Sildedød indenfor vej-dæmninger i Kolgrafafjörður fjord
Róbert A. Stefánsson og Menja von Schmalensee, Náttúrustofa Vesturlands Vest Island centret for naturhistorie
Herring (Clupea harengus)
• Three distinct populations based on... – Size
– Growth patterns
– Time of spawning
– Migration
The Icelandic „summer spawning herring“
• Close to the shore
• 0-2 years: North and East coast
• 2-4 years: South
• Spawns from age 4 (27 cm & 180 g)
• Wintering areas different between years/periods
– SE & E
– Breiðafjörður Bay (W)
– Looks for cold waters
Herring mass mortality 1 Feb. 2013
©Róbert A. Stefánsson
52.000 tons!
-similar to the total annual catch of all ships 2009-2012
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Causes of herring mass mortality
• Oxygen deficiency – The lowest oxygen concentration ever measured in Icelandic waters
– High biomass of herring
– Prolonged calm weather
– (In February) Decomposition of herring from the first event
• Causeway and bridge built in 2004?
Lambahnúkur at Kolgrafafjörður fjord ©Daníel Bergmann
Can the causeway and bridge be blamed?
• Tides almost unchanged
• Currents changed
Kolgrafafjörður bridge ©Róbert A. Stefánsson
Kolgrafafjörður ©gauiella.is
• Current studies by IRA and MRI
– Preliminary results suggest that the road was not responsible for the herring death!
• The events will affect the design and environmental impact assessment in the future
Causeway and bridge?
No examples of herring mass mortality of this magnitude!
Herring mortality in Kvænnes, Troms, Norway, 1 Jan. 2012 ©Jan Petter Jørgensen
Birds wintering in Kolgrafafjörður and Hraunsfjörður 2000-2006
0
5.000
10.000
15.000
20.000
25.000
2000 2002 2004 2006 2008 2010 2012
No
. of
ind
ivid
ual
s
Year
0
5
10
15
20
25
30
2000 2002 2004 2006 2008 2010 2012
No
. of
spe
cie
s
Year
Typically: Eiders: 900-1600 Oystercatcher: 200-500 Glaucous gull: 30 Great black backed gull: 10
Birds wintering in Kolgrafafjörður and Hraunsfjörður 2000-2006
0
5.000
10.000
15.000
20.000
25.000
2000 2002 2004 2006 2008 2010 2012
No
. of
ind
ivid
ual
s
Year
0
5
10
15
20
25
30
2000 2002 2004 2006 2008 2010 2012
No
. of
spe
cie
s
Year
Birds wintering in Kolgrafafjörður and Hraunsfjörður 2000-2011
0
5
10
15
20
25
30
2000 2002 2004 2006 2008 2010 2012
No
. of
spe
cie
s
Year
0
5.000
10.000
15.000
20.000
25.000
2000 2002 2004 2006 2008 2010 2012
No
. of
ind
ivid
ual
s
Year
Birds wintering in Kolgrafafjörður and Hraunsfjörður 2000-2013
Increase because of translocation – not population growth!
Herring in max. abundance in 2008
0
5.000
10.000
15.000
20.000
25.000
2000 2002 2004 2006 2008 2010 2012 2014
No
. of
ind
ivid
ual
s
Year
0
5
10
15
20
25
30
2000 2002 2004 2006 2008 2010 2012 2014
No
. of
spe
cie
s
Year
The Change
Species 2000-2005 2012
B-b. gull 8 10.000
Glauc. Gull 27 7.500
Eider 995 4.021
Iceland gull 3 1.100
Shag 6 522
Raven 10 214
Gannet 0 100
Cormorant 8 93
Sea eagle 1 12
Gulls in Kolgrafafjörður ©Róbert A. Stefánsson
Bird census 22 Jan. 2013
~90 thousand birds! 60 thousand gulls 12 thousand fulmars 9 thousand eiders 2500 shag/cormorant >1000 gannets 800 oystercatchers 25 eagles
Fish oil in Kolgrafafjörður ©Kristinn Haukur Skarphéðinsson
Fish oil: A potential threat to birdlife?
Fish oil on shoes ©Róbert A. Stefánsson
Feathers (insulation and flight) destroyed death from hunger or cold!
The effect of herring on local birdlife
• Positive
– Overabundance of food
– Extensive translocations of birds
• Negative
– Fish oil
• Eagle, raven, eider, oystercatcher, merganser and gulls
• No quantitative data on mortality
– Gannets
Immature Iceland gull ©Daníel Bergmann
Immature Glaucous Gulls and an immature Great Black-backed Gull (right) ©Jóhann Óli Hilmarsson
Herring abundance positive for those who survived!
Benthic life?
• Skessuhorn 14 March 2013: „... dead sea creatures everywhere at
the shoreline, e.g. blue mussel, sea urchins, crabs, snails, kelp and more lies lifeless
and black at the shoreline due to the decaying herring in the fjord“
Sampling from the intertidal zone 23-24 June 2013 ©Róbert A. Stefánsson
Comparison to Agnar Ingólfsson´s (1999) data
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• Dramatically decreased biodiversity • Capitella capitata dominant -opportunistic species -tolerant of stressful conditions -often found in polluted waters
What´s ahead?
• The biota will recover in some years time without human interference
• More herring mortality? – More and more unlikely!
The view north to Kolgrafafjörður fjord ©Daníel Bergmann