Title: Assessment of the sea cucumber (Isostichopus badionotus) stock in the northeast of Isla de La Juventud, Cuba

Abstract

Patricia Mulén's final project will be published in due time. Until then we share the abstract and a link to a poster.

The sea cucumber Isostichopus badionotus is a valuable commercial species in Cuba, but signs of overexploitation have emerged in several regions. In the Isla de la Juventud fishing area, evaluations indicate catches peaked in 2008, followed by a decline in yield and CPUE, with signs of a recovery only evident since 2021. This study aimed to estimate the density and fishable biomass of I. badionotus in fishing sites northeast of Isla de la Juventud using a spatial and spatiotemporal distribution model (sdmTMB), and to compare its performance with the dynamic surplus production model (SPM) currently used for management. Fishery-independent sampling (2014-2019, 2023) based on referenced GPS transects, along with catch and effort data from PESCAISLA (2005-2023), were used. The sdmTMB model was fitted using the Tweedie GLMM (Generalized Linear Mixed Effects Model) variant, which captured significant spatial and temporal variations. The model estimated densities between 0.02 and 0.09 n/m², with peaks in 2017 and 2023. The fishable biomass reached 422 tons in 2023, surpassing the 100-ton projected by the SPM. The sdmTMB model revealed a higher and more localized biomass than the SPM, which assumes homogeneous populations and no spatial structure. However, the spatial model had limitations due to the lack of accurate georeferencing and absence of fishing effort data per site, which may have led to overestimated biomass. Comparison of the models showed similar trends but differing values. The sdmTMB model's ability to detect local aggregations and the SPM's presentation of a uniform perspective suggest that the SPM might underestimate biomass in dense patches, while the sdmTMB could overestimate if accessibility and connectivity are not accounted for. The study highlights the need to consider both spatial heterogeneity and fishing effort for sustainable management. Additionally, the lack of precise catch coordinates limits the spatial accuracy of the sdmTMB. The high levels of fishable biomass, combined with the absence of catches in certain years (e.g., sites 3 and 6) suggest that fishing efforts are not being focused on areas where the fish stock is most concentrated.