# 2.8.6. Fishing parameters (Osmose >= 4.3)¶

In the Osmose versions >= 4.3, changes in the parameterization of fisheries have been implemented, although the spirit remains close to the one in versions 4.

## 2.8.6.1. Fishing period¶

There is now the possibility to define a fishing period, i.e. a period when the fishery is active.

 fisheries.period.number.fsh# Number of fishing periods within one year ($$N_{per}$$) fisheries.period.start.fsh# Start of the fishing period (fraction of year, default = 0, $$Y_{start}$$) fisheries.rate.byperiod.fsh# Fishing mortality rate. **Must me in $$year^{-1}$$

Note that the number of values expected in the fisheries.rate.byperiod.fsh# parameter depends on $$Y_{start}$$.

If $$Y_{start} = 0$$, then $$N_{per} \times N_{year}$$ values are expected (one value for each fishing and non-fishing season).

If $$Y_{start} \neq 0$$, then $$N_{per} \times N_{year} + 1$$ values are expected. Fig. 2.8 Fishing period for two values of $$Y_{start}$$

## 2.8.6.2. Fishing seasonality¶

In order to distribute the fishery mortality over the season, the user can define a seasonality file.

 fisheries.seasonality.fsh# Array of fishing seasonality. Must contain $$\frac{N_{step}}{N_{season}}$$ fisheries.seasonality.file.fsh# File containing the fishing seasonalities (must contain $$N_{step}$$ values)

Danger

The sum of fishing seasonalities must equal one over the fishing seasons! No automatic normalisation is performed by Osmose!

## 2.8.6.3. Size selectivities¶

 fisheries.selectivity.tiny.fsh# Selectivities values below which selectivity if forced to 0 ($$\epsilon$$) fisheries.selectivity.type.file.fsh# File containing the selectivity types fisheries.selectivity.type.shift.fsh# Array containing the selectivity periods fisheries.selectivity.type.fsh# Selectivity types (one value per shift period). Must be 0, 1 or 2 fisheries.selectivity.a50.file.fsh# File containing the age selectivities. fisheries.selectivity.a50.shift.fsh# Array containing the $$A_{50}$$ shift periods fisheries.selectivity.a50.fsh# Age selectity (one value per shift period). If set, assumes that fishery selectivity is age-based fisheries.selectivity.l50.file.fsh# File containing the $$L_{50}$$. fisheries.selectivity.l50.shift.fsh# Array containing the $$L_{50}$$ shift periods fisheries.selectivity.l50.fsh# $$L_{50}$$ (one value per shift period). fisheries.selectivity.l75.file.fsh# File containing the $$L_{75}$$ fisheries.selectivity.l75.shift.fsh# Array containing the $$L_{75}$$ shift periods fisheries.selectivity.l75.fsh# $$L_{75}$$ (one value per shift period).

Note that type, a50, l50 and l75 are parameterized in the same way. If the .file parameter is defined, then it is used. If it is not set, then values are defined by using the other two parameters. The shift array contains thresholds, where the values are to change.

The selectivity type must contain 0 (knife-edge), 1 (sigmoid) or 2 (Gaussian).

If one of the a50 parameter, it is assumed that age selectivity is used.

Warning

Only knife-edge selectivity can be used with age.

Note

If only knife-edge selectivity is used, then the l75 parameters are not used.

### 2.8.6.3.1. Knife-edge selectivity¶

Knife-edge selectivity is computed as follows:

$S(L) = 1\ if\ L \ge L_{50}$

### 2.8.6.3.2. Sigmoid selectivity¶

Sigmoid selectivity is computed as follows:

\begin{align}\begin{aligned}S(L) = \frac{1} {1 + exp^{S_1 - S_2 L}}\\S_1 = \frac{L_{50} \times \ln 3}{L_{75} - L_{50}}\\S_2 = \frac{S_1}{L_50}\end{aligned}\end{align}

### 2.8.6.3.3. Gaussian selectivity¶

Gaussian selectivity is computed as follows:

\begin{align}\begin{aligned}S(L) = \frac{F(L)}{F(L_{50})}\\F(L) = exp\left(-\frac{L - L_{50}}{2 \sigma^2}\right)\\\sigma = \frac{L_{75} - L_{50}}{q_{75}}\end{aligned}\end{align}

with $$q_{75}$$ is the inverse cumulative standard normal distribution for the 75th percentile.

## 2.8.6.4. Catchability¶

Fishery cathabilities are parameterized in a similar way as predation accessibility matrix.

 fisheries.catchability.file Name of the catchability file fisheries.catchability.file.cat# Name of the catchability file fisheries.catchability.initialYear.cat# First year when the catchability matrix should be used fisheries.catchability.finalYear.cat# Last year when the catchability matrix should be used fisheries.catchability.years.cat# List of years when the catchability should be used. fisheries.catchability.steps.cat# List of steps within a year when the catchability should be used.

Fishery catchabilities should be provided as a CSV file, with fisheries as column (predators) and species (background and focal) as rows (preys).