IS THERE A NEED FOR FLAT OYSTER (Ostrea edulis) RESTORATION IN DENMARK?

Nielsen, P. (Speaker), Saurel, C. (Guest lecturer), Freitas, P. S. (Guest lecturer), Barreau, P. D. A. (Guest lecturer), Lene Friis Møller (Guest lecturer), Petersen, J. K. (Guest lecturer)

Activity: Talks and presentationsConference presentations

Description

Historically, the European flat oyster (Ostrea edulis) population in Denmark has been mainly located in sheltered areas on the West coast, i.e. Wadden Sea, Ringkøbing Fjord and in the Limfjorden, and less so in the Kattegat. The current flat oyster population is located in the Limfjorden, where it has survived for more than 165 years after it re-colonized the Limfjorden again, as the resumed salt water inflow increased the salinity in the Limfjorden when the North Sea broke through at Agger Tange in 1825. Although the population has been fluctuating, the wild flat oyster population is currently thriving and is supporting a sustainable regulated dredge fishery with landings up to 320t in 2018/19. For the last three years, the population has increased substantially from 1,500t to 6,000t and a similar trend is observed in 2019. Although, Bonamia disease was registered in 2014 in the Limfjorden and it lost its status as being declared Bonamia free. However, no mass mortality has been observed neither in aquaculture facilities nor in the wild population. The reasons for such increase are mainly due to successive successful natural recruitments and the establishment of flat oysters in new areas. Thus, unlike most other European flat oyster populations, which have reduced and sometimes disappeared from overfishing and disease, the flat oyster population in the Limfjorden is flourishing despite external pressure. A natural question could then be if there is a need for a flat oyster restoration program in the Limfjorden?
The recent discovery of Bonamia, the irregularity in successful recruitment of flat oysters and the recent massive expansion of the invasive Pacific oyster (Crassostrea gigas) in the Limfjorden have raised some concerns regarding the future of the wild flat oyster population in the Limfjorden and aquaculture development. Spat collectors for flat oysters are colonized by Pacific oysters and mixed bottom oyster populations are now emerging in some areas of the Limfjorden. Despite the positive development in the flat oyster population in the Limfjorden, research efforts at DTU Aqua are focusing on: i) developing and securing a hatchery production from a potentially genetically diverse wild population of flat oyster to supply both restoration and aquaculture activities, ii) monitoring the possible development of Bonamia in the Limfjorden, iii) mapping the development, dynamic and interactions of both native and invasive oyster beds in the Limfjorden and iv) investigating potential areas for flat oyster restoration in the Limfjorden but primarily elsewhere in Denmark.

Results and discussion
The presentation will give a short status of the development of both hatchery production and the wild population of flat oysters in the Limfjorden. It will also describe the various challenges facing the industry regarding: i) recent observations of the parasite, Bonamia ostrea, ii) competition from non-native species, iii) natural fluctuations in population size and recruitment but also new possibilities for marked development regarding i) breeding programs, ii) restoration and aquaculture production. Furthermore, an outline of perspectives for initiating flat oyster restoration programs in Denmark will be presented.
Period10 Oct 2019
Held atEuropean Aquaculture Society Meeting 2019
Event typeConference
LocationBerlin, Germany