2026/01/21 by Nathan D. Stewart, Alex Hanke, Dheeraj Busawon +4 · 1 voice
Environmental Science · #Fish Ecology and Management Studies #Isotope Analysis in Ecology #Marine and fisheries research
paper · doi:10.3354/meps15108
openalex publication_date 2026/01/21 · openalex created_date 2026/01/22 · openalex updated_date 2026/06/11
Characterizing individual diet specialization in predators is key for understanding food webs and their potential for change. Monitoring the diets of apex predators is therefore particularly important for informing multi-species management. We assessed individual diet specialization and daily ration in Atlantic bluefin tuna Thunnus thynnus sampled from Newfoundland (Canada) waters during 2022-2023 using stomach contents with DNA metabarcoding on a subset of unidentified prey items, and liver-based stable isotope mixing models. Short-term (i.e. daily) diets were highly specialized, with Atlantic cod Gadus morhua accounting for 87.2% of prey by weight and occurring in 79.1% of stomachs. However, stable isotope mixing models indicated that longer-term (i.e. summer-fall feeding season) tuna diets were more generalized, with high contributions from both Atlantic cod (mean: 49.2%) and northern sand lance Ammodytes dubius (33.5%). Comparing our recent results with historical data from 1966 revealed a dietary shift in Atlantic bluefin tuna in Newfoundland waters from primarily consuming forage species such as capelin Mallotus villosus and squid ( Illex spp.) to a substantially greater reliance on Atlantic cod. The recent high consumption of Atlantic cod by Atlantic bluefin tuna resulted in the highest daily ration estimate for the species in the western Atlantic (4.2 ± 4.8% body mass d -1 ). Such high consumption rates may reflect tuna preying on cod and scavenging near cod fishing boats. Tuna condition metrics (Fulton’s K and C:N ratios) did not improve during the feeding season, indicating that cod-dominated diets may be insufficiently lipid-rich to accumulate fat reserves for optimal fitness.