, and the wastewater was discharged without treatment, which could cause the serious consumption of water resources. Regardless of the mode, reducing water consumption in the aquaculture process is the key to reducing the ecological footprint of shrimp culture. In the current research, recirculating aquaculture is the most effective way of reducing water resource consumption. This system is suitable for wastewater treatment and recycling in high-density pond cultures. Compared to the traditional culture mode, this mode had the advantages of water saving, land saving, high-density intensification, and high controllability, which can meet the requirements of sustainable development. However, owing to the high cost of the circulating water treatment device, the production cost of the factory mode was significantly improved. In addition, once shrimp diseases or natural disasters occur, breeding enterprises usually suffer losses with a high risk. From the perspectives of economy and risk, breeding enterprises are more inclined to direct drainage and water exchange, which can greatly increase the consumption of water resources and fail to achieve water resource recycling.

4.2. Energy Consumption of Factory Mode Is Higher than That of Pond Mode

The ecological footprint of energy consumption in the factory mode was 3.70%, which was higher than that in the pond mode (1.14%). The energy consumption per unit of output of the pond mode was 1758.2 kW·h/t, whereas that of the factory mode was 6709.6 kW·h/t. Obviously, more energy was needed to produce per ton of shrimp in the factory mode. The difference in the energy consumption between these two modes could be related to the different intensities and energy demands of the breeding production. The factory mode used more electricity because of the input of a large amount of production equipment, such as water regulation equipment and water collection equipment. Moreover, the factory mode was at a higher level from the perspective of the ecological footprint of energy consumption. This mode relied on a variety of energy-intensive production equipment, such as protein separators and micro-strainers, to maintain the ecological environment in the rearing tank, which is always in operation until the middle and later stages of farming; this energy consumption increased accordingly [25]. The electricity consumption in the farming process was directly proportional to the electricity cost; the higher the electricity consumption, the higher the electricity cost was. Therefore, energy-saving measures during the breeding process play an important role in effectively reducing the ecological footprint of shrimp farming.

4.3. The Feed Conversion Ratio of Shrimp Needs to Be Improved

Except for water consumption, the ecological footprint of the feed components accounted for the highest proportions in both culture modes. As shown in

Table 8. Feed conversion ratio of shrimp.

Culture Mode	Feed Consumption (t)	Total Production (t)	Stocking Density (tail/m³)	FCR
Pond	35.25	33.53	37.44	1.05
Factory	30.03	16.56	319.64	1.82

Note(s): FCR = Feed consumption ÷ total production of shrimp.

, the feed conversion ratios of shrimp in the two modes were 1.05 (pond) and 1.82 (factory). The feed conversion ratio (FCR) of shrimp refers to the ratio of feed consumption to the total shrimp production. The higher the ratio, the lower the feed utilization ratio. The factory mode did not reflect this advantage; its feed conversion ratio was as high as 1.82, that is, it took 1.82 kg of shrimp feed to produce 1 kg of shrimp, which was contrary to the common belief that advanced technology can produce more shrimp with the same amount of feed. Meanwhile, this study shows that the feed conversion ratio of shrimp was related to the density of seedlings, and the higher the seedling density, the higher the feed conversion ratio [26]. As shown in Table 8, the seeding density of the pond mode is 37.44 tail/m³, while that of factory mode is 319.64 tail/m³. It can be seen that the seeding density and feed conversion ratio of factory mode were both higher than that of the former. The reason is that, in the pond culture mode, aquaculture waste easily accumulates at the bottom of the pond, which provides conditions for the proliferation of pathogens, and shrimp disease occurs easily; therefore, the breeding density is generally kept at a low level. In the factory culture mode, with the increase in the stocking amount per unit of volume, the overfeeding of feed, and other reasons, the seedling density and feed feeding amount are far higher than that those in the pond mode, which inevitably leads to the accumulation of various feed residues in the aquaculture tank, thus resulting in an increase in the feed conversion ratio and low feed utilization [26]. At the same time, under the conditions of high-density culture, feed feeding and the rapid accumulation of biological feces increases the pollution load of water bodies, leading to a significant decline in the self-purification capacity of water [27]. Therefore, reasonable aquaculture input is also an important factor in aquaculture.

4.4. The Ecological and Economic Benefits of the Factory Mode Are Generally Higher than Those of the Pond Mode

The ecological footprint per ton of Penaeus vannamei produced by the factory mode was 17.38 ghm², which was higher than that of the pond mode (14.79 ghm²), indicating that under the same production conditions, this mode had a greater environmental impact. From the perspective of ecological economic benefits, the ecological footprint of the factory mode was 6.33 ghm² for every CNY 10,000 of economic profits, which was lower than that of the pond mode (27.57 ghm²). In other words, the model only needed a 6.33 ghm² bio-productive land area to provide the required natural resources and absorb generated wastes for every CNY 10,000 of economic benefits. This shows that, under the same supply of resources, the factory mode could obtain higher economic profits. Liu et al. evaluated two shrimp culture modes based on the ecological footprint model [12] and concluded that the intensive mode had greater sustainable development potential compared to the semi-intensive culture mode by calculating the per capita fishery ecological footprint. Tao et al. calculated the ecological footprint of a compound pond circulating the aquaculture mode [11], and the results showed that the ecological footprint of 2.92 ghm² for every CNY 10,000 of economic profit produced by the culture mode was lower than that of the traditional pond mode (4.91 ghm²), which is consistent with this paper’s results showing that the industrial mode had the lowest ecological footprint per CNY 10,000 of profit. These results indicate that an intensive mode could create more profits with the same resources, and the innovation of culture technology has a positive promoting effect on improving the ecological and economic benefits of shrimp culture. However, the factory culture mode needs to invest a large amount of production equipment in the early stages, which leads to an increase in production costs. This mode also has high requirements for the level of breeding technology, which restricts its promotion in the shrimp culture industry to a certain extent.

