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Trilateral Wadden Sea Plan Eighth Trilateral
Governmental Conference
on the Protection of the
Wadden SeaStade, Germany,
October 22, 1997
10 Marine Mammals The Common Seal, the Grey Seal and the Harbour Porpoise may be regarded as indigenous Wadden Sea species. Water is the main or exclusive element of these marine mammal species. The year round, the Common Seal uses other habitats than water, such as sand banks in the tidal area and beaches, the Grey Seal uses also dunes and salt marshes. All these habitats are essential for the maintenance of the vital biological functions of seals, such as whelping, nursing, breeding, moulting and feeding.
The species groups with an overlapping habitat demand, such as marine mammals and birds, need special attention because of their vulnerability to disturbance and pollution, and a possible food resource competition with Man. As top predators, these species have an important indicative function of the quality of the Wadden Sea ecosystem. Seals are the ambassadors and most attractive species of the Wadden Sea Area. Therefore, the opportunity for tourists to observe seals in their natural environment should be maintained.
Status The present and short term conservation status of Common Seals, Grey Seals and Harbour Porpoises in the Wadden Sea Area is primarily determined by two developments: disturbance, as a result of various human activities (such as tourism and recreation activities, air traffic, some military activities) and pollution, in particular, by heavy metals and organic micro-pollutants. The present situation regarding food supply does not influence the conservation status of seals. Whilst measures to reduce pollution have to be taken mainly outside the Wadden Sea Area, measures to protect seal habitats have to be achieved within the area itself by creating seal reserves in such a way that disturbance is limited to a minimum.
In the years after the virus epidemic in 1988, the population of the Common Seal has shown a rapid recovery. During coordinated flights in the entire Wadden Sea Area, a total of 12,927 seals was counted in 1997, of which 2,783 were pups.
Today, two Grey Seal breeding sites exist in the Wadden Sea Area. One near the island of Vlieland in The Netherlands with about 315 animals, where at least 30 pups are born each year, and one small reproductive colony of about 30 to 40 animals in Schleswig-Holstein, Germany.
According to sightings, the Harbour Porpoise mainly inhabits coastal waters not deeper than
20 m.
Systematic aerial and shipping surveys, which were carried out in the framework of the European Commission project SCANS and a project of the University Kiel in the entire North Sea and parts of the Baltic Sea, have documented that the area west of the Knobsände off Amrum and the island of Sylt is the most densely populated one within the German Bight. Long-term surveyscarried out by volunteers on the islands Amrum and Sylt, documented that Harbour Porpoises in this area also occur directly near the beach the whole year round. Compared to other parts of the North Sea, there is an extraordinarily high density of mother calf-groups (the suckling-period of this species lasts approx. 8 months) in this area. It can be concluded that this area is an important rearing area for Harbour Porpoises.
Targets
Viable stocks and a natural reproduction capacity of the Common Seal including juvenile survival.
Viable stocks and a natural reproduction capacity of the Grey Seal including juvenile survival.
Viable stocks and a natural reproduction capacity of the Harbour Porpoise.
Assessment The term "viable stocks" has to be specified in such a way that a connection with management is possible. The numbers that can be expected according to the natural carrying capacity of the Wadden Sea Area depend on factors that are defined by the fish stocks in the North Sea, suitable undisturbed haul-out sites and on the effects of diseases and parasites in dense populations. The absence of significant human impact on the population, to be judged and monitored in the course of years, is the standard for the first part of the Target.
The "natural reproduction capacity" of seals depends on many factors - water quality, disturbance, population size - and can, probably, not be expressed by a simple number or range. Based upon regular best expertsí judgement, it will have to be assessed whether the reproduction can be regarded as natural. This second part of the Target is one of the main, still not really solved, problems of the last decades: the reduced reproduction rates due to PCBs and other organic micro-pollutants. The production of 0,85 - 0,95 pup per mature female per year is the proposed reference for the natural reproduction capacity.
In terms of numbers, the present Common Seal population is regarded as viable. However, the juvenile mortality is very high (over 40% instead of 20 - 25%). Despite the good protection of the main resting and nursing places, the environmental conditions are still not satisfactory.
The present Grey Seal population in the Wadden Sea Area cannot be regarded as viable. The stock in The Netherlands mainly grows because of immigration from Great Britain. Grey Seals need high sands (not flooded during high tide) or beaches and salt marshes during whelping and nursing. There ought to be means to keep areas free of interference in a flexible way. Furthermore, there is not enough knowledge about the natural reproduction capacity of Grey Seals in the Wadden Sea Area.
