| Summary: | The fatty acid content and composition of the Antarctic krill Euphausia superba Dana, 1850were investigated using samples collected by a commercial fishing vessel. This dataset allowedcomparison between seasons, years (2013–2016), and different fishing locations. Quantities ofomega 3 fatty acids 20:5n-3 and 22:6n-3 (mg/g dry mass; DM) were highest in autumn anddecreased through winter to reach a spring low. Quantities of the flagellate marker 18:4n-3and diatom marker 16:1n-7c were variable and did not display the same seasonal fluctuations.In summer, krill had high percentages (% total fatty acids) of 20:5n-3 and 22:6n-3, totalPUFA, and low 18:1n-9c/18:1n-7c ratios, indicating a more herbivorous diet. Krill becamemore omnivorous from autumn to spring, indicated by increasing ratios of 18:1n-9c/18:1n-7cand percentages of Σ 20:1 + 22:1 isomers. Bacterial fatty acids (Σ C15 + C17 + C19 isomers)were minor components year-round (0.9–1.8 %). Seasonal levels of herbivory and omnivorydiffered between years, and levels of specific fatty acid ratios differed between fishing locations.The fatty acid 18:4n-3 was a major driver of variability in krill fatty acid composition,with no obvious seasonal driver. This is the first study to report krill fatty acid data during allfour seasons over consecutive years. This large-scale study highlights the value of using fisheriessamples to examine seasonal and annual fluctuations in krill diet and condition.
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