Length, Weight, Energy Density, and Isotopic Values of Fish from Rivers in Northwest Alaska, 2015-2019

Fish were collected in June, August, and early September from 2015 to 2019 using beach seines, fyke nets, gill nets, hook and line, minnow traps, and backpack electrofishing. The beach seine (1.22 m ft x 6.1 m, 1.27 cm sq. mm mesh) was pulled upstream through shallow pools. The fyke net (0.6 cm mesh; 9 × 1 m wings; a 1 m diameter opening) was set in beaver ponds. Sinking monofilament gill net (six 6 m long mesh panels = total net length of 36 meters; mesh size per panel: 10.0 mm, 12.5 mm, 18.5 mm, 25.0 mm, 33.0 mm, and 38 mm) was deployed in the deepest area of beaver ponds. Hook and line casting was done opportunistically in streams and beaver ponds. Collapsible mesh minnow traps (25.4 cm x 25.4 cm x 43.18 cm; mesh 0.32 cm Sq; two 5.08 cm throat openings) were deployed in pools of streams and secured to the bank. Backpack electrofishing (Smith-Root, LR-24 Backpack Electrofisher) was used in streams by sampling upstream with one pass of a stream reach.

Prior to laboratory work all fish were stored frozen at -20°C. Fish were thawed, and epaxial muscle and caudal fin samples were collected, and frozen again at -20°C. Samples were next freeze-dried for at least 48 hours. Freeze-dried muscle and caudal samples were sent to the University of Wyoming Stable Isotope Facility in Laramie, WY, USA (www.uwyo.edu/sif/) for isotopic analysis. In short, samples were homogenized, weighed, and loaded into an elemental analyzer coupled to an isotope ratio mass spectrometer (EA-IRMS). Replicate samples the Stable Isotope Facility ran for QAQC are included in this data release. Energy density was determined using bomb calorimetry. A pellet of freeze-dried muscle tissue was pressed, weighed to the nearest 0.0001 g, and loaded into a semimicro Parr 6725 calorimeter to measure energy density. Benzoic acid standards were used to validate the efficacy of the machine.