josianne g. støttrup, claus stenberg, karsten dahl … · blue reef josianne g. støttrup, claus...

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


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


Document

–Stop further erosion


Document

–Re-establish original depth of ~1.2 m (now at ~4 m)


Document

–Restore perennial vegetation and bottom fauna

–Ensure good habitat for fish and shellfish


Nyt rev

• New stone areas at depthintervals:

– 1½-4½m - 7 175 m2

– 4½-7½m - 11 725 m2

– 7½-10m - 8 500 m2


2006 (før)2008200920112012


Bivalves (red) in 2007 replaced in part by crustaceans(green)

and somegastropods

(blue)


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.


Relative abundance of wrasses(Labridae), cod-fish (Gadidae) and Other fish in the multi-mesh gillnets

Wrasse

Codfish

Other fish

Wrasse

Codfish

Other fish


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


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).



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%


< 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



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



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


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:


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.


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

http://lifevideos.eu/videos/?id=LIFE06_NAT_DK_000159_01_EN_HABIT.mp4


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.


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

josianne g. støttrup, claus stenberg, karsten dahl … · blue reef josianne g. støttrup, claus...

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