R. Dijkema
P. Hagel
Netherlands Institute for Fishery Investigations.
ABSTRACT
This contribution gives an overview of the state of the art in the Netherlands molluscan shellfish industry, including sanitary control and related regulations. Culture, fishery and processing of mussels, oysters and cockles are dealt with, as well as the organization of the different branches. A view is given of the present standards for the protection of public health and shellfish stocks, their enforcement and the monitoring and laboratory methods used for their maintenance. Attention is paid to research and development activities for the shellfish industry.
I. PRODUCTION: CULTIVATION AND FISHERY
The principal species cultivated and/or fished in the Netherlands on a regular basis are the blue mussel (Mytilus edulis L), the native European flat oyster (Ostrea edulis), the Pacific oyster (Crassostrea gigas) and the cockle (Cerastoderma edule). Their average yearly production, cultivated and fished, is presented in the table below:
| Species | Production method | Mean production (MT fresh weight) |
|---|---|---|
| Mytilus edulis | culture | 100,000 |
| Ostrea edulis | culture + fishery | 800 |
| Crassostrea gigas | culture + fishery | 800 |
| Cerastoderma edule | fishery | 60,000 |
Other species, fished and/or marketed in minor quantities, comprise cut-trough shells (Spisula subtruncata), whelks (Buccinum undatum), periwinkles (Littorina littorea), scallops (Pecten maximus) and queen scallops (Chlamys opercularis). The shallow and exposed coastal waters do not allow suspended cultivation methods, and the cultivated mussels and oysters are produced by bottom culture. Fishery on wild banks in the coastal waters is practiced on mussel spat and half-grown mussels, on the two oyster species, on cockles and, in some years, on the cut-trough shell.
Mussels
Mussels are cultivated in the Waddenzee (60–75% of the national production) (Fig. 1), and in the Oosterschelde estuary (Fig. 2). Culture plots in shallow coastal waters are mostly situated on the banks of tidal channels, from the intertidal range to 10–15 m below low tide level. Plots measure between 7 to 25 ha. There are 78 mussel growers who rent a total area of about 10,000 ha. However, 30–50% of this is not or hardly utilized because of unfavourable bottom or current conditions. An average grower cultivates 70–80 ha and harvests between 900 and 1,500 metric tons of mussels per year. In the period between 1984 and 1987 this represented a gross yield of 375,000–850,000 Dutch guilders (one guilder equals about US$ 0.5).
The average production of Dutch mussel cultivation is 100,000 MT per year. The yield fluctuates strongly (Fig. 3) due to a high frequency of westerly gales and a gradual silting up of the bottom in the Western part of the Waddenzee. During storms, this increases the exposure of the plots to waves and currents which can dislodge the mussels from the culture plots. Losses have been particularly high in the last decade. In years of heavy losses, tens of thousands of tons of mussels have to be imported, mostly from the German and Danish part of the Waddenzee, to satisfy market demand. Natural, one-year old spat, 2–3 cm long, is dredged predominantly in the Waddenzee. As fishing for wild mussels is prohibited, special permission is given to the mussel growers to fish for spat during 6 weeks in May/June and one week in September in designated areas. Certain areas can be closed for seed fishery for conservation. If they can find them, the mussel growers also like to take half-grown mussels (3–4 cm), growing on wild banks in the intertidal range. These mussels are hardy (thick shell and well developed adductor muscle), and need less time to reach the minimum market size (40% longer than 50 mm). Part of the collected spats are seeded on intertidal plots, where they are kept for a year. During this time, the mussels gain little weight, but acquire a thicker shell and a stronger adductor muscle, which increases their shelf life. These mussels are preferred for more distant export markets. The remaining spat is often seeded directly on deeper plots, where growth rate is higher and the mussels can reach market size by November. These mussels can obtain a high meat yield (up to 35–40%), but have a thin, often transparent shell and hence a shorter shelf life. They are preferred by the processing (canning) industry.
Predators which can cause serious damage are eider ducks (Somateria mollissima), sea-gulls (Larus argentatus), oyster-catchers (Haematopus ostralequs) and starfish (Asterias rubens).
Figure 1. Western part of the Waddenzee with the mussel cultivation plots.
Figure 2. Oosterschelde and Lake Grevelingen. Shown are the flood barrier, the mussel rewatering plots, Yerseke and the locations of the weekly sanitary monitoring programme (circles).
