True cultivation of shellfish in Greece has only begun in the last five years and is at present only concerned with one species, the Mediterranean mussel, Mytilus galloprovincialis. All other species, and much of the mussel production, are still only fished from wild stocks. The situation is likely to change for two species, however, namely the European flat oyster, Ostrea edulis, and the clam, Venerupis decussatus (Fr. palourde, Gr. akivada).* Pressure on existing stocks of oysters, reflected in declining catches in the main fishery in Thermaikos Gulf, is a stimulus for steps to be taken to supplement ‘spatfall’, the collection of seed oysters from natural settlement. In the case of palourde, commercial pressure for increased production of this high value species is generating interest in its cultivation, methods for which are now evolving on a commercial scale in France, Spain and Italy. Interest in crustacean (penaeid shrimp) culture is at a similar level. Small lagoon fisheries exist for the native species, Penaeus kerathurus, and basic research on the maturation cycle of this species has been carried out. A commercial proposal has been made to establish a penaeid hatchery on the island of Skyros and the Ministry of Agriculture are considering a shrimp hatchery in their plans for state marine hatcheries.
* Because the French ‘palourde’ distinguishes this species the least ambiguously, this name is used throughout this report. Venerupis and Tapes are synonymous, and both have been used in this report.
The historical lack of interest in mollusc farming can be related to the absence of a home market for anything other than a small quantity of mussels and cockles (Cerastoderma edule). As well as being small, the market has a strong regional bias. Only in the north of the country is there an established tradition of eating molluscan shellfish, while in the major centre of population, Athens, molluscs are viewed with suspicion and are only offered by a minority of restaurants.
The oyster and palourde fisheries depend entirely on export markets in Spain and Italy, with some oysters going into France. Most of the oysters are dredged from Thermaikos Gulf, south west of Thessaloniki, but here the catch has declined from about 2 000 t/year to just over 1 000 t. A smaller fishery yielding 150 t has developed in Stilida (Maliakos Gulf) over the last two years. About half of the national production of palourde come from a small area of inter-tidal beach near Alexandropoulis in the north east, which yields about 75 t/year. The remaining 75 t is drawn together for marketing by the same cooperative from small beds around the country, such as Stilida, and Geras Gulf (Lesvos). Some are sold from a shore on Salamis, close to Piraeus.
Total molluscan production was estimated by Arrundale to be 6 000 t in 1986. This would have consisted approximatey as follows:
|Oysters (wild)||1 800|
|Mussels (wild)||3 250|
Mussel cultivation is expanding rapidly, especially around Thermaikos Gulf, albeit from a very low base, and is likely to be doubled in 1987, with a major long line farm established at Makrigialos (Katerini) and expansion around Thessaloniki.
Current State of Mussel Cultivation
|Estimated Yield t|
|Coast of N. Greece (W - E)|
6 ha, Long-line/Pergolari
30 × 0.2 ha, Poles/Pergolari
4 units, Poles/Pergolari & Ropes
6 × 0.5 ha, * Poles/Pergolari
1 × 0.5 ha, Long-line/Pergolari
Trials only, Poles/Pergolari
|Sub-Total||1 220–2 190|
6 × 0.25 ha
|Total Capacity from Cultivation||1 300–2 300|
|Likely yield (allowing for optimistic estimates)||1 300–1 800|
* Area of concessions 0.5 ha, area of structures 0.1 ha
A second long-line farm is in the process of being installed at Makrigialos.
The stock of oysters in Thermaikos Gulf is one of the few remaining commercially important concentrations of native oysters left in Europe. With the exception of two isolated populations, one in Lake Grevelingen (Netherlands) and one in Mar Menor (Spain), all others have been either severely depleted by dredging, or have suffered massive mortalities following infection by protozoon parasites (Marteillia and Bonamia). The decline in landings registered in the Thermaikos Gulf fishery gives cause for concern that dredging is reducing stocks, either by fishing pressure or by damage to larval settlement surfaces, and consideration is given in this report to appropriate methods of supplementing spatfall, this being the first step towards aquaculture of the species. Greek oysters are exported at a very low price (Dr 180–280/kg), so only low cost production methods can be considered.
Initial efforts in cultivating palourde will probably also be based on capture of wild ‘seed’, though this will only consist of relaying undersized clams from the fishery into managed beds or parcs. In France, Spain and Italy, commercial efforts at palourde cultivation are now centred on the introduced Pacific species, Tapes semidecussatus, the Manila clam. This is the only molluscan species for which hatchery production might be considered in Greece, and this is discussed later. The high unit value of this species (Dr 1 000/kg) is attracting interest in its cultivation in those areas where fisheries exist.
Mussel cultivation is developing rapidly, but knowledge of the full range of methods available and practised elsewhere in Europe is lacking in Greece. With little exception, all existing efforts are based on Italian pergolari methods, either hanging from fixed scaffolding frames or from floating long-lines. Rope culture, as practised widely in Spain, is unknown. This is a method which could have application in Greek waters, especially as it permits a high degree of mechanization.
Lack of knowledge of practical marine farming methods has hindered the development of aquaculture for all shellfish species. The only resident company offering equipment and technical advice is ITI, an Italian-based company.
