How many conditional age-at-length data are needed to estimate growth in stock assessment models? Xi He, John C. Field, Donald E. Pearson, and Lyndsey Lefebvre Fisheries Ecology Division, SWFSC Santa Cruz, CA CAPAM Growth Workshop Lo Jolla, CA November, 2014

2 Introduction Conditional age-at-length (CAAL) data are often used in stock assessment models to internally estimate growth and natural mortality Recent studies (Wetzel and Punt 2011, Hulson et al. draft, One et al. 2014) showed effects of quality and quantity of composition data on assessment outputs. Bocaccio is an important commercial species, especially in California. It has been assessed 12 times since 1986, and has been under rebuilding plan since the early 2000s. But no age data have been used in these assessments since it is extremely difficult to age

3 When lengths are better than ages: The complex case of Bocaccio (Ralston and Ianelli 1998) Ralston and Ianelli 1998 study: Difficulty in Bocaccio ageing Unable to detect recruitments due to ageing bias and imprecision

4 Introduction – cont. Ageing criteria for Bocaccio are recently developed, and over 6000 thousands of fish have been aged – time consuming Ageing Bocaccio otoliths requires specific skills and is time consuming, as compared to ageing other rockfish Questions still remain: How many fish do we need to age and how do we chose which otolith samples to age?

5 Study objectives Focused on numbers of fish that need to be aged and which annual age samples have high priority Examine effects of numbers of fish aged and numbers of yearly samples on stock assessment outputs To provide general guidelines for ongoing effort in Bocaccio ageing

6 Methods Used three recent West Coast assessment models: 2011 Blackgill rockfish, 2013 Bocaccio, and 2013 Pacific sanddab Numbers of fish aged: randomly select 75%, 50%, 25% and 10% of age data used in the original assessment models. Each model with reduced data were run 100 times Numbers of annual age data: intermittently remove data from assessment models (i.e. removing data every other year, etc.) These real stock assessment models represent different levels of data availability and model complexity, and different life histories Results from model runs with reduced data were compared to the models with all available data, including estimated key parameters and stock status

7 Blackgill rockfish Max age: 60 (64 – 90?) CAAL data: (15 years) Last assessed: 2011 M and steepness fixed Bocaccio Max age: 34 (45 – 57?) CAAL data: (20 years) Last assessed: 2013 (update) M fixed at 0.15 (too high?) Pacific Sanddab Max age: 11 CAAL data: (9 years) Last assessed: 2013 (first time) M fixed at base-model values

8 Key assumptions and limitations No time-varying growth Natural mortality not internally estimated

9 Comparisons: Use only portion of CAAL data Spawning biomassDepletion Blackgill: Spawning biomass and stock depletion

10 Comparisons: Use only portion of CAAL data Blackgill: Female growth

11 Comparisons: Use only portion of CAAL data Spawning biomassDepletion Bocaccio: Spawning biomass and stock depletion

12 Comparisons: Use only portion of CAAL data Bocaccio: Female growth

13 Comparisons: Use only portion of CAAL data Spawning biomassDepletion Sanddab: Spawning biomass and stock depletion

14 Comparisons: Use only portion of CAAL data Sanddab: Female growth

15 Comparisons: Use only portion of CAAL data Key assessment outputs * Not estimated Note: For reduced data set, values are medians of 100 runs Species & ModellnR0SteepnessDepletion Blackgill all data (N=6258) *0.314 Blackgill 75% *0.330 Blackgill 50% *0.330 Blackgill 25% *0.357 Blackgill 10% *0.213 Bocaccio all data (N=6073) Bocaccio 75% Bocaccio 50% Bocaccio 25% Bocaccio 10% Sanddab all data (N=7970) Sanddab 75% Sanddab 50% Sanddab 25% Sanddab 10%

16 Comparisons: Removal of annual CAAL data Key assessment outputs * Not estimated Species & Model No. year with CAAL data No. fish aged for CAALlnR0SteepnessDepletion Blackgill all data *0.314 Blackgill 1 out *0.332 Blackgill 1 out *0.384 Blackgill 1 out *0.376 Blackgill 1 out *0.423 Bocaccio all data Bocaccio 1 out Bocaccio 1 out Bocaccio 1 out Bocaccio 1 out Sanddab all data Sanddab 1 out Sanddab 1 out Sanddab 1 out

17 Summary Important to obtain age data from early years In case for Bocaccio, need to age otoliths from late 1970’s and early 1980’s More data for long lived species May want to consider to estimate growth externally for long- lived species when age data are limited

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