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