FAO FISHERIES TECHNICAL PAPER   255     FIRI/T255

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Cage and Pen fish farming

Carrying capacity models and environmental impact
CONTENTS

by
Malcolm C.M. Beveridge
FAO André Mayer Fellow
IFDR, College of Fisheries
University of the Philippines
Diliman, Quezon City
Republic of the Philippines


The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.


M-40
ISBN 92-5-102163-5


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PREPARATION OF THIS DOCUMENT

In 1956 the Food and Agriculture Organization established a Programme of André Mayer Research Fellowships in memory of an outstanding scientist and humanitarian who was very active in the formation and early history of the Organization. The Programme provides a number of fellowships in each biennium to young scientists to carry out specific research tasks for the Organization. In 1982, Mr. Malcolm Beveridge was awarded an André Mayer Fellowship to carry out “Cage culture research with special emphasis on techniques employed for estimating the carrying capacity of the water bodies used”. Mr. Beveridge, who had already carried out research on the environmental impacts of cage culture on some Scottish lakes, spent ten months in the Philippines, working in collaboration with the University of the Philippines, studying environmental factors related to cage culture under tropical conditions. This Technical Paper is a report of his findings.

Mr. Beveridge has returned to the Institute of Aquaculture, Stirling University, where he is teaching and carrying on research in various aspects of aquaculture. The Organization is grateful to both the University of Stirling and the Overseas Development Administration of the United Kingdom who also helped support this project.

Distribution:For bibliographic purposes this document should be cited as follows:
FAO Fisheries Department
FAO Regional Fisheries Officers
FAO Representatives
CIFA
IPFC
Selector SI
Beveridge, M.C.M., 1984 Cage and pen fish farming. Carrying capacity models and environmental impact. FAO Fish.Tech.Pap., (255) : 131 p.

ACKNOWLEDGEMENTS

I wish to thank the following people and organisations who helped by providing advice and information during the compilation of this report

I would also like to thank ODA, particularly Mr. J. Stoneman (Fisheries) and Mr. A. Armstrong (U.N. Desk) for assistance during the course of my work, and Mr. A. Kyle, British Council, Manila, for help with communications.

I would also like to express my gratitude to the Director and Staff of FAO in Manila, and the Director and Staff of FIRI, FAO, Rome, for all their help.

Finally, I would like to thank Mrs. Moira Stewart, Institute of Aquaculture, Stirling, for typing this report.

ABSTRACT

The use of cages and pens to rear fish in inland waters is an increasingly popular method of fish culture, involving relatively low initial costs, and simple technology and management methods. However, these water-based culture methods differ from land-based operations such as ponds and raceways in that they are open systems, where interaction between the fish culture unit and the immediate environment can take place with few restrictions, and they are often sited in publicly-owned multipurpose water bodies. Thus any impacts may lead to a conflict of interests.

A number of studies have demonstrated that the cage and pen structures can affect the multi-purpose nature of water bodies, by restricting space which might otherwise be used for fisheries, recreation or navigation, and by interfering with currents and sediment transport. In some circumstances predators and disease-bearing organisms have been introduced or attracted to the site. However, the most significant impacts are due to the method of culture employed.

Intensive operations can affect water quality, and influence the biomass and diversity of the benthos, plankton and nekton. It is argued that the P loadings to the environment are the most important components of the wastes. The role of P in the diets of fishes is reviewed, total-P loadings are quantified for both intensive tilapia and trout culture operations, and the P loading models developed by Dillon and Rigler (1974) adapted to predict the environmental impact of intensive cage culture on the aquatic environment. Tentative development limits are also proposed.

Following a review of current information on energy transfer from plant to herbivorous fish in ponds and lakes, efficiencies of 1.0 – 3.5% plant carbon : fish carbon are suggested as attainable from extensive cage or pen culture. This is considerably higher than yields from lentic bodies managed for fisheries. The efficiency of transfer will vary with productivity, and the relationship between primary production and fish yield is likely to be sigmoid, as suggested by Liang et al (1981) for fisheries yields.

The carrying capacity of freshwaters for semi-intensive culture depends upon the quality and quantity of feed used, and the productivity of the site. A simple model, combining extensive and intensive-type models is proposed.

