De Levende Natuur nummer 6 van 2009 (English summary)




DLN 2009-6

The increasing human use of the sea has large impacts upon the marine ecosystem

H.J. Lindeboom, H.J.L. Heessen, M.S.S. Lavaleye & M.F. Leopold

Comparisons of historical and recent data indicate that the Dutch part of the North Sea has already been influenced tremendously and if no measures are taken, several species will vanish from our sea forever. To turn the tide it has been decided to create Marine Protected Areas. The boundaries of these areas are determined by habitat characteristics, such as sandbanks and reefs, and the presence of exceptional ecology values for benthos, fish, birds and marine mammals. The results of extensive analyses show that the coastal sea, the Frisian Front, the Central Oystergrounds, the Cleaverbank and the Doggerbank are areas with exceptional ecological values, worthy to protect. The same could be true for a few other areas but more data must first be collected. This article describes how the choices for the assigned Marine Protected Areas were made.

The Harbour porpoise in the North Sea: enmeshed in fishing gear and legislation

C.J. Camphuysen & A. Trouwborst

The Harbour porpoise (Phocoena phocoena) became virtually extinct in Dutch coastal waters in the early 1960s. A small, but gradually increasing number of sightings in the mid-1980s was followed by spectacular over the last 20 years. The historic decline and the recent increase are concurrent with similar trends in strandings data. Unambiguous explanations for the initial decline have never been given and it is equally difficult to fully understand the come-back, but distributional shifts rather than North Sea population fluctuations underlie the trends observed. The re-distribution of Harbour porpoises in the North Sea may have been triggered by regional reductions or shifts in principal prey availability. The major threat for harbour porpoises around the world are high levels of bycatches in passive, nearshore fisheries (set nets). Substantial numbers of porpoises, approximately 50% of all animals washing ashore annually, were found to have drowned in Dutch waters.
The Harbour porpoise is a protected species under international, European and Dutch law. Like no other species, it illustrates the complexity of the legal regime for nature conservation in the North Sea. The Harbour porpoise is specifically mentioned in (appendices of) five different international conservation treaties, and is listed on two appendices of the EU Habitats Directive. Several marine sites have been or stand to be designated by The Netherlands as protected areas pursuant to these instruments, inter alia for the Harbour porpoise. The aforementioned instruments, and the Habitat Directive in particular, also contain comprehensive obligations regarding the protection of the Harbour porpoise which apply outside these areas as well. These imply a duty for The Netherlands government to investigate and control the bycatch of porpoises in fishing gear and other causes of mortality.

Sharks, skates and rays in the North Sea

H.J.L. Heessen & J.R. Ellis

Our paper summarises information on commercial landings of Spurdog from the Northeast Atlantic and rays and skates from the North Sea: Spurdog landings have declined to almost zero from a peak of over 60 thousand tonnes in 1963, landings of rays and skates are declining from around 15 thousand tonnes after World War II to very low values in recent years. Nine shark species and eleven species of rays and skates were caught in research vessel surveys. A few examples are given of distributions and time series of catches. The time series show an increasing trend for lesser spotted Dogfish and spotted ray and no clear trends for the other species. Nine out of 13 shark species mentioned in the paper are on the IUCN Red List. A Community Plan of Action for Sharks is under development.

Underwater sound: one of the major threats to marine organisms

R.A. Kastelein

To estimate the audibility and effect of anthropogenic underwater noise sources on the behavior of marine fauna, information is needed about the acoustic parameters of the noise sources, the sound propagation between the noise sources and the animals, the ambient noise, the hearing parameters of the animals, and the animals’ behavioral reactions to specific man-made sounds. At the moment very little information is available, which makes predictions about the audibility ranges and effect-on-behavior ranges very imprecise. Almost all marine animals use sound to survive and reproduce. Not only marine mammals, but also most fish species and lower organisms. Because of their positioning in the food chain, the effect of anthropogenic underwater sound on lower organisms may have the biggest impact on the marine ecosystem. For instance, wind turbine parks in the North Sea increase the underwater background noise level both during the construction phase (pile driving), the operational phase (gear box noise, and maintenance craft), and probably the demolition phase (explosions). It is vital to consider the importance of sound for marine organisms during human activities at sea. In many cases noise reduction measures can prevent negative impacts of human activities on marine fauna.

