Accounting for linefish dependency in management of the South African small pelagic fishery

To further implement an ecosystem approach to management of the small pelagic fishery in South Africa, we attempted to develop functional relationships between spatialised time-series of the biomass of three small pelagic fish species and the catch per unit effort (CPUE) of four linefish species (i.e. species caught on hook and line, excluding longlines) that could be used to account for the forage needs of dependent predators. Granger causality tests indicated significant effects of anchovyEngraulis encrasicolusbiomass on silver kobArgyrosomus inodorusand yellowtailSeriola lalandiCPUE, significant effects of sardineSardinops sagaxbiomass on geelbekAtractoscion aequidensCPUE, but no significant effects of biomass of west coast redeye round herringEtrumeus whiteheadiand east coast redeye round herringEtruemus wongratanaion any linefish CPUE. Sequentialt-test analysis of regime shift (STARS) indicated temporal matching in regimes between anchovy biomass east of Cape Agulhas (EoCA) and yellowtail west coast (west of Cape Point) CPUE, and between sardine biomass EoCA and geelbek southwest coast (Cape Point to Cape Infanta) CPUE. Convergent cross mapping found no causality for anchovy biomass EoCA on yellowtail west coast CPUE but causality in the reverse direction. A high degree of causality in both directions for sardine biomass EoCA and geelbek southwest coast CPUE was observed, indicating strong predator-prey interaction, and a highly significant linear relationship between sardine biomass EoCA in year(n-1)and geelbek southwest coast CPUE in yearnwas obtained. This functional relationship should be considered for inclusion as a proxy for ecosystem state in management procedures that adopt the ecosystem approach to fisheries for the South African small pelagic fishery.