3. SEA FARMING AND SEA RANCHING SYSTEMS IN CHINA

3.1 Pond Culture
3.2 Floating Raft Culture
3.3 Mud Flat Culture
3.4 Pen Culture
3.5 Inshore Cage Culture
3.6 Offshore Cage Culture
3.7 Artificial Reefs
3.8 Sea Ranching and Restocking

The choice of a particular cultural system for sea farming or sea ranching depends on several factors such as existing natural conditions, availability of financial support and education/training level of fishermen. In China, several cultural systems are now commonly adopted (Table 27).

Table 27. Sea farming and sea ranching systems in China

System	Cultured organisms	Production scale
Pond culture	Fish, shrimp, crab, molluscs, Gracilaria spp.	Commercial
Floating raft culture	Seaweed, scallop, oyster, abalone	Commercial
Mud flat culture	Laver, razor clam, hard shell clam, oyster	Commercial
Pen culture	Abalone, shrimp	Commercial
Inshore cage culture	Fish	Commercial
Offshore cage culture	Fish	Commercial and trials
Tunnel culture	Abalone	Small scale
Submerged cage culture	Abalone, fish	Small scale (trials)
Indoor tank culture with water recirculation	Flounder, turbot and other fish, abalone	Commercial and trials
Sea bottom culture and sea ranching	Abalone, Japanese scallop, giant cockle, sea cucumber, sea urchin	Commercial
Stock enhancement	Chinese shrimp, red sea bream, flounder, large yellow croaker, mullet, jellyfish	Trials

3.1 Pond Culture

A high proportion of the area under cultivation is devoted to pond culture in marine and brackish waters. Most ponds are built in mud flat areas and used for farming shrimp and crab. A smaller area produces fish, molluscs and seaweed (Table 28).

Ponds are fed sea water either as tidal ponds or by pumping. Figure 20a shows typical coastal ponds for shrimp and finfish farming. Figure 20b shows ponds for farming mud crab, enclosed by fences to prevent crabs from escaping.

Since the early 1980s, pond culture developed rapidly throughout the country not only because its technology was relatively simple and it required less investments but also because of the traditional knowledge of fish pond culture which existed in China. An ample supply of penaeid shrimp postlarvae and profitable economic returns from shrimp culture further stimulated development.

Table 28. Areas used for sea farming/ranching, 1994-1998 (in ha)

Zone	1994	1995	1996	1997	1998
Total area	653 530	715 750	822 073	937 933	1 004 407
Shallow seas	113 390	131 760	114 184	167 852	195 211
Bays/lagoons	169 530	159 420	174 770	180 431	190 626
Mud flats	370 610	424 570	533 119	589 650	618 570
Shrimp culture	150 710	136 610	143 970	178 778	194 624
% total area	40.66	32.17	27.00	30.31	31.46

But overexploitation and pollution of natural resources opened the way to various diseases and in particular to the 1993 viral epidemics. The latter led policy makers, investors and farmers to review existing policies and cultural systems. Nearly 10 years later, people agree that it is indispensable to pay more attention to bio-ecological protection, to socio-economic aspects and, in general, to all factors which might impact on sustainable development.

Figure 20. Coastal pond culture of shrimp, fish and crab

(a) Ponds for marine shrimp and fish farming

(b) Ponds for mud crab farming

3.2 Floating Raft Culture

There is a long history of using floating rafts for shallow-sea farming. This system can be used for a variety of species such as seaweed (kelp and laver), filtering organisms (scallop, oyster, mussel) and abalone, combined with culture in small submerged cages (lantern cages).

Figure 21. Floating rafts for shallow-sea farming

(a) Oyster farming in southern China

(b) Kelp, scallop or oyster farming in northern China

The system shown in Figure 21 is widely adopted for farming kelp, oyster, scallop, abalone, etc. These species being either autotrophic or filtering organisms, there is no pollution of the environment, particularly with kelp farming as mentioned before. The system shown in Figure 22 is typically used in the Zhejiang Province for farming oyster, the raft being made of bamboo, an excellent natural material.

