Evaluation of the Danish mussel fishery: suggestions for an ecosystem management approach

Abstract

In Limfjorden, Denmark, an extensive mussel fishery exploits the wild stocks of Mytilus edulis with annual landings of 80,000-100,000 t of mussels. During the last 10 years the impact of mussel dredging on the ecosystem has been studied, including the effect of resuspension of sediment and nutrients and the impoverishment of in-and epi-fauna assemblages. Furthermore, dredging changes the physical structure and complexity of the seabed which affects mussel growth and interactions among zoobenthic species. The blue mussel constitutes the dominant fraction of the zoobenthic suspension feeders, and is important for the transport of material and energy from the pelagic to benthic systems and the control of phytoplankton biomass. In order to evaluate the impact on clearance capacity of a reduction in mussel densities due to mussel dredging, mussel filtration activity measured in situ has been related to the mixing of the water column and the amount of near-bed phytoplankton. Fishery practice for mussel dredging in Limfjorden is discussed in relation to its known impact on the ecosystem and the ecological role of the mussels, and modifications towards an ecosystem management approach and a more sustainable fishery are suggested. The suggested modifications include: a fishery practice where the mussel beds are thinned out when the mussels have attained good quality, and a transplantation practice of mussels from areas with a high mortality to areas with a high growth rate. Both practices intensify the production in a certain area, leaving other areas open for alternative production or for permanent closure for the benefit of the benthic flora and fauna. In addition, other shellfish species represent interesting new resources for fishing or aquaculture. Habitat restoration, such as the relaying of mussel shells from the mussel industry, is another important management tool that should be included in an ecosystem management approach of the mussel fishery.

Establishment of Blue Mussel Beds to Enhance Fish Habitats

“…Extraction of resources from shallow coastal areas reduces the complexity of the bottom and the habitat quality (Nielsen and Petersen, 2013). In other coastal areas in Denmark, dredging activities with towed fishing gears for fin-and shellfish (Dolmer and Frandsen, 2002;Kaiser et al, 2006) also deteriorate habitat quality. Furthermore, climate change, increased water temperature and acidification may impact coastal habitats (IPCC, 2014; Mackenzie et al, 2014).…”

Clam dredging effects and subsequent recovery of benthic communities at different depth ranges

“…In fact, the effect of wave action has been previously suggested as a forcing function for the restoration and recovery of fisheries-disturbed grounds (Kaiser et al, 1998;DeAlteris et al, 1999;Gaspar et al, 2003;Flåten et al, 2004). It has been reported that the effects of storms may be much greater that anthropogenic stress (Hall et al, 1990;Brylinsky et al, 1994;Dolmer and Frandsen, 2002).…”

“…Dolmer and Frandsen, 2002;Carbines et al, 2004). According to the studies undertaken in subtidal grounds the magnitude of the impacts caused by such fisheries depends on several factors, namely gear type, habitat, depth, benthic communities and scale of disturbance (Collie et al, 2000).…”

Review of recent carrying capacity models for bivalve culture and recommendations for research and management

“…It comprises the above three categories of carrying capacity as well as tradeoffs between all stakeholders in order to meet the demands of both the population (socioeconomic factors such as traditional fisheries, employment and recreational use) and the environment (Dolmer and Frandsen, 2002;Hoagland et al, 2003;Stead et al, 2003;Gibbs, in press). Development of this category is at the heart of Integrated Coastal Zone Management (ICZM) and it must be fully developed so that responsible management decision may be made (Kaiser and Stead, 2003).…”