Oral Presentation Australian Society of Fish Biology and Oceania Chondrichthyan Society Conference 2016

Simulation-based evaluation of reserve network performance for a vulnerable deep-sea shark (#11)

Ross Daley 1 , Alistair Hobday 2 , Jayson Semmens 3
  1. University of Tasmania, West Moonah, TAS, Australia
  2. CSIRO, Hobart
  3. University of Tasmania, HObart

An individual-based simulation model of the movements of C. zeehaani was developed and applied to determine how long a depleted population would take to recover from 8% of un-fished numbers to a target of 20%. Individual movements were based on tracking results and simulated across closures and fished areas. Key uncertainties were length of the female breeding cycle, natural mortality and spatial variation in population density. The base case (three year cycle, 2% natural mortality) predicted recovery in 63 +- 3 years. Poor matching of closure locations to population density would delay recovery by 31.9 years. Sensitivity testing predicted the target would be reached 19.2 years earlier with a 2-year cycle or 16.5 years later with a four-year cycle. If natural mortality were half the base case estimate then the target would be reached 13.5 years earlier or, significantly, if the natural mortality were doubled, recovery to the target would take 98.3 years longer. Improving handling practices for sharks or changing fishing methods on the continental shelf would not significantly affect the time for recovery but re-introducing trawling for orange roughy in deep waters would delay recovery by 45.9 years. Doubling or halving the size of a closure located where C. zeehaani is abundant would change recovery by +12.6 or -9.9 years but such changes have no significant effects where C. zeehaani are not abundant. The model can be used to evaluate the consequences of alternative management interventions and can be applied to other species with telemetry data.