Figure 3. Total Dutch mussel production and the production in Zeeland province (1951–1987).
These predators can completely clear a culture plot containing 100 MT of mussels within a few days. Seagulls, attracted by the processing plants, constitute a special problem, as their dropping can cause incidental increases in coliform counts in the water. Birds are difficult to chase away. The mussel producers organization in Yerseke employs a falconer, who keeps the processing plants free from gulls with a hawk and a peregrine falcon. On the intertidal plots hunters are sometimes deployed to chase birds away. Starfish are dredged up, sometimes with mussels and all, sometimes with a special, spiked “star-dredge”, and killed with salt or by immersion in fresh water for one night. The mussels survive the operation and are seeded back on the plot.
The mussels generally reach the required market size in 2 years after seeding of spat. On very productive plots, this size is even reached at the end of the first growing season, in November. Most of the mussels are, however, harvested in the course of the following season, which runs from mid-July to the first week of April. The efficiency of the culture, as all forms of mollusc bottom cultivation, is low compared with off-bottom techniques. As an average, 1.5–2 MT of mussels are harvested from 1 MT of mussel spat, and 1 MT from 1 MT of half-grown mussels. On the most productive plots, a skilled grower can harvest 3 or even 4 MT “from one”. Seeding density of the spat ranges between 3 and sometimes as much as 10 kilograms per square meter, especially in years when seed mussels abound on the wild banks. Mortality on the culture plots is high, often reaching 90% or more of the individuals seeded. At harvest, the density of the mussels is 6– 8 kg/sq. m.
The ships for dredging the mussels and the seed mostly measure between 30–35 m in length and 6–9 m in width, with a draught of 0.6 m and a loading capacity of 120–150 MT of mussels. A shipload can be completed in 4–5 hours using 4 dredges, each 1.9 m wide. Most of the ships have a false bottom and double sides, which permits efficient unloading of the mussels by pumping water into the two holds, after which the mussels are washed out of the holds by gravity without damage. After harvest, all mussels are shipped to the township of Yerseke at the Oosterschelde (Fig. 2), where the mussel auction is located. There the mussels are sold to the highest bidding mussel merchant. After a merchant has bought a lot of mussels (mostly 50 or 120 MT), and prior to processing these, he has to relay the mussels on his own special plots, situated at a short distance from the area where the processing plants for fresh mussels are located. On the rewatering plots the mussels have to pass a period of 10–14 days, during which weak and damaged mussels are eliminated by seagulls, crabs and fishes and the survivors can recover from stress, contracted during fishing and the 12-hour transport from the Waddenzee to the Oosterschelde. After the re-watering period, the mussels are fished up carefully, in order not to stress and damage them. In contrast with the mussel ships of the growers, the catch on many ships is not dropped into the hold, but collected into containers on the vessel deck. This minimizes handling and transport damage. The containers are subsequently hoisted ashore at the processing plant, where the mussels pass a rotating rinsing sieve. Then a final de-sanding treatment is carried out. The containers with the mussels are connected to a sea water distribution system, which creates a vertical flow through the layer of mussels in the container. In a number of firms, this water is UV-sterilized to ensure bacteriological purity. During a period of 4–6 hours, the mussels cleanse themselves and discard the rest of the sand which has remained in the intestinal tract or in the mantle cavity after dredging. The water flow and the thickness of the mussel layer vary and are based on experience and research.
Purification of mussels for sanitary reasons, which is compulsory in a number of countries, is not necessary in the Netherlands, as all shellfish waters meet the required national bacteriological standards, as well as those of the European Community (see Section 3).
Finally, the mussels are ready for processing or marketing. They pass a de-clumping mill to break up clumps formed by the byssus, and are subsequently led over a blower to remove algae (mostly sea lettuce, Ulva lactuca) and empty shells. Then de-byssing takes place and, if necessary, grading. Often, the mussels are rather uniform in size and do not need grading. After a final manual sorting of damaged mussels, stones, peat, etc., the mussels aimed for the fresh market are packed in 20 kg wholesale bags or in 1, 2 or 2.5 kg perforated plastic bags for home consumption.