For Harbour Porpoises, a detailed assessment is not yet available due to limited knowledge. Small cetaceans are especially sensitive to disturbance and effects from high-speed boats (e.g. jet-skis) and to the impact of fishery (by-catch). Possible effects of leisure boats and ships are strong underwater noise, which disturbs the communication and orientation system of small cetaceans, the risk of collision with high-speed boats, which can hardly be located by wales, and disturbance causing permanent separation of mother and calf.
By-catches from fishery are a main threat to Harbour Porpoises. Based on an extrapolation, the number of animals killed in Danish gill-nets in the whole North Sea is some 7,000 animals per year.
How to proceed Both with regard to the chemical and physical conditions - i.e. disturbance level - of the habitat of Common and Grey Seals, as well as, Harbour Porpoises, improvements are necessary.
For a better assessment of the status of the Grey Seal in the Wadden Sea Area, the general knowledge on reproduction and mortality should be improved. The same holds true for Harbour Porpoises because, at present, there is not enough knowledge about this species to be able to develop references, neither for viable population nor for natural reproduction parameters.
10.1 Trilateral policy and management Common and Grey Seal
The 'Agreement on the Conservation of Seals in the Wadden Sea' (Seal Agreement) was enacted on October 1, 1991 as the first agreement as defined in Article 4, of the Convention on the Conservation of Migratory Species of Wild Animals (The Bonn Convention). The agreement was concluded between the Wadden Sea states with the aim to cooperate closely in achieving and maintaining a favorable conservation status for the Common Seal population of the Wadden Sea Area. The Seal Agreement contains provisions, amongst others, on research and monitoring, on taking and on the protection of habitats, which have been specified in the 'Conservation and Management Plan for the Wadden Sea Seal Population 1991 - 95' (Seal Management Plan) and the revised Seal Management Plan 1996 - 2000. The latter also includes additional measures for the protection of the Grey Seal.
Regarding the implementation of the Targets for the Common and the Grey Seal, reference is made to the specific measures related to the different habitat types and, especially, to the Seal Management Plan 1996 - 2000. The revised Seal Management Plan is based on a comprehensive evaluation of the first Seal Management Plan 1991 - 1995, as well as, the results of the Joint Seal Project and the principles and guidelines concerning taking of seals, rehabilitation and releasing of seals, which are given in the § 60 of the Leeuwarden Declaration. (See LD §56 - 60; Conservation and Management Plan for the Wadden Sea Seal Population 1991 - 1995, ED §26; Conservation and Management Plan for the Wadden Sea Seal Population 1996 - 2000, SO March 1996).
Measures for the implementation of the Targets on seals are especially listed under "Required effort and objectives" and "Actions in 1996 - 2000" in the Seal Management Plan which are divided into actions on the trilateral and national level. These actions include measures which should be implemented in different habitats and for different purposes, such as research, monitoring and protection of habitats. In the following, the existing trilateral decisions, which have already been taken in the Esberg and Leeuwarden Declarations, are mentioned and some new proposals regarding trilateral policies, management measures and actions are listed. The general management measures regarding specific habitat types such as tidal area, salt marsh and offshore area, can also be relevant for marine mammals in general.
According to the Leeuwarden Declaration §61, the principle and guidelines "to reduce the current number of seals taken from, and released to, the Wadden Sea to the lowest level possible" should also apply to the Grey Seal. Therefore, the "Conservation and Management Plan for the Wadden Sea Seal Population 1996 - 2000" (Senior Officials, March 1996) includes "Additional measures for the protection of the Grey Seal".
Harbour Porpoise
This species was not taken into special consideration during the decisions of the last Trilateral Governmental Conferences. In the framework of the Agreement on the Conservation of Small Cetaceans of the Baltic and the North Sea (ASCOBANS), the Harbour Porpoise was included and the Wadden Sea Conferences welcomed the agreement and the cooperation with its respective bodies (ED §28 and LD §63).
10.1.1 It is the aim to protect important breeding/rearing areas of the Harbour Porpoise in the Wadden Sea Area and adjacent areas through appropriate measures.
10.1.2 The public will be informed about small cetaceans in the Wadden Sea Area and the North Sea on a common basis in cooperation with ASCOBANS.
10.2 Trilateral projects and actions 10.2.1 The consideration, on the basis of scientific evidence, of the designation of areas in the Wadden Sea Area and adjacent areas off Sylt and Amrum, as well as, in the Danish part, as areas of special concern, especially as breeding/rearing area for the protection of the Harbour Porpoises.
10.2.2 An investigation, in consultation with responsible local governments and relevant groups into the available possibilities for closing, in a flexible way, areas where Grey Seal pups rest regularly.
10.2.3 An investigation of technical solutions and improvements in consultation with responsible fishery groups, for the prevention of incidental catch of marine mammals in drift nets and set nets, with the aim of minimizing by-catch.
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