Investigating the Implications of Alternative Spatial Management Strategies for Toothfish in the Ross Sea Region Using a Spatially Explicit Model

Spatial population models provide a useful tool for the investigation of spatial management. We use spatially explicit age-structured population dynamics models for Antarctic toothfish in the Ross Sea region to investigate the potential effects of alternate spatial catch management scenarios on the toothfish population, including the effect of closed areas consistent with the proposed Ross Sea MPAs.  

Scenarios were evaluated with reference to overall yields consistent with the CCAMLR harvest control rules (spawning stock biomass at the end of a 35 year projection period is equal to 50% B₀), and to resulting levels of localised depletion in individual spatial cells with high local exploitation rates. 

We show that while the most spatially uniform pattern of depletion was achieved by distributing fishery removals in space proportionally to the vulnerable biomass, that strategy produced the lowest catch yields and was unlikely to be possible due to operational constraints. The introduction of additional closed areas consistent with proposed MPA boundaries resulted in increased yields due to the redistribution of effort away from areas with younger (lower yield) fish towards areas with older (higher yield) fish, but also resulted in increased levels of localised depletion in some spatial cells with high local exploitation rates.