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Daniel Cooper and Susanne McDermott Fisheries Interaction Team (FIT), AFSC

Spatial and temporal variability in Atka mackerel ( Pleurogrammus monopterygius ) female maturity at length and age. A component of NPRB project 0522: Reproductive ecology of Atka mackerel, Pleurogrammus monopterygius , in Alaska.

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Daniel Cooper and Susanne McDermott Fisheries Interaction Team (FIT), AFSC

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  1. Spatial and temporal variability in Atka mackerel (Pleurogrammus monopterygius) female maturity at length and age.A component of NPRB project 0522: Reproductive ecology of Atka mackerel, Pleurogrammus monopterygius, in Alaska. Daniel Cooper and Susanne McDermott Fisheries Interaction Team (FIT), AFSC James Ianelli, AFSC, SSMA

  2. Introduction • Maturity at age/length used to estimate spawning biomass • Maturity varies temporally and spatially in some other species • Growth differences • Temperature • Population density • Decreases caused by fishing pressure • Maturity estimates in ecological studies

  3. Introduction – Atka mackerel maturity • Previous Atka mackerel maturity estimates (McDermott and Lowe 1997) • Maturity at age constant (Age 50% maturity ~3.6 years • Maturity at length decreases from East to West • Atka mackerel growth decreases from East to West • Growth differences hypothesized to explain spatial maturity differences • Temporal maturity variability unknown • Some strong year classes

  4. Questions • Does maturity vary spatially and/or temporally? • Is maturity determined by length or age? • Does growth affect maturity? • How do large year classes affect maturity?

  5. Collection sites West East No genetic difference found using microsatellites (Ingrid Spies, AFSC, unpublished data)

  6. Methods – New Data • Platform was tag recovery cruises East: 2002, 2003, 2004 West: 2002, 2003 • Ovaries from 5 females randomly collected per trawl haul • Histology completed • Fish aged by AFSC age and growth program

  7. Methods (cont.) • Maturity determined using histology plus visual ID of remnant ova • Maturity determined for some females from presence of POFs* alone (Saborido-Rey and Junquera 1998, Narimatsu et al. 2005) *Post-Ovulatory Follicles

  8. Remnant Ova and POF Remnant ova persist at least one year (Not present in all mature females) Post-ovulatory follicle (unknown persistance time)

  9. Methods (Cont.) • GLM applied geographic area and time period as factors Where Y = Proportion mature, x = length or age, α,β are parameters • Chi-squared approximation used to test significance of GLM terms

  10. Results: Maturity at age Proportion mature Age (years) Area not significant p=0.4

  11. Results: Maturity at length by area Proportion mature Fork length (cm) Area significant, p<<0.0001

  12. Maturity at length by age 4+ Year olds Proportion mature 3 Year olds Fork length (cm)

  13. Growth Effect

  14. Length at age Fork length (cm) Age (years)

  15. Affect of growth on maturity at age 0.04 Mean Length of 4 YO In East and West Proportion mature Mean Length of 3 YO In East and West 0.08 Fork length (cm)

  16. Model:Growth affect on maturity at length • Predicted length determined separately for each area from von Bertalanffy model • Maturity at age constant for each area

  17. Model:Growth affect on maturity at length Proportion mature Predicted fork length (cm)

  18. Year class strength effect

  19. Results: Maturity at length over time (East)

  20. Results: Maturity at length over time (West)

  21. Number of Females Fork length (cm)

  22. Maturity at length by age 4+ Year olds Proportion mature 3 Year olds Fork length (cm)

  23. Year Class Effect Model • Constant maturity at age • Constant growth (age/length key) • Numbers at age vary according to stock assessment estimates

  24. Model resultsMaturity at length changes due to year class strength Proportionmature Fork length (cm)

  25. Discussion • Atka mackerel maturity determined more by age than length (although length has effect) • Growth affects maturity at length (McDermott and Lowe 1997) • Year class strength affects annual maturity at length (4 cm expected variability)

  26. Maturation trade-off (Stearns 1992) X Size Age

  27. Maturation trade-off (Stearns 1992) Constant size = mortality risk X X X Size Constant age = fecundity loss Age

  28. Lowered fecundity risk Mortality risk Closer to constant maturity at age • Mortality risk relatively high. M~0.3. • Lowered fecundity risk mitigated by nest guarding.

  29. Discussion • Atka mackerel spawning biomass estimates robust to growth changes (stock assessment uses maturity at age) • Stock assessments should incorporate maturity at length or age based on what controls maturity for each species • Growth changes in a trend (climate trends) would cause consistent bias

  30. Error of using constant length for maturity when age is appropriate Stock assessment assumes X X Error in Length of maturity X Size Actual Age

  31. Actual X Stock assessment assumes Error of using constant age when length is appropriate Error in maturity at age X X Size Age

  32. Acknowledgements • Field collections by Barney Baker, Eric Dobbs, Allen Harvison, Elaine Herr, Justin Keesee, Scott McKillip, Sandi Neidetcher, James Nimz, Kimberly Rand, Ty Yasenak, Ingwar • Kimberly Rand,Peter Munro, Liz Conners, Bing Shi, Sandra Lowe • Cascade fishing, F/T Seafisher • NPRB (Project 0522)

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