In all areas visited, the consultant spent much of the time describing techniques used elsewhere for mussel, palourde and oyster cultivation. It was only in the case of mussels that any progress had been made towards adapting techniques to Greek conditions and establishing a cultivation industry, based exclusively on Italian pergolari systems.
All the molluscan species of shellfish considered have sources of natural spat available in Greece, so it would only be in the case of Manila clam introduction that there would be any reason for considering hatchery production. It follows that the methods appropriate to mussel, oyster and native palourde are all low technology, based on the capture of wild spat, and its subsequent nurture to market size. They are all low in capital requirement, but relatively high in labour input, even allowing for Spanish-style mechanization of mussel farming. The technical and financial risks are less than in hatchery-based culture, and the industry can expand in a progressive manner rather than in the major steps dictated by investment in hatcheries. Such industries, based on capture of seed from the wild, are sensitive to natural failures of spatfall. This is unlikely to limit mussel culture, provided growers take steps to gather seed. Growth is so fast in Greek waters that relatively little time is taken in growing rope collected seed to a size similar to that obtained by bottom dredging (c. 2 cm), and setting an adequate number of collector ropes is a very minor cost. Oyster and palourde farming operations dependent on natural spatfall are always subject to annual fluctuations in the abundance of seed, which may even fail entirely in some years. Producers need to be aware of the damaging effects of tri-butyl tin (T.B.T.) antifoulants, used on either boats or fish cage nets, on the survival of molluscan larvae. Instances of spat failure of oysters, mussels and scallops in the vicinity of such antifoulants are well documented, and the lack of strong tidal streams will render them particularly damaging in Greek waters. The consultant was concerned by the lack of awareness of this problem both among shellfish fishermen and fish-farm personnel met during the visits. The only exception was among the Keramoti Lagoon Cooperative (Kavala), where the use of any antifoulant other than traditional black tar is forbidden.
A subject of major concern to the molluscan industry, whether wild fishery or cultivated, is public health and the public's perception and trust in the products. Molluscan shellfish in Greece suffer from low public trust in Mediterranean shellfish in general, following the wide publicity given to Mediterranean pollution over the past decade. More locally, there is great suspicion, especially of mussels, in Athens and around the Gulf of Saronikos. The fact that the majority of the country's shellfish production is in areas remote from this does not convince a public whose perception of the sea is based on the state of pollution in Piraeus and Elefsis, and who are aware that at least some shellfish are being marketed from here, either legally or illegally.
The expansion of cultivation gives a real opportunity to tackle this question, as concessions for growing sites are regulated and are proscribed in heavily polluted areas. Depuration can be enforced where necessary. Publicity can be directed at increasing the public's trust in cultivated shellfish, and marketing and product labelling should reinforce the image of cultivated shellfish. At the same time, public health measures must ensure that no polluted mulluscan shellfish reach the market from any source and that any taken from heavily polluted areas must be relaid for at least a month prior to depuration. The shellfish industry must be persuaded that it is in its own interest to see such controls maintained.
The market exerts a powerful influence on the production of molluscan shellfish in Greece, which is distinct in mainland Europe in having no strong home demand. The small trade in mussels actually commands a high unit price (Dr 200–300/kg), with small local sales achieving the higher price ex producer. In order to compete in export markets in western Europe, however, a price of Dr 70–100/kg needs to be met. Producers in the Thessaloniki area believe they can achieve this. Given the very high growth rate of mussels in Greek waters, production can be on a 1-year cycle rather than the 2 years (18 months with sub-grade relaid for further growth) needed in Spain. Greek producers ought to be able to compete, despite high delivery costs.
The fact that only export markets exist for oysters and palourde has differing influences. In the case of oysters, which do not have a very high market value (c. Dr 280/kg), production is concentrated around those areas able to produce quantities sufficient to export (i.e., 20 t consignments). The very high value of palourde (c. Dr 1 000/kg) justifies assembling small quantities from various remote sources for central export marketing based in Thessaloniki.
The rate of growth which is already taking place in mussel farming will necessitate a growth of the domestic market in the very near future, and producers are aware of this. Export opportunities exist; France is estimated to have had a shortfall of c. 40 000 t in mussel supplies in 1986, and disruptions to the Spanish export trade following the detection of neurotoxins in Spanish mussels in December 1986 gave an opening for supplies from other countries, had they been available. Netherlands bottom relaid mussels fetched between f. 1 500 and 2 100/t (Dr 100–140/kg) in 1986, giving processors a severe problem with supplies. The opportunity exists, therefore, for a major expansion in mussel farming in Greece, but both home and export markets are highly sensitive to public health concerns. If the industry is to grow to a large scale it cannot afford to face market disruptions caused by localized pollution when the majority of production is coming from clean waters.
All shellfish require hygienic handling subsequent to landing and depuration, and this becomes more critical when marketing is of meats only. Peeled shrimp is unlikely to be considered, but a trade is developing in fresh mussel meats, and this must carry significant public health risks unless carried out hygienically. The consultant witnessed mussel meats being stirred by hand in a bucket on the floor, while the operator was smoking a cigarette. There is a clear need for advice on handling, storage and distribution of shellfish post landing, and of the dangers of ‘rewatering’ molluscan shellfish, a practice which can defeat all the public health controls which may exist at the production site. The industry must be aware that a good public health record and image is in its own interest and must be prepared to undertake much of the policing of this through its own organizations.