Predation by birds on blue mussel Mytilus edulis beds of the tidal flats of Spiekeroog (southern North Sea)

Abstract

Predation by birds on mussel beds was evaluated in the tidal flats of the East Frisian island Spiekeroog (Lower Saxony, Germany) based on measurements in 1991 and 1994. In May 1991,32 locations with blue mussels Mytilus edulis covered an area of 5.2 km2, 311 t AFDLV blue mussels being available in the whole study area. Areal extent decreased thereafter. In May 1994, there were 20 locations covering an area of only 2.3 km2, a total biomass of 48 t AFDW being available. After the strong spatfalls in the summers of both years, 1290 t biomass were available in the study area in 1991, and 550 t in 1994. Herring gulls Larus argentatus, oystercatchers Haematopus ostralegus and eiders Somateria rnollissjma are the main predators on blue mussels. During one year (1992), oystercatchers were present on 3.7 million bird days, eiders on 1.1 million bird days and herring gulls on 0.7 million bird days. The annual consumption of blue mussels by birds In the intertidal flats was est~mated at 165 t AFDW.The highest proportion of total consumption was by oystercatchers (54 'Yo)), while eiders consumed 39% and herring gulls 7 % . Consumption by all 3 species amounted to 32 g AFDW per m' of mussel bed in 1991 and to 71 g AFDW per m2 in 1994. Predation could be compensated by 12% of production in 1991 and by 29% in 1994. In order to evaluate the relevance of predation for the mussel stocks, the share of the total biomass eliminated annually by predation was assessed on the basis of standing stock and annual production. Predation was responsible for 7 % of total elimination in 1991 and for 15% in 1994.Thus, factors other than predation were responsible for 85 to 93 % of eliminat~on of mussel biomass

Effect of infection by the metacercarial trematodes Renicola roscovita on growth in intertidal blue mussel Mytilus edulis

“…This may be a strategy by the parasite to enhance its transmission to its final bird host (Poulin 1995), since mussels may thus remain within the prey size range of the parasite's final host for a longer period of time. Common bird predators such as the eider Somateria mollissima and the oystercatcher Ostralegus haematopus are known to prefer smaller mussels (Nehls 1989, Hilgerloh 1997. However, growth reduction could also be a side effect of R. roscovita infection, arising from the 3 mechanisms discussed earlier (Poulin 1995).…”

Assessment of Blue Mussel Mytilus edulis Fisheries and Waterbird Shellfish-predator Management in the Danish Wadden Sea

“…This amount is more than three times the amount that was set-aside in the original mussel management scheme. However, diet studies show that the proportion of mussels in the species' diet occasionally can be even higher than those used in our estimations (Hilgerloh 1997;Ens et al 1996a, b;Smit et al 1998;Dernedde 1994;Goss-Custard et al 1996;Hilgerloh 1999;Maagaard and Jensen 1994;Wilkens and Exo 1998;Kubetzki and Garthe 2003), and thus raising the total amount of blue mussels necessary for the species. In addition, the ecological factor used to multiply the physiological food amount to get the ecological food demand is uncertain for both eider (Goss-Custard et al 2004) and herring gull.…”

“…Survey results from the entire Wadden Sea show that the three mussel-eating bird species decreased significantly since 1987 (the eiders since 1996), probably due to food limitations caused by an intensive shellfish fishery in the Netherlands Wadden Sea that supported large parts of the total number of mussel-eating birds (Ens 2006;Blew et al 2005). The bird species feeding habitat differs, while the eiders dive for mussels in the sub-littoral zone (Nehls and Ketzenberg 2002), the oystercatcher together with the herring gull feed on the exposed mussel beds during low tide (Hilgerloh 1997;Ens et al 1996a, b). The species difference in feeding habitat and the shellfish fishery practice between the Netherlands and Denmark is probably the reason for contrasting trends amongst bird species over time between the two regions.…”

Behavioural interactions of seabirds with suspended mussel longlines

“…The main Fig. 1 Diagram showing the typical structure of mussel longline aquaculture (single headrope design) in Bantry Bay invertebrate predator of blue mussels is the shore crab Carcinus maenus (Davies et al 1980;Enderlein et al 2003); however some fish, such as flounders Platichthys flesus L. and plaice Pleuronectes platessa, also predate on young mussels (Hilgerloh 1997). The starfish Asterias rubens and the European Lobster Homarus gammarus also prey on the blue mussel and may themselves provide food for diving seabirds (Dolmer 1998;Cote and Jelnikar 1999).…”