The estimation of uncapped acoustic survey biomass from capped data

Management of the South African sardine and anchovy resources is critically dependent on estimates of recruitment and spawner biomass obtained from hydroacoustic surveys. These surveys commenced in 1984, but in 1997 new equipment (an EK500 echo sounder) replaced the older EK400 echo sounder. The introduction of the EK500 echo sounder revealed a saturation problem with the EK400 echo sounder, particularly for sardine (Coetzee 2003). Survey estimates since June 1997 were initially ‘capped’ at - 29dB for assessment purposes, to maintain a comparable time-series from 1984