9. STATE OF THE FISHERY
9.1 Yield
Examination of Table 6 listing the total catch in the inland waters of Italy as recorded by FAO for the 1965–87 period shows a relatively stable catch varying between 17 000 and 21 300 t during the period of 1965–76 and then a rise culminating in a “catch” of 50 203 t in 1987. However, examination of the statistics for species groups shows that it is only the trout “catch” that has risen over the entire period and - as has been emphasized - this rise is due to inclusion of the cultivated trout production in the catch tables.
It should also be noted that during the period of 1965–69, the FAO Fishery Yearbooks did not list the catch in Italy of either trout or common carp separately. In fact, as late as 1974, the Yearbook (No. 36) apparently lumped them together with other “miscellaneous freshwater fishes” from 1965 through 1973 (see Dill, 1976, p. 74).
From the corrected table then, it seems apparent that the recorded catch of carp and other freshwater fishes was reasonably constant during at least the 1970–87 period but that the catch of eel in fresh waters declined during the 1972–83 period.
None of these figures casts any light on the trends in catch or “production” of such fishes as eel or mullets in lagoons, valli or other brackish waters of Italy, but with the gradual elimination or degradation of many brackish waters, it seems certain that these fisheries have declined overall.
As has been shown before, the major commercial catches from the fresh waters of Italy are in the large Lombard lakes lying south of the Alps. From statistics more than 50 years old (Italia, 1931), one can calculate the annual yield in kg/ha to commercial fishermen in 1929 in a number of these lakes: Como - 131; Iseo -32; Maggiore - 15; Garda - 13.31. During the same year, the yield from Lake Trasimeno in Central Italy was 16.4 kg/ha. A more recent estimate of the annual yield from Lake Maggiore (290 t in 1965), said to be that of both commercial and sport fishermen, is 17.1 kg/ha/year. Of this total yield, 12.8 kg/ha is said to be of pelagic fish such as trout, coregonids, bleak and shad, and 4.3 kg/ha of littoral species such as tench, chub, other cyprinids, pike and perch (Bonomi et al., 1970). With respect to Lake Garda, annual yields in later years can be calculated as follows: 5.4 kg/ha in 1953, 18.9 kg/ha in 1965 and 13.5 kg/ha in 1975 (based on catches reported by Grimaldi, 1980) (see section 9.2).
Yields of carp in some Italian rice fields in 1975 were said to be 30–35 kg/ha/year by Brown (1983).
If one accepts the figures of De Angelis (1986) there is an average annual yield to the commercial fishermen of about 60 kg/ha from the 17 main lakes of north and central Italy.
Reports on yields from brackishwater areas in Italy vary widely. Some are old, some are new, some are based on the statements of fishermen or owners who may have a bias, many fail to distinguish between the yields from lagoons with a predominantely capture fishery and those subjected to aquacultural processes. In short, they should be taken cum grano salis, which - like fish - is a major product of a lagoon. Zerbinato (1981) for example cites various studies in which the yields from valli in the Northern Adriatic range from 25 to 190 kg/ha/year. Of these, the yields from the best well tended and fertile lagoons appear to be about 150 kg/ha/year. These are close to those of D'Ancona (1954) who estimated 150 kg/ha/year, and more recently, Ravagnan (1972 and 1981) who estimated yields of 100–150 kg/ha/year.
Some recent annual yields of finfish per hectare from specific Italian lagoons with capture fisheries follow: Burano (65 kg), Fogliano (150–250 kg), Manaci (200 kg), Fondi (150 kg), Sacca di Scardovari (100 kg), and Orbetello (123 kg). In addition to the above yields (cited by Ardizzone, 1984; Rossi, 1981; Cognetti et al., 1981), some Italian lagoons have produced some rather amazing annual yields. For example, the highly eutrophicated 830-ha Santa Giustia lagoon in Sardinia had an average annual fish yield of 669 kg/ha during the 11-year period of 1967–77, and actually attained an average of 800 kg/ha/year during 1972–77, while the 220-ha Tortoli, another naturally rich but unpolluted Sardinian lagoon, produced an average of 342 kg/ha/year of finfishes during 1968–77 (Cottiglia, 1981). Quignard (1984) states that the average yield from the Mediterranean lagoon (including finfish and invertebrates) is about 40 kg/ha/year and can rise to 150 kg/ha/year. Kapetsky (1984), using worldwide statistics, has estimated that the median lagoon capture fishery yields 51 kg/ha/year with a mean of 113 kg/ha/year, and a median finfish yield of 47 kg/ha/year. Using these estimates as a basis of comparison, the yields from Italian brackishwater lagoons seem quite good.