Figure 22. Bamboo floating raft for oyster farming

(a) Details of the bamboo infrastructure

(b) Farmer harvesting oysters

3.3 Mud Flat Culture

This system is especially suitable for farming benthic species such as blood cockle (Tegillarea granosa), hard-shelled clam (Meretrix meretrix), manila clam (Ruditapes philippinarum), razor clam (Sinonovacula constricta) and seaweed such as Porphyra spp. It is very popular in China because it does not require large quantities of food and it does not pollute the environment.

Before the 1980s, mud flat culture was limited to particular areas because of the difficulty to obtain seed which had to be collected from wild stocks. The seed supply is now greatly improved. For blood cockle, Cyclina sinensis, seed are produced on a commercial scale. For other species including hard-shell clam and manila clam, protecting wild broodstock has been an effective way to enhance seed production. For razor clam, which has been farmed in China for decades, wild seed are collected following a rather sophisticated system involving site selection, smoothening the spawning area, forecasting seed settling, collecting and transporting seed.

In general, the mud flat ecological system is rather vulnerable, lying at the interface between sea and land. For example, in some areas, mud flats have been blindly exploited, even overexploited, for shrimp farming which has resulted in destroying the original ecological system and shrimp farming itself. This has occurred too frequently which has led to give priority to the protection of mud flat and mangrove forest areas.

3.4 Pen Culture

Sites for pen culture are selected in intertidal areas where low fences and water gates are built (Figure 23). At low tide, water depth drops to a minimum of 50 to 80 cm inside the pens. As the next high tidal water starts coming, it enters the pens where water depth increases progressively again.

This culture system is popular in some provinces of China, but problems are the same as with pond culture, pollution having serious impacts on the environment. The development of this system should therefore be strictly controlled and confined to selected areas.

Figure 23. Pen culture in the Zhejiang Province

3.5 Inshore Cage Culture

Inshore cage culture is very popular world-wide, especially in Asia. Advantages include low investment and easy routine management. But this system is one of the main sources of inshore pollution and the main cause for red tides. It has been reported that, in areas where inshore cage culture is well developed, phosphorus content of the sea bottom is 2 000 times higher than the legal value accepted for environmental protection. Policy makers have begun to notice the problems and to issue regulations controlling the development of this cultural system, to protect the natural environment and the aquaculture industry itself.

Crowded inshore cages are shown in Figure 24. As most farmers use trash fish to feed cultured fish with a high commercial value, it does not take long before a great quantity of faeces and food residues accumulate on the sea floor and pollute the entire area.

Figure 24. Floating cage culture in inshore areas

(a) Details of floating cages

(b) Crowded cages inside a bay

Another problem is that floating cages cannot resist strong winds and waves. After a typhoon, few cages are still functional and many of the farmed animals have escaped (Figure 25). In the near future, offshore cage culture (Section 3.6) should become the main cage culture system.

Figure 25. Damaged inshore cages after a typhoon

3.6 Offshore Cage Culture

China experiences typhoons seasonally, especially in its southern regions from the Zhejiang Province to the Hainan Province. Even if typhoons are only occasional in the northern regions, losses can also be very serious.

Traditionally, only floating cages are used in inshore waters. Due to pollution and overexploitation of these waters, fish cage farming should be moved offshore. At present there are two types of offshore cages recently introduced into China. One type is a sinkable cage (Figure 26a), the other being a plastic gravity cage (Figure 26b).

Researchers and farmers have been encouraged to design new models of cages which would be able to withstand typhoons and strong sea currents. In the near future, offshore cage culture should develop rapidly.

Figure 26. Offshore cage culture

(a) Sinkable offshore cage

(b) Plastic gravity cage

3.7 Artificial Reefs

Another way of sea ranching is using artificial reefs (Figure 27). This method was experimented in the 1980s for five years. Theoretically, it contributes to the enrichment of fishery natural resources. But its success depends on many factors such as site selection, shape of the artificial reefs, desirable species and other environmental conditions. Financial support is also important because returns on investments should be considered on the long term only. The development of this system has been stopped.

Figure 27. Artificial reefs for sea ranching

(a) Assembly of an artificial reef

(b) Installation of an artificial reef at a selected site

(c) Artificial reefs awaiting to be installed offshore

3.8 Sea Ranching and Restocking

In the 1970s, Dr C. K. Tseng presented a series of talks and published a thesis entitled “Sea ranching and sea farming”. He defined “ranching” as a culture system where “... at first, the crop is reared in restricted areas, then its juveniles are released into the natural environment and finally its adults are fished from this natural environment”.

