ICES BERGEN 2004

Effects of predation from 0-group cod on mortality Effects of predation from 0-group cod on mortality rates of capelin larvae in the Barents Searates of capelin larvae in the Barents Sea

Elvar H. HallfreElvar H. Hallfreðsson and Torstein Pedersenðsson and Torstein Pedersen

ICES BERGEN 2004

OVERALL OBJECTIVESOVERALL OBJECTIVES

Can predation from 0-group North-east arctic cod Can predation from 0-group North-east arctic cod have a significant effect on mortality rates of the have a significant effect on mortality rates of the

Barents Sea capelin larvae?Barents Sea capelin larvae?

Part of a multi disciplinary project to study Part of a multi disciplinary project to study recruitment variability in the capelin stock recruitment variability in the capelin stock

(BASECOEX)(BASECOEX)

ICES BERGEN 2004

DATA COLLECTIONDATA COLLECTION

- Two surveys in June/July 2002 and 2003 Two surveys in June/July 2002 and 2003 - Pelagic trawlPelagic trawl- AcousticsAcoustics- Gulf III Gulf III - CTDCTD

- Prey recognition experimentsPrey recognition experiments

ICES BERGEN 2004

CAPELIN LARVA IN 23% OF COD STOMACHSCAPELIN LARVA IN 23% OF COD STOMACHS

Abundance of capelin larvae

Catches of 0-group cod(circles)

andpercent frequency of capelin

larvae in cod stomachs(numbers)

ICES BERGEN 2004

TEMPERATURE ISOCLINES 2002TEMPERATURE ISOCLINES 2002

Average for upper 50m Average for upper 50m

FirstFirst coveragecoverage7.07.0

7.57.5

7.07.0

7.07.0

7.07.0

7.07.0

6.56.5

SecondSecond coveragecoverage

8.08.07.57.5

7.07.0

7.07.07.57.5

7.57.5

Juvenile cod

ICES BERGEN 2004

CAPELIN LARVAE IN 9% OF COD STOMACHSCAPELIN LARVAE IN 9% OF COD STOMACHS

Abundance of capelin larvae

Catches of 0-group cod(circles)

andpercent frequency of capelin

larvae in cod stomachs(numbers)

ICES BERGEN 2004

6.06.0

5.55.5

6.56.5

5.05.05.55.5

5.55.5

5.55.55.05.0

5.55.5

6.06.0

TEMPERATURE ISOCLINES 2003TEMPERATURE ISOCLINES 2003

Average for upper 50m Average for upper 50m

ICES BERGEN 2004

PREDATION IN RELATION TO COD LENGTHPREDATION IN RELATION TO COD LENGTH

Data from the 2002 surveyData from the 2002 survey

Numbers ofcapelin larvae

in cod stomachs

Numbers ofKrill

in cod stomachs

Numbers ofCopepods

in cod stomachs

Length of cod (cm)

0

5

10

15

1.5 2.5 3.5 4.5 5.5

rs = -0.09

0

20

40

60

1.5 2.5 3.5 4.5 5.5

rs = 0.19

0

2040

6080

100

1.5 2.5 3.5 4.5 5.5

rs = 0.38

ICES BERGEN 2004

PREDATION MODEL INCLUDING EFFECTS OF PREDATION MODEL INCLUDING EFFECTS OF ALTERNATIVE PREYALTERNATIVE PREY

stomachCopepodsfstomach

KrilldenvirCopepodscenvir

Krillb

envirlstomachl eCaN __

a = 0.0013 Concentration of capelin larvae increases numbers

b = 0.682 Krill in the environment increases numbers

c = -1.263 Copepods in the environment decreases numbers

d = 0.150 Krill in the stomach increases numbers

f = -0.112 Copepods in the stomach decreases numbers

Maximum likelihood fit, Poisson error distributionMaximum likelihood fit, Poisson error distribution

ICES BERGEN 2004

EFFECTS OF ALTERNATIVE PREY AT AVERAGE EFFECTS OF ALTERNATIVE PREY AT AVERAGE CAPELIN LARVAE ABUNDANCE (328 LARVAE / MCAPELIN LARVAE ABUNDANCE (328 LARVAE / M22))

Data from the 2002 surveyData from the 2002 survey

Average numbersof capelin larvae

per stomach

Krill (n per m2/1000) Copepods (n per m2/10000)

0.00

0.40

0.80

1.20

1.60

0 1 2 3

0.00

0.40

0.80

1.20

1.60

0 1 2 3

Average density of krill in 2002

Average density of Copepods in 2002

ICES BERGEN 2004

PREY RECOGNITION EXPERIMENT PREY RECOGNITION EXPERIMENT

Cod juveniles were fed single Cod juveniles were fed single capelin larvae and slaughtered capelin larvae and slaughtered

at different timesat different times

Time of 50% prey recognition Time of 50% prey recognition was estimated by logistic was estimated by logistic

regression regression

For a 31mm long cod eating For a 31mm long cod eating 10mm capelin larvae it was 10mm capelin larvae it was

75min, giving a digestion rate of 75min, giving a digestion rate of D = 0.55 per hour D = 0.55 per hour

ICES BERGEN 2004

hDNN StomachEaten 24

Numbers eaten per predator per dayNumbers eaten per predator per day

Numbers of capelin larvae eaten per cod per day Numbers of capelin larvae eaten per cod per day

(average 2002 data)(average 2002 data)

2.62455.047.0 1 hhNEaten

MORTALITYMORTALITY

ICES BERGEN 2004

PREDATOR ABUNDANCEPREDATOR ABUNDANCE

Densities of cod juveniles was estimated by acoustical echo Densities of cod juveniles was estimated by acoustical echo integration for each station integration for each station

Target strength for the juvenile cod was determined as:Target strength for the juvenile cod was determined as:

TS = 20 log(L) – 70 ; Ona, E. 1994TS = 20 log(L) – 70 ; Ona, E. 1994

ICES BERGEN 2004

1.11.14.64.6

13.513.5

FirstFirst coveragecoverage

0.90.9

1.51.511.011.012.812.80.40.4

1.01.0

0.10.1

5.05.0

2.02.0

1.81.8

SecondSecond coveragecoverage

PERSENT CAPELIN LARVAE EATEN BY COD PER PERSENT CAPELIN LARVAE EATEN BY COD PER STATION PER DAY IN 2002STATION PER DAY IN 2002

On average for all stations with overlap, 1.9% On average for all stations with overlap, 1.9% of the capelin larvae were eaten by cod per dayof the capelin larvae were eaten by cod per day

ICES BERGEN 2004

CONCLUSIONSCONCLUSIONS

- Per capita predation was affected by abundance of Per capita predation was affected by abundance of euphausiids ( ) and copepods ( )euphausiids ( ) and copepods ( )

- In years with spatial overlap and high densities of 0-group - In years with spatial overlap and high densities of 0-group cod (as in 2002), predation might cause substantial mortality cod (as in 2002), predation might cause substantial mortality on capelin larvae in the Barents Seaon capelin larvae in the Barents Sea

- Capelin larva have low growth rates (2-3% per day) and - Capelin larva have low growth rates (2-3% per day) and the growth/mortality ratio may be reduced due to cod the growth/mortality ratio may be reduced due to cod predationpredation

ICES BERGEN 2004

SOME COD HAD MANY CAPELIN LARVAE SOME COD HAD MANY CAPELIN LARVAE IN THE STOMACHIN THE STOMACH

Number ofcod stomachs

analysed

Number of capelin larvae in cod stomachs