Reef restoration in Denmark Example Blue Reef and other current initiatives

Transcription

1 Reef restoration in Denmark Example Blue Reef and other current initiatives Josianne G. Støttrup Contirbutors to the Blue Reef results presented: DTU Aqua: Claus Stenberg (FishStats), Louise Christensen, Jon C. Svendsen AU: Karsten Dahl, Cordula Göke KU: Katherine Richardsen, DHI: Sanne Niemann, EEA: Johnny Reker, Min Env. Food: Else Marie Stamphøj DANCORE Day 2016 Marine Habitats

2 Why do we need to restore shallow cavernous reefs in Danish waters? Map from one fisher involved in boulder extraction 2 DTU Aqua, Technical University of Denmark

3 Some history on marine boulder extraction Stenfiskeri 1880 Starts getting organised; mainly <2 m 1920 Motors in boats. Boulders collected from 2-8 m depth 1925 Introduction of winches and diverpumps. Up to 10 m depth Organised forum for extraction Stenfisker sammenslutning Photo: Svend Christensen 3 DTU Aqua, Technical University of Denmark

4 Some history on marine boulder extraction Stenfiskeri By 1950 Sector developed due to larger construction works (e.g. bridges, etc.); better technology; more ships After 1971 restrictions started: Ramsar convention, New Laws implemented. 1997: Extractions could only take place in designated areas. Most stone fishing decreaed after 2000 and forbidden in Banned in Germany in DTU Aqua, Technical University of Denmark

5 Blue Reef 1831:1.25m; 1930:2.2m; 1970:4m 1991: National Marine Monitoring Program: Not in a good ecological state. Dominated by ephemeral algae Restored to acchieve good ecological state 5 DTU Aqua, Technical University of Denmark 1831: 1.25m m 5

6 Blue Reef AIM: 1) stabilize the uppermost part of the study area, 2) restore crevices of different sizes, 3) restore a diverse topography with varying heights and inclinations 4) restore former shallow reef structures to support functions and services of the habitat. 6 DTU Aqua, Technical University of Denmark 6

7 Blue Reef tons or Norwegian quarry boulders m 2 sea bed covered Shallow part restored from 4m to 1.5m 7 DTU Aqua, Technical University of Denmark Stenberg et al 2015; Støttrup et al. Submitted.

8 Nyt rev New stone areas at depth intervals: 1½-4½m m 2 4½-7½m m 2 7½-10m m 2 8 DTU Aqua, Technical University of Denmark

9 Blue Reef BEFORE Bathymetry, sea bed sediment mapping and geotechnical investigations. Hydrodynamic modelling used for reef design Sediment transport modelling Size of boulders needed Støttrup et al. Submitted 9 DTU Aqua, Technical University of Denmark

10 Blue Reef AFTER Bathymetry in 2009 and 2012 Hydrodynamic data and simulations of conditions after the restoration. Sediment transport modelling Støttrup et al. Submitted 10 DTU Aqua, Technical University of Denmark

11 Blue Reef BEFORE and AFTER biological monitoring of flora and fauna including fish Here I discuss the results on some of the fish data. 11 DTU Aqua, Technical University of Denmark

12 Method - Fishing Before Reef restored After Multi mesh gillnets Fyke nets 12 DTU Aqua, Technical University of Denmark Illustration:

13 Biodiversity and evenness 13 DTU Aqua, Technical University of Denmark 13

14 Relative abundance of wrasses (Labridae), cod-fish (Gadidae) and Other fish in the multi-mesh gillnets Wrasse Codfish Other fish Wrasse Codfish Other fish 14 DTU Aqua, Technical University of Denmark

15 Increased catch of cod 15 DTU Aqua, Technical University of Denmark

16 Broadening of size spectrum of cod Before After 16 DTU Aqua, Technical University of Denmark

17 80000 < 20 cm P>0.55 On Blue Reef: Cod < 20 cm; p< CPUE (number per ½ hour haul) cm P<0.02 Cod cm; p= > 30 cm P<0.001 Cod >30 cm; p= Before After Period CPUE from research trawl surveys Before = After = DTU Aqua, Technical University of Denmark Støttrup et al. 2014

18 Cod behaviour on reef - Method Map of buoys on Læsø Trindel Acustic telemetry: - Before: 17 tagged cod - After: 16 tagged cod - 4 receiver stations - Observation period 180 days 18 DTU Aqua, Technical University of Denmark

19 Results BEFORE Before AFTER After ID TL (mm) Total number days observed % days observed ID TL (mm) Total number days observed % days observed Mean Mean Sum 272 Sum % 94% 19 DTU Aqua, Technical University of Denmark

20 Residence time in weeks 20 DTU Aqua, Technical University of Denmark Weeks

21 Increased residence time of cod Residence time for cod in reef area Before After July August September October November 21 DTU Aqua, Technical University of Denmark Months

22 Stomach content of cod > 20 cm Relative occurrence in stomach (in numbers) Cod >20 cm Bivalvia Small crustecean Big crustacean Gastropoda Cnidaria Mollusca Fish Polychaeta Oct-2007 Oct-2012 Bryzoa Other 22 DTU Aqua, Technical University of Denmark Groups For more detail: Stenberg, Støttrup et al

23 Blue Reef: Restoration of the stone reef attracts purpoises F Mikkelsen et al

24 Results 18 Læsø Trindel Reference PPM per day Year PPM (Porpoise Positive Minute) Mikkelsen et al

25 Best Practice for Reef restoration: ments/bestpracticestonereefenglishversion. pdf See Video at: T_DK_000159_01_EN_HABIT.mp4 25 DTU Aqua, Technical University of Denmark

26 Conclusions Reef stabilised and shallow part restored Fish fauna Before / After was dominated by species belonging to the wrasse family (Labridae). Cod and saithe (Gadidae) were Before infrequent but increased significantly After (factor 3-4). A full BACI may have given more conclusive results as to whether the increase in cod was due to the restored reef. 26 DTU Aqua, Technical University of Denmark

27 Conclusions Size distribution patterns in fish changed to include larger individuals (relative occurrence of fish >14 cm increased by a factor 2) Higher frequency of larger cod in restored reef area relative to surrounding area Activity of cod on the reef increased After. Porpoises spent more time on Blue Reef After restoration 27 DTU Aqua, Technical University of Denmark

28 Gendannede rev i Danmark Aalborg, 2002 Læsø, 2008 Salling, 2013 Århus, 2013 Liseleje, 2012 Vejle Fjord, 2005 Lillebælt, 2014 Amager, 2007 Nørrefjord, 2011 Als, DTU Aqua, Technical University of Denmark

29 Acknowledgements We would like to express our gratitude to all the participants in the field programme and lab. work: Local fishermen: Poul Olsen and Jørgen Rulle DTU Aqua: Jesper Knudsen, Per Dolmer, Thomas Møller, Stine Kjærulf Andersen, Per Ladewig, Hans-Jørn Aggerholm Christensen, Lars Thomsen, Søren Post, Ole Henriksen, Marie Plambech, Nidia Graff Aarhus University: Jan Damgaard Nielsen and Jens Larsen Copenhagen University: Peter Rask Møller, Tammes Menne and Stine V. Christensen