INTRODUCTION

In 1993, the new fisheries policy was introduced. In the new policy, the aim was to promote responsible fisheries, taking into account the values of the natural ecosystem. For the Wadden Sea, the goals were, a.o., a larger area of intertidal mature mussel beds and seagrass fields, and the prevention of food shortages for birds.

The responsibility for maintaining the natural values was, to a great extent, laid upon the fishermen, the so called co-management.

In the policy, three tracks can be recognized:

• Parts of the intertidal (25%) are closed for shellfish fishery in order to promote the undisturbed development of biotopes like mussel beds, cockle beds and eelgrass fields.
• In years with low stocks of shellfish, the food requirements for birds are guaranteed by regulation of the fisheries. It is assumed that 60% of the calculated food requirement is sufficient because birds are assumed to be able to cover the remaining 40% by alternative prey.
• In order to prevent negative impacts, and make an efficient use of the available cockles and mussel seed, the sector develops a management plan.

This management plan follows two lines:

• Setting the limits for an annual 'TAC' (TAC = Total Allowable Catch), and dividing this TAC between the fishermen;
• Decreasing or preventing negative impacts in the free zone (75%) by controlled fisheries, not fishing on seagrass beds etc.

EFFECTS OF REGULATIONS

Effects on fisheries

Only in the autumn of 1994, there was a sufficiently large inter-tidal mussel population (more than the 60% limit) open for fishery. In all other years, few intertidal mussels were present and the inter-tidal was closed for mussel fishery. Still, the mussel sector had good years. Prices were high, and yearly production was reasonable. There was sufficient seed in the sub-tidal. The sub-tidal seed was well divided between the fishermen, and survival during fishing and subsequent culture was much better than in the years before the management plan came into operation.

The cockle sector experienced bad years. The harvestable cockle stock has been low in most years, and after good spattfall, another severe winter killed most of the stock. If there had been no regulations (60% rule and closed areas), the sector would have been able to generate a higher income, but this would have meant a severe reduction of the cockle population.

Effects on natural values

There have been clear impacts of food shortages on birds. Oystercatcher numbers have decreased, winter mortality has increased. Because food availability is only partly regulated by fisheries impact, and storms and severe winters had great impacts in the last four years, no firm conclusions can be drawn on the relative importance of the fisheries impacts in the long run. Eider ducks did not have enough intertidal mussels or cockles and started robbing the sub-tidal culture beds. After being chased away, they moved to the coastal zone where they fed on spisula beds.

Few mussel beds have recovered. In 1994, there was a good spattfall in part of the Wadden Sea, but the majority of the young and unstable beds disappeared in a storm in the spring of 1995.

Also, the winter of 1995/1996 had a severe impact on the remaining beds. At present, only 100 à 200 ha (more than 3 years old) intertidal mussel bed are present. The reference value for the Dutch Wadden Sea is 4,000 à 5,000 ha. The old beds now present have never been fished because they occur within the 25% closed area (2 beds). They were voluntarily closed in the management plan (1 bed) or were closed on the basis of the 60% regulation (6 beds).

In 1997, about half of the cockle biomass occurred in the areas closed for fisheries. Because of good spattfall in 1997, and a mild winter, cockle biomass seems to have recovered, and cockles are now (spring 1998) occurring in high densities in many parts of the area.

Seagrass seems to be recovering in the Ems estuary and the coastal region of Friesland and Groningen. Areas where seagrass is encountered have been closed to fishery, and fishermen have obeyed the rules as indicated by the black boxes.

CONCLUSIONS

Closing areas for fisheries (track 1) has proven successful. There has been no fishing, but (commercial) hand gathering and destruction of mussel beds by Nereis collectors is still a threat. In the Ems estuary, a considerable eelgrass field has developed, and on the Balgzand some well developed mussel beds occur. Also, the majority of the cockles occurred on the Balgzand flat. If this flat had been open when cockle stocks were low, they would certainly have been fished.

There are still discussions about the effectivity of the 60% rule (track 2). On the question whether 60% is enough, or whether 70%, 100% or, in the case of mussels, even 300% of the calculated food supply has to be safeguarded, no answer can yet be given, because there are still uncertainties about the minimum cockle density at which feeding is profitable, the availability of alternative prey in winter, and the maximum numbers of territorial oystercatchers which can feed on a ha of mussel bed.

An alternative question has been whether reduction of fisheries in years with low stocks (< 60%) has improved the survival of birds. This question is stressed by the fishermen. Of course, it has been an advantage for the birds that fishing is stopped when food stocks are low, and these stocks have been left for the birds.

Setting a TAC and dividing this between partners (track 3a) has been very successful. The cockle fishery has been well regulated by the sector, and the mussel sector obtained a good survival of the available seed, and managed to reach much higher production ratios (production/seed) than in the past two decades.

The cockle sector has obeyed the regulations in the management plan (track 3b), and has had strong sanctions on fishermen that did not act accordingly. Little is known about the long-term impact of cockle fisheries on the development of shellbanks and other sedimentary aspects. These aspects require further studies, and the results may lead to adjustments of the management plan.

No conclusions can be drawn about the effectivity of track 3b (responsible fisheries) concerning the mussel sector. Only in 1994 limited fishing occurred in the inter-tidal. Almost all young beds of the 1994 spattfall disappeared, both fished and non-fished. From 1995 onwards, fishing was prohibited because of the 60% rule. Information from the past, and recent investigations in Niedersachsen indicate that intertidal mussel beds cannot stand much fishery pressure.

Results from investigations in the 80s indicate that fisheries on intertidal mussel beds can be held responsible for the disappearance of these beds. The majority of the beds that developed afterwards was unstable and disappeared after the first storms and winters. The few older beds that are now present seem to withstand storms and ice-shear relatively well, and attracted good spattfall in the last few years when spattfall in the rest of the inter-tidal was minimal. It has become clear that stable mussel beds are a more certain food supply than the cockle population which does show large natural variations between years.

FUTURE POLICY

In March this year, the Minister of Agriculture, Nature Management and Fisheries has submitted an evaluation report on shellfish fisheries to Parliament. In the accompanying letter, he has outlined his ideas for new policies for the coming five years. These ideas are a matter of debate at the moment.

The importance of intertidal mussel beds has been clearly recognized. It is proposed to stop all fishery (cockles and mussels) in areas where there is a considerable possibility for mussel beds to develop. The same is the case for areas where eelgrass has good opportunities.

If mussel beds redevelop to the old extent, this may have considerable advantages for the fishermen. The eider ducks will find sufficient food on these beds and cause less damage in the culture plots, and in years with low spattfall in the sub-tidal, there may be possibilities to fish in the inter-tidal to keep the business going.

For the natural values of the Wadden Sea, the reoccurrence of the mussel beds will also be important. As a reliable food source for birds, as an important biotope containing a variety of organisms, and as an important factor in the sediment dynamics of the area. The mussel beds collect great amounts of silt and sand and are important in a period of sea level rise and soil subsidence. They also enrich large areas with organic matter, thereby increasing the production of deposit feeding organisms which are an important food-item for migratory birds and juvenile fish.

Authors address:

IBN-DLO
Postbus 167
NL - 1790 AD Den Burg / Texel
e-mail: n.m.j.a.dankers@ibn.dlo.nl