Stock assessment of Queensland east coast school mackerel (Scomberomorus queenslandicus).

Abstract

There has been no previous stock assessment for school mackerel. This stock assessment used an age structured model with a yearly time step and length based selectivity. Only the south-east stock was considered for assessment as harvests for the north-east stock were small. Data inputs included total harvest, standardised catch rates and age and length structures. The south-east coast stock model uses data from the 1988-89 to 2017-18 fishing years (comprising commercial harvest (1988-89 to 2017-18); recreational harvest (1994-95 to 2013-14); length structures (2014-15 to 2017-18) and age-length information (1991-92 to 1994-95)).

Model analyses suggested that biomass declined from the mid-2000s to around 65% of unfished biomass in 2017-18. Maximum sustainable yield (MSY) was estimated at 104–119 t per year, and the yield consistent with a biomass ratio of 60% was estimated at 84–95 t. The time series of harvests modelled may be underrepresented, causing an overestimate of the biomass ratio. Results reflect a low level of confidence, and precautionary interpretations are warranted.