The models proposed for use in predicting the environmental impact of cage and pen culture are in the initial stages of development and have yet to be validated and calibrated. Several methods for reducing the impact of intensive culture methods are proposed, and these include combining with extensive operations. Finally, it is proposed that some categories of water body may be unsuitable for large scale culture operations.

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, 1984 © FAO

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CONTENTS

1.   GENERAL CONSIDERATIONS

1.1   INTRODUCTION
1.2   CAGE AND PEN CULTURE AND ITS HISTORY
1.3   CURRENT CAGE AND PEN CULTURE METHODS
1.4   ADVANTAGES AND DISADVANTAGES OF CAGE AND PEN CULTURE

2.   LIMITATIONS OF CAGE AND PEN CULTURE METHODS

2.1   CLASSIFICATION
2.2   LIMITATIONS AND PROBLEMS
2.3   DISCUSSION

3.   ENVIRONMENTAL IMPACT

3.1   INTRODUCTION
3.2   THE IMPACT OF ENCLOSURE STRUCTURE ON THE ENVIRONMENT

3.2.1   Space
3.2.2   Water flow and currents
3.2.3   Aesthetics

3.3   THE IMPACT OF ENCLOSURE CULTURE METHODS ON THE ENVIRONMENT

3.3.1   Environmental impact common to all methods of enclosure culture

3.3.1.1   Disease
3.3.1.2   Predation
3.3.1.3   Wild fish populations
3.3.1.4   Toxic chemicals and drugs

3.3.2   Problems associated with intensive culture
3.3.3   Problems associated with extensive and semi-intensive enclosure culture

3.4   DISCUSSION

4.   MODELLING OF ENVIRONMENTAL IMPACT

4.1   INTRODUCTION
4.2   TROPHIC STATE AND PRODUCTIVITY
4.3   THE CARRYING CAPACITY OF INLAND WATERS USED FOR INTENSIVE ENCLOSURE CULTURE

4.3.1   Phosphorus and fish diet
4.3.2   Quantification of P losses
4.3.3   Modelling of the aquatic ecosystem response to P loadings from intensive cage and pen culture

4.3.3.1   Choice of model
4.3.3.2   Using the model

4.4   THE CARRYING CAPACITY OF INLAND WATERS USED FOR EXTENSIVE ENCLOSURE CULTURE

4.4.1   Introduction
4.4.2   Species and diet
4.4.3   The theoretical potential of fish production from extensive culture methods
4.4.4   Actual fish yields from extensive aquaculture methods. Stocked fisheries vs cages
4.4.5   Designing an extensive cage farming operation and determination of site carrying capacity

4.5   THE CARRYING CAPACITY OF INLAND WATERS USED FOR SEMI-INTENSIVE ENCLOSURE CULTURE

4.5.1   Introduction
4.5.2   Computation of carrying capacity

4.6   DISCUSSION

5.   DISCUSSION

6.   REFERENCES

TABLES

Table 1.   Commercially important species in inland water cage and pen farming

Table 2.   Advantages and limitations of cage fish culture technique (from Balarin and Haller, 1982)

Table 3.   Theories proposed to explain floating and stationary Fish Attraction Devices (FAD's), and their applicability to inland water cage and pen structures

Table 4.   Predators reported from cage and pen fish farms. Data taken from Salmon and Conte (1982), Martin (1982) and Ranson and Beveridge (1983)

Table 5.   Summary of the results from studies of the environmental impacts of intensive cage fish culture in various countries

Table 6.   Extensive cage tilapia production figures from the Philippines

Table 7.   Life span of various materials used in temperate and tropical cage and pen construction (modified from IDRC/SEAFDEC, 1979)

Table 8.   The relative supply and demand of elements required by plants and algae and derived from soils and rocks (lithosphere) of the catchment area (from Moss, 1980)

Table 9.   N:P ratios (by weight) in a range of freshwater bodies

Table 10.   Dietary phosphorus requirements of fish, expressed as percentage weight of diet (after Beveridge et al., 1982)

Table 11.   Ranges and mean values (%) of total-P content of commercially available salmonid diets in the U.K. Data based on the analysis of feeds produced by six manufacturers.

Table 12.   Total-P content (% wt.) of carp and tilapia diets used in intensive culture in various parts of the tropics

Table 13.   Recommended food particle sizes for salmonids and tilapias. The term ‘crumb’ refers to round particles, whereas ‘pellet’ refers to cylindrical (1 ≤ 3d) particles. Sizes refer to particle diameter (d).

