BigUrchin is a population model. This model was developed to allow accurate examination of the effects of spatial management of an invertebrate fishery, in addition to the effects of conventional management by size limit and fishing effort. It consists of 24 size structured subpopulations, linked by larval dispersal. The size structure is described by von Bertalanffy growth with variation in L¥ among individuals. Larval dispersal is described by a dispersal matrix. Post-dispersal density-dependence is a Beverton-Holt relationship.
The program was originally designed to model the population of the red sea urchin (Strongylocentrotus franciscanus) along the northern California coast. It has been modified to be more generic. While being more generic, the model still has implicit assumptions about the life cycle of the organism that should be considered before using it to model other species.
The model assumes that the population disperses only during the larval phase and adult movement is within each subpopulation's range only. The population has synchronous spawning and a coherent settlement cycle. The current version has explicit assumptions about the size of the organisms but this can be adjusted by scaling the inputs. The growth, mortality and settlement functions are fixed, though parameter values may be varied as described in the Model section.
The model currently has default values corresponding to the northern California red sea urchin fishery. Parameter values of the size structured subpopulation models were estimated from size distribution and growth increment data. The 24 locations correspond to deep and shallow areas in each of the 12 CDF&G sectors which are 10' of latitude. These are likely management areas.
The model can be run in either a batch mode or an interactive mode through a graphical interface. Source of abstract: BigUrchin On-Line User Manual at: http://www.itd.ucdavis.edu/~dale/bigurchin/help.htm