Selectivity is one of the main components of a stock assessment model, and different assumptions can have a large influence on the stock assessment results and management advice. Selectivity is used to model the vulnerability of fish to the gear as well as the availability. The availability may be related to the spatial stratification of size or age of fish. The most robust method for estimating selectivity is using tagging data.
Typically, selectivity estimate studies are primarily designed to make use of conventional tagging data, which rely on fishery recaptures. As an alternative, pop-up satellite archival tags (PSAT) potentially provide much more information on temporal and spatial specific movements than conventional tags. Perhaps their biggest advantage is that they provide fishery independent observations of tagged fish. The tremendous increase in the use of these tags, especially over the last 10-20 years, has greatly improved scientific understanding of the behavior and movements of a number of fish species. However, no previous study has explored the use of these tags to estimate selectivity.
The study carried out by Carvalho et al. provides evidence that PSAT data can also be used to estimate selectivity. Furthermore, the authors illustrate how the estimated selectivity can assist implementing stock assessments that capture some of the spatial variability of pelagic fish species.
The authors used the blue shark as a case study, which is possibly the most wide-ranging shark species found in temperate, subtropical and tropical waters, with high bycatch rates in pelagic longline fisheries.
Blue shark; photo: Diogo Martins Nunes
Article title: Using pop-up satellite archival tags to inform selectivity in fisheries stock assessment models: A case study for the blue shark in the South Atlantic Ocean
Authors: Felipe Carvalho, Robert Ahrens, Debra Murie, Keith Bigelow, Alexandre Aires-Da-Silva, Mark N. Maunder, and Fábio Hazin