Knowing how Pacific halibut (Hippoglossus stenolepis) distribute in relation to ocean conditions is of primary importance to halibut managers, as they are tasked with estimating stock size and designing effective monitoring programs amidst a changing climate. This research examined near‐bottom environmental data alongside halibut survey catch data for the years 2006–2009 on the continental shelf of Oregon, Washington, and southern British Columbia. The objectives of the research were to: (1) characterize summer environmental conditions and halibut distribution; (2) explore ranges and possible tolerance thresholds for halibut in relation to temperature, dissolved oxygen (DO), salinity, and pH; and (3) identify the primary environmental factors affecting distribution of halibut and model the observed relationships. Seasonal hypoxia is an annual feature of the study area and results suggest halibut exhibited an apparent DO minimum threshold of 0.9 mL L−1. Ordinary least squares multiple regression analysis indicated that depth, temperature, and DO were significant variables in predicting halibut distribution, whereas salinity and bottom type were not. Ambiguity in model results led to the use of two additional analytical methods, geographically weighted regression (GWR) and tree regression, to examine regional variation and the overarching structure of halibut distribution. The three models yielded similar results indicating the importance of DO and temperature as variables describing structure. The GWR model yielded the best fit of the three when using DO as a predictor variable, indicating that regional variation is a factor. These results suggest that low, but above‐threshold, DO may be contributing to catchability differences in the survey.

Pacific halibut (Hippoglossus stenolepis) is managed as a single stock throughout the Gulf of Alaska (GOA) and eastern Bering Sea (BS), but biogeographical barriers and the potential for differential impacts of climate change may alter habitat use and distributions, and restrict connectivity between these ecosystems. To improve our understanding of larval dispersal pathways and migrations of young fish within and between GOA and BS, we (a) examined potential pelagic larval dispersal and connectivity between the two basins using an individual‐based biophysical model (IBM) focusing on years with contrasting climatic conditions and (b) tracked movement of fish up to age‐6 years using annual age‐based distributions and a spatiotemporal modeling approach. IBM results suggest that the Aleutian Islands constrain connectivity between GOA and BS, but that large island passes serve as pathways between these ecosystems. The degree of connectivity between GOA and BS is influenced by spawning location such that an estimated 47%–58% of simulated larvae from the westernmost GOA spawning location arrived in the BS, with progressive reductions in connectivity from spawning grounds further east. From the results of spatial modeling of 2‐ to 6‐year‐old fish, we can infer ontogenetic migration from the inshore settlement areas of eastern BS toward Unimak Pass and GOA. The pattern of larval dispersal from GOA to BS, and subsequent post‐settlement migrations back from BS toward GOA, provides evidence of circular, multiple life stage, connectivity between these ecosystems, regardless of climatic variability or year‐class strength.

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Sensitivity analyses have identified uncertainty regarding sex ratios within commercial landings of Pacific Halibut Hippoglossus stenolepis as an influential source of variance within annual stock assessments for this species in U.S. and Canadian waters. Sex composition of dockside landings cannot be directly observed because all retained fish must be eviscerated at sea, and sex cannot be visually determined in the absence of the gonads. In the current study, a marking program was evaluated in which sex-specific marks were applied by fishers to their retained catch, the mark was recorded during dockside monitoring, and the accuracy of the recorded sexes was validated using genetic techniques. The chosen marks (two vertical cuts in the dorsal fin for females and a single cut in the operculum of males) were considered by fishers to be easy to apply during at-sea processing and produced sex-ratio estimates that were equivalent to genetic results for 65% of sampled landings. However, vessel-and region-specific accuracy was variable. Additional incentives to encourage vessels to participate in the program, continued outreach, or potentially a regulatory requirement to mark fish would be required to produce sufficient data to satisfy stock assessment needs, and ongoing validation would likely need to accompany such a program to ensure consistent and acceptable data quality.