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PRSB online Supplementary information:
Ecological and genetic impact of Atlantic cod larval drift
in the Skagerrak
Nils Chr. Stenseth, Per Erik Jorde, Kung-Sik Chan, Elizabeth Hansen, Halvor Knutsen, Carl
André, Morten D. Skogen & Kyrre Lekve
• Supplementary table S1 provides the parameter-estimates for the ecological model assuming all fjords
being characterized by fjord-specific values of the parameters. Inclusion of fjord-specific parameters for
the effect of the spawning cod stock in the North Sea and the effect of the net inflow of North Sea water
were judged on the basis of adjusted R2.
• Supplementary table S2 assessing the direct effect of flow (affecting again the transportation of
0
zooplankton into the Skagerrak area), using the model n
t,j =
f(past abundances & environmental
conditions)+γjCt +ηt,j.
• Supplementary table S3 provides the results of the statistical analysis of the ecological model, when only
including the 8 fjords that were found to be consistent with the common-structure assumption (all of
which demonstrating fjord-specific effects; see Supplementary table S1).
• Supplementary information on the linking of our genetic and ecological findings.
Unless given in the following text, references are found in the main paper.
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Supplementary table S1: Parameter estimates for the fjord-specific model, describing the
effect of ocean currents from the North Sea into Skagerrak (φ) and the biomass of the North
Sea spawning stock (ς) on the abundance of juvenile 0-group cod in Norwegian Skagerrak
fjords. The κ’s represent the background local recruitment rate (on log-scale). Inclusion of
fjord-specific parameters for the effect of the spawning cod stock in the North Sea and the
effect of the net inflow of North Sea water were judged on the basis of adjusted R2 (Chan et
al. 2003a; see also Hamilton 1994)*. Notice that no κ estimates are significantly different
from 0, reflecting the 0-group abundance being residuals.
Fjord
Parameter
Estimate
SE
t-value
P-value
1 Torvefjord
ς1
φ1
κ1
κ2
κ3
ς4
φ4
κ4
ς5
φ5
κ5
ς6
φ6
κ6
ς7
φ7
κ7
ς8
φ8
κ8
κ9
ς10
φ10
κ10
ς11
φ11
κ11
κ12
κ13
ς14
φ14
κ14
κ15
0.09
0.15
0.62
0.54
0.14
0.09
1.53
0.14
-0.37
0.41
-0.90
0.38
-0.13
0.11
-1.20
0.24
2 Topdalsfjord
3 Høvåg
4 Bufjord
5 Flødevigen
6 Sandnesfjord
7 Søndeledfjord
8 Risør skerries
9 Stølefjord
10 Kilsfjord
11 Soppekilen
12 Nøtterø
13 Holmestrand
14 Vestfjord
(Oslo)
15 Hvaler
*
0.10
0.09
1.10
0.28
-0.17
0.14
-1.27
0.22
0.06
0.09
0.68
0.50
0.37
0.37
0.99
0.33
-0.35
0.19
-1.81
0.08
0.09
0.12
0.73
0.47
1.01
0.53
1.92
0.07
-0.18
0.07
-2.60
0.02
0.04
0.04
0.98
0.34
0.40
0.20
2.03
0.05
-0.08
0.09
-0.89
0.38
0.18
0.06
3.23
0.00
-0.17
0.25
-0.66
0.52
0.31
0.10
3.23
0.00
-0.04
0.06
-0.69
0.50
-0.62
0.27
-2.29
0.03
-0.03
0.15
-0.17
0.86
-0.32
0.13
-2.44
0.02
0.24
0.08
2.84
0.01
0.38
0.36
1.07
0.30
-0.27
0.16
-1.72
0.10
0.15
0.10
1.54
0.14
0.45
0.42
1.06
0.30
0.09
0.12
0.73
0.47
0.22
0.07
2.91
0.01
0.01
0.11
0.08
0.93
0.28
0.07
4.03
0.00
-0.16
0.31
-0.50
0.63
-0.03
0.12
-0.27
0.79
(Fredrikstad)
See Chan, K.-S., Stenseth, N.C., Lekve, K. & Gjøsæter, J. Modelling the population dynamical
effects of pulse disturbances: the algae bloom along the Norwegian Skagerrak coast in 1988.