Oysters
Cultivation of the flat oyster Ostrea edulis is carried out on culture plots in the Southeastern part of the Oosterschelde (1,700 ha) and in non-tidal Lake Grevelingen (380 ha) (Fig. 2). Spats are collected on mussel shells, which are seeded on plots on the sea bottom as soon as monitoring, carried out by the Netherlands Institute for Fishery Investigations, demonstrates sufficient concentrations of ripe oyster larvae in the water. After two years, the oyster seeds are fished and re-seeded to other plots where growth rate is higher. Market size is reached after 4–5 years from spatfall at a weight of 65–90 g. The biggest oysters are marketed at a weight of 100–120 g. The 16 Dutch oyster growers and exporters produce about 10 million (800 MT) of flat oysters per year. About half of this originates from fishery on wild banks. After the introduction and subsequent outbreak of the epizooty caused by the protozoan Bonamia ostreae in the Oosterschelde estuary in 1980, fishing and cultivation of O. edulis in Lake Grevelingen, which had not been infected, had become the economic cork which kept the Dutch oyster industry floating (Dijkema, 1988). In 1988, however, Bonamiasis also broke out in Lake Grevelingen. The high mortalities caused by this disease make the prospects for production of this species in the Netherlands bleak. Like in other oyster-producing countries, e.g. France, England and Spain, high mortalities among oysters more than two years old renders lucrative exploitation of the wild and cultivated oyster beds extremely difficult.
Pacific oysters (C. qiqas) locally called by their French name “creuses” of the Kumamoto and the Myagi strain, have been cultivated in the Oosterschelde from the late seventies, after they were introduced from Japan in 1965. The decision to introduce this species was made on the supposition that natural spawning would not occur. The water temperature maxima in the area (21–24 °C) were thought to be too low for natural spawning. The contrary proved true: reproductive success appeared to be surprising in some years, probably due to warming up of enclosed intertidal pools of water during low tide. After about 10 years, wild oyster banks appeared on intertidal dike slopes and sandflats. Natural spatfall of any significance is now taking place every few years and constitutes the sole source of spat for cultivation. Spats are collected on mussel shells, seeded on plots in the tidal areas. The plots used are often shallow. The lack of hatchery-produced spat is a constraint for further expansion of the culture. Every year about 100 MT of Pacific oysters are cultivated and fished.
Cockles
A) Mechanical fishery
Although pilot-scale growth and re-seeding trials with this species have been successful (Dijkema et al., 1987), no commercial culture exists in the Netherlands. Both the mechanical and the hand cockle fishery are practiced in the Waddenzee (70% of the catch) and the Oosterschelde (20%), about 10% is dredged in the subtidal waters off the Dutch coast. During the last half decade, the fishery yields a yearly average of 10,000 MT of cooked meat, equivalent to about 60,000 MT of fresh cockles. The fishing season runs from the end of August to December. There are 37 cockle dredging ships, licensed to fish in the coastal waters, and another 7 that are allowed to fish only in the deeper offshore area. Almost the entire production is captured with these dredging vessels. They measure about 30 × 10 m and have a draught as shallow as 0.5 m. A ship is equipped with two one-meter wide suction dredges. The cockles and the sediment are whirled up by means of a powerful water jet and are then scooped up with an oblique blade into a mesh cage, from which the catch is pumped aboard. There the cockles are separated from water and sand in rotating sieves. On a number of vessels, the catch is then spread out on deck and immersed in sea-water for a few hours for de-sanding. The cockles are cooked on board. Cooking is mostly done at low tide, when fishing on the intertidal flats is not possible. Special cooking locations are designated in areas where the bacteriological water quality is approved. After being cooked, the cockles are shucked by vibration, rinsed and often chilled. There is one deep-freeze factory ship. The meat is then shipped to shore, where it is further processed.
B) Manual fishery
At present, 90 licensed manual cockle fishermen dig for cockles in the intertidal zone. All together they harvest about 5,400 MT of fresh cockles. Part of their catch is sold to processors, while the larger categories are sold fresh. The number of licenses has recently been restricted to 90 for reasons of wildlife protection.
II. ORGANIZATION OF THE INDUSTRY AND MARKETING
Mussels
Most of the mussel culture firms are independent family enterprises, whereas most of the merchants and exporters of mussels and the mussel processors are firms. A few larger grower's firms exist, owning more than one ship. Firms are gradually becoming more common. There are 78 growers, owning 86 ships. A regular mussel ship is manned by a skipper (mostly the owner), a mate and a deck hand. Culture plots are rented from the government. The total rent for all growing plots, following a drastic increase from 1990 on, will rise stepwise from Dfl 750,000 to Dfl 4,500,000 in the coming years. Each grower will be charged according to his share in the total landings, and no longer according to the production value of his plots. In the trading and processing industry, the firms are generally larger than in the cultivation sector. Often, mussel traders are also active in mussel processing and in other shellfish branches like cockles, oysters and in the lobster trade. In 1989, there has been an increased incidence of takeovers by British food chains.
