Folie 1 - Naturstyrelsen

Cod investigations at the artificial reef area Nienhagen,
Western Baltic
Territorial waters of the state of Mecklenburg -Western Pomerania
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Location
Main aims
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Modifying an aquatic ecosystem
Prime reason for Nienhagen reef deployment was to improve, increase, or at least
maintain the fishery resources in this local area
Assess the species richness of fish and macroinvertebrates
Assess the abundance, biomass, growth, age composition, sex ratio etc. of the target
species cod inside the reef and at a reference site
Describe the local behaviour, the local movement inside the reef and the migration
pattern out of the reef
Increase commercial fishing harvest for alternative capture methods, e.g. cod pots
Create recreational skin diving sites
Create submarine tourism sites
Control fishing mortality
Habitat protection
Method-1
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Used gears:
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1 Gill net: mesh size 60 mm; length 45 m, drop 2.4 m
1 Gill net: mesh size 55 mm; length 45 m, drop 2.4 m
1 Trammel net: mesh size 50/350 mm; length 50 m, drop 2.0 m
2 Nordic coastal survey nets: mesh size 6.5–15–20–26–35–50–70 mm
length 49 m each, drop 2.0 m
5 Eel basket chains
Several Cod pots
Annually 8 to 12 surveys, launching time: 24 h
Method-2
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Marking and tagging:
Sonar (acoustic) tags
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„Coded“ (with ID number)
pingers send acoustic pings at 69 kHz
Floy tags (www.floytag.com)
VR2W singel channel receiver
Results cod abundance
Local behaviour of cod and growth
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No. tagged cod 2007-2012: 2.731
Year
2007
Recapture rates
2008
2009
2010
2011
2012
ges.
24,5
11,3
29,6
8,1
23,14
3,80
[%]
inside
ouside
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15,3
0,5
12,9
2,9
21,1
2,4
Multiple recature in cod pots: 12 times within 8 month
30,0
2,6
Recapture sites (outside the reef)
D 111 Dänemark
D 112
D 114
D 110 D 120
Seegebiet 1
21 WF O S T S E E Fehmarn
D 107
D 101
D 102
D 103
Seegebiet 2
14 WF D 314
See‐
gebiet 4 43 WF D 301
D 305
Mecklenburg‐
SG 3
23 WF Length of stay within the reef
Marke
Juni
ID‐Nr. 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1
keine Signale
tot
5219
5220
5221
5222
5223
Marke abgerissen im BH
5224
5225
tot
k. Signale
tot
5226
5228
5229
5231
5232
5234
5235
5236
Legende:
5237
Hälterungszeit
5238
Aufenthalt am Riff
5239
Gefangen in Fischfalle
5240
1 Te ils tric h 6 h; 0-6, 6-12, 12-18, 18-24 Uhr
5241
5242
5243
5244
5245
5246
5247
5248
5249
Juli
2
3
4
5
6
7
8
Juli
August
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21
tot, am 21.09. neu markiert
neu markiert
tot, am 21.09. neu markiert
T M entfernt
Stellnetz gefangen
T M entfernt
T M entfernt
neu markiert
Résumé
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The biomass and abundance of the target species cod at the reef
Nienhagen is about 30% higher comparing with a reference site.
The reef structures offer space for preventing small fish from predation
by lager fish; and young cod from cannibalism
Unsolved is still the question whether the reef increases the biomass of
fish on that site or attract fish from the surrounding areas
There is evidence that cod stay for several month in the reef or return
to the reef
The reef does not influence the year class strenth of cod, due to its
small dimension (hundrets of reefs will do!)
The reef is a small marine park and protect this area from beeing
exploited by fishing activities
Thank you for your attention!
Men at work/Down Under