Table 14.   Summary of data from Glebokie Lake, Poland (Penczak et al., 1982). Units in kg, and total losses (F + C + U; see p. 41 for terminology) calculated assuming mortalities were not removed from the lake.

Table 15.   Feed Conversion Ratios (FCR's) for various intensive trout and tilapia diets. The composition of tilapia diets are detailed in Table 12

Table 16.   Theoretical calculations of total-P released into the environment during intensive cage culture of trout and tilapia

Table 17.   Total-P loadings associated with intensive land-based salmonid culture (modified from Beveridge et al., 1982)

Table 18.   Food Conversion Ratios (FCR) of rainbow trout grown in cages and in ponds, using commercial dry pellets as food source

Table 19.   Summary of [P] predictive models (r = correlation coefficient; S.E. = standard error)

Table 20.   Tentative values for maximum acceptable [P] in lentic inland water bodies used for enclosure culture of fish

Table 21.   Regression equations relating annual mean chlorophyll levels [chl] and peak chlorophyll levels to each other, and to mean in-lake total phosphorus concentrations [P].

Table 22.   Relationship between [chl] and ∑ pp in some tropical lakes

Table 23.   Empirical models for calculating the sedimentation rate, ρ, retention coefficient, R (I/ρ), and the sedimentation coefficient, V, of phosphorus, for both general and specific categories of temperate water bodies

Table 24.   Diet of tilapias and carps commonly used in aquaculture (tilapia data modified from Jauncey and Ross, 1982)

Table 25.   Assimilation efficiencies (Aε) of tilapias feeding on various diets (modified from Bowen, 1982)

Table 26.   Increases in yields from lake fisheries in China, following the implementation of stocking and other management policies. Data from FAO (1983)

Table 27.   The relationship between gross areal photosynthetic rates and fish yields from seven suburban lakes near Wuhan, China (data from Liang et al., 1979). Efficiencies of energy transfer (fish yield/primary production) are based on a conversion factor of 0.375 for photosynthetic O2 production → photosynthetic C production (APHA, 1980), and a fresh fish C content of 10% (Gulland, 1970)

Table 28.   Conversion efficiencies of ∑ pp to annual fish yield (Fy), for water bodies of different productivities. Conversion efficiencies for lakes and reservoirs with ∑ pp ≤ 2500 g C m-2 y-1 have been derived from Fig. 25, whilst for those with ∑ pp > 2500 g C m-2 y-1, yields have been assumed to lie on the upper portion of the logistic curve described by Liang et al. (1981).

Table 29.   Feeding practices of 70 cage operators at Lakes Buhi and Bato, Camarines Sur, Philippines (after Escover and Claveria, 1984, in press)

Table 30.   Total-P content and P loadings of various feedstuffs commonly used as supplementary feeds in semi-intensive tilapia culture. FCR values refer to O. mossambicus. Data from Jackson et al. (1982), NRC (1977), and Balarin and Hatton (1979).

Table 31.   Summary of problem areas associated with the predictive models discussed in the text

Table 32.   Production of O. niloticus in cages and pens, without supplementary feeding, in Cardona, Laguna de Bay, Philippines, 1982–83. Cages are 3–5 m deep.

Table 33.   Estimated potential for reduction in total-P wastes associated with intensive fish culture through various feed manufacturing and management options. Costs estimated as ranging from * (inexpensive) to *** expensive.

FIGURES

Fig. 1.   Freshwater fish cages and pens. (a) milkfish pens in Laguna de Bay in the Philippines; (b) flexible frame floating cages for rainbow trout culture, in Lake Titicaca, Bolivia; (c) fixed cages for tilapia culture, at SEAFDEC, Binangonan Station, Rizal, Philippines (Note that the mesh bags have been lifted, and are drying in the sun prior to cleaning and restocking).

Fig. 2.   Some types of floating cages. (a) a raft of floating cages used for bighead carp culture, with guard house, in Durian Tungal Reservoir, Melaka, Malaysia; (b) smolt production cages, attached to land by a walkway, in a freshwater loch in Kintyre, Scotland; (c) a solitary cage of rainbow trout, with timber and oil drum frame, in Lake Titicaca, Bolivia.