The mussel industry as a whole is represented in the Government in the mussel section of the Board of Fish and Fish Commodities. Besides, the mussel growers are organized in a cooperative: Producers Organization (PO). In addition, they have their own local associations in each of the three mussel harbour towns and also they are united in a regional fishermen's organization. The degree of organization of the mussel industry is by far the highest in the Dutch fishing industry. Although membership in the PO, according to EEC regulations, is no longer compulsory and the regulations of the organization have lost their force of law, almost all growers are members and comply with its regulations. These regulations are revised each season and encompass, among others, a minimum size (a shell length of 40% of the mussels longer than 50 mm), minimal meat yield (16% meat of fresh weight), and a minimal percentage of tare. Funds exist to finance research and promotion campaigns. All activities of the PO are financed by separate, specific levies per MT landed or marketed.
The personnel of the mussel auction is also responsible for quality control. An equally voluntary, intervention fund exists for those mussels which, at landing, appear not to meet the requirements for size or meat weight, or which do not fetch the minimum price, in the season 1989–1990 established at Dfl 0.24 per kg. These mussels are re-seeded on special plots and sold back to the growers at the end of the season. About 65% of the national production is sold fresh by 27 merchants who clean, debyss and pack the mussels destined for the local market (15%), Belgium (60%), and France (15%). The remaining percentage of the production is processed. A variety of commodities is offered to the consumers, like Individually Quick Frozen (IQF), breaded, deep frozen in the half shell, on skewers, pasteurized or sterilized in glass jars with all kinds of sauces, or just “au naturel”. Promotion is financed jointly by producers and traders. It encompasses manifestations such as “free-for-all” mussel festivals, TV commercials, posters, pamphlets and recipes booklets in both the Netherlands and in the export countries. Such aimed campaigns have succeeded in enhancing the local mussel consumption by almost 50%. Due to the proximity of the main export markets: Brussels (1.5 hours by road), Antwerp (45 mins) and Paris (5 hours), the fresh product can reach its destination in a matter of hours after having left the water. To ensure optimal quality, transport takes place in cooled trucks at a temperature of 7–10 °C, in summer often after pre-chilling in cooled water at the processing plant.
Oysters
Oyster growers export their own product. Apart from the cultivation plots he rents from the Government, an oyster grower owns a ship, a number of on-shore storage basins and a building in which cleansing, sorting and packing of the oysters is carried out. The start of the season for O. edulis depends on the condition, mainly the shelf-life, of the oysters, and mostly starts in the first week of September. The season peaks between Christmas and New Year and ends at Easter. C. gigas is marketed throughout the year. Inland consumption is small; the majority of the oysters are exported to Belgium and France. Oyster growers operate much more individually than the mussel growers, illustrated by the fact that there are three separate associations of oyster growers, each of them representing only its own members, coordinating fishery, and to a certain degree marketing. Agreements are made each season upon the weight classification of the oysters.
Cockles
The 20 or so companies which own cockle-dredging licenses are organized in two associations, which negotiate each year with the government on the length of the fishing season and fishing areas. Regulations exist as to the minimum size (15 mm shell width), mean size (expressed as the number of cooked individuals per kg) of the cockles, the percentage of damaged cockles in the catch and the width of the blade of the dredge. Cockle meat is mostly canned (about 70%), IQF or block frozen. The entire production is exported, mainly to Spain and Italy. The major share in capture, processing and export is in the hands of about 4 large companies which own 21 of the 37 ships. Also in this sector, foreign capital is increasing strongly. Small amounts of fresh mostly large-size cockles, captured by hand, are exported to Belgium and France.
III. REGULATIONS CONCERNING PUBLIC HEALTH AND THE PROTECTION OF MOLLUSC STOCKS.
3.1 General
In 1992, the internal frontiers between the countries of the European Community will disappear. Consequently, control measures will no longer be carried out at these frontiers, but only at the external frontiers for imports from non-member countries. Uniform regulations will be implemented for the waters in which shellfish are fished or kept, as well as for fish and shellfish, imported from outside the EC. Concomitantly, standards will apply to processing techniques, hygiene and buildings. All these regulations are now (1989) in the stage of drafting and approbation by the member-countries. Some of them, like the regulation for shellfish waters, are already being applied in a number of countries. A survey of the present regulations is given in the next section.
