In pacific-hake/hake-assessment: Stock Assessment for Pacific Hake

Response SRG

r end_yr-1 SRG Assessment Recommendations

We respond here to three requests that the JTC would like to get feedback on at the meeting.

Responses to all other requests can be found in the assessment document, which include:

• Reference points in the MSE
• Conduct key sensitivities
• CPUE distribution
• Time-varying maturity
• Age-1 index distribution
• Age-1 index CVs
• Freezer trawler sampling
• Ageing error study
• 2D AR selectivity

Dynamic unfished spawning biomass

The SRG recommends that the JTC include dynamic unfished spawning biomass in the 2024 assessment as a comparator with the equilibrium unfished spawning biomass used to provide management advice. The SRG also encourages the continued outreach regarding the use of dynamic reference points to stakeholders and managers, including identifying pros and cons of using dynamic unfished spawning biomass.

Response: Dynamic unfished spawning biomass

:::::: {.columns} ::: {.column width="40%"} Fished time series is the current estimates of spawning biomass \textcolor{red}{Unfished time series removes fishing mortality from modeled population dynamics, thereby directly showing the influence due to fishing} Assume environment (not fishing) affects recruitment deviations Maintain assumptions of no density dependence in life history parameters :::

::: {.column width="60%"}

plot_biomass_fished_unfished(base_model,
                             model_nms = c("Base model - Fished",
                                           "Base model - Unfished"),
                             leg_pos = c(0.6, 0.9),
                             xlim = c(1963,
                                      year(Sys.time())),
                             rel = FALSE)

::: ::::::

Response: Dynamic $B_0$

plot_biomass_fished_unfished(base_model,
                             model_nms = c("Base model - Static B0",
                                           "Base model - Dynamic B0"),
                             leg_pos = c(0.6, 0.9),
                             ylim = c(0, 2.75),
                             rel = TRUE)

Natural mortality

The SRG recommends that the JTC explore alternative ways of estimating natural mortality to update the current approach in the model, which is based on methods from more than a decade ago, since newer methods are available. Information presented during the SRG meeting implies that natural mortality on age-2 Pacific Hake is higher than currently assumed in the assessment model and should be explored more fully.

Response: Natural mortality

Investigate estimating a vector of natural mortality (M) parameters:

• Breakpoints at different ages -- no combination led to M decreasing with age as hypothesized given the diet data of predators of Pacific Hake (prior highly influential; no prior led to lower M for young fish)
• Tagging studies could be used to help inform age-specific M
• Diet data could be used to externally estimate M at age (CEATTLE model work)
• Other modeling frameworks, such as the Woods Hole Assessment Model have more flexibility in modeling natural mortality and might also be an option for future explorations

Input sample size

The SRG encourages the JTC to consider methods to determine the maximum input sample size for the age compositions.

Response: Input sample size

Determining input sample sizes is important for how annual fishery and survey age compositions are initially weighted, which then provides the basis from which wholesale re-weighting of data sources (fishery or survey) is done with the Dirichlet-multinomial data weighting model parameters.

• Considered alternative methods, including that of Stewart and Hamel (2014), and determined that the first step is to explore the handling of survey age-composition data
• Initial effective sample sizes and data source weighting is relative to other data sources in the model
• Survey age compositions represent age structure associated with the acoustic survey as viewed through an estimated selectivity curve for the acoustic-trawl sampling net
• Selectivity for ages two and older with acoustics is theoretically at or near one
• JTC plans to investigate whether there is a more informative way to utilize survey age-composition information in the stock assessment model in the coming year

pacific-hake/hake-assessment documentation built on July 21, 2024, 8:19 a.m.