Ecological Monographs 73, 151-171 (2003). (ref. 4 in the main paper) and Hamilton, J.D. 1994. Time
Series Analysis, Princeton University Press.
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Supplementary table S2: Assessing the effect of the inflow of North Sea waters on the 0group cod at the Norwegian Skagerrak coast. The table lists two-sided P-values for the
common ocean current effect, γ, influencing the abundance of 0-group cod along the
Norwegian Skagerrak coast. Eight fjords (1, 4, 5, 6, 7, 10, 11 and 14; see legends to Fig. 1)
are used and common parameters are assumed for them.
P-values for net inflow
Period
Direct effect of Current (γ)
I (March 1-15)
II (March 16-31)
III (April 1-15)
IV (April 16-30)
V (March 1-31)
VI (March 16 to April 15)
VII (April 1-30)
0.053
0.021
0.213
0.076
0.014
0.022
0.951
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Supplementary table S3: Common ocean current effect model based on eight fjords. The
parameters ς and φ gives respectively the (direct) effect of the size of the spawning stock in
the North Sea, and the (indirect) effect of ocean current from the North Sea into Skagerrak
on juvenile cod abundance along the Norwegian Skagerrak coast. The κ’s represents the
background fjord-specific local recruitment rate (or more precisely, the residual values: see
the main text).
Parameter
Estimate
SE
t – value
P - value
ς
−0.11
0.11
0.19
0.17
0.38
0.16
−0.016
−0.033
0.091
0.31
0.074
0.047
0.24
0.23
0.26
0.21
0.22
0.23
0.24
0.23
−1.52
2.43
0.78
0.73
1.46
0.79
−0.08
−0.14
0.39
1.32
0.14
0.023
0.45
0.47
0.16
0.44
0.94
0.89
0.70
0.20
φ
κ1
κ4
κ5
κ6
κ7
κ10
κ11
κ14
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Supplementary information on the linking of our genetic and ecological findings.
While subject to considerable uncertainty, the estimated Nm=108 indicates that a substantial
number of cod-larvae transported from the North Sea survives in the coastal locations into
adulthood and may be integrated into the local, coastal populations. Because of the high
annual mortality at all ages, and in particular at juvenile stages (see Julliard et al. 2001), the
number thus estimated from genetic data must be multiplied manifold to reach the actual
number of immigrant juveniles. Using the results reported by Julliard et al. (2001) on the
survival of a 0-group cod in November one year until the mature stage 3 to 4 years later
[being in the order of 0.001836 (≈exp(-3.8)exp(-0.5)exp(-1)exp(-1))] and assuming a fraction
ranging from 0.002479 to 3.372●10-6 surviving the first 7 months (see Chan et al. 2003b), we
may calculate how many larvae in March three to four years earlier 100 mature individuals
correspond to, namely 16,149,747,558 (assuming a mortality rate of 0.14 d-1 for the first 60
days and then 0.14/5 d-1 afterwards) to 21,969,600 (assuming a mortality rate is 0.08 d-1 for
the first 60 days and then 0.08/10 d-1 afterwards). These estimates are likely to vary both with
variation in the inflow of North Sea waters (i.e., variation in Ct) and variation in the size of
the North Sea cod stock (i.e., variation in bt) as well as the sampling variation in the
parameter φj. Using the observed strength of the inflow and the North Sea stock size the
estimated number of larval drift from the North Sea is seen, on average, to have contributed
to about 0.62% to 8.4% of the 0-group cod in Southern Skagerrak (a result which follows
from the 95% C.I. for exp(∑φd Ct , d bt ) ranging from 1.006157 to 1.083787, based on the 8d
fjord model using only significant φ d from March 1 to March 24, and with the products
Ct ,d bt evaluated at their averages computed over the study period).