sildedød indenfor vej-dæmninger i kolgrafafjörður fjord

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

©Róbert A. Stefánsson

Loftmynd af Google Earth

Herring mass mortality 13 Dec. 2012


Herring mass mortality 1 Feb. 2013



Dauð síld í Kolgrafafirði ©Róbert A. Stefánsson



52.000 tons!

-similar to the total annual catch of all ships 2009-2012

Tínsla og hreinsun

Herring collection in Kolgrafafjörður fjord ©Tómas Freyr Kristjánsson

Counter-measures in Kolgrafafjörður fjord ©Tómas Freyr Kristjánsson

©Bjarni Sigurbjörnsson

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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

Killer whale / Orca ©Daníel Bergmann

Killer whales / Orcas ©Róbert A. Stefánsson

White-beaked dolphins ©Alexa Kershaw

Gannets ©Róbert A. Stefánsson

Birdlife before the herring arrived

Æður ©Daníel Bergmann

Annual winter bird surveys

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

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s

Year

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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


0

5.000

10.000

15.000

20.000

25.000

2000 2002 2004 2006 2008 2010 2012

No

. of

ind

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ual

s

Year

0

5

10

15

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25

30

2000 2002 2004 2006 2008 2010 2012

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. of

spe

cie

s

Year


0

5

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20

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30

2000 2002 2004 2006 2008 2010 2012

No

. of

spe

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s

Year

0

5.000

10.000

15.000

20.000

25.000

2000 2002 2004 2006 2008 2010 2012

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. of

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ual

s

Year


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

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s

Year

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2000 2002 2004 2006 2008 2010 2012 2014

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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 at the causeway by the Kolgrafafjörður bridge ©Róbert A. Stefánsson

Fish oil and fresh herring©Róbert A. Stefánsson

Fish oil on shoes ©Róbert A. Stefánsson

Feathers (insulation and flight) destroyed death from hunger or cold!

Immature sea eagle at Kolgrafafjörður ©Daníel Bergmann

An oystercatcher severely impacted by the fish oil ©Sumarliði Ásgeirsson

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“

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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

sildedød indenfor vej-dæmninger i kolgrafafjörður fjord

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