Recent application of the daily egg production method to Jack Mackerel (Trachurus novaezelandiae)

<p>Jack Mackerel (<em>Trachurus declivis</em>) is a key target species of the Australian Commonwealth Small Pelagic Fishery (SPF), which has been subject to extensive public scrutiny following an attempt to introduce a large factory-trawler. This study reports on the first dedicated application of the Daily Egg Production Method (DEPM) to Jack Mackerel. Large numbers of eggs and adults were sampled concurrently from the key spawning area off eastern Australia. The spawning biomass of Jack Mackerel<em> </em>off eastern Australia during January 2014 was estimated to be approximately 157,805 t (95% CI = 59,570 – 358,731). Sensitivity analyses indicate this estimate is robust to likely uncertainty in estimates of key parameters. The study established a method for sampling adult Jack Mackerel that appears to provide samples that are unbiased with respect to sex, spawning activity or size. Large fish were collected from both the inner shelf and shelf break; however, spawning fractions and egg densities were high inshore and low offshore. These findings suggest complex spatio-temporal patterns of spawning, contrasting previous studies that have suggested most spawning occurs at the shelf break (∼200 m).  Results were used to provide recommendations for optimising future survey design. Perhaps most importantly, extending future adult surveys beyond the spawning area would address a major limitation of the DEPM, by providing estimates of the relative abundance of non-spawning adults outside the spawning area.  </p>