The role of cod in the decline in arctic fishes in the Barents Sea
The 18
thRussian Norwegian symposium Murmansk June 5-7 2018
Edda Johannesen
1, Andrey Dolgov
2and Geir Ottersen
11Institute of Marine Research, Norway
2PINRO, Russia
CoDINA - Cod: DIet and food web dyNAmics, Norwegian Research Council project no 255460/E40
Background
The «borealization» of the Barents Sea….
Frainer et al 2017 PNAS
Boreal fishes are expanding north - Arctic fishes are retracting
Fish communities Atlantic (red)
Central (yellow) Arctic (blue)
Fossheim et al. 2015 Nature Clim. Change
Data from ecosystem survey 2004-2012
2004
2012
2012 2004
Cod has expanded North…..
Change in distribution cod 2004-2012
Blue: decline, Red: increase 0
1 2 3 4 5
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Cod Biomass 3+
Million tons
The most abundant Arctic fishes have declined...
The most abundant Arctic fishes have declined
Boreogadus saida – Polar cod
Change in dsitribution Polar cod 2004-2012 Blue: decline, Red: increase
0 500 1000 1500 2000 2500
Biomass Polar cod 1000 tons
Triglops nybelini
Bigeye sculpin
Liparis fabricii
Gelationus snailfish
Johannesen et al 2017
What is cod’s impact on the local arctic fish fauna?
Frequency of occurrence % of non-target demersal fish in cod diet North of 76°N
Predation
0 1 2 3 4 5 6 7 8 9
FO %
Ecosystem survey 2004 -2017 Based on Briskina (1939)
Competition
Based on Dolgov and Benzik 2014
Diet similarity cod and non target fishes North of 76°N
Cod eats some of the same food
Cod feeds on the local arctic fishes (ca 25-30% of diet by weigth in the Northern Barents Sea) They interact…
But what is the impact?
Cod and the resident arctic fishes
N 1 = N 0 + B − D + I − E
Birth Death
Immigration Emigration
+ Growth
How large is the impact of predation from cod on arctic fishes?
Potentially large but….
depends on several factors…
Currently 1663 million cod 3 years or older
Eating over 5 millions tonn prey per year
• How many cod are found there
• How long do they stay there
• What cod eat there
• How much do they eat relative to the biomass of prey
From Ingvaldsen et al 2014
September 2013 February 2014
The predation on resident arctic fishes
in Northern Barents Sea depends on:
0 500 1000 1500 2000 2500
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Biomass Polar cod 1000 tons
0 100 200 300 400 500 600 700 800 900
Biomass Polar cod Consumed by cod
1000 tons
0 0.5 1 1.5 2 2.5
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Predation index
Triglops nybelini
Bigeye sculpin
Liparis fabricii
Gelationus snailfish
Johannesen et al 2017
Sculpins and Liparids
0 200 400 600 800 1000 1200 1400
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Millions of cod 3+ in the "arctic" Barents Sea In September
NB very crude estimate!
From ecosystem survey 2004-2017:
~200-2000 cod per km2
~20 kg cottids and liparids per km2
Preliminary consumption estimate:
1 gram cottids + liparids per day
How long do they stay in the area?
«arctic» Barents Sea ca 0.7 mill km2
1000 cod eat 1 kg per day
Conclusion
Cod eat arctic fishes in the Northern Barents Sea Cod has partly overlapping diet with arctic fishes
- large cod and predatory arctic fishes compete for fish prey - small cod and planktivorous species compete for plankton Cod likely contributed to the decline in arctic fish species
In addition to changes in abiotic factors and food
Thank you!
0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %
30-40 cm 40-50 cm 50-60 cm 60-70 cm 70-80 cm 80-90 cm 90 cm+
Capelin Other crustaceans Polar cod Pandalus borealis Other fish Sculpins Krill Other invertebrates Hyperiids Liparids
