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    Multi-fleet stock assessment modelling with the Grym

    Request Meeting Document
    Document Number:
    WG-SAM-2021/10
    Author(s):
    J. Liu, S. Wotherspoon and D. Maschette
    Submitted By:
    Mr Dale Maschette (Australia)
    Approved By:
    Dr Philippe Ziegler (Australia)
    Abstract

    Recommendations

    When modelling multiple fleets in a GYM assessment, we recommend the use of the presented extension to the Grym package based on its shown capacity to model more complex fisheries and fishing practices with a high degree of consistency in results.

    Abstract

    Grym is an implementation of the Generalized Yield Model in R that provides greater transparency and extensibility (Maschette et al., 2020, Wotherspoon & Maschette, 2020). This paper describes an extension of the Grym to permit multiple fleets within a season, allowing the Grym to model more complex fishery behavior and evolving fisheries practices. Results from the expansion are compared with existing analyses from the Grym. The model can include vessels using different gear types (e.g. trawl and longline) or identical selectivity. An example is presented for Patagonian toothfish.