Oral Presentation Australian Society for Fish Biology Conference 2017

Accounting for depletion levels in juvenile biomass when determining stock status (#140)

Fay Helidoniotis 1
  1. ABARES, Canberra, ACT, Australia

Estimating depletion levels of stock biomass are important for preventing recruitment overfishing. For many fisheries, fishing occurs on both the juvenile and mature portion. In many assessments however, depletion level estimates are limited to the spawning biomass while depletion levels in the juvenile portion is overlooked.  A simulation framework was developed to examine stock depletion in both the mature and juvenile portion and the implications on stock status.  Two fishing scenarios were explored 1) fishing above the size at maturity and 2) fishing on both the juvenile and mature portion. In both scenarios the spawning biomass was depleted to 20%  of the unfished state. Results show that when fishing occurs above the size at maturity, and the spawning biomass is depleted to 20%, the depletion level of the entire stock is only 49%. However when fishing occurs below the size at maturity and both the spawning and juvenile biomass is depleted to 20%, the depletion level of the entire stock might be as low as 36%.  Limiting the reporting of depletion levels to just the spawning biomass and overlooking the juvenile biomass may underestimate stock depletion and have implications for stock recovery.