4.10. Predation

The predation.accessibility.file is the CSV file containing the accessibility matrix for every species and stages (if stages are defined, see the parameters predation.accessibility.stage.threshold.sp# and predation.accessibility.stage.structure). This matrix must not be used to define diet preferences but rather to take into account for a difference of positions in the water column (meaning some schools might evolve around the same geographical area but never meet because they do not occur at the same depth).

Table 4.1 Example of a CSV predation accessibility file.
Prey / Predator euphausiids cephalopods < 0.22 year cephalopods > 0.22 year
euphausiids 0.8 0.8 0.8
cephalopods < 0.22 year 0.0 0.0 0.0
cephalopods > 0.22 year 0.0 0.0 0.8

Each line of the matrix corresponds to a prey (including plankton groups), and each column to a predator. The file must be understood as follow: euphausiids (line 1) are accessible to all the predators (columns) by 80%; cephalopods < 0.22 (line 2) are not accessible to any predator; and cephalopods > 0.22 (line 3) are not accessible to euphausiids and cephalopods <= 0.22 but are accessible by 80% to cephalopods > 0.22.

Warning

The order of the rows and columns must follow the indexing of the species and stages (e.g., species0; species1; species2 stage0; species2 stage1; species3).

predation.accessibility.stage.structure defines the Metrics to define the predation/prey size ratio stages (either age or size).

predation.accessibility.stage.threshold.sp# is the thresholds array between accessibility stages, expressed either in years or in centimeters. One threshold value means that two accessibility stages are defined for this species: younge and older than the threshhold. Two threshold values mean that three stages are defined. If value is set to null, then stages are not defined.

predation.predPrey.stage.structure defines the netrics to define the predation/prey size ratio stages, either age or size.

predation.predPrey.stage.threshold.sp# defines the stages for predation/prey size ratios. It controls how many predator/prey size ratios will be defined for each species. If the value of this parameter is set to null, then no stage is defined for predator/prey size ratios.

predation.predPrey.sizeRatio.max.sp# is the array of maximum predator prey size ratio for the different stages of each species. A maximum predator/prey size ratio = 5 means that the largest prey for a fish of this species will be 5 times smaller the fish: \(L_{max_{prey}} = \dfrac{L_{pred}}{50}\)

predation.predPrey.sizeRatio.min.sp# is the array of minimum predator/prey size ratio for the different stages of each species. A minimum predator/prey size ratio = 500 means that the smallest prey for a fish of this species will be 500 times smaller than the fish: \(L_{min_{prey}} = \dfrac{L_{pred}}{500}\)

predation.ingestion.rate.max.sp# is the maximum ingestion rate for each species, expressed in grams of food per gram of fish and per year. It means that, at a given time step, a school will be able to predate at maximum (biomass of the school * max ingestion rate / number of time step in one year).

predation.efficiency.critical.sp# is the critical predation efficiency. Predation success for a school is defined as the ratio of is the biomass preyed over the maximum biomass that can potentially be preyed (and the maximum biomass that can be preyed is defined as biomass of the school * max ingestion rate / number of time step in one year). This critical predation efficiency parameter defines the threshold of the predation success. If predation success is smaller than the critical predation efficiency, the starvation process will be applied to the school and the fish will not grow. Conversely if the predation success is bigger than the critical predation efficiency, the starvation process will not occur for the school and the fish will grow.