5. Policy Suggestions

5.1. Feed Composition Should Be Improved to Reduce the Feed Conversion Ratio

It can be seen that the ecological footprints of the feed components in both modes were very high, and the feed conversion ratio (FCR) of the factory mode was at a high level. In this mode, the feed demand per unit of area is very large, which leads to a rapid decline in the self-purification capacity of the water body, resulting in a large amount of waste and feed residues in the rearing tank, which is not conducive to shrimp growth. Therefore, to reduce the ecological footprint of the feed components, it is necessary to reduce the feed conversion ratio, improve the feeding efficiency, and guide farmers to establish scientific production concepts. Government departments should organize a group of professional technical teams to set up online breeding courses or provide on-site guidance to breeding enterprises, establish feed feeding intervals at each stage, and promote scientific and standardized breeding production. Simultaneously, relevant departments should strengthen policy support and improve the processing technology and quality of the shrimp feed.

5.2. Implement Energy-Saving Measures to Reduce Energy Consumption

The energy consumption of the pond mode is relatively low, while the factory mode introduces a series of water treatment facilities and farming technology, which reduce the impact of climate and temperature on the growing environment of the shrimp and can realize off-season farming; its essence is to exchange electricity for the economy. A large amount of water treatment equipment and production facilities need to be invested in the early stages of farming, such as micro-strainers, protein separators, and oxygen generators, which are always in operation at a later stage; thus, the energy consumption is extremely high. Therefore, energy conservation measures should be implemented to reduce the energy ecological footprint of aquaculture processes. The introduction of special instruments could improve aquaculture water quality to avoid the heavy load of biological filtration. It is recommended to use a combination of a micro-strainer and a main circulation pump and adjust the specifications of the micro-strainer according to the specifications of the aquaculture tank to reduce the energy consumption of the system. In addition, the government should provide financial subsidies to enterprises that introduce energy-saving equipment and encourage aquaculture enterprises to adopt energy-saving measures.

5.3. Consider Production Planning of Different Culture Modes

In terms of the ecological footprint per unit of profit, the factory mode had a lower ecological footprint per CNY 10,000 of profit, indicating that it can obtain greater economic benefits under the same resource conditions. In terms of the ecological footprint occupation per unit of output, although the factory mode adopts advanced technology and equipment, it did not show an advantage in the resource demand per unit of output; that is, it did not have an advantage in ecological sustainability. This result indicates that local governments and fishery management departments should not ignore the impact of development on the environment while actively promoting the factory mode in pursuit of higher economic benefits. They should start from the perspective of ecological protection, balance the ecological and economic benefits of shrimp farming, weigh the production planning of different culture modes, improve the efficiency of resource utilization, and realize the ecologically sustainable development of shrimp aquaculture.

5.4. Improve the Efficient Use of Water Resources

The ecological footprint ratio of water consumption in these two modes was the highest, and water resources are not being fully utilized. However, in the field investigation, it was found that many aquaculture enterprises directly adopt groundwater, such as the factory mode, which directly exploits groundwater by drilling wells and buried pipelines, resulting in wastewater being directly discharged into the sea without treatment, causing serious pollution in the adjacent sea area. To improve this situation, the local government should strengthen its support for environmental protection and encourage enterprises to invest in recycling aquaculture systems and reduce the production costs of aquaculture enterprises with financial subsidies by purchasing incentives and other forms. At the same time, the fishery development department should actively cultivate an awareness of the environmental protection of aquaculture practitioners, encourage farmers to introduce wastewater treatment equipment, and strengthen supervision and management in the process of aquaculture to improve the environment.

In this study, the ecological footprint model was used to quantitatively analyze the environmental impact of Penaeus vannamei in northern China, and the advantages and disadvantages of the factory culture mode compared to the traditional pond mode were discussed. At the same time, the ecological and economic benefits of shrimp culture were refined, and relatively reasonable policy suggestions were put forward. There are also some shortcomings of this study. Only seven indicators were selected in this study to calculate the ecological footprint. However, there are many other indicators affecting the ecological environment of shrimp culture, such as the aquaculture equipment and the biological agents. Unfortunately, due to the lack of ecological footprint research on aquaculture equipment and biological agents, there was no practical method to measure the ecological footprint occupation of this part, so the analysis of these components was not involved in this study. In future studies, these components should be combined with the culture of Penaeus vannamei.