Evolution of a stock assessment tool: Acoustic surveys of spawning hoki (Macruronus novaezelandiae) off the west coast of South Island, New Zealand, 1985–91

Improvements in estimating an acoustic target strength–length relationship for hoki (Macruronus novaezeladiae)

“…The observed distribution of tilt angles from the hoki in Cook Strait was approximately normal with a mean of 11.8 • (head up) and standard deviation of 29.1 • (Coombs and Cordue, 1995). This standard deviation of tilt angles was similar to what we observed on our moored cameras (25 • ), although in our data hoki observed when the lights first went on had mean tilt of −1 • .…”

“…Our new relationship was closest to that of Coombs and Cordue (1995), TS = 22.32log 10 (TL) − 79.84, which was derived from modelling of hoki swimbladders using the methods of Do and Surti (1990) and using tilt angle measurements from stereophotographs of 193 fish in Cook Strait. The observed distribution of tilt angles from the hoki in Cook Strait was approximately normal with a mean of 11.8 • (head up) and standard deviation of 29.1 • (Coombs and Cordue, 1995).…”

“…There are currently several contradictory TS-length relationships for hoki obtained from in situ measurements and scattering models (Coombs and Cordue, 1995;Cordue et al, 2001;Kloser et al, 2011), and large differences in the TS used to estimate hoki abundance in Australia and New Zealand (Kloser et al, 2011;O'Driscoll, 2012). For a recent New Zealand survey, use of the Australian TS-length relationship (Kloser et al, 2011) changed hoki abundance estimates by a factor of four (O'Driscoll, 2012).…”

“…Acoustic surveys of spawning hoki have been conducted regularly in New Zealand since 1984 (Coombs and Cordue, 1995), and acoustic estimates from the main spawning areas have been inputs into hoki stock assessments for 25 years (O'Driscoll, 2002). When using fisheries acoustics methods to estimate fish abundance, knowledge of the acoustic backscatter from a single fish, commonly known as the target strength (TS), is required for converting the measured acoustic backscatter to species-specific biomass.…”

Assessing evacuation rates and spawning abundance of marine fishes using coupled telemetric and acoustic surveys

“…Marine fish populations are often surveyed during spawning periods when distributions are concentrated and species mixing is minimal (Godø, 1989;Coombs and Cordue, 1995;Kloser et al, 1996;Williamson and Traynor, 1996;Lawson and Rose, 2000a). Such surveys are sometimes repeated during a season in attempts to estimate the error around abundance estimates.…”