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Stock Status and Conservation Information
(From ISC26 Plenary Report)

Pacific Blue Marlin

Click here to see the ISC25 stock status and conservation information.

Stock Status

The base model indicated the Pacific blue marlin stock was likely not overfished and likely not subject to overfishing. Estimates of population biomass (age 1 and older) for the Pacific blue marlin stock declined from 183,150 mt in 1993 to 123,300 mt in 1999, with a steady further decline to average 102,490 mt in 2021–2023, and a terminal year increase to an estimated 127,300 mt in 2024 (Figure 6.6.3). Estimated fishing mortality rate (F, expressed as exploitation rate of biomass) increased through the 1970s–1990s, and fluctuated around 0.20 before declining to 0.12 in 2023 and 0.14 in 2024. Fishing mortality rates have been below FMSY for the entire assessment period. The recent spawning stock biomass of 42,038 mt (average for 2021-2023) was greater than SSBMSY (SSBMSY = 31,651 mt) and the recent F of 0.13 (average for 2021-2023) was 50% below FMSY. The base model indicated under current conditions the Pacific blue marlin stock was virtually certain to be not overfished (>99% probability) and was virtually certain to be not subject to overfishing (>99% probability) relative to MSY-based reference points.

MSY-based biological reference points and a depletion-based reference point (20% of virgin population mature female biomass; denoted 20%SSB0) were computed for the base model. The point estimate of annual catch at FMSY was 24,306 mt and at 20%SSB0 was 24,119 mt. The point estimate of the female SSB to produce MSY (mature female biomass) was 31,651 mt. The point estimate of FMSY, the fishing mortality rate to produce SSBMSY was 0.26 (when F is calculated as exploitation rate of total biomass) or 0.22 (when F is calculated as average F for ages 1–10). F20%SSB0, the fishing mortality rate to maintain the population at 20%SSB0 was 0.23 (F as exploitation rate of total biomass) or 0.20 (average F for ages 1–10). The corresponding equilibrium value of spawning potential ratio (SPR) at SSBMSY was 19.6%; SPR corresponding to 20%SSB0 was 23%.

    Based on these findings, the following information on the status of the Pacific BUM stock is provided by the ISC26 Plenary:

  1. No target or limit reference points have been established for BUM by the IATTC and the WCPFC;
  2. Spawning stock biomass was estimated to be 42,038 mt in 2021-2023, or about 33% above SSBMSY and 9% above 20%SSB0;
  3. Fishing mortality on the stock averaged roughly F = 0.13 during 2021-2023, or about 50% below FMSY and 56% below F20%SSB0; and
  4. Blue marlin stock status relative to MSY-based reference points, overfishing was virtually certain to be not occurring (>99% probability) and Pacific BUM is virtually certain to be not overfished (>99% probability).

Conservation Information

Projections started in 2025 and continued through 2034 under fishing mortality levels corresponding to four harvest scenarios: (1) FHigh = F2003, the highest fishing mortality rate estimated for the entire time series (1971–2024); (2) FMSY; (3) FRecent = F(2021–2023), corresponding to the average fishing intensity (SPR) over 2021–2023; and (4) F30%SPR, corresponding to SPR = 30%. Under the FRecent scenario, projected catches remained below 2024 levels for several years, then increased to about 80% of MSY by 2034, while biomass increased to well above SSBMSY. In contrast, the FMSY scenario showed increased catch to above the historical maximum, followed by a decline to MSY as biomass decreased. The remaining scenarios produced intermediate trajectories with catches initially increasing and later declining as stock biomass is reduced. The most stable catch trajectory was observed under F30%SPR, with projected annual catches remaining approximately constant at 23,000 mt.

The lack of sex-specific size data for all but one fishing fleet, and the simplified treatment of the spatial structure of Pacific blue marlin fishing fleets and population dynamics remain as two important sources of uncertainty for improving future assessments.

    Based on these findings, the following conservation information is provided for the Pacific BUM stock by the ISC26 Plenary:

  1. There is no evidence of fishing mortality exceeding FMSY or substantial depletion in spawning potential or spawning stock biomass relative to MSY level; and;
  2. The Pacific blue marlin stock has produced annual removals of 13,690–20,400 mt since 2019, corresponding to approximately 53–84% of the MSY catch. The stock may be able to support somewhat higher removals.
  3. The results show that projected female spawning biomass is expected to increase or remain stable under the Fstatus quo and F30% harvest scenarios and decline to SSBMSY under the high F and FMSY harvest scenarios. The probability that the stock is overfished or overfishing occurring by 2034 under each harvest scenario is low.