Climate change in the North Sea: consequences for fish

I. Tulp, R. van Hal, R. ter Hofstede & A.D. Rijnsdorp

The fish fauna of the North Sea has shown major changes in the past decades. In this article we discuss the possible contribution of climate warming to the observed changes, along with other factors such as overfishing and eutrofication. There are indications that climate change has played a role in several developments. The species spectrum has changed, with more southerly species and the disappearance of a few northerly species. Because this development coincided closer with the rise in sea water temperature in the early 1990’s, than with the gradual increase in fishing effort, climate change seems the major driving factor. The new species spectrum is characterized by more smaller sized species. This is likely related to a release from predation pressure, because the large predatory fish have disappeared due to overfishing. We have also observed changes in growth rate, time of spawning and distribution in several flatfish species. Contrasting species with a cold versus warm water preference allows to investigate the mechanisms involved. The role of the nursery areas along the North Sea coast has changed, as several species tend to move into colder, deeper water earlier in life than they used to.

Nourishment: coordination of combating coastal erosion and nature conservation

G.M. Janssen & M.J.C. Rozemeijer

Retaining the coastline despite of continuing erosion of the coast is accomplished by a constant transfer of sand from deeper water to the coast. The extraction of sand and the nourishment are, however, not without environmental consequences. Ecological values of the North Sea and the coast are protected by conservation laws. It is both for coastal defence and nature conservation of great importance that both aspects are mutually aligned. Therefore the government acts with appropriate care, taking into consideration the nature values, legislation, safety and financial consequences. Mitigation measures at the implementation of nourishment can ensure that the adverse environmental effects of combating erosion are reduced.

Wind energy offshore: effects on birds

S. Dirksen, K.L. Krijgsveld & R.C. Fijn

Increasing numbers of wind turbines are built offshore to fulfill the growing demand for renewable energy. Effects of wind turbines on birds on land are well studied in the last decades. Collisions of birds with turbines, disturbance and habitat loss for birds in the impacted areas and barrier effects on flight paths are regularly found effects of turbines. Over the past years increasing numbers of studies are conducted in offshore wind farms, especially in Denmark. Similar type effects as on land, but not of alarming magnitude, have been reported so far. In 2006 the OWEZ wind farm was erected 10-18 kilometres offshore in the Dutch North Sea. A monitoring and evaluation program on the effects of the wind farm on local and migrating birds in the area is in progress. Both research in Denmark and The Netherlands showed that seaducks and the true seabirds (Gannets, alcids) were the main species groups where effects on flight behaviour and occurrence were found. On the contrary, gulls, terns and cormorants seemed to be attracted to wind farms. The OWEZ monitoring program is still running but some preliminary results are discussed in this article. In relation to the foreseen growth of wind energy offshore, especially cumulative effects on bird populations of the proposed wind farms in the North Sea need more attention.

Flora- and fauna communities on hard substrate types in the North Sea

S. Bouma, W.M. Liefveld, W. Lengkeek & H.W. Waardenburg

At the end of the nineteenth century approximately 20% of the North Sea floor was covered by natural hard substrates (mainly peat banks and oyster reefs), providing suitable conditions for diverse flora and fauna communities. Nowadays most of the North Sea floor consists of sand and hard substrate communities have become scarce. Hard substrate communities are now mainly found on artificial substrates like ship wrecks, airplane wreckages and oil platforms. With the development of offshore wind farms new hard substrates are introduced. This article provides an under water view on flora and fauna communities on artificial hard substrates on the North Sea floor and compares its diversity to that of the natural substrate of the Klaverbank.

Green light for migrating birds

J. Marquenie, F. van de Laar & H. Poot

The North Sea is an important migration route for a large number of bird species. Some species are known to be attracted to the lights of the offshore platforms. This is due to disorientation during overcast and/or foggy nights. The birds keep circling around the platforms, and frequently die due to collision with the installation. Over 40% of the observed bird species experienced negatively impacts of the platform lights. The use of new lights with a reduced red spectrum reduced this impact with 50-90%.

Fisheries and Nature Protection Policy: one sea, two separate worlds

A. Blees-Booij & S.J. van Leeuwen

This article focuses on the impact of fisheries on marine nature and the main results of the policy to enhance ecological sustainability of fisheries. We describe this on the basis of reports of The Netherlands Court of Audit and the National Environmental Agency. We conclude that fisheries policy and nature policy need to be integrated in order to protect commercial fish stocks and marine ecosystems as well.

Marine protection in a variable ecosystem, problems and possibilities in the North Sea

H.J. Lindeboom

The Netherlands has designated five areas for marine protection in the Dutch part of the North Sea and is now in the process of setting ecological targets and management measures. However, the North Sea has a highly variable ecosystem. What is the usefulness of static targets in a system that has a high natural and man-induced variability and where the effects of climate change become more and more noticeable. In this article, the variability of the North Sea ecosystem is described, including the occurrence of regime shifts. Possible causes are natural drivers such as changing climate and man-induced pressures such as fisheries. It is argued that static ecological targets are not applicable in such a variable system and that it would be better to set targets for the amount of human pressure that can be allowed. E.g. if we strive for a system as natural as possible, the impact of bottom touching fishing gears should be minimized. Not the presence of certain amounts of organisms, but the absence of human pressures should then become the leading principle in managing Marine Protected Areas.

