Using multivariate state-space models to examine commercial stocks of redfish (Sebastes spp.) on the Flemish Cap

Abstract

There are three different species of redfish (Sebastes spp.) in the waters of the Flemish Cap (Division 3M, NAFO Regulatory Area): S. fasciatus, S. mentella, and S. norvegicus. Historically, S. fasciatus and S. mentella have been managed together as a single stock because of similar biology and difficulty in species identification. Here we use multivariate autoregressive state-space models to examine the abundance trajectories of the three species and to determine whether they can be treated as a single stock for management purposes or whether they should be treaty separately. We also included covariates to evaluate relationships with climate, commercial catch, and the abundance of predators and (or) competitors and prey. We did two separate analyses: (i) a single-period analysis over the full time series and (ii) a blocked, two-period analysis over different regulatory periods. In both analyses, the best-fit model included separate trajectories for each species at each depth but one overall stock growth rate; both also included commercial catches as a covariate. These analyses suggest that a single assessment for the Sebastes complex is acceptable.