9.2 Factors Affecting the Fishery
Italy has a wide variety of rivers, ranging from glacier- and snow-fed streams in the Alps to what are essentially wadis in southern Italy and the islands. Most of them are essentially unstable waters with geat variations in flow, sometimes in spate, sometimes almost dry. Even in the north many of the larger streams are braided, with narrow interlacing channels during dry spells but filled to the brim or over during flood stage. Some, like the Tiber, which flow through easily erodible areas carry a heavy silt load, and despite their size do not furnish a satisfactory environment for aquatic life. Steep gradients and wide variations in volume have caused many of the peninsular or Mediterranean rivers to incise their beds deeply in their middle courses, and their silt-choked lower reaches are often swampy or deltaic. Good stream fishing is, therefore, primarily confined to waters in the north or in some mountain streams of the Apennines (e.g., the Sangro), or in the lower courses of larger streams in the lowlands. In some of these, the abundance of limestone promotes water of good quality for fish growth, as does the general Mediterranean climate.
Italian lakes furnish more stable conditions for fish, and the country possesses a considerable lake area especially in the continental north. Conditions in these lakes range from oligotrophic to eutrophic. Not only are there a considerable number of small glacial lakes in the Italian Alps, but the huge sub-Alpine lakes provide large areas for both commercial and recreational fishing. Although significant acidification of rainfall has been reported in Italy, the lithological features of most of these lakes have minimized its effect (Mosello, 1981).
The inland fish fauna is similarly diversified, ranging from alpine chars to euryhaline marine fishes in brackish waters. Acclimatized fishes such as coregonids and rainbow trout add to the variety, and fish of the smallest size receive attention from the Italian fisherman.
In addition to the basic natural factors, several types of land and water use have long been important in affecting the inland fisheries of Italy. Continued deforestation since ancient times has affected the flow pattern of the streams, and coupled with other causes of erosion, such as mining, has aided in the process of lagoon formation and their subsequent aggradation1. Brackish lagoons, although faunistically poor, are usually quantitatively rich and have a high level of productivity which attracts migratory fish. Balanced against this is the inconvenience of eutrophism, especially stagnation and insufficient oxygenation. Thus, without renewal of water by tidal currents in summer, conditions of asphyxiation and high mortality may endanger lagoon fisheries.
For many years, agriculture in Italy has depended heavily upon both drainage and irrigation. Drainage, which commenced centuries ago, has reduced many water areas, some important as producers of aquatic life. The necessity for irrigation has reduced the amount of water available to fish in natural channels and has resulted in a loss of fish through diversion to cultivated fields. Nevertheless, although the net effect on fisheries has not been appraised, the addition of many kilometres of canals has extended fluvial fishing waters, and the creation of many small ponds to supply irrigation water has also provided fish habitat.
The overall effect of hydroelectric development, stimulated in Italy by lack of fossil fuels, is also unknown. In the absence of anadromous salmonids, the construction of dams and diversions has not had the deleterious effects that it has had in countries with salmon or sea trout fisheries. Furthermore, regulation of lakes and reservoirs for hydroelectric purposes may have provided more constant flows in the streams below them, and the construction of new reservoirs has expanded lacustrine habitat. However, catcment areas are generally small, so most Italian hydroelectric reservoirs do not provide much fishing area. Barrage construction has, however, been responsible for hindering the migration of eels (Italy/EIFAC, 1970), and in the case of streamflow plants, some long areas of Italian streams contain little or no water.
Water pollution, is a major factor in large Italian industrial areas some of them having extremely high loads of dangerous chemicals (e.g., mercury and chromium). Both streams and lakes have been affected by metallic pollution. There are, for example, high concentrations of mercury in the Pallanza Basin of Lake Maggiore. Examination of five edible fish from this basin has shown mean values from 0.19 ppm in Coregonus to 1.28 ppm in Esox lucius (Locht et al., 1981). But pollution is also widespread and generally serious because of the multitude of small industries and general lack of sewage treatment. As a rough estimate of the extent to which water quality can be maintained, one notes that the average runoff per caput in Italy is only 3 248 m3.
