getYield: Calculate the rate at which biomass of each species is fished

In mizer: Dynamic Multi-Species Size Spectrum Modelling

Calculate the rate at which biomass of each species is fished

Description

This yield rate is given in grams per year. It is calculated at each time step saved in the MizerSim object.

Usage

getYield(object)

Arguments

object

An object of class MizerParams or MizerSim.

Details

The yield rate y_i(t) for species i at time t is defined as

y_i(t)=\int\mu_{f.i}(w, t)N_i(w, t)w dw

where \mu_{f.i}(w, t) is the fishing mortality of an individual of species i and weight w at time t and N_i(w, t) is the abundance density of such individuals. The factor of w converts the abundance density into a biomass density and the integral aggregates the contribution from all sizes.

The total catch in a time period from t_1 to t_2 is the integral of the yield rate over that period:

C = \int_{t_1}^{t2}y_i(t)dt

In practice, as the yield rate is only available at the saved times, one can only approximate this integral by averaging over the available yield rates during the time period and multiplying by the time period. The less the yield changes between the saved values, the more accurate this approximation is. So the approximation can be improved by saving simulation results at smaller intervals, using the t_save argument to project(). But this is only a concern if abundances change quickly during the time period of interest.

Value

If called with a MizerParams object, a vector with the yield rate in grams per year for each species in the model. If called with a MizerSim object, an array (time x species) containing the yield rate at each time step for all species.

See Also

getYieldGear()

Other summary functions: getBiomass(), getDiet(), getGrowthCurves(), getN(), getSSB(), getYieldGear()

Examples

yield <- getYield(NS_sim)
yield[c("1972", "2010"), c("Herring", "Cod")]

# Running simulation for another year, saving intermediate time steps
params <- setInitialValues(getParams(NS_sim), NS_sim)
sim <- project(params, t_save = 0.1, t_max = 1, 
               t_start = 2010, progress_bar = FALSE)
# The yield rate for Herring decreases during the year
getYield(sim)[, "Herring"]
# We get the total catch in the year by averaging over the year
sum(getYield(sim)[1:10, "Herring"] / 10)

mizer documentation built on Oct. 17, 2024, 9:07 a.m.