Fish Species Composition and Diet Information in Lakes of the Arctic Coastal Plain, Alaska, 2011-2013

From Laske et al., 2018: We sampled fish from 16 lakes using unbaited minnow traps (6 mm steel mesh, 23 cm diameter, and 44.5 cm length with two 2.5 cm openings), fyke nets (0.6 cm mesh, 15.2 x 1.2 m wings, and a 1.1 m square opening; or 0.6 cm mesh, 9 x 1 m wings, and a 1 m diameter opening), and gill nets (24.8 x 1.8 m, eight panels with mesh size from 19 to 64 mm [North American standard). Each lake was sampled on a minimum of four days over the span of the study, with a minimum of 6 h of fishing per sampling event. We deployed gear over short time intervals (3-4 h) to reduce losses due to digestion and to limit the potential for net feeding. Additional overnight net sets were employed during 2013 to capture more fish for stable isotope samples. At each lake, we sampled stomach contents up to approximately 30 individuals of each species, depending on availability. We sampled diets with gastric lavage using a 60 ml syringe filled with filtered water and a 5 fr catheter tube, or through direct collection of the stomach. We preserved contents from all stomachs with 95% ETOH. We collected muscle tissue for stable isotopes for each species at eight lakes (northern site only) – up to 11 individuals per species per lake. With a scalpel, we extracted a small plug of dorsal muscle from the left side of the fish, anterior to the dorsal fin, and preserved muscle plugs in 95% ETOH. Small fishes (< 45 mm length) were preserved and ground whole for stable isotope analysis (Swanson et al. 2010). Fourteen fish (55 – 60 mm length), of two genera (Pungitius and Coregonus), were used to test for mean differences between whole body and muscle samples

From Laske et al., 2018: We identified stomach contents to the lowest reasonable taxonomic level, given digestion, referencing taxonomic keys (Borror, Triplehorn, and Johnson 1989; Pennak 1989; Merritt, Cummins, and Berg 2008). We also specified the life stage of prey (e.g., larva). We placed muscle tissue into individual 4 ml glass vials and freeze-dried at -50°C for 48 hours (LABONCO FreeZone 1 Liter Benchtop Freeze Dry Systems 77400 Series, Kansas City, MO). Once dry, we used petroleum-ether to extract any remaining lipids (Kelly and Martínez del Rio 2010).We sent all samples to the Stable Isotope Facility at the University of Wyoming, Laramie, where they ground and analyzed samples for of δ15N and δ13C with a continuous flow stable isotope ratio mass spectrometer (Costech 4010, Carlo Erba 1110, Thermo Flash Elemental Analyzer coupled to a Thermo Delta Plus XP and Delta V IRMS). Analytic precision was ± 0.2‰, with standards L-glutamic acid and liver (36-UWSIF-Glutamic 1, δ15NAIR = -4.6‰, δ13CVPDB = -28.3‰; 39-UWSIF-Glutamic 2, δ15NAIR = 27.9‰, δ13CVPDB = 24.4‰; and UWSIF01 [Liver], δ15NAIR = -6.8‰, δ13CVPDB = -17.8‰).