Protection of biodiversity in the North Sea: policy and management

M. Harte & W. Broeksma

The North Sea, of which the Dutch part covers about 58.000 km2, is important for the Dutch economy and is at the same time our largest nature conservation area. The urge for sustainable development in balance with the marine environment and the Dutch spatial needs for sand extraction and wind energy is integrated in the National Water Plan and the North Sea Policy Plan. These policy plans describe the integral framework for all policy choices in the near future.
The North Sea policy regarding biodiversity is largely determined by international frameworks. This finds its expression in national policy through the assignment and protection of areas with special ecological values in the North Sea. Rijkswaterstaat, responsible for the co-ordination of management tasks, integrates biodiversity needs with other functions through management plans. Among others, participation and area development processes play an important role. In the near future, protection of biodiversity will be supported by the (international) network of North Sea management organizations.

Designating Marine protected area’s on the North Sea

M.M. Giesen

The aim of this contribution is to show how the Dutch authorities will cooperate with important stakeholders to realise marine protected areas (MPA’s), in a process in which transparency, participation and knowledge play a key role.
The North Sea is an intensively used marine area. The designation of Special Areas of Conservation (SAC’s) or marine protected areas (MPA’s) brings along the necessity of involving stakeholders like the fishing industry, the environmental protection organisations and many others. In implementing the Bird- and Habitat directive five MPA’s have been identified (Doggerbank, Cleaver Bank, Frisian Front, North Sea coastal zone, Vlakte van de Raan). Starting point of the process is the adoption of conservation targets for the identified sites. These targets will be adopted for habitattypes 1110 (permanently with seawater covered sandbanks) en 1170 (reefs). In addition to the habitats, targets for several associated species will be adopted: Harbour porpoise (Phocoena phocoena), seals (Phoca vitulina and Halychoerus grypus) and some (migrating) fish species. For the Bird Directive several species of birds will also be subject to conservation targets.
In order to validate the research of IMARES Wageningen UR proposing conservation targets, several workshops with experts and stakeholders have taken place. Special attention will be given to particularly complex protection issues like the protection of the Harbour porpoise. This species appears all over the North Sea, but measures may still be necessary in the designated areas. After the adoption of the report, the next step will be to identify environmental pressures, like fishing activities, with regard to the measures to be taken in order to protect the designated sites.

Policy to conserve marine biodiversity in the North Sea: does it work?

S.J. van Leeuwen & J.P. Beck

In the Nature Balance 2008, the Environmental Assessment Agency of The Netherlands assessed the results of government policy to preserve marine biodiversity in the North Sea. To achieve the targets of nature policy for the North Sea it is essential to improve spatial regulation, the sustainability of the fishery and the water quality. The legal protection of North Sea nature is less developed than the protection of terrestrial nature. This situation will improve now the government started to develop a network of protected areas in the North Sea. The legal protection can be further improved by enforcing the national nature protection legislation on the national continental shelf.

Marine Protected Areas: speed and ambition needed

T.J.A. Rammelt

The North Sea Foundation is of the opinion that The Netherlands should hurry in protecting Marine Protected Areas (MPA’s) at the North Sea. Ambitious levels of conservation should hereby be achieved; aimed at recovery of the marine ecosystem where it is still possible. Also areas that do only qualify as OSPAR MPA’s should be protected. Speed and ambition in protecting these areas is also necessary to give the Ecosystem Based Approach a fair chance at the North Sea. For it is the starting-point of maritime spatial planning. An alternative for Natura 2000 is a system that is primarily focused on regulating human impacts on the marine ecosystem, instead of trying to achieve rigid goals as in Natura 2000. Zoning fisheries activities could serve as an example. The Marine Strategy Framework Directive offers chances for a more integral protection of MPA’s.

Chances for restoration in the North Sea

B.F. van Tooren, W. Broeksma, I.C. Knevel, S.J. van Leeuwen, H.J. Lindeboom, H.L. Schimmel-ten Kate & L. van der Veen

The biodiversity of the North Sea has decreased strongly during the last decades. The last years this decrease gradually receives more attention. There are many causes for the reduced biodiversity, the large intensity of fishery, especially bottom trawler fishery, being the most prominent one. Other problems are water pollution with chemicals, nutrients and waste products, lack of spatial planning, climate change, winning of sand and gravel, wind mills and oil platforms and noises below water (for example as a consequence of the building of wind mills).
The main problems have been identified, and in many cases options for reducing the negative effects are known. Now these options have to be implemented, the creation of marine nature reserves where bottom fishery is not allowed, being the most prominent one.