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Data from commercial fishing vessels may enhance the range of observations available for monitoring the marine environment. However, effort and catch data provide information on fish distribution with a bias due to spatial targeting and selectivity. Here, we measured the shortcomings of standard fishery-dependent data and advocate for the utilization of more precise datasets indirectly collected by the commercial fishery. Data from a Danish traceability system, which records size of commercial fish at the haul level, are held against the set-up of current eLog and sales slips’ data collected for the Danish fisheries. We showed that the most accurate mapping of the spatial distribution of catches per size group is not only possible through size records collected at the haul level but also by high resolution on fishing effort data. In Europe, the regulation to land all catches with a quota or minimum size limit, including unwanted, has increased the focus on avoidance and discards; we show the potential of such data sources to inform on fish abundance and distribution, especially of importance where fishery-dependent data are the only source of information. [ABSTRACT FROM AUTHOR]

Fisheries science and fisheries management advice rely on both scientific and commercial data to estimate the distribution and abundance of marine species. These two data types differ, with scientific data having a broader geographical coverage but less intensity and time coverage compared to commercial data. Here we present a new type of commercial data with high resolution and coverage. To our knowledge, the dataset presented in this study has never been used for scientific purposes. While commercial datasets usually include the total weight by species on per haul basis, the new data also include the commercial size class for the species landed, recorded directly on a haul-by-haul basis. Thus, this dataset has the potential to provide knowledge on landed fish with as high spatio-temporal resolution as when coupling logbooks and sales slips but with the addition of detailed knowledge on the size distribution. Such information may otherwise be obtained through on-board observer programmes but unlike the observers’ data, the dataset presented here is routinely collected on most of the trips of the vessels involved, which means that the coverage of the data for the individual vessel is larger than observers’ data. Furthermore, the risk of changes in fishing behaviour due to the presence of an observer on-board is avoided. This paper describes the coverage and completeness of the dataset, and explores the reliability of the data available. We conclude that the main limitation is the small number of fishing vessels covered by the program, but that the data from those vessels are accurate, detailed, and relatively reliable. [ABSTRACT FROM AUTHOR]