3.2 European Community regulations for shellfish water quality.
The European Community recommends standards for the quality of waters in which molluscs are cultivated and fished. These EEC standards are maintained by the Ministry of Public Works and Waterways, which is responsible for the quality of surface waters. Standards exist for the following environmental parameters: pH, temperature, water color intensity, suspended solids, salinity, oil, flavour, taste, thermo-tolerant coliforms, dissolved oxygen, halogenated organic carbons and a number of metals. In general, the standards say that the values of these parameters may not exceed the normal values under natural conditions by a certain factor. For all parameters sampling intervals and often determination methods are prescribed. The procedure will be described here for monitoring the bacteriological quality of shellfish waters, being the most relevant one for molluscs. This monitoring program is carried out by the Netherlands Institute for Fishery Investigations in Yerseke. On a quarterly basis, 5 samples of mussels or cockles, with a distance between them of at least 100 m, are taken on each of 8 fixed locations in each of the 6 shellfish growing and fishing areas in the country (Fig. 4). These samples are analyzed for thermo-tolerant faecal coli bacteria, the median value for each location is reported. This quarterly monitoring is supplemented by a weekly monitoring on relevant locations, which will be discussed in section 3.3.
Determination of the concentrations of thermo-tolerant faecal coli bacteria in shellfish meat is done, using incubation on McConky agar plates at 44.5 °C during 24 hours. If positive, confirmation is carried out of 10% of the colonies found, using lactose, brilliant-green bile broth medium and the Kovacs reaction. As the levels found in water samples are generally too low to give reliable and conclusive analysis results, only mussel samples are examined.
Figure 4. Mussel sampling locations for the quarterly E.C. sanitary monitoring programme.
3.3 National regulations for mollusc waters, landings and sales.
Also partly covered, and in future supplanted by regulations of the European Community, domestic quality standards are maintained for molluscan shellfish, as well as for the water they are captured or cultivated in. These standards are laid down in the governmental Decree for the Pureness of Molluscan Shellfish and are being maintained by the National Inspection Service for Meat and Livestock of the Ministry of Agriculture, Nature Management and Fisheries.
Bacteriological standards.
For shellfish waters:
• Conform with the E.C. standard
For molluscan shellfish:
• Less than 300 thermo-tolerant E. coli in 100 ml mollusc flesh + intervalvular liquid.
• Absence of Salmonella in 25 ml mollusc flesh + intervalvular liquid.
In addition to the sampling programme following the EC regulations, weekly mussel samples are analyzed from 8 locations (Fig. 2), such as cultivation plots in the principal cultivation area in the Oosterschelde, the mussel re-watering plots in the vicinity of Yerseke and the area where the water for de-sanding of the mussels is pumped up. In order to keep a close watch on sanitary water quality, these samples are taken much more frequently than the 3-month intervals prescribed for the EC monitoring programme.
Chemical standards.
For molluscan shellfish:
• Mercury: Less than 0.7 mg/kg mollusc flesh + intervalvular liquid.
• Cadmium: Less than 1.0 mg/kg mollusc flesh + intervalvular liquid.
• Lead: Less than 2.0 mg/kg mollusc flesh + intervalvular liquid.
Monitoring the coastal and inshore waters for pollutants such as heavy metals, Polycyclic Aromatic Carbons (PAC's), pesticides and many others is carried out monthly by the Ministry of Public Works and Waterways. The concentrations of these pollutants in fish and mollusc tissue are being monitored by a combination of institutes of the Ministry of Agriculture, Nature Management and Fisheries. Coordination and sampling is done by the Netherlands Institute for Fishery Investigations.
Biological standards.
For molluscan shellfish water:
For molluscan shellfish:
Absence of lipid-soluble biotoxins originating from dinoflagellates, e.g. breve-toxins (NSP) and Dinophysis toxins (DSP).
Concentration of water-soluble biotoxins originating from flagellates not higher than 40 microgram per 100 ml of mollusc flesh + intervalvular liquid (saxitoxin (PSP).
Concentrations of water-soluble biotoxins originating from diatoms not higher than 20 mg/kg mollusc flesh + intervalvular liquid (domoic acid (ASP).
