Ecosystem Indices

A suite of ecosystem indices are calculated as the model runs. These are output as annual time series. The indices are calculated during the final time step of each year. These include:

• Simpson's diversity index - A measure of species richness (the number of species) and evenness (their relative abundance).
  • Based on population size (annual population is calculated as the mean number of individuals over the number of timesteps in a year)
  • Based on catch (index calculated using catch composition is the same way)
• Large fish index - % of largest size class relative to total
  • Based on biomass
  • Based on catch composition
  • Based on population size
• Predator:prey ratio (see species categorizations below)
  • Based on annual biomass (averaged over number timesteps in year)
• Piscivore:planktivore ratio (see species categorizations below)
  • Based on annual biomass (averaged over number timesteps in year)
• Variability of Landings
  • Uses standard deviation of annual landings over last m years
  • m is an input parameter
• Variability of biomass
  • Uses standard deviation of annual average biomass over last m years
  • m is an input parameter
• True exploitation rate for each species
  • Uses ratio landings of species :total biomass of species
• True exploitation rate for system
  • Uses ratio total landings: total biomass
• Species depletion
  • Whether biomass of species falls below 20% of virgin biomass
• Guild depletion
  • Whether biomass of guild falls below 20% of virgin biomass

Species categorization

Species	Predator or Prey	Complex	Fishery
Spiny dogfish	Predator	Elasmobranch	Fixed Gear
Winter skate	Predator	Elasmobranch	Fixed Gear
Goosefish	Predator	Piscivore	Demersal
Cod	Predator	Piscivore	Demersal
Silver Hake	Predator	Piscivore	Demersal
Herring	Prey	Planktivore	Pelagic
Mackerel	Prey	Planktivore	Pelagic
Haddock	Prey	Benthivore	Demersal
Yellowtail flounder	Prey	Benthivore	Demersal
Winter flounder	Prey	Benthivore	Demersal

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