Blue ReefJosianne G. Støttrup,
Claus Stenberg, Karsten Dahl
North Sea Days – Vlissingen, Holland 1-2 October 2015
Before After
DCE, Århus UniversityDanish Center for Environment and Energy
2 DTU Aqua, Technical University of Denmark
Why do we need to restore shallowcavernous reefs in Danish waters?
Map from onefisher involved in boulder extraction
3 DTU Aqua, Technical University of Denmark
What happens when large boulders areremoved from reef areas?
4 DTU Aqua, Technical University of DenmarkPhoto: Karsten Dahl
Project aims:
• To restore/improve the nature quality status for Læsø Tindelreef.
• Document the effect on biological communities
– General flora and fauna (AAU)
– Fish communities (DTU Aqua)
Blue Reef: 2006-2013
5 DTU Aqua, Technical University of DenmarkPhoto: Karsten Dahl
Document
–Stop further erosion
6 DTU Aqua, Technical University of DenmarkPhoto: Karsten Dahl
Document
–Re-establish original depth of ~1.2 m (now at ~4 m)
7 DTU Aqua, Technical University of DenmarkPhoto: Karsten Dahl
Document
–Restore perennial vegetation and bottom fauna
–Ensure good habitat for fish and shellfish
8 DTU Aqua, Technical University of Denmark
Nyt rev
• New stone areas at depthintervals:
– 1½-4½m - 7 175 m2
– 4½-7½m - 11 725 m2
– 7½-10m - 8 500 m2
9 DTU Aqua, Technical University of Denmark
2006 (før)2008200920112012
10 DTU Aqua, Technical University of Denmark
11 DTU Aqua, Technical University of Denmark
Bivalves (red) in 2007 replaced in part by crustaceans(green)
and somegastropods
(blue)
12 DTU Aqua, Technical University of Denmark
What is the netto increase in biological biomass?
• What was lost in Ash-Free Dry Weight (the ”old” bottom – now buried)
– Fauna 220 kg
– Algal vegetation 1.280 kg
– Total 1.480 kg (< 3% infauna)
• What was gained – so far?
– Fauna 3.075 kg
– Algevegetation 7.400 kg
– Total 10.475 kg
Estimated gain of: 6100 kg ASFD algal biomass
2850 kg fauna biomass
For more detail:
Stenberg, Støttrup et al. 2015.
13 DTU Aqua, Technical University of Denmark
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
Abundance of codfish, wrasses, flatfish and other fish in multi-meshed gillnets, before and after the restoration of the reef.
Støttrup et al. 2014
a. Gadidae
West 6-10 m Central 2-6 m East 6-10 m
CP
UE
(e
st.
catc
h i
n n
um
be
rs s
tati
on
-1)
0
10
20
30
40
50
BeforeAfter
b. Labridae
West 6-10 m Central 2-6 m East 6-10 m0
100
200
300
400
500
600
BeforeAfter
c. Pleuronectiformes
Area
West 6-10 m Central 2-6 m East 6-10 m
CP
UE
(e
st.
catc
h i
n n
um
be
rs s
tati
on
-1)
0
10
20
30
40
BeforeAfter
d. Other
Area
West 6-10 m Central 2-6 m East 6-10 m0
5
10
15
20
25
BeforeAfter
15 DTU Aqua, Technical University of Denmark
Not a full BACI - Lack of a control site
CPUE from research trawl surveys (BITS) within 50 km distance from reef.
Cod data: noincrease in abundance Before(2005-2007) to After(2010-2012).
Støttrup et al. 2014
16 DTU Aqua, Technical University of Denmark
Fre
quen
cy
0.0
0.1
0.2
0.3
0.4
Fish length (cm)
0 10 20 30 40 50 60
Fre
quen
cy
0.0
0.1
0.2
0.3
0.4
Change in overall size distribution of fish
Before
After
Fish>14 cm 16%
Fish >14 cm 30%
17 DTU Aqua, Technical University of Denmark
< 20 cm
0
20000
40000
60000
80000
20-30 cm
CPU
E (n
umbe
r per
½ h
our h
aul)
0
50
100
150
200
250
> 30 cm
Period
Before After0
20
40
60
80
100
120
140
160
CPUE from research trawl surveys
Before = 2005-2007
After = 2010-2012
P>0.55
P<0.02
P<0.001
On Blue Reef:
Cod >30 cm; p=0.0004
Cod < 20 cm; p<0.0001
Cod 20-30 cm; p=0.0001
Støttrup et al. 2014
18 DTU Aqua, Technical University of Denmark
Tracking cod throughout the day/night in July 2007 – one cod data
Time of day
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Reg
istr
atio
ns %
0
2
4
6
8
SunsetSunrise
Stenberg, Støttrup et al. 2015.
19 DTU Aqua, Technical University of Denmark
Average number of hours/month per tagged cod spent on the reef at Læsø Trindel before and after the restoration.
Cod (G. morhua)
Month
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May
llog1
0 (h
ours
)
0.0
0.5
1.0
1.5
2.0
2.5
BeforeAfter
20 DTU Aqua, Technical University of Denmark
Stomach content of cod > 20 cm
Cod >20 cm
Groups
Big crustacean
Small crustecean
Bivalvia
Cnidaria
Gastropoda
Mollusca
Polychaeta
FishBryzoa
Other
Relat
ive oc
curre
nce i
n stom
ach (
in nu
mber
s)
0.0
0.2
0.4
0.6
0.8
Oct-2007 Oct-2012
For more detail:
Stenberg, Støttrup et al. 2015.
F
Blue Reef: Restoration of the stone reef attracts purpoises
Mikkelsen et al. 2013.
Results
PPM (Porpoise Positive Minute)
Year
2006 2007 2008 2009 2010 2011 2012
PP
M p
er d
ay
0
2
4
6
8
10
12
14
16
18 Læsø Trindel
Reference
Mikkelsen et al. 2013.
23 DTU Aqua, Technical University of Denmark
www.bluereef.dk
Best Practice for Reef restoration:
http://naturstyrelsen.dk/media/nst/Attachments/Bestpracticestonereefenglishversion.pdf
See Video at:
http://lifevideos.eu/videos/?id=LIFE06_NAT_DK_000159_01_EN_HABIT.mp4
24 DTU Aqua, Technical University of Denmark
Conclusions
• Reef stabilised and shallow part restored
• Significant increase in benthic macrophyte and bottom fauna biomasses
• 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.
25 DTU Aqua, Technical University of Denmark
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 showed a clear daily rhythm (active on shallow parts during the night and passive in deeper parts during the day). Activity on reef increased After.
• Porpoises spent more time on Blue Reef After restoration
AcknowledgementsWe 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