Including close-kin mark-recapture data in statistical catch-at-age stock assessments and management strategies

Abstract

Close-kin mark-recapture (CKMR) data can be used on their own to provide estimates of fish spawning stock biomass, adult mortality rate and fecundity-at-age. However, CKMR data can also be integrated directly into a stock assessment. We present a simplified example of integrating CKMR data within the Stock Synthesis assessment framework, and use simulation to evaluate management strategies based on the harvest control rule used to set catch limits for fish stocks off southeast Australia. The simulations are tailored to jackass morwong, Nemadactylus macropterus, a moderately-long lived (up to 46 years) fish species that is believed to have exhibited a regime-shift reduction in recruitment. We identify the sample sizes needed for a CKMR-based management strategy to achieve similar performance to an (optimistically parameterized) catch-per-unit-effort (CPUE)-based approach for this species. A CKMR-based management strategy can perform at least as well as a CPUE-based approach and CKMR data provide information to better estimate parameters such as adult natural mortality. Moreover, CKMR-based management strategies are not subject to the risk associated with CPUE-based approaches related to trends in catchability. The performances of CKMR-based assessment methods and management strategies are likely case-specific, but this paper shows the viability of including CKMR data in next generation stock assessments and harvest control rules.