  The natural mortality (M) and purse-seine catchability and selectivity were
estimated for Trachurus novaezelandiae, Richardson, 1843 (yellowtail scad)-a
small inshore pelagic species harvested off south-eastern Australia. Hazard
functions were applied to two decades of data describing catches (mostly stable
at a mean +- SE of 315 +- 14 t p.a.) and effort (declining from a maximum of
2289 to 642 boat days between 1999/00 and 2015/16) and inter-dispersed (over
nine years) annual estimates of size-at-age (0+ to 18 years) to enable survival
analysis. The data were best described by a model with eight parameters,
including catchability (estimated at < 0.1 x 10-7 boat day-1), M (0.22 year-1)
and variable age-specific selection up to 6 years with a 50% retention among
5-year olds (larger than the estimated age at maturation). The low catchability
implied minimal fishing mortality by the purse-seine fleet. Ongoing monitoring
and applied gear-based studies are required to validate purse-seine
catchability and selectivity, but the data nevertheless imply T. novaezelandiae
could incur substantial additional fishing effort and, in doing, so alleviate
pressure on other regional small pelagics.