Absence of “foreign” flavours and tastes.
Fishing and cultivation areas where values of phytoplankton or toxins exceed the standards, are closed. As the Oosterschelde area is only affected occasionally, mussel stocks in the rewatering and cultivation plots in most years are sufficient to maintain the output during the closure of (parts of) the Waddenzee.
Monitoring the coastal waters for toxic phytoplankton is done weekly during the period July-November, or longer if deemed necessary. Water samples are taken in all mollusc growing areas and are examined microscopically; mussel samples are collected and are examined by means of rat-bioassay (see below). The 15 sampling locations are indicated in figure 5. The method, followed for the rat bio-assay is a modified version of the method described by Kat (1983). As test animals white, female wistar random rats are used (species: Rattus norvegicus), with a body weight from 80–100 g to about 300 g.
Procedure:
A test animal of known weight is starved for 24 hours, starting around 1600 hrs. Drinking water supply is ad libitum.
After 24 hours (again at 1600 hrs) hepatopancreas tissue of the mollusc to be examined is fed to the test rat in portions of 10 grams of hepatopancreas per 100 grams of body weight.
The results of the test is recorded the next morning at 0900 hrs. The (partial) refusal of the hepatopancreas and the consistency of the faeces produced (diarrhoea of soft faeces) are used for scaling the presence of diarrhetic shellfish toxins according to the following schedule:
Figure 5. Sampling locations for the DSP monitoring programme in the Waddenzee (12 stations) and in the Oosterschelde (3 stations). (6+12: phytoplankton and water samples; 1+13: water and mussel samples; 2–11, 14, 15: mussel samples).
| Percentage of hepatopancreas eaten | Consistency of the faeces | Degree of toxicity | Rating |
|---|---|---|---|
| 100 – 90% | normal | negative | - |
| 100 – 90% | normal/soft | very slightly toxic | ± |
| 90 – 50% | soft | slightly toxic | + |
| 90 – 50% | soft/diarrhetic | moderately toxic | ++ |
| >50% | diarrhoea | seriously toxic | +++ |
In case of total refusal of hepatopancreas tissue, an admixture is prepared with normal rat fodder, type RMH-B, obtained from Hope Farms B.V., P.O. Box 85, Woerden, Netherlands, in an appropriate ratio (e.g. 1:1 or 2:1, etc.).
Standardized in okadoic acid, the detection limit of the test is 10–50 microgram per rat of 100 grams. As the first signs of intestinal complaints in humans may arise at about 50 micrograms, a rating of “±” may produce its first effect on humans at a portion of 10–50 grams of hepatopancreas tissue, corresponding with about 20–100 grams of shellfish meat.
Physical standards
For molluscan shellfish:
- The concentrations of radio-active nuclides may not exceed:
| 80 | Bq/kg | α-emitters |
| 1250 | Bq/kg | Cesium isotopes |
| 2000 | Bq/kg | Iodine-isotopes |
| 750 | Bq/kg | Strontium isotopes |
3.4 Imports
The quality standards for imports as well as for domestic landings and sales of cultivated and fished fish and shellfish and their commodities, are maintained by the National Inspection for Livestock and Meat, part of the Ministry of Agriculture, Nature Management and Fisheries. Organoleptical, bacteriological, chemical, toxicological and radioactivity analyses are either carried out in the laboratories of this service or are performed by contracting laboratories, such as the Netherlands Institute for Fishery Investigations.
For import into the Netherlands, mussels and oysters, as well as the water they originate from, have to be accompanied by certificates, issued by competent authorities in the countries of origin, stating that the following standards are met:
Microbiological standards
For shellfish water:
For molluscan shellfish:
Biological standards
For shellfish water:
For molluscan shellfish:
For the determination of Diarrhetic Shellfish Poison (DSP), the rat bio-assay method is applied (see 3.3). The standard: “absence of DSP” means in practice a negative rat-bio-assay outcome, based on feeding hepatopancreas-tissue to starved rats on a basis of 10% of the live weight of the animal. A negative outcome corresponds with a dose of less than 10 μg okadoic acid per rat.
Paralytic Shellfish Poison (PSP) does not occur in the Dutch coastal waters. However, it has been reported in almost all of our neighbouring countries. The risk of introducing into the Dutch coastal waters the dormant stages or “cysts” of phytoplankton species which can cause PSP is considered very high. To minimize this risk, import prohibitions for specific regions of countries have been replaced since 1988 with a general regulation:
It is prohibited to immerse in Dutch coastal waters imported shellfish, unless:
They are originating from the Wadden Sea bordering the North Sea, pertaining to Germany or Denmark.
