Integration of Mussel Dredging Into Coastal Zone Management: An

ICES CM 2001/Y:04 Integration of coastal fisheries into coastal zone management: An example from mussel dredging in the Limfjord, Denmark. Peter Blanner County of North Jutland. Niels Bohrsvej 30, 9220 Aalborg, Denmark. Introduction The Danish counties have the obligation to establish long-term regional plans for the spatial use of the terrestrial parts of the county. These plans are passed by the County Councils, they operate with a planning period of 12 years, and are revised every 4 years after two phases of public consultation. Among many other issues, these plans contain a set of water quality objectives for groundwater, surface waters and coastal waters, expressing the fact that the County Councils are responsible for the quality of these water types. The obligation also covers the responsibility to monitor the quality of the waters, to take actions against polluting enterprises or to initiate mitigating actions if the actual water quality does not meet the plans. This regional regulation of water qualities has one important exception: The environmental effects of the run-off of nutrients from arable land cannot be regulated by the county councils, but are subject to national legislation. Another major drawback of the spatial planning obligation within the County Councils is that it stops on the beach, at mean water level (MWL). As the seabed in principle is government estate, the authorities at sea are in Denmark split up between a large number of primarily state offices. There is no authority planning for the use of coastal areas seaward the MWL. As fishery in general - and trawl fishery and mussel dredging especially - has been shown to have an effect on the ecological quality of the fjord ecosystem, the three counties initiated a now well established Coastal Zone Management group with the Ministry for Fisheries (now Ministry for Food, Agriculture and Fisheries) and the Ministry for Energy and Environment in 1987. The aim of this group was to co-ordinate commercial and recreative use of the fjord and to ensure a sustainable long-term development in the area. Background Since the late 1970’ies the three counties bordering the Limfjord – Ringkjøbing County, Viborg County and the County of North Jutland - have undertaken increasingly comprehensive monitoring programmes in the Limfjord, with the aim to describe the main components of the ecological web, and to determine development trends and their causes. One of the scientific cornerstones in this work has been the early marine biological investigations into the food basis for the fish stocks in the fjord, initiated in the beginning of the 20. century (Blegvad 1951). Ever since then, there has been an official record of the commercial fish landings from the Limfjord fishermen, forming an unique reference material through app. 100 years (Flintegaard et. al.1982). Fishing in the Limfjord has up to the late 1970’ies been the living for app. 400 families inside the fjord (Flintegaard et. al.1982), but now only a handful of families can actually make a living from fishing fish in the fjord. The official landings have dropped from an annual level around 4000 tonnes through most of the 20. century and up to 1985 to app. 200 tonnes in the late 90’ies, fig. 1, having great socio-economic impact on the local communities. t/year 7000 6000 5000 4000 3000 2000 1000 0 1940 1950 1960 1970 1980 1990 2000 Fish for consumption Fish for fishmeal Fig. 1. Official landings from commercial fisheries in the Limfjord, in tonnes/y (data from DIFRES) To-day the only profitable fishery in the fjord is mussel dredging, which is carried out by 51 boats, having the necessary license from the Ministry. During the last 10 years the annual landings have been between 60.000 and 120.000 tonnes of mussels (fig. 2), representing a value of app. 120 mio. Danish kr. at the primary level. The landings have increased dramatically as they in the period from 1945 to 1975 did not exceed 20.000 t/y t/ year 120000 100000 80000 60000 40000 20000 0 1940 1950 1960 1970 1980 1990 2000 Fig. 2. Landings of blue mussel from the Limfjord (data from DIFRES). In co-operation with the Danish Institute for Fisheries Research (DIFRES), we have during the last 15 years made annual fish stock assessments as part of the environmental monitoring programme. The major results of these have been published in (Hoffman 1999) and show a dramatic decrease in all demersal fish stocks in the fjord during the latest 10-20 years. Many reasons have been shown to account for this situation, depending on the kind of fish species. One common factor for all species however (plaice, flounder, viviparous blenny, father-lasher, gobies) is the annual occurrence of oxygen deficiencies that strike between 5 and 30% of the whole bottom area of the fjord and last for 2 to 10 weeks (Limfjordsovervågningen 2001), depending on the