Photo-based approach as an alternative method for collection of albacore (Thunnus alalunga) length frequency from longline vessels

Length frequency data are essential to the stock assessments of albacore (Thunnus alalunga) which has been either fully- or over-exploited in many regions of the world. To obtain ‘visible’ and verifiable length data, a photo-based length measurement approach was previously developed in which fishers take photos of fish adjacent to a plastic calibration board with colored squares using ordinary digital camera technology. Here we assess the feasibility of implementing the photo-based approach using direct comparisons with measured lengths from observer programs. Data from the Taiwanese longline albacore fishery are used to assess the utility of the photo approach in terms of accuracy (with considerations of on-board photographing and at-land length estimation) and cost (comparing with port-sampling and observer programs). Results indicate potentially significant cost savings compared with the other two programs, with acceptable levels of estimation error.