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Environ Biol Fish (2015) 98:14111430 DOI 10.1007/s10641-014-0368-y
Diet and condition of Atlantic bluefin tuna (Thunnus thynnus) in the Gulf of Maine, 20042008
John M. Logan & Walter J. Golet & Molly E. Lutcavage
Received: 6 May 2014 /Accepted: 12 November 2014 /Published online: 22 November 2014 # Springer Science+Business Media Dordrecht 2014
Abstract Atlantic herring (Clupea harengus) are the primary forage for Atlantic bluefin tuna (Thunnus thynnus; ABFT) in the Gulf of Maine. Recent studies have documented significant declines in ABFT somatic condition and shifts in their size and spatial distribution in the Gulf of Maine, which may be linked to trophic changes. We collected stomachs (n=122) as well as liver (n=110) and white muscle (n=382) samples for carbon and nitrogen stable isotope analysis and lipid analysis to determine if diet composition had changed relative to the late 1980s to early 2000s for large, commercially harvested ABFT (185 cm curved fork length (CFL)).
Samples of smaller ABFT (<185 cm CFL) were also collected (stomachs: n=21; liver: n=17; white muscle: n=19) to compare diet between size classes. Large ABFT diet was similar among current and historic studies, Atlantic herring being the main prey (39.5 to 52.8 % weight). Small ABFT fed at a lower trophic position (TP=3.9) than larger individuals (TP=4.9) due to higher consumption of sand lance (Ammodytes spp.) and euphausiids (65.6 vs. 4.5 % weight). Mean and maximum lipid stores of large ABFT increased from spring through fall, but lean fish were observed in all seasons. In the fall, lean ABFT were lighter with lower nitrogen and higher carbon isotope values than co-occurring ABFT with higher lipid stores. These patterns are consistent with shelf vs. offshore isotope baseline differences in the western North Atlantic and variable arrival and residency patterns for ABFT in the Gulf of Maine.
Keywords Carbon . Food web . Herring . Lipids . Nitrogen . Stable isotopes
Introduction
In the Gulf of Maine, Northwest Atlantic, Atlantic bluefin tuna, (ABFT; Thunnus thynnus) remain an iconic and valuable emblem of New Englands seafood history, culture and economy (Grey 1927; Crane 1936) still pursued with passion by recreational and commercial fishermen. Historically (19501990s), the ABFT assemblage in the Gulf of Maine was composed mainly of adult fish that supported an extensive commercial
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