weather conditions. Based on the bottom fauna investigations in the beginning of the 20. centuary (Blegvad 1951) the occurrence and frequency of oxygen deficiencies can be estimated to once every 4 years in 3-4 small areas on an average through the period 1928-1950. Recent multiple regression analyses on the monitoring data from the Limfjord, initiated by the county councils, have shown that the reduction of oxygen in the bottom water is significantly correlated with nitrogen run-off from land (Møhlenberg 2001), which confirms on a statistical basis the immense impact from agricultural nutrient losses on the ecological conditions in coastal waters. On top of this, there are several other factors influencing the ecosystem. These include the effects of an immense increase in the number of cormorant nests in the Limfjord area, from 45 in 1986, passing 1000 in 1992, to 5.300 in 1999 (Eskildsen 1998), and an increase in the number of harbour seals inside the fjord from app. 700 in 1988 to app. 1.500 in 1998 (DMU 2001). Investigations on the casts have shown that the cormorants in 1998 have consumed app. 800 tonnes of fish, primarily father-lasher, gobies and blennies. Plaice and flounder constituted not more than 10% of the food (Hald-Mortensen 1995). The seals consumed 2.200 tonnes of fish in 1998, where blennies and gobies constituted almost 98% of the meny on an annual base, but with a significant addition of herring in the spring months, based on investigations on the ear-stone countings found in faeces (Holm Hansen et.al. 2001). The size of the eel population in the Limfjord seems to be affected not only by the conditions in the bottom of the Limfjord and in the watercourses in the Limfjord catchment area, but also by a marked reduction in the numbers of glass eels returning to – not only Danish waters, but to most European and American waters (Moriarty 2000). Moreover, special investigations into the effects of the mussel fishery have revealed significant long-time changes in sea bed structure (Dolmer & Frandsen 2000) and short-time changes in bottom fauna composition (Dolmer & Hoffmann 2000) in areas having been dredged in comparison with areas where no mussel dredging has taken place. Fig. 3 shows the changes in the occurrence of pebbles, of mussel spat, and of shell debris inside and outside areas affected by dredgers. 1000 pebbles 500 weight (g) 0 78910 3000 shell debris 2000 1000 weight (g) 0 78910 ) 300 spat -2 200 100 density (spat m 0 78910 station Fig. 3: Weight of pebbles and shell debris and density of juvenile mussels at two stations where there have been fished mussels four months before sampling (sts. 7 and 8) and two stations in two nearby permanently closed areas (sts. 9 and 10). The rates are given as means + 2 S.E. (Dolmer & Frandsen 2000). State-of-the-art The results of the monitoring programmes and the special investigations are clear: - A loss of biological diversity in the fjord, both regarding the fish fauna and the bottom invertebrate fauna, due to several anthropogenic reasons - A loss of habitat, due to the effects of the mussel dredgers. Both effects have been shown not to comply with the quality objectives of the Regional plans from the three counties. The challenge The efforts to reduce nutrient run-off from land have been defined in the two Danish Actions Plans for the Aquatic Environment, passed by the government in 1987 and 1998. The expected ecological improvements are beginning to show up now, unfortunately not quite as clear in the Limfjord as in other Danish coastal areas. As all responsibility for fishery in Danish waters lies outside the legal authority of the county councils, and likewise with the responsibility for nature restoration, the challenge was to create a formal Coastal Zone Management group with the relevant ministries, and to start a public debate on the future utilisation of the fjord. Accordingly the two ministries were invited to join a long term co-operation with the counties in 1988. This forum has now been working for 11 years. The primary aims of the group was to obtain an overview of the situation and development of the fisheries, to initiate research activities to complete our knowledge, and to elaborate a long term plan for a sustainable fishery in the fjord. The planning process was initiated by issuing a proposal for public debate in 1997. All relevant interest groups/stakeholders were invited to join the debate, meetings were held with the stakeholders, a first edition of the plan was sent to everybody who had expressed an interest and they were asked for their comments. The plan The final plan was issued by the 5 authorities in August 2000, with the overall aim - safeguard the natural populations of fish and mussels in the Limfjord - secure sustainable exploitation of the fish and mussel stocks - to reduce the effects of fishery on the sea bed.

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