Since the 1970s, sea ranching was tried with several species in various sites as shown in Table 29.

Shrimp of the species Penaeus chinensis were restocked on a commercial scale, especially in the late 1980s and early 1990s, at the annual rate of more than a milliard juveniles. Due to unknown reasons, this activity was stopped. It was observed that recapture rate of tagged shrimp depended on the individual size of stocked shrimp as well as on the duration and location of the restocking programme (Tables 30 and 31). Tabulated figures show that recapture rate varied greatly. The highest rate reached 1.88 percent, the lowest only 0.001 percent. It seems that some unknown factors influence recapture also.

Table 29. Sea ranching trials in China

Species	Site	Duration	Remarks
Penaeus chinensis	Shandong, Liaoning and Zhejiang	1980s to 1990s	Restocking juveniles 3 cm long on a commercial scale
Paralichthys olivaceus	Beidaihe, Hebei	1980s to 1990s	Experimental
Liza haematocheila	Beidaihe, Hebei	1980s to 1990s	Experimental
Pagrosomus major	Beidaihe, Hebei	1980s to 1990s	Experimental
Haliotis discus hannai	Shandong, Liaoning	Since 1980s	Restocking young abalone 3 cm long for commercial purpose
Stichopus japonicus	Hebei, Shandong	Since 1980	Restocking young sea cucumber (1-2 cm long) for commercial purpose
Patinopecten yesoensis	Liaoning	Since 1990s	Restocking young scallop (3 cm long) for commercial purpose
Rhopilema esculentum	Liaoning	1990s	Experimental with juveniles

Table 30. Relationship between stocking location and recapture rate of shrimp *

Year	Location	Juveniles size (mm)	Stocking number	Recapture number	Recapture rate (%)
1985	Weihe estuary	40.1	26 913	30	0.11
1985	Yellow River estuary	40.1	46 438	73	0.16
1985	North of Liaodong Bay	46.9	50 777	765	1.51
1986	Weihe estuary	30 to 50	103 413	1	0.001
1986	Bohai Bay	30 to 50	46 679	408	0.87
1986	Liaodong Bay	30 to 50	95 272	19	0.02

* Based on data from Fan Ningchen, Yellow Sea Fisheries Research Institute, for P. chinensis

Table 31. Relationship between stocking size and recapture rate of shrimp*

Year	Location	Juveniles size (mm)	Stocking number	Recapture number	Recapture rate (%)
1984-1985	Liaodong Bay	35	36 408	125	0.34
1984-1985	Liaodong Bay	52	30 000	345	1.16
1984-1985	Liaodong Bay	63	34 369	713	2.07
1984	Laizhou Bay	32	18 336	68	0.37
1984	Laizhou Bay	40	18 394	121	0.66
1984	Laizhou Bay	48	18 443	347	1.88
1985	Laizhou Bay	32	26 110	177	0.68
1985	Laizhou Bay	40	26 721	281	1.05
1985	Laizhou Bay	48	26 148	364	1.34

* Based on data from Fan Ningchen, Yellow Sea Fisheries Research Institute, for P. chinensis

Figure 28. Restocking abalone juveniles into a selected site

(a) Young abalone remain attached to their rearing substrate

(b) Stocking young abalone into the selected site

Recapture rate for other species, such as abalone (Figure 28) and sea cucumber, is much more predictable than for shrimp. According to data recorded from commercial captures, recapture rate for abalone may be as high as 50 to 70 percent if stocking size is greater than 30 mm. If stocking size is less than 20 mm, recapture rate is very low. For sea cucumber, this rate depends more on site selection and improvement, such as increasing sheltered areas.

In general, sea ranching is a good system to enhance or to re-establish a population which has declined, but numerous factors influence results. Practically, at least four groups of factors should be taken into account:

- Species and natural population composition

- Food web relationships of stocked species with natural population

- Environmental improvement

- Factors influencing recapture rate, including stocking location, duration of programme, size at stocking and potential predators.