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Port Authority studies baby fish in North Sea

Researchers are currently looking at the condition of juvenile fish in the North Sea. These are the fish which ‘hatched' this spring. Species, numbers and length will be recorded. This study will be carried out at some 100 locations, up to about 50 km from the coast, between Flushing and Den Helder. As far as anyone knows, such a comprehensive study of all fish species has never before been held in this part of the North Sea. It is a so-called zero measurement. By repeating the study during the sand extraction for Maasvlakte 2, and comparing the sets of results, any possible effects of the sand extraction can be charted. The study will focus specifically on the baby fish, because any impact the construction of Maasvlakte 2 might have is expected to be noticed first there.

About 325 million cubic metres of sand will be needed to build Maasvlakte 2. Most of this will have to be extracted from the North Sea, close to the area where it will be sprayed on. After all, this reduces to a minimum the distance the dredgers have to travel with the sand. The Environmental Impact Report (EIR) for the Construction of Maasvlakte 2 describes what the anticipated effects on marine life will be as a result of the sand extraction. This is based on existing scientific knowledge and specially developed, state-of-the-art computer models. According to this report, the expected effects on life in the North Sea are not significant.

Permit under the Earth Removal Act
Before construction starts, a permit under the Earth Removal Act must be obtained to extract sand from the North Sea. As part of this process, the effects of the sand dredging will have to be measured to see if they remain within the range predicted in the EIR.

Voordelta
The sand extraction will take place at quite a distance from the coast, where the North Sea is deeper than 20 metres. This marks the boundary of the so-called Voordelta, which lies directly along the coast. The Voordelta is home to richer and more varied marine life than deeper parts of the North Sea. The Voordelta is protected by the European Birds and Habitats Directive, which imposes strict requirements on intervention in this area. All current sand-extraction locations in the North Sea are to be found beyond the 20-metre line.

Zero measurements
The Port of Rotterdam Authority, which is responsible for the construction of Maasvlakte 2, must and wants to treat the marine environment with respect. For this reason, life on (epifauna) and in the seabed (infauna) will be mapped out before construction starts, as with the condition of the juvenile fish. Life on and in the seabed was already charted last year by means of a zero measurement. This will be repeated in September 2007. For the baby fish, the zero measurement will be made now.

This latter measurement will cost in excess of € 200,000. On top of this there will be the costs during construction of monitoring, investigating whether or not the effects are occurring as predicted. All told, the Port Authority will spend around € 3 million on the study into the effects of the sand extraction on nature and ecology.

Nets overboard 100 times
The researchers will throw their nets overboard at some 100 set locations. These will be between Flushing and Den Helder, at various distances from the coast. The nets are trawls, which glide along the seabed mainly to catch the flatfish, and ordinary nets, which are pulled through the water. Both types of net are fine meshed (approximately 1 cm and 1 mm respectively) so that not only the big, but also and more particularly all small fish are caught. On board, the researchers will separate all juvenile fish from the other sea-dwellers, and count and measure them according to species. Of which there are more than 30. For every species, at least 10 small fish will be frozen per location, so that they can be studied in more detail later, if necessary. As far as anyone knows, such a comprehensive study of all fish species has never before been held in this part of the North Sea.

Scientific knowledge
The development of advanced computer models, the zero measurements and the subsequent monitoring and thereby verification of the new computer models, will produce a great deal of new knowledge on the effects of sand extraction on life in the North Sea. According to the Second Regional Earth Removal Plan for the North Sea (RON2) from 2004, which describes government policy on sand extraction at sea, there are gaps in our knowledge of the effects of large-scale, deep sand extraction. RON2 therefore wants to use the first relevant project as a pilot with an extensive monitoring programme, in order to increase knowledge in this field. The zero measurements currently under way fit the bill. In this way, the Port Authority is making a real contribution to knowledge of the North Sea.

Deep sand extraction pits
The sand for Maasvlakte 2 will be obtained by sucking sand up, giving rise to so-called sand pits. Removal up to a depth of 2 metres is usual, but, considering the quantity of sand needed, that would mean digging up a stretch of the North Sea bed measuring 11 by 30 km. The sand will therefore be obtained from pits with a much smaller surface area but quite a bit deeper. Digging to a depth of 10 to 15 metres with respect to the current seabed is an obvious choice. Pits of this depth get filled with fresh water by the current at every tide, so that no oxygenless water arises. The latter would make life on the seabed virtually impossible.

Floating sludge particles
The effects predicted as a consequence of the sand extraction are twofold. On the one hand, marine life at the extraction site itself will disappear. Through so-called recolonisation, this will return to the old level again within a few years. On the other hand, sludge particles from the bed will enter the seawater. That happens because the trailing suction dredgers pump not only sand upwards, but also water. This water flows, with a limited quantity of sand and sludge particles, back into the sea via the dredger's overflow. The sand then sinks quickly to the bottom, but the lighter sludge is carried some distance by the current before it sinks. This sludge muddies the water, so that less light penetrates. This therefore retards the growth of algae, so that less of this so-called primary production is available as food for snails and shells, which, in turn, serve as food for creatures higher in the food chain.

If the water becomes muddied, this can also have consequences for fish and birds which hunt by sight. At the same time, this could be a good thing for the species which serve as prey. It remains to be seen, however, if such theoretical possibilities will actually materialise and also be measurable.

Natural phenomenon
The presence of floating sludge in the seawater is, in itself, a natural phenomenon. Rivers carry sludge to the sea all the time. From the Straits of Dover too, 10 to 40 million tonnes of sludge a year enter the North Sea. It sinks in stagnant or slowly-flowing water and is churned up when the current increases or by waves when there is a strong wind. Hence, there is a lot of sludge in the water of the Voordelta and the so-called coastal river, the ongoing flow of relatively fresh (because river) water from south to north close to the coast.

Expert meetings
In preparing for the study, the Port Authority held a number of expert meetings. Here, the objectives and research methods were discussed in detail with a group of around 20 experts in the field of maritime ecology and research. Following an EU tendering procedure, the study is being conducted by the Institute of Estuarine and Coastal Studies (IECS) of Hull University (GB). It is being carried out from the cutter MS Jade and will take about 2 weeks.

Page updated at: 07-07-2009