3.5 Water Column Compartment
49
and reduced recruitment. If Imp total < Critical oil mortality, the “gate model” is
used (Brönner et al. 2015): Modelled natural survival up until recruitment is the
reference level against which oil impact on eggs and larvae is measured (scientifically
most valid approach). If Imp total > Critical oil mortality, oil-induced mortality of
larvae equals reduction in recruitment. Critical oil mortality can be set low for added
conservativity.
ERA Acute, using the gate model, calculates N i as the spawning stock size without
oil impact and N oil,i is spawning stock size where the population in the first year was
impacted by oil-induced mortality.
Recruitment modification: In the gate model, annual recruitment (E) is simulated
as a modification of the potential recruitment weight (W) using probabilities (P) of
periods of favorable and unfavorable conditions.
The expected value of the recruitment weight modification (E(W)) in a randomly
chosen year is:
E(W ) =[P unfavorable ∗ E(W ) favorable ] + [P shift ∗ E(W ) shift ]
+ [P favorable ∗ E(W ) favorable ]
(3.15)
The simulated recruitment is calculated as:
R 1 = 1000 ∗ [W 1/E(W )], R 2 = 1000 ∗ [W 2/E(W )], . . . , R k = 1000 ∗ [W k/E(W )]
(3.16)
Population model: In the population model:
X t represents the number of spawning adults in year t. Average abundance of
the spawning stock is denoted E(X). Three parameters are needed in the iteration
equation, and these values are different for different species depending on whether
they are long-lived (cod) or short-lived (capelin) (Table 3.4):
• Annual natural mortality in percentage (m),
• age at recruitment (tr),
• age at sexual maturity (tm).
Table 3.4 Input data to the
Population model used in
ERA Acute for long-lived and
short-lived species (Table
from Brönner et al. 2015)
Parameter
Long-lived species Short-lived species
Annual mortality of
immatures (%)
20
40
Annual mortality of
matures (%)
20
40
Age at recruitment
3
1
Age at first
spawning
8
5
Maximum age
25
5
49
and reduced recruitment. If Imp total < Critical oil mortality, the “gate model” is
used (Brönner et al. 2015): Modelled natural survival up until recruitment is the
reference level against which oil impact on eggs and larvae is measured (scientifically
most valid approach). If Imp total > Critical oil mortality, oil-induced mortality of
larvae equals reduction in recruitment. Critical oil mortality can be set low for added
conservativity.
ERA Acute, using the gate model, calculates N i as the spawning stock size without
oil impact and N oil,i is spawning stock size where the population in the first year was
impacted by oil-induced mortality.
Recruitment modification: In the gate model, annual recruitment (E) is simulated
as a modification of the potential recruitment weight (W) using probabilities (P) of
periods of favorable and unfavorable conditions.
The expected value of the recruitment weight modification (E(W)) in a randomly
chosen year is:
E(W ) =[P unfavorable ∗ E(W ) favorable ] + [P shift ∗ E(W ) shift ]
+ [P favorable ∗ E(W ) favorable ]
(3.15)
The simulated recruitment is calculated as:
R 1 = 1000 ∗ [W 1/E(W )], R 2 = 1000 ∗ [W 2/E(W )], . . . , R k = 1000 ∗ [W k/E(W )]
(3.16)
Population model: In the population model:
X t represents the number of spawning adults in year t. Average abundance of
the spawning stock is denoted E(X). Three parameters are needed in the iteration
equation, and these values are different for different species depending on whether
they are long-lived (cod) or short-lived (capelin) (Table 3.4):
• Annual natural mortality in percentage (m),
• age at recruitment (tr),
• age at sexual maturity (tm).
Table 3.4 Input data to the
Population model used in
ERA Acute for long-lived and
short-lived species (Table
from Brönner et al. 2015)
Parameter
Long-lived species Short-lived species
Annual mortality of
immatures (%)
20
40
Annual mortality of
matures (%)
20
40
Age at recruitment
3
1
Age at first
spawning
8
5
Maximum age
25
5