Assessing primary production constraints in New Zealand fisheries

Abstract

We investigate the use of an energetically based fishing pressure index (FPI) as a rapid assessment tool to investigate harvests of fishing stocks in relation to energetic limits in New Zealand's (NZ) exclusive economic zone (EEZ). Calculation of the FPI is undertaken by comparing satellite-derived spatial estimates of net primary production (NPP) with estimates of primary production required to support a given catch (PPR) using the simplified trophic model applied by Pauly and Christensen [Pauly, D., Christensen, V., 1995. Primary production required to sustain global fisheries. Nature 374, 225–257]. Historic comparisons of PPR to NPP in NZ's EEZ highlight a reduction in fishing pressure from 20% of NPP required to support catches in 1998 to below 10% in 2006, which suggests NZ fisheries are generally operating well within their energetic limits for the stocks under consideration. However, analysis of data at finer spatial scales shows that in 2006 some fished areas may have exceeded local energetic limits. The use of this technique is discussed in relation to the production and conservation goals of fisheries and in focusing science effort to the most affected areas and species. In particular, the efficacy of applying the technique to finer scale analysis is discussed with regard to the active management of NZ's migratory hoki ( Macruronus novaezelandiae) fishery, where a number of catch areas with high fishing pressures were identified from 1998 to 2002, preceding a large reduction in the total allowable commercial catch (TACC) in 2004.