[OANNES Foro] Spawning dynamics and biomass estimates of an anchovy Engraulis australis population in contrasting gulf and shelf environments

[Mario Cabrejos]

Journal of Fish Biology
Volume 75 Issue 7, Pages 1560 - 1576
Published Online: 3 Dec 2009

Spawning dynamics and biomass estimates of an anchovy Engraulis australis population in contrasting gulf and shelf environments
W. F. Dimmlich *?? , T. M. Ward ? and W. G. Breed § 
  * School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia ,   ? South Australian Research and Development Institute (Aquatic Sciences), P.O. Box 120, Henley Beach, Adelaide, South Australia 5022, Australia and   § Department of Anatomical Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia 
? Author to whom correspondence should be addressed at present address: Marine Stewardship Council, 6-20 Elizabeth St, London SW1W 9RB, U.K. Tel.: +44 (0) 2078113325; fax: +44 (0) 2078113301; email: wetjens.dimmlich en msc.org

ABSTRACT
The spawning biomass of Australian anchovy Engraulis australis in gulf and shelf waters of South Australia was compared using the daily egg production method (DEPM). The total survey area was 128 700 km2 with recorded spawning areas in gulf and shelf waters of 4898 and 44 618 km2, respectively. High egg densities in the warm, shallow gulf waters were produced by small, young (<1 year old) E. australis that spawned relatively small batches of eggs (c. 855) approximately every 3 days. In cooler, deeper shelf waters, where larger, older E. australis are found, lower egg densities occurred despite individuals producing much larger batches of eggs (c. 15 572) approximately every 7 days. In shelf waters, the highest densities were recorded at inshore sampling stations. Spawning appeared to peak between 0000 and 0100 hours. Females were more abundant than males in samples from both gulf and shelf waters with sex ratios of 0·61 and 0·56, respectively. The spawning biomass of E. australis in shelf waters was 101 522 t, whereas the estimate for gulf waters was 25 374 t. Due to the differences in mean size of the spawning females, however, c. 6 × 109E. australis were present in each region. The results support the hypothesis that variability in habitat conditions may directly influence E. australis reproduction. A large reserve of young fish in the relatively stable gulf environment may increase the resilience of the E. australis population in South Australia to unfavourable interannual changes in offshore environmental conditions.
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