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Reproduction

Reproduction. Jewfish Workshop 2006. Aim. Establish the reproductive strategy of black jewfish. Objectives. Determine the spawning season and the relevance of the annual aggregations. Establish the size of sexually mature black jewfish (minimum and I 50 ).

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Reproduction

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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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