Background Information
Stock condition
The 2023 ISC benchmark assessment finds the Western & Central North Pacific striped marlin stock overfished and likely subject to overfishing when judged against MSY- and rebuilding‑based reference points. Spawning biomass in 2020 was estimated at ~1,696 t versus a rebuilding benchmark of 3,660 t (20% of dynamic unfished SSB), while recent fishing mortality (2018–2020) was about 28% above the level compatible with that rebuilding target. The assessment also highlights a two‑decade stretch of below‑average recruitment and sustained catches of immature fish, both of which depress rebuilding potential.
Current fishery status
Catches were very high through the late 1970s–1990s (≈7,200 t/yr on average during 1977–1999) and have since settled near ~2,500 t/yr in 2018–2020. Gear has shifted from historic driftnets to longline fleets (Japan, Chinese Taipei, and the U.S. among the largest), with the assessment noting lingering uncertainty in historical driftnet catch reporting.
Importance of the fishery
Striped marlin is a broadly distributed billfish mostly taken as longline bycatch in mixed tuna/swordfish fisheries. Its management therefore affects many fleets and EEZs across the North Pacific, and the science depends on data contributed by multiple CCMs.
Science
Stock status – latest assessment
The integrated Stock Synthesis model (1977–2020) estimated 2020 SSB at ~1,696 t and recent biomass (age 1+) at ~7,300 t. Reference points in the assessment give F_{20%SSB(F=0)} = 0.53 and F_{MSY} = 0.63; recent F averaged ~0.68 (2018–2020), exceeding both rebuilding F and F_{MSY}. Recruitment averaged ~366,000 age‑0 fish over the full period but only ~225,000 since 2001. The ISC concluded the stock is very likely overfished (>99%) and likely experiencing overfishing (>66%) relative to the Commission’s dynamic 20%SSB_{F=0} reference points.
Scientific advice to managers
Given uncertainties especially in growth and historical catches, the ISC advised keeping catch at or below recent levels (2018–2020 average ≈ 2,428 t). Projections under a constant‑catch future around 2,400 t show the stock rebuilding above SSB_{MSY} and toward the 20%SSB_{F=0} target by ~2040 when recent (low) recruitment persists; stronger recruitment would accelerate that timeline.
How does the WCPFC manage the North Pacific striped marlin fishery?
Current management framework
At WCPFC21 the Commission adopted CMM 2024‑06, replacing CMM 2010‑01 and locking in a total catch limit (TAC) of 2,400 t per year for 2025–2027 across the high seas and EEZs north of the equator. The TAC represents a ~60% reduction from the highest catches in 2000–2003 and triggers an automatic review if the 2,400 t cap is exceeded in any year. National limits were established for five major catching CCMs: Japan 1,454.4 t; Chinese Taipei 358.4 t; Korea 214.8 t; United States 228.4 t; China 68.8 t (total 2,324.8 t), with the residual available to others.
The measure also creates an underage reserve: unused TAC accrues to a shared pool, and each of the five listed CCMs may draw up to an additional 165 t in a later year if reserve tonnage exists. Notably, an 826 t underage from 2023 is available to 2025 fishing; priority access goes to CCMs whose domestic rules would otherwise shut a target fishery. Once a CCM’s limit is reached, live release of striped marlin is required to maximize post‑release survival, and CCMs must report catch, effort, and live/dead discards, with a deadline to meet improved data requirements by 2027. The measure is scheduled for review and amendment in 2027, aligned with a new ISC assessment.
Management issues
Negotiations at WCPFC21 revealed practical and equity concerns. In the striped marlin SWG, CCMs debated whether baseline years for limits should recognize historical effort (2000–2003) or pivot to the more recent 2018–2020 period used in the rebuilding analysis. Non‑retention was raised but set aside due to the value of landings data for assessments; instead, the final text uses a live‑release trigger after limits are reached. The SWG also flagged the challenge of balancing reductions across fleets with very different dependency on the fishery.
Implementation and monitoring are central. Pacific SIDS stressed that effective control of longline catches on the high seas will require stronger monitoring and verification, including electronic monitoring (EM). That message connects to the Commission’s broader adoption of interim EM minimum standards at WCPFC21, which members see as a key tool for validating catch and discard data relevant to striped marlin.
Scientifically, the ISC still flags two big uncertainties that matter for management: the growth curve (which affects the absolute scale of biomass and F) and stock mixing across boundaries. The assessment also notes that many fish are caught before maturity, which suppresses SSB and argues for measures that reduce juvenile mortality.
Improving Future Management
WCPFC21 paired the new measure with near‑term science tasks and operational improvements. The Commission asked the Scientific Committee to develop safe‑handling and live‑release guidelines for billfishes and to review the methods used to estimate discards, both aimed at making the new live‑release requirement effective and measurable. It also requested the ISC to update projections using the adopted national allocations to confirm the rebuilding trajectory under CMM 2024‑06.
The preambular note that FFA members will move to zone‑based longline limits within their EEZs points to a future where coastal states hold operators accountable at the zone level, complementing flag‑based limits on the high seas. Combined with the Commission’s EM standards and the measure’s strengthened reporting on live/dead discards, these steps are the practical levers to tighten compliance and reduce juvenile and over‑limit mortality while the science on growth and stock structure is refined.
Summary
The science and management now line up. The ISC says hold catches near ~2,400 t while uncertainties are resolved; the Commission has set a binding 2,400 t TAC through 2027, allocated national limits, created a reserve to smooth year‑to‑year variability, and added a live‑release requirement once limits are hit, with improved discard reporting due by 2027. If CCMs keep within those limits and strengthen monitoring (especially for longline bycatch), the stock is expected to climb above SSB_{MSY} and move toward the 20%SSB_{F=0} interim target over the next two decades under conservative recruitment assumptions; stronger recruitment would speed that recovery. A full review is slated for 2027 alongside the next ISC assessment.