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INCLUDING DEPREDATION IN STOCK ASSESSMENTS

INCLUDING DEPREDATION IN STOCK ASSESSMENTS. COLTO DEPREDATION WORKSHOP 2016. WHAT ARE THE QUESTIONS?. What depredates toothfish? Where, when, how often? Does it matter for fishery efficiency? Does it matter for stock status? Does it matter for the predators?. WHAT IS A STOCK ASSESSMENT?.

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INCLUDING DEPREDATION IN STOCK ASSESSMENTS

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  1. INCLUDING DEPREDATION IN STOCK ASSESSMENTS COLTO DEPREDATION WORKSHOP 2016

  2. WHAT ARE THE QUESTIONS? • What depredates toothfish? • Where, when, how often? • Does it matter for fishery efficiency? • Does it matter for stock status? • Does it matter for the predators?

  3. WHAT IS A STOCK ASSESSMENT? Harvest Strategy: • Ensure enough fish survive to breed (MSY) Ecosystem-Based Harvest Strategy: • Ensure enough fish survive to breed • Ensure enough fish to support predators • Ensure enough fish to eat prey species

  4. WHAT IS A STOCK ASSESSMENT? • CCAMLR OBJECTIVES • 50% ESCAPEMENT • <10% CHANCE OF BEING <20% ESCAPEMENT

  5. WHAT IS A STOCK ASSESSMENT? :)# Model “Reality”

  6. WHAT IS A STOCK ASSESSMENT? Index of abundance • Surveys • Tag recaptures • CPUE time series • CAUTION – CPUE based assessments can create an incentive to over-estimate depredation

  7. WHAT IS A STOCK ASSESSMENT? Population Dynamics Model Spawning Stock Recruits

  8. WHAT IS A STOCK ASSESSMENT? Population Dynamics Model Spawning Stock • Feeding • Growth • Mortality • Maturation • Movement • Spawning • Fertilization • Dispersal • Feeding • Growth • Mortality • Settlement Recruits

  9. WHAT IS A STOCK ASSESSMENT? Population Dynamics Model Spawning Stock • Growth • Mortality • Maturation • ? Recruits

  10. WHAT IS A STOCK ASSESSMENT? Population Dynamics + Fishery Model Spawning Stock Removals by age and sex Recruits

  11. WHAT IS A STOCK ASSESSMENT? Spawning Stock • Growth • Mortality • Maturation • Catch at age/sex • Selectivity • Catch rate? • Tag recoveries? Recruits

  12. WHAT IS A STOCK ASSESSMENT? UNFISHED STATE

  13. WHAT IS A STOCK ASSESSMENT? FISHDOWN

  14. WHAT IS A STOCK ASSESSMENT? PROJECTION

  15. WHICH PARAMETERS ARE IMPACTED? Spawning Stock • Growth • Mortality • Maturation • Catch at age • Selectivity • Catch rate? • Tag recoveries? Recruits

  16. TYPES OF DEPREDATION “OPPORTUNISTIC” “FACILITATED”

  17. TYPES OF DEPREDATION? “OPPORTUNISTIC” Could be modelled as a separate ‘fleet’ with its own catch, selectivity etc.. “FACILITATED” Could be included as part of the natural mortality, if the fish are part of the diet.

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