 |
| ||||||||||||||||||||||||||||||||||||||||||
There are several ways in which fish processing can affect the environment. By increasing the demand for fish, a depletion of fish resources can occur with severe socio-economic as well as environmental consequences. The other possible detrimental effect of fish processing is the possibility of environmental pollution resulting from the waste material which may be created. Each of these will be considered in turn.
Fish resources are renewable and under normal conditions it is possible to harvest a proportion of that resource one year without reducing its size during the following year. The largest amount of fish that may be harvested each year without permanent damage to the resource is known as the maximum sustainable yield (MSY). When the fish catch is less than the MSY, there is no serious environmental impact, at least as far as the fish resource is concerned. However, if the demand is such that the resource is reduced below the level at which it can reproduce itself, the effect on the environment can be devastating in that greater and greater effort is expanded in an attempt to catch fewer and fewer fish. This situation will have serious consequences on the aquatic fauna and the socio-economic conditions of the fishing community.
Fortunately, traditional small-scale or artisanal fisheries in the tropics rarely indulge in over-fishing. There are, however, a few cases on record where this has happened. In areas, such as the Malacca Straits and the Northern coast of Java, the artisanal fisheries, conducted on a most intense scale has resulted in a considerable reduction of the catches by individual boat crews and fishermen. These are multi-species fisheries, and, unfortunately, statistical records did not adequately indicate the decline in productivity which was taking place. In some other cases, the statistical records are somewhat better. In a number of African freshwater lakes, for example, gill netting has been the dominant fishing method for over a century and it is possible to note how the average size of the fish (mainly Tilapia spp.) has declined over the years. Although size is not in itself necessarily of great importance1, it does mean that the situation must be watched very carefully if damage to the environment is to be avoided.
1 In terms of food production, it is the tonnage of fish caught annually which is the determinant factor rather than the average fish size.
In general, small scale fish processing in the tropics has little effect on fish resources but the introduction of modern fishing methods to supply highly industrialised fish processing factories has sometimes had disastrous effects on the fish stocks. Two examples are well documented. The anchoveta fishing industry of Peru provides an excellent illustration of the way in which a fishing industry may affect an ecological system (Loftas, 1972). Until the early 1950s, the anchoveta were only lightly fished. It was then discovered that a rich resource existed and a purse seining industry developed in which the entire catch was converted to fish meal. Whereas in 1955 there were only 16 relatively small fish meal plants in Peru, the industry grew until in 1970 Peru accounted for 44% of world production of fish meal. In that year, the Peruvian fleet caught 12 million tonnes of fish which was processed into a little over 2 million tonnes of fish meal. However, in 1972, the anchoveta fishery failed almost completely with devastating effect on the population which had become dependent upon it. Many companies and individuals became bankrupt and although the anchoveta stocks have now recovered to a certain extent, they have still not reached their former size. An interesting sideline is provided by the variation in the seabird population over a similar period. In earlier years, the guano produced by the sea birds was one of the more important Peruvian exports but, during the late 1960s and early 1970s, when fishing for anchoveta was in its peak, the bird population fell to less than 4% of its former total.
The development of trawl fishery in Thailand offers a further example of the problems which can result from over-fishing (Tiews, 1973). Until the early 1960s, despite a number of attempts, trawl fishing had not been established in Thailand. At almost the same time, pair trawling was introduced from Taiwan and single boat otter trawling was introduced by a German bilateral aid project. The single boat trawl proved to be the most profitable to operate and soon predominated. As a result of trawling activity, the landing of marine fish in Thailand increased by a factor of 10 from approximately 150 thousand tonnes in 1958 to almost 1.5 million tonnes in 1970. The catch consisted of upwards of 200 species of bottom-dwelling fish, many of which are used for reduction to fish meal in Thailand although they are potentially perfectly good for human food. The fishery was permitted to develop without control, a large number of wooden trawlers were built and eventually trawling operations became uneconomic again causing bankruptcies and severe hardship for many fishermen and their families.
All fish processing operations require that waste water and pieces of fish be discarded. Often, the reservoir from which water is obtained for use in processing is also the ultimate destination of water borne wastes. If the wastes are not treated properly before disposal, they may cause pollution of the water body and make it unsuitable for use. It can also result in an upset in the biological balance in the water body causing a change in the animal and plant life.
All contaminated water discharged from fish processing operations should be treated so as to keep pollution of natural waters to a minimum. The types of waste water produced can be divided as follows:
(i) Blood water and contaminated process water: this water results mainly from the washing of fish and contains fish blood and some fish protein;(ii) Ice melt water and used ice containing fish protein, blood and bacteria;
(iii) Wash-down water containing larger pieces of fish and fish protein;
(iv) Domestic sewage from toilets and urinals; and
(v) Specialised waste waters such as press liquor and stick water from fish meal operations and cooling water from canning operations, etc.
The sort of treatment required depends on the type of waste water and the quantity involved. Screening, filtration, flotation, sedimentation and/or centrifugal methods may be necessary to remove solid particles. This may be preceded by chemical treatment with alums and lime which will control coagulation and pH. The use of coagulating agents such as these prior to physical removal of solids can enhance the subsequent treatment. In many industries a crude filtering process is used which will remove most solids.
The Canadian Department of Fisheries (Blackwood, 1978) recommends that:
- The treatment of waste water for solids removal should be equivalent to that achieved by a screen with an opening size of 0.7 mm. Slightly contaminated process water may be discharged directly into the receiving water.- Domestic sewage must be treated by the plant or the municipality prior to discharge.
