Population modelling software

CASAL2 is an advanced software package developed by NIWA for modelling the population dynamics of marine species.

CASAL2 is NIWA’s new integrated assessment tool for modelling population dynamics of marine species, including fishery stock assessments. CASAL2 expands functionality and maintainability over its predecessor, CASAL. CASAL2 can be used for quantitative assessments of marine populations, including fish, invertebrates, marine mammals and seabirds.


CASAL2 software implements a generalised age-structured marine population model that allows a great deal of choice in specifying the population dynamics, parameter estimation, and model outputs. CASAL2 is designed for flexibility. It can implement an age-structured model for a single population or multiple populations using user-defined categories such as area, sex and maturity. One major change from CASAL is that structural elements are generic and not predefined, but these are easily constructed. CASAL2 models can be used for a single population with a single anthropogenic event (in a fish population model this would be a single fishery), or for multiple species and populations, areas, and/or anthropogenic or exploitation methods.

The time period and annual cycle of CASAL2 is completely defined by the user. Observational data used can be from many different sources, for example removals-at-size or -age from an anthropogenic or exploitation event (e.g. fishery or other human impact), scientific survey and other biomass indices, and mark-recapture data. Model parameters can be estimated using penalised maximum likelihood or Bayesian methods.

As well as generating point estimates of the parameters of interest, CASAL2 can calculate likelihood or posterior profiles and can generate Bayesian posterior distributions using Monte Carlo Markov Chain methods. CASAL2 can project population status into the future using deterministic or stochastic population dynamics, or simulate observations from a set of given model structures.


CASAL will still be maintained by the development team. For information on CASAL you can download the manual from:

CASAL user manual (PDF 3.9 MB)

CASAL software, documentation, example files, and R utility files are also available on request. A copy of CASAL is freely available on request. Requests for CASAL or more information about CASAL can be made by contacting the CASAL2 Development Team.


Research subject: FishModelling