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Reproductive Strategy of Black Jewfish: A Study on Spawning Season, Maturity, and Size

Explore the reproductive strategy of black jewfish through a comprehensive study on spawning season, sexually mature sizes, and size/age structure of landings. Detailed methods and results provide insights into the species' reproductive patterns.

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Reproductive Strategy of Black Jewfish: A Study on Spawning Season, Maturity, and Size

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  1. Reproduction Jewfish Workshop 2006

  2. Aim Establish the reproductive strategy of black jewfish.

  3. Objectives • Determine the spawning season and the relevance of the annual aggregations. • Establish the size of sexually mature black jewfish (minimum and I50). • Document the current size/age structure of black jewfish landings.

  4. Over a two year period, 70 fish per month were measured, weighed and sampled. Fish sourced from commercial fishers and fishing tour operator landings. Additional fish (<50 cm & >130 cm) sourced from commercial and rec. fishers. General Methods

  5. Reproduction Study Methods • Gonad sampling: • Individual lobes weighed; section of one lobe preserved. • Gonad processing: • Sectioned and stained; Classified based on oocyte stages.

  6. Classification System

  7. Spawning Season Relative gonadosomatic index and standard deviation for females (n = 529). Mean GSI

  8. Histological Results F2 – Developing gonads

  9. Histological Results F3 – Developed gonads

  10. Histological Results F4 & F5 – Near spawning gonads

  11. Histological Results F6 – Spent gonads

  12. Histological Results F7 – Resting gonads

  13. Histological Results F2 Developing (July) F3 Developed (October) F4-5 Near Spawning (November) F6 Spent (February) F7 Resting (May)

  14. Spawning Size Size at first maturity • Minimum size of maturity = 85 cm • Maximum size of immaturity = 100 cm • I50 estimate = ~90 to 95 cm. • Need to run logistic model.

  15. Size Structure Length/weight of black jewfish harvested near Darwin, 2004-06 (n = 1490). Weight (kg) Length (cm)

  16. Size Structure Length/weight of black jewfish harvested near Darwin, 2004-06 (n = 1490). Mature Fish Weight (kg) Length (cm)

  17. Size Structure Length/weight of black jewfish harvested near Darwin, 2004 (n = 415). Weight (kg) Length (cm) Length (cm)

  18. Size Structure Length/weight of black jewfish harvested near Darwin, 2005 (n = 636). Weight (kg) Length (cm) Length (cm)

  19. Size Structure Length/weight of black jewfish harvested near Darwin, 2006 (n = 438). Weight (kg) Length (cm) Length (cm)

  20. Summary • GSI indicates extended spawning = Aug to Jan. • GSI and histology suggests serial spawning. • Minimum size = 85 cm; I50 = ~90-95 cm. • No apparent difference in size between years.

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