Mussels are cleansed, de-byssed and packed in consumers package.
They are kept in quarantine installations which guarantee that no effluent of any kind can reach the coastal waters, unless it is sterilized in an approved manner.
It can be proven that waste water from processing operations as well as tare, do not reach the coastal waters.
Chemical and physical standards
Biological standards for mollusks, concerning the protection of their stocks and of the marine environment:
3.5 Exports
The National Inspection Service for Meat and Livestock of the Ministry of Agriculture, Nature Management and Fisheries is also equipped for the inspection of all fish and shellfish destined for export. Inspection is performed at the request of the exporter and/or of the country of destination. Random samples are taken of all lots of shellfish destined for export. If a lot is approved, a certificate for export or a health certificate is issued. The inspection is done at the level of “fit for human consumption”, but may also contain any other additional elements. A quality inspection with “indicated quality grades” is also possible. The norms used for this inspection are based on the governmental “Decree on the quality of fish and fish products”, which also applies to all fish and shellfish, imported, landed and sold on the domestic market.
IV. RESEARCH AND DEVELOPMENT FOR THE MOLLUSC INDUSTRY
Many of the technical development activities are carried out by the industry itself (large firms have technical departments and develop their own gear and machinery). For instance, a large manufacturer of mollusc processing equipment specialize in process technology and machinery. It serves a part of the industry, but is mainly depending on foreign markets. There are two governmental institutions for research and development in fishery: the Netherlands Institute for Fishery Investigations (RIVO) in IJmuiden, which has a field station for mollusc research in Yerseke, and the fisheries department of the Institute for Agriculture Economics (LEI), both part of the Ministry of Nature Management and Fisheries. These institutes also give advice to the Ministry on governmental fishery management. Although they are governmental institutions, they carry out contract research and consultancy services, both in the Netherlands and abroad. A large share of the contract work abroad is in development cooperation projects. The Institute for Fishery Products Technology, IVP-TNO in IJmuiden, a division of the government-subsidized Organism for Applied Scientific Research, carries out contract research into fishery products technology, whereas the RIVO concentrates on the biological, environmental and technical aspects of fishery and aquaculture. Below, a survey is given of the experience and know-how in the field of mollusc cultivation and fisheries, available in the Netherlands:
Netherlands Institute for Fishery Investigations (RIVO)
Zootechnical aspects of mollusc cultivation
Development of (refrigerated) recirculated on-land storage-facilities for live shellfish.
Monitoring programs for toxic phytoplankton in coastal waters, determination of DSP in shellfish with rat-bioassay.
Sampling and monitoring pollutants in fish and shellfish, stock assessments for mollusks.
Fishing gear technology: traditional and suction dredges.
Site-selection for mollusc cultivation: currents, food supply, water exchange, exposition. Review of project proposals
Monitoring and interpreting growth, mortality and condition of molluscs. Setting up of research and monitoring programmes.
Institute for Agricultural Economics (LEI)
Producers Organization (PVV)
Franken B.V., Goes
V. LITERATURE
Dijkema, R., 1988. Shellfish cultivation and fishery before and after a major flood barrier construction project in the southwestern Netherlands. Journal of Shellfish Research, Vol 7, No 2, 241 – 252.
Dijkema, R. and M.R. van Stralen, (1989). Developments in mussel cultivation in the Netherlands after a large-scale coastal engineering project. World Aquaculture, dec. 1989 (in press).
Dijkema, R. and M. van Stralen, (1989). Management-supporting research into interaction of bottom cultivation of mussels (Mytilus edulis L) with local ecosystems in the Netherlands. International Council for the Exploration of the Sea, 1989 EMEM/No 70.
Dijkema, R., J. Bol and C.S. Vroonland, (1987). Enhancement of the production of cockles (Cerastoderma edule L.) by thinning out a dense natural bed and reseeding, Oosterschelde, SW Netherlands. Intern. Council for Exploration of the Sea, C.M. 1987/K:12.
Kat, M., (1983). Diarrhetic mussel poisoning in the Netherlands related to the dinoflagellate Dinophysis acuminata. Antonie van Leeuwenhoek 49, 417–427.
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