Centuries of cultivation, fertilization and encroachment on the margins of major lakes and streams have greatly increased the eutrophic processes. For example, the relatively shallow Lake Varese, a naturally eutrophic lake situated in a highly populated and industrial area near Milan, has received the impact of strong “cultural” eutrophication for about 30 years. This has caused anoxic conditions in the hypolimnion, disappearance of bottom fauna, and extensive algal blooms (Ruggiu, Saraceni and Mosello, 1981). But eutrophic processes have also been noticeable at the large and deep sub-Alpine lakes where originally oligotrophic waters have lost their clarity, become more fertile, and changed the composition of their fish populations. At Lake Maggiore, for example, the human population in its drainage basin (6 598 km2) almost doubled from 350 000 people in 1860 to 670 000 in 1973, and supported about 12 million tourist-days annually, of which 5 million concentrated in the shore region (Grimaldi, 1980).
This same author has, however, warned against attributing all the changes in the fish populations of the Lombard lakes to trophic changes. He has pointed out that although the landlocked shad has disappeared from Lake Maggiore and that its coregonid fishery has collapsed, these changes may be due to competition with unexploited cyprinids and excessive fishing pressure. He notes, for example, that shad are still present in even more eutrophic lakes such as Lugano and Como. He also notes that although Lake Garda has been characterized by very stable oligotrophic conditions until recently, its catch has declined probably because of high fishing pressure. De Bernardi, Giussani and Grimaldi (1984) have similar observations with respect to Lake Maggiore, pointing out that eutrophication is not necessarily the only reason for population changes.
Italy has a general tradition not only for the use of brackishwater fisheries, but for fishing all inland waters both commercially and for subsistence combined with pleasure. Of late years, the latter factor has increased decidedly, facilitated by extension of the highway system, increased automobile ownership which ranks among the highest in Europe, and more leisure time.
The natural lagoon area coupled with the complex of brackishwater species, as well as the large number of cold springs (over 1 000 in Lombardy alone) have made both extensive and intensive aquaculture readily possible. Lagoon production has been limited by the availability of fry, but this picture is changing. See below. Fish diseases, such as viral haemorrhagic septicemia (VHS) and an eel disease, have had importance in recent years, but Italy remains a leader in table trout production today.
9.3 Prospect
No major increase in fishing area can be expected, since the construction of many more sizeable reservoirs is not anticipated. In the north, most of the good hydro sites are occupied, and in the south reservoir construction is very expensive because of the seasonal flows. There will, however, be more transbasin diversions.
Small-scale commercial fishing will continue in a more or less traditional manner in the Italian lakes, but with the composition of the catches changing toward less valued species, i.e., from pelagic to littoral species and gradual diminution of the practice. Conversely, angling will continue to increase in importance, along with an increase in “put and take” fishing near urban areas.
Trout and other forms of freshwater fish culture will continue to increase, sources of good water and suitable land being important determining factors. It has been predicted that with increased disease control and more intensive use of the available water, trout production might attain about 30 000 t annually (Brown, 1977, 1983). It has already surpassed this amount (Table 12).
Brown (1977, 1978) also estimates that eel culture, presumably in fresh water, might increase to 10 000 t, and that brackishwater production of mullets, gilthead, and sea bass might rise to over 90 000 t annually. If the latter type of production is to occur, it will have to follow far more intensive methods than those now practised in traditional lagoons or valliculture. It will involve the construction of smaller rearing areas (sometimes essentially ponds), better regulation of water movement, fertilization, feeding, and regulated stocking of fry and juveniles. A major deterrent to increased production in brackish waters is scarcity of stocking material from wild sources. Ravagnan (1981) has pointed out that in the upper Adriatic, the ascent of fry from the sea is of little or no importance. For years, fry have been collected in all the bays of the Po delta to restock the semi- or completely closed lagoons in which natural recruitment is insufficient. The collection of fry, regulated by the Government, varies according to the season, and a considerable effort is now being made to insure a constant supply of young stock through artificial propagation in hatcheries and grow-out facilities. Importation of wild stock from other countries (e.g., elvers from France) is also an uncertain business, and self-sufficiency is an objective.
Recent legislation has allocated Governmental funds to the development of both aquaculture and inland capture fisheries. Nevertheless, one can say that until quite recently there has been a general lack of environmental concern in Italy. This has been reflected in the ineffectiveness of watershed management, and a disorderly competition between different uses for land and water (Italy still has no general water code), resulting in diminished sustained flows in rivers, a dwindling of lagoons and coastal wetlands, and a degradation of water quality. To a large extent, the future of the Italian inland fisheries will depend upon the increased environmental awareness which is slowly taking form.
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