Standard Talk (15 mins) Australian Society for Fish Biology Conference 2022

How precise are estimates of spawning area and spawning biomass of sardine off southern Australia? (#131)

Gretchen Grammer 1 , Alex Ivey 1 , Frederic Bailleul 1 , Richard McGarvey 1 , Tim Ward 2
  1. SARDI Aquatic Sciences, West Beach, SA, Australia
  2. Institute of Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia

Previous studies have shown that Sardine (Sardinops sagax) abundance is strongly correlated with spawning area (A). Application of the daily egg production method (DEPM) to Sardine off southern Australia between 1995 and 2019 confirmed that A is a good proxy of adult abundance for this stock. Ward et al. (2021) showed that spawning biomass could be calculated most precisely using estimates of all parameters, except A, that were calculated from historical (cf. annual) data. Using this approach, inter-annual fluctuations in estimates of spawning biomass are driven entirely by changes in A. Like most other DEPM studies, Ward et al. (2021) did not estimate the precision of A. The precision of A is critical to understanding the precision of estimates of spawning biomass. This information is needed because spawning biomass is the key biological performance indicator for the South Australian Sardine Fishery. During recent DEPM surveys off South Australia, a second plankton sample was taken in each sampling grid at a randomised distance from original sampling site. Two gear types were tested: a CalVET net, which was the standard sampling gear for the surveys, and a bongo net, which filters more water per tow than a CalVET net and provides different estimates of A (higher) and mean daily egg production (P0, lower). Estimates of A, P0 and total daily egg production obtained using each sampling method for each survey are compared to evaluate the precision of the estimates of these parameters.