Grym is an open-source implementation of the generalised yield model in R that
provides greater transparency and extensibility (Maschette et al., 2023; Wotherspoon and
Maschette, 2020). This paper describes an extension of the Grym to permit modelling
of multiple fleets within a season, allowing the Grym implementation to model more
complex fishery behavior and evolving fisheries practices. Results from the extension are
compared with existing analyses from the Grym. The model can include vessels using
different or identical selectivities with an example presented for Patagonian toothfish.