Final Report - 2013-053-DLD - Summer spawning patterns and preliminary Daily Egg Production Method survey of Jack Mackerel and Sardine off the East Coast
This study was undertaken collaboratively by fisheries scientists from the South Australian Research and Development Institute (SARDI) and the University of Tasmania.
Principal Investigator: Tim M. Ward
Key Words: Jack Mackerel; Trachurus declivis; Australian Sardine; Sardinops sagax; Daily Egg Production Method; Spawning Biomass; Small Pelagic Fishery; eastern Australia; Tasmania; Bass Strait
This study was the first dedicated application of the Daily Egg Production Method (DEPM) to Jack Mackerel, Trachurus declivis. It successfully collected large numbers of samples of eggs and adults concurrently from the key spawning area off eastern Australia during what has been previously identified as the main spawning period. The study established an effective method for sampling adult Jack Mackerel and provides the first estimate for this species of the adult reproductive parameters required for application of the DEPM. The spawning biomass of Jack Mackerel off eastern Australia during January 2014 was estimated to be approximately 157,805 t (95% CI = 59,570 – 358,731).
This was also the first study to investigate the spawning habitat of Australian Sardine Sardinops sagax off eastern Australia during summer. It showed that during January 2014 spawning occurred between northern Tasmania and southern Victoria. The spawning biomass at this location during this period was approximately 10,962 t. This estimate should be treated with caution as adult samples were not collected during the study. It is also important to note that this is not an estimate of the total adult biomass of Australian Sardine off eastern Australia. It is only an estimate of the portion of the population that was spawning in this southern part of the range during that period. The main spawning area of Australian Sardine off eastern Australia occurs off southern Queensland and northern NSW during late winter and early spring.
Jack Mackerel and Australian Sardine are the only two Small Pelagic Fishery species that have not been subject to dedicated DEPM surveys off eastern Australia. This project was conducted to acquire the knowledge needed to support ongoing ecologically sustainable management of these species. Knowledge of the summer spawning patterns of Jack Mackerel and Australian Sardine is needed to underpin future assessment of these stocks. The DEPM was used to estimate the population size of Jack Mackerel and Australian Sardine off eastern Australia because this was the preferred stock assessment technique specified in the harvest strategy for the SPF and considered to be the most appropriate for this species.
Results from the present study provides insights into the catch levels that may be suitable for any developmental fishery that may be established in the Tasmanian and Bass Strait region. Egg samples collected in the present and related studies (e.g. FRDC Project 2014/033) could potentially be used to support a cost-effective study of the stock structure of Australian Sardine off eastern Australia.
This study made some crucial technical developments (e.g. established an adult sampling method for Jack Mackerel) and filled several key knowledge gaps (e.g. provided the first estimates of adult reproductive parameters for Jack Mackerel). However, a follow up study is required to fill both remaining gaps (e.g. the size-fecundity relationship for Jack Mackerel) and those identified during the course of the project (e.g. spatial, temporal and size-related variations in spawning fraction of Jack Mackerel) and to further improve the accuracy of the work.