A life cycle model to assess the abundance of black scabbardfish, a widely distributed fish with cryptic migrations

The spatio-temporal dynamics of the black scabbardfish (Aphanopus carbo Lowe, 1839) abundance in the northeast Atlantic was modeled using two linked Bayesian state-space models fitted to fishery-dependent data from trawlers operating to the west and north off the British Isles and longliners off the west coast of Portugal. The stage-structured life cycle models included species vital processes and fishing, and are linked by the migration flow between the two areas. Although data on spawner abundance and recruitment are missing, the hierarchical nature of state-space models allows a convenient representation of black scabbardfish dynamics using reliable data from the two studied areas, which correspond to two of the three main fishing grounds for the species. The approach presented is comparable to the few models developed for other species, such as European eel, where spawning and recruitment occur at restricted and distant regions. This approach is likely to remain the only option for black scabbardfish stock assessment and fisheries monitoring, as it is unlikely that data about the unobserved spawning and early life stages will become available in the near future.