Kobe Plot Alternatives for Model 0.14

Published

May 29, 2026

This report uses h1_0.14, stock 1. The no-fishing spawning biomass is taken from df1 in the model output object as SSB_Nofishing; the reported depletion comparison is taken from SSB_NoFishR, with SSB0_Dynamic included as a consistency check.

1 Spawning Biomass

Figure 1: Estimated spawning biomass with fishing and the model counterfactual spawning biomass without fishing.
Figure 2: Fished spawning biomass since 2000 across productivity assumptions. Dashed horizontal lines show Bmsy for each run.

The post-2000 view in Figure 2 shows that the recent fished SSB trajectories are broadly similar, but the Bmsy reference levels diverge strongly among productivity assumptions. The low-steepness, long-SR run has the highest Bmsy (9130 kt), while the high-steepness, short-SR run has the lowest Bmsy (2998 kt). As a result, terminal status relative to Bmsy is mostly a productivity-assumption result: the same recent biomass scale is below the low-steepness Bmsy levels but above the high-steepness Bmsy levels.

Figure 3: Spawning biomass depletion ratio estimated as fished spawning biomass divided by no-fishing spawning biomass, compared with the reported depletion estimate.
Table 1: Terminal-year spawning biomass impact and depletion comparison.
year ssb_with_fishing ssb_without_fishing difference ratio reported_depletion ssb0_dynamic ratio_minus_reported ssb0_minus_reported
2025 5772.81 19620.5 13847.69 0.2942 0.2942 0.2942 0 0

2 Majuro Plot

A Majuro plot is a WCPFC-style modification of a Kobe plot that puts fishing pressure on the y-axis as F/Fmsy, but puts biomass on the x-axis as depletion relative to unfished spawning biomass, SSB/SSBF=0, rather than SSB/Bmsy. The vertical line at 0.2 follows the common WCPFC tuna-stock display convention and is shown here only as a visual reference, not as a proposed jack mackerel limit reference point.

Figure 4: Majuro plot for model 0.14 productivity assumptions, showing the 2000-2025 trajectory. Larger points mark terminal-year status. The vertical line marks SSB/SSB_F=0 = 0.2 for orientation and the horizontal line marks F/Fmsy = 1.
Table 2: Terminal-year Majuro plot coordinates for the productivity sensitivity runs.
model scenario year SSB_over_SSB_F0 F_over_Fmsy
h1_0.14 Low steepness, short SR 2025 0.2942 2.5361
h1_0.14ll Low steepness, long SR 2025 0.2558 2.5322
h1_0.14hl High steepness, long SR 2025 0.4020 0.9191
h1_0.14hs High steepness, short SR 2025 0.4150 0.9480

In Figure 4, the low-steepness runs are above F/Fmsy = 1 in the terminal year, while the high-steepness runs are just below 1. The biomass axis shows the same productivity contrast: terminal SSB/SSBF=0 is lower for the low-steepness runs (0.256-0.294) than for the high-steepness runs (0.402-0.415). This is the same pattern as the Fmsy and Bmsy diagnostics: the stock-status interpretation is sensitive to the productivity assumption, even though the recent fished biomass trajectories are similar.

3 Productivity Range

The productivity sensitivity runs span Fmsy values from 0.315 to 0.878. The low-steepness runs produce the lower end of the range, while the high-steepness runs shift the F profile peak to substantially higher F values.

Table 3: Fmsy values across productivity assumptions. Intervals use the reported standard errors from the .std files; profile_Fmsy is the F value at maximum yield in Fprof.yld.
model scenario steepness sr_years Fmsy Fmsy_se F35_est F_at_SPR35_profile Fcur_Fmsy Bmsy Bmsy_se Bcur_Bmsy profile_Fmsy MSY SPR_at_profile_Fmsy
h1_0.14 Low steepness, short SR 0.65 2000-2022 0.3148 0.0280 0.4623 0.4623 2.5361 6380.9 1405.00 0.9047 0.314 1217.07 0.4231
h1_0.14ll Low steepness, long SR 0.65 1970-2022 0.3167 0.0279 0.4662 0.4662 2.5321 9130.4 1194.30 0.6424 0.316 1740.14 0.4233
h1_0.14hs High steepness, short SR 0.85 2000-2022 0.8430 0.1345 0.4625 0.4625 0.9480 2997.6 450.53 1.9120 0.840 1118.53 0.2546
h1_0.14hl High steepness, long SR 0.85 1970-2022 0.8777 0.1389 0.4745 0.4745 0.9191 4653.5 472.11 1.2944 0.874 1747.21 0.2535
Figure 5: Fmsy and F35% estimates across productivity assumptions. Horizontal bars show approximate 95% intervals for Fmsy using the reported standard errors.

The contrast in Figure 5 is mostly a steepness effect. The low-steepness cases put Fmsy near 0.315-0.317, while the high-steepness cases shift Fmsy upward to 0.843-0.878. Changing from the short to the long stock-recruit fitting period has a much smaller effect within each steepness assumption than changing steepness itself.

F35% is comparatively stable across these runs, ranging from 0.462 to 0.475. That is expected because the SPR-based reference point is controlled mainly by selectivity, maturity, growth, and natural mortality, whereas Fmsy also depends strongly on the assumed stock-recruit productivity. Under low steepness, F35% sits above Fmsy, so it would imply a more aggressive F than the production-based MSY estimate. Under high steepness, Fmsy is well above F35%, so F35% becomes the more conservative reference point.

Figure 6: Yield profiles across productivity assumptions. Points mark the profile maximum and dashed vertical lines mark the reported Fmsy values.

4 SPR Reference Point

Table 4: SPR reference point from the refreshed model run. SBF35 is interpolated from the yield profile at SPR = 0.35.
model stock F35_est F_at_SPR35_profile Fmsy SBF35 yield_at_SPR35 yield_at_Fmsy SPR_at_Fmsy recruitment_at_SPR35 total_biomass_at_SPR35
h1_0.14 1 0.4623 0.4623 0.3148 4771.575 1184.616 1217.07 0.4226 8532.228 7849.583
Figure 7: F profile from Fprof.yld. Vertical lines mark F35% and Fmsy on the profile.
Table 5: Fishery ratios used to apportion F-based reference points. Ratios are based on mean end-year F by fishery, matching the Fratio calculation used for SPR rates.
fishery end_year mean_f max_selectivity_scaled_f f_ratio F35_est_contribution F_at_SPR35_profile_contribution Fmsy_contribution
N_Chile 2025 0.0410 0.0813 0.0513 0.0237 0.0237 0.0162
SC_Chile_PS 2025 0.7253 2.0370 0.9086 0.4200 0.4200 0.2860
FarNorth 2025 0.0251 0.0453 0.0315 0.0146 0.0146 0.0099
Offshore_Trawl 2025 0.0069 0.0142 0.0086 0.0040 0.0040 0.0027

5 Total Biomass

Figure 8: Estimated total biomass with fishing and the model counterfactual total biomass without fishing.
Figure 9: Absolute difference between no-fishing and fished total biomass compared with the total-biomass ratio.
Table 6: Terminal-year total biomass impact and fished/no-fishing ratio.
year total_biomass_with_fishing total_biomass_without_fishing difference ratio
2025 9678.61 25914.7 16236.09 0.3735