FAR 2025/18 Additional analyses for orange roughy (ORH 3B)

• We investigated orange roughy stock assessments for Chatham Rise, part of ORH 3B.
• Stock assessments for this region have encountered problems, with models much more optimistic about stock status than suggested by fisheries statistics and some research surveys.
• We describe skipper information on orange roughy behaviour and target fishing, the biology of orange roughy with respect to their sensory abilities, and observations of orange roughy responding to objects in the water column and to fishing disturbance.
• Investigations of fisheries catch per unit effort found evidence of disturbance, where recent fishing activity reduced catch rates. The disturbance effect was considered useful but was not a “game changer”.
• Seasonal trends in sea temperature, primary productivity, weather, and sea state, could be simply described using a “month” variable.  Spatial and regime shift models improved the fits to data.
• Observed changes in orange roughy age frequency distributions have been poorly fitted in recent stock assessment models, but were better fitted here by models assuming reproduction had dropped to a very low level once the fishery started. One hypothesis that might explain this result is that fishing disturbance reduced reproductive output. 

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