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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Disturbance of waterbirds by water-based recreational activities - a review
Auteurs :	Karsten Laursen, Auteur ; Thomas Bregnballe, Auteur ; Ole Roland Therkildsen, Auteur ; Thomas Eske Holm, Auteur ; Rasmus Due Nielsen, Auteur
Type de document :	Article
Dans :	Dansk Ornitologisk Forenings Tidsskrift (111(3) 2017)
Article en page(s) :	96-112
Langues:	Anglais
Résumé :	Thousands of waterbirds breed, stage, moult and winter in Danish waters in concentrations that require the authorities to protect them according to the EU Birds Directive. In addition to waterbirds, the more than 7000 km of coastline around Denmark offer excellent opportunities for recreational activities. This is reflected in the 43 million annual visits to these habitat types by 64% of the adult Danish population (Friluftsradet 2013, Laursen etal. 2016a) and in that 67% of all tourism in Denmark is connected to the coastal zone (Regeringen 2016).However, human activities may disturb birds and displace them from preferred sites. In this paper we compile current knowledge about water-based recreational activities in Denmark in relation to documented and potential disturbance effects on waterbirds during different seasons. Our review of water-based activities includes all human activities along the coast and on the water surface of marine and fresh water sites.The number of members of the Danish sailing associations increased markedly in the 1970s but has been stable in recent years (Fig. 1). In contrast, the number of members of the Danish Canoe and Kayak association has increased steadily since the 1930s. In addition to the number of members in clubs, a large and increasing number of both residents and tourists use Danish waters for kayaking. There is no exact information on the numbers of pleasure boats in Denmark. In 2003, the numbers were estimated at 41 000 sailboats and 12500 motor boats over 6 m in length, but in addition there are many smaller boats not included in these official statistics. Surveys in different parts of Denmark recorded about 3000 small and medium sized vessels at harbours or anchored in Ringkobing Fjord, West Jutland, in 1981-1982 and about 1000 small and medium sized boats in the Danish section of Wadden Sea annually in 1980-1995 (Eskildsen 1984, Laursen et al. 1997). In the same areas, an average 45 vessels were active in Ringkobing Fjord (with a maximum of 300 vessels active at the same time) and 75 vessels (and 10-15 wind surfers) active in the Danish part of the Wadden Sea (maximum of 110 vessels). In addition, 500 active vessels (sailboats and motorboats) were recorded south of Funen during 1991-1992 with a maximum of 1000 present at the same time (Petersen 1995).The extent of disturbance depends on the spatiotemporal overlap between recreational activities and the occurrence of birds, i.e. disturbance can only take place if human activities and birds occur at the same time and at the same place. In Ringkobing Fjord there was a great overlap between human activities and birds in autumn (August-September; Eskildsen 1984). In the Wadden Sea, there was only a modest overlap between human activity and dabbling ducks, but a large overlap between waders and human activities in May and again in August-October (Fig. 2; Laursen et aL 1997). Surveys in Nibe-Gjol Bredning in Limfiorden in July-December 1985-89 showed that the largest overlap took place in September-October where disturbance from motor boats and by wind surfers occurred on average twice a day and once a day, respectively, in the study area (Madsen 1998).Several studies show that flight distance of waterbirds varies depending on a range of factors such as the species, the number of individuals in the flock, weather conditions, body size and hunting induced shyness (Blumstein etaL 2003, Laursen etaL 2005, Whitfield etaL 2008, BregnbaIle etaL 2009a). The escape distance or flight distance is often used to obtain information about the sensitivity of birds to different types of human activity.The results from various studies (Tab. 1) suggest that inflatable boats, rowboats and kayaks cause shorter mean flight distances (165 m) compared to sailboats and motor boats (335 m), wind and kite surfers (390 m) and personal watercraft (765 m). The average flight distances for waterbird species are estimated from the information in Tab. 1.Studies indicate that small boats, sailboats and people moving slowly and following certain routes cause modest disturbance, whereas motor boats, wind surfers and kite surfers that move fast, are noisy or shift direction cause extensive disturbance (Regular 2007, Anon. 2012). In Fig. 3, several types of boats are assessed and given a score (1-10 units) depending on the impact on waterbirds. Tab. 2 demonstrates how increasing human activity generally influence bird abundance at site and population level.Body condition of individual birds has been used to express the level of disturbance effect at population level in e.g. geese (Madsen 1995). If the disturbance continues and includes most of the available habitats, a population decrease can be the result. Another measure of a disturbance is the size of the area on which birds are prevented from feeding. If the birds are steadily displaced from a site, they cannot benefit from the food resource left behind. If there is no alternative feeding site, and food is scarce, the size of the lost feeding area can be estimated as the number of individuals the area could have supported if they had not been displaced (Gill etaL 1996). In practice on water, the area affected by a disturbance (F) can be estimated as (Platteew they swam away at distances of 100-500 m. For larger cabin boats, and other boat types with an out-board motor, the escape distance increased to 1000 m and the degree of disturbance varied from modest to intensive, where birds left optimal feeding sites (disturbance level 1 and 2 in Tab. 2; Eskildsen 1984). Rowboats and canoes caused large disturbances because they often sailed in shallow water areas and in areas with otherwise low activity. The most extensive disturbance was caused by small sailboats, wind surfers and water-skiers that were active in shallow water at high speeds and often changed direction.In Limfiorden, northern Denmark (1985-1989), birds stopped feeding when disturbed by motor boats and wind surfers. For Mute Swan Cygnus olor, breaks in feeding lasted between 22-32 min., for Eurasian Wigeon Anas penelope 2024 min. and for Common Coot Fulica atra, 9-11 min. The Mute Swans compensated for the lost feeding time by feeding after the disturbance, whereas Wigeon and Coot did not compensate (Madsen 1998).Studies in three estuaries in England showed that birds were easily disturbed by human activity on the water body and on the intertidal mudflats compared to activities along the shoreline (Liley et al 2011). Although wind and kite surfers only constituted 2% of all activities, they caused most of the disturbances because of long flight distances. This is because these types of sailing are particularly disturbing (Fig. 6), and estimations based on GPS measurements showed that wind and kite surfers displaced birds from 8 ha on average and canoes and kayaks displaced birds from 1.7 ha. For comparison, dogs off leash displaced birds from 3 ha on average.Numbers of Great Cormorant Phalacrocorax carbo, Black necked Grebe Podiceps nigricollis, Common Goldeneye Bucephalus clangula, Common Pochard Aythya ferina, Red-breasted Merganser Mergus serrator, Common Teal Anas crecca and Eurasian Oystercatcher Haematopus ostralegus are reduced, or the birds leave a site entirely, when sailing activities occur (Parr 1974, Hume 1976, White 1986, Fox et al. 1994, Blew Laursen 2014). Sailing activities also prevented moulting Eiders from feeding on a large mussel bed. However, the mussel bed was intensively used during wintertime, when sailing activity was low (Fig. 8). In the northern part of Kattegat between Denmark and Sweden, about 100000 Common Scoters Melanitta nigra moult and the sites the birds used were on average at least about 10 km from sailing routes used by ships and pleasure boats. The result indicates that the Common Scoter avoids sites adjacent to sailing activity (Petersen (2) a screening of potential threats to waterbirds from recreational activities in important bird areas; (3) identification of appropriate measures aimed at ensuring protection of the most valuable areas for waterbirds in different regions of Denmark; and (4) a better understanding of how zonation of different recreational activities may ensure that single localities remain valuable to waterbirds.

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