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

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Presentation on theme: "Spatial and temporal variability in Atka mackerel (Pleurogrammus monopterygius) female maturity at length and age. A component of NPRB project 0522: Reproductive."— Presentation transcript:

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 1.Does maturity vary spatially and/or temporally? 2.Is maturity determined by length or age? 3.Does growth affect maturity? 4.How do large year classes affect maturity?

5 East West Collection sites No genetic difference found using microsatellites (Ingrid Spies, AFSC, unpublished data)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 persist at least one year (Not present in all mature females) Remnant Ova and POF 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 Area not significant p=0.4 Age (years) Proportion mature

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

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

13 Growth Effect

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

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

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 Predicted fork length (cm) Proportion mature

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 Fork length (cm) Proportion mature 3 Year olds 4+ Year olds

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 results Maturity at length changes due to year class strength Proportion mature 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) Age Size X

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

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

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 Age Size X X X Stock assessment assumes Actual Error in Length of maturity

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