Information based on material provided for the 102nd Session of the IPHC Annual Meeting (AM102). ↗ Meeting page

Longevity

> 50 yrs

Age at Maturity

50% of females are mature at 11 yrs

Distribution

Off the West Coast of the U.S.A, British Columbia, Alaska, Russia and Japan

Spawning

Annually from November to March on the outer continental shelf and slope at depths of 300–600 meters

Migration & Population Dynamics

Genetic Baseline

731 individuals

winter samples collected in 5 known spawning grounds, 1999–2020

SNPs RETAINED

3.68 million

of 8.46 million SNPs identified (MAF ≥ 0.05, after QC)

Assignment Accuracy

Low: < 33%

Population Structure

Single genetic group

Consistent with coastwide stock assessment model

Principal Component Analysis (PCA)

First two principal component axes, 709 winter-collected individuals by geographic area

PCA biplot of Pacific halibut genetic samples by geographic area
Additional information ↗

Why it matters for stock assessment

Pacific halibut in IPHC Convention Waters are currently modeled as a single coastwide stock. Low coverage whole-genome resequencing (lcWGR) was used to test this assumption using genetic samples from fish collected during the spawning season in five known spawning grounds.

  • No discrete genetic clusters were detected, even at ~3.7M SNP resolution
  • Individuals could not be reliably assigned to their sampling location
  • Results support IPHC's current stock assessment practices that model the Pacific halibut stock as a single coastwide unit
Map showing winter-collected sample locations across IPHC Convention Waters
The IPHC Secretariat is also developing an epigenetic clock for non-lethal age estimation in Pacific halibut. This method is based on the identification of DNA methylation patterns in fin tissue that are associated with age through the development of an age estimation model (i.e., an epigenetic clock) for Pacific halibut. Fin tissue samples from 250 fish of known ages (6–30 yrs) have been sequenced and bioinformatic analysis is currently underway.
Additional information ↗

Reproduction

Histology samples collected (2022-2025)

4,528

Ovarian samples, all 4 Biological Regions

New histology-based maturity ogive

A50 = 9.8 yrs

Coastwide, 2022–2024 combined

New calibrated coastwide maturity ogive

A50 = 11.0 yrs

â–¼ 0.6 yrs vs. previous ogive - used in the 2025 stock assessment

Fecundity Samples Collected

2,351

2023–2025, FISS + special collections

Map of Histology sample collections by year

Ovarian samples for maturity classification, coastwide

Coastwide map of 2022, 2023 and 2024 maturity samples for histology collected on FISS

New coastwide calibrated visual maturity ogive

Calculated using averaged calibrated visual maturity estimates from the 2002 to 2024 FISS (23 years)

Estimated mean calibrated visual maturity ogive compared with the previous coastwide ogive
Additional information ↗

Fecundity assessment: collection effort

YearRegionPlatformSamples
20233FISS452
20242FISS149
20244FISS359
20242Special collection271
2025AllFISS878
20252Special collection242
Total——2,351

Special collections target large females (85–200+ cm FL) and those planned for late summer/early fall 2026 contemplate the collection of samples from all three Biological Regions.

Growth

Objective: understand the effects of potential drivers of the long-term changes in weight-at-age.

Integrated transcriptomic, proteomic, and stable isotope analyses demonstrated that temperature promotes growth plasticity in juvenile Pacific halibut, and identified candidate growth biomarkers that could help characterize somatic growth variation coastwide.

Findings published: Planas et al. (2025), Journal of Experimental Biology 228: jeb251013.

Relevance to stock assessment

Informs yield-per-recruit and productivity evaluations that support mortality limit-setting.

Relevance to MSE

Improves simulation of growth variability and enables climate-change scenario testing in the Operating Model.

Status

Future studies on drivers of size-at-age change are planned under the 2026 Integrated Research & Monitoring Plan.

Mortality & Survival Assessment

Survival Estimation Methodology

Acceleration-logging pop-up archival transmitting tags were used to infer individual survival outcomes for Pacific Halibut that were released following capture

Pacific halibut released bearing an acceleration-logging pop-up archival tag

Discard Mortality Rate – Directed Commercial Fishery

4.2%

Minimum estimated DMR with a 95% confidence interval of 0.0–8.7% from fish in excellent viability

Discard Mortality Rate – Guided Recreational Fishery

1.3%

Minimum estimated DMR with a 95% confidence interval of 0.0–3.9% from fish in excellent viability

Viability categories assigned to fish discarded by the directed fishery

Proportions of Pacific halibut assigned to viability category by size and release method

Proportions by legal and sublegal size (top) and by release method (bottom); bars show mean ± 95% credible intervals. See Loher et al. (2022) and Dykstra et al. (2024).

Viability categories assigned to fish discarded by the guided recreational fishery

Proportion of Pacific halibut viability categories by hook size in the guided recreational fishery

Proportion of viabilities assigned to Pacific halibut after capture with recreational gear on different sized (12/0 and 16/0) circle hooks; bars show mean ± 95% credible intervals.