Fig. 3.   Ranges of productivity values for tropical and temperate freshwater bodies. Data from Likens (1975), Hill and Rai (1982), and Tundisi (1983) (redrawn from Hill and Rai, 1982).

Fig. 4.   Fixed cages for extensive and semi-intensive tilapia culture crowded together in the outflow from Lake Buhi, Camarines Sur, Philippines.

Fig. 5.   The growth of milkfish culture in Laguna de Bay, Philippines. Data from PCARRD (1981), Dela Cruz (1982) and the Philippine Bulletin Today (see text). A refers to fishkills, and B to typhoons.

Fig. 6.   Map of Laguna de Bay, Philippines, showing legal fishpen belt and fish sanctuary (redrawn from Felix, 1982).

Fig. 7.   Aerial photograph of part of the West Bay and Talim Island, Laguna de Bay, Philippines, November 1983, showing the extent of fishpen development.

Fig. 8.   Map of fishpens in Laguna de Bay, April 1983 (redrawn from Bulletin Today, May 2, 1983). Note the huge variation in pen size, and the proliferation of pens outside the legal fishpen belt (see Fig. 6).

Fig. 9.   Two cores from a Scottish freshwater loch where rainbow trout cages are sited. The core on the left was taken from directly under the cages and shows the build up of organic debris - fish scales, faeces, uneaten food, etc. The core on the right was taken from a point some distance from the cages, and does not have this organic layer (photograph courtesy of Dr. M. Phillips).

Fig. 10.   Typical pattern of development at an extensive cage or pen culture site (see text). Production refers to whole lake reservoir.

Fig. 11.   The relationships between specific growth rate of caged 50g tilapia, and visibility to gross primary production, in Sampaloc Lake, Philipinnes (redrawn from Aquino, 1982).

Fig. 12.   The impacts of enclosure structures on the aquatic environment.

Fig. 13.   The impacts of cage and pen culture methods on the environment.

Fig. 14.   The effects of intensive, semi-intensive and extensive cage and pen culture on aquatic productivity.

Fig. 15.   Some of the principal energy pathways in freshwater ecosystems.

Fig. 16.   Relationship between P-intake, P-excretion and growth in fishes (from Beveridge et al, 1982).

Fig. 17.   Summary of principal P losses to the environment associated with intensive cage fish culture.

Fig. 18.   Suggested acceptable (dotted line) and ideal (solid line) P concentrations associated with freshwater bodies used for different purposes.

Fig. 19.   The relationship between areal water loading, qs, and P retention, R, in the southern African lakes. The curve shown in the figure is that of Kirchner and Dillon (1975). From Thornton and Walmsley (1982).

Fig. 20.   The relationship between response time and water residence time, Tw, for water bodies with different mean depths, z. From OECD, (1982).

Fig. 21.   The relationship between fish yield and primary production in tropical water bodies (redrawn from Marten and Polovina (1982)).

Fig. 22.   Summary of reasons for stocking freshwater bodies with fishes which feed at the aquatic food web base (see text).

Fig. 23.   Relationship between theoretical fish yields, and primary production, assuming conversion efficiencies of 10% and 15%.

Fig. 24.   Summary of the principal factors influencing the exploitable stock biomass inland water fisheries (redrawn from Pitcher and Hart, 1982).

Fig. 25.   Fish yields vs primary production. The dotted and dashed lines represent theoretically possible yields (Fig. 23 redrawn), whilst the lowermost plot represents typical fish yields from tropical freshwater bodies (Fig. 21 redrawn). The middle plot represents tilapia yields from inorganically fertilised ponds (data from Almazan and Boyd, 1978).

Fig. 26.   The relationship between “risk” and intensive cage fish production. As production at a particular site increases, “risk” increases exponentially. The exact slope of this curve will vary with site, species and management (see text).

Fig. 27.   The effect of a series of mesh panels with Cd panels of 1.46 and 1.09 (see Appendix 4) on current velocities, assuming an initial velocity of 4 cm s-1.

Fig. 28.   The distribution of cages of extensively cultured bighead carp, at Selator Reservoir, Singapore. Note how widely dispersed they are.

Fig. 29.   Development patterns at extensive cage and pen culture sites. The typical pattern, A, could be modified to B, providing the carrying capacity of the environment was calculated prior to the introduction of fish culture.

APPENDIX 1

APPENDIX 2

APPENDIX 3

APPENDIX 4