Science Centres: Fisheries

NIWA fisheries scientists recently made the first-ever acoustic measurements of live tethered hoki, in a bid to verify data from earlier acoustic surveys.

The measurements allow ‘target strength’ to be accurately assessed from live swimming fish which were subsequently identified and measured onboard. Target strength is an estimate of the amount of sound returned by an individual fish in acoustic surveys. It’s used to calculate hoki abundance from the overall echoes picked up by a scientific echosounder.

Past measurements of hoki target strength have been made on dead or free-swimming fish. In this Ministry of Fisheriesfunded study, the hoki were caught on hook-and-line from a charter vessel in Cook Strait. They were brought up slowly under an acoustic transducer which had been specially fitted to the vessel.

“We now have an accurate picture of the echo marks of hoki,” says project leader Dr Richard O’Driscoll. “We hope these data will resolve the large differences that exist between in situ estimates of hoki target strength previously collected by New Zealand and Australian researchers.”