- Blood water, stick water, press liquor, etc. should not be discharged directly into the receiving water because of their high organic material content which would result in a high biological oxygen demand (BOD) in the receiving waters. Solids removal by screening and scum and oil removal by flotation are minimum requirements for treatment of these effluents.
- Storm water not contaminated by fish or its constituents may be discharged directly into the receiving water, otherwise it must be treated as other wastes.
In most fish processing operations, there will be a certain amount of solid waste. This may be in the form of fish offal, heads and trimmings from cutting operations, or waste fish which may be too small to use. These wastes must be treated properly if they are not to become a nuisance and a hazard to public health.
Where small quantities of waste are produced in a small scale operation, then the most feasible way of disposing of them may be to bury them in a pit. The pit should be at least 6 ft. deep and offals, once put into the pit, should be buried under at least 6 inches of earth. This will stop the residues becoming infested with flies, etc. and also accelerate the rotting process.
Small quantities of fish waste can be also used for feeding animals such as ducks and chickens. Alternatively, the offal can be used fresh as a manure for plants adding valuable nitrogen and minerals to the soil. These possibilities are only feasible where relatively small quantities are involved as, without some form of preservation, the waste will become spoilt before it is eaten or is absorbed into the soil.
Where larger quantities of waste are being produced, then it may be feasible to produce a by-product from the main fish processing operation. In Japan, for instance, cod stomach, gills and gullets are salted for preservation and human consumption. In many countries, viscera are fermented to produce sauces and pastes while in other countries the viscera can be sold on the market at very low prices thus providing protein and food for the less well-off members of the community.
It may be possible to produce animal feedstuffs from larger quantities of offals. The acidification of fish offals with mineral and organic acids can produce a product known as fish silage. Much interest has been shown recently in silage production which represents a simple, cheap yet very effective alternative to the large scale production of fish meal. Briefly, silage is prepared by adding acid (usually formic acid) to pieces of fish waste and letting the whole mass break down to a liquid. This liquid can then be dried for inclusion into chicken feeds or can be fed as a liquid to pigs. Fish silages can also be produced by the fermentation of the fish offals using lactic acid producing bacteria such as Lactobacillus sp.
Where very large quantities of offal are generated by a fish processing plant or where a number of smaller plants are in close proximity, then fish meal production may be feasible. However, fish meal equipment and the running of a fish meal plant require high capital investments and a large amount of continuous supply of raw material which may not be available to the small-scale producer.
Fish glue can be made from skins and heads of fish by steaming fresh material over a perforated screen within a steam-jacketed vessel for about 8 hours. Fish glues were once used extensively in furniture making, book-binding, leathergoods, etc. However, with the advent of synthetic glue from petro-chemicals, fish glues have gone out of favour.
Filleting waste or small trash fish or shrimp waste can be sun dried and used as a fertiliser to improve crop production on the land.
Fish oils may also constitute an important byproduct from fish wastes processing. These are often derived from the fish meal process. Good quality fish meal must not have an oil content of more than 10%. Where oily fish are used in the production of fish meal, there may be a need for the extraction and removal of oil from the meal. This oil can be used for either human consumption in the production of margarine and cooking fats, or it can be used for the production of various compounds such as paints and varnishes. Oils can also be extracted from the livers of fish. Liver oils are often high in vitamins A and D and were of economic importance until fairly recently. However, in recent years, these vitamins have been produced synthetically.
It is rare for fish processing operations to cause air pollution which is dangerous to health, but they can cause unpleasant smells and an unpleasant environment. Fish meal plants are one of the main producers of unpleasant smells which, although harmless, may lead to complaints from the neighbouring population. To reduce odours as much as possible, raw material for fish meal production must be as fresh as possible, and processing should begin as soon as the raw material arrives at the factory. The main contribution to the odours associated with fish meal production comes from the cooking and, particularly, the drying stage. Commercial equipment is available for odour reduction which involves the passing of vapours through water (scrubbing) and/or the burning of the vapours. The efficient operation of this equipment requires that the quantity of vapour is kept as small as possible and that the ducts and flues carrying the vapour are kept in good condition in order to prevent any vapours from escaping. A detailed guide to the efficient management of a fish meal plant so that air pollution is kept to a minimum is given in Torry Advisory Note No. 72 (Anon).
Other methods of fish processing can cause unpleasant smells even when processing is undertaken at a relatively small scale. The main processes include smoking and sun drying. With smoking operations, however, relatively small quantities of usually not unpleasant woodsmoke are produced which are seldom a cause for complaint from the surrounding population. With sun drying, on the other hand, the smell generated during the process can be strong and unpleasant. This is particularly the case when elasmobranch fish such as sharks and rays, are being salted and sun dried. A strong smell of ammonia produced by the fish will pervade the surrounding area making living conditions almost unbearable. It is important, therefore, that fish curing yards be sited away from urban areas or at least down-wind of them so that nuisance is kept to a minimum.
Although it is uncommon for traditional small scale fishing or processing operations to have a serious impact on the environment, there are situations where this has occured and it should, therefore, not be ruled out. Possible effects on fish resources and environmental pollution should be taken into account by fish processors and extension workers when considering improved processing techniques, particularly when they will result in a greater throughput of raw material. Industrial scale fish processing on the other hand can have a devastating effect on fish resources and, before it is embarked upon, the effect on the environment and the population traditionally dependent on the fish resource must be carefully evaluated.
 |
 |
