Limnological Data from Experimental Exposure of Juvenile Coho Salmon (Oncorhynchus kisutch) to Elodea in a High Latitude Lake

The field experiment was established in McKinley Lake (60.454310°, -145.199505°), Chugach National Forest, AK in 2017 and 2018 using limnocorrals (Curry Industries Ltd., Winnipeg, Manitoba, Canada R2G 1C2). Six limnocorrals (5 m diameter x 2 m depth; sidewalls with 4.76 mm mesh) were installed in the littoral zone at a depth of approximately 1.5 m across three bays of the lake.

At the end of the experiment, stocked juvenile coho salmon were trapped from the limnocorrals using baited minnow traps and cast nets. Dorsal muscle tissue and fin clips were collected for stable isotope analysis at the University of Wyoming Stable Isotope Facility (Laramie, WY USA). Macroinvertebrates were collected by sweeping a 243-µm mesh D-frame sweep net (Wildco, USA) for 1 minute in a 1 m2 area. Macroinvertebrates were collected at a depth of 1.5 m. Samples were collected at the beginning, middle, and end of the experiment each year. Zooplankton were collected by combining three vertical tows of an 80-µm mesh Wisconsin net. Zooplankton were collected from a depth of 1.5 m to the surface minimizing bottom disturbance. Samples were collected at the beginning, middle, and end of the experiment each year. Individual zooplankton were counted in each sample. If more than 200 individuals in the total sample, then 20% of the sample was counted to estimate total sample. At the start of the experiment in 2018, ceramic tiles were suspended at approximately 0.5 m depth to collect periphyton. At the end of the experiment, the standing biomass of green algae, diatoms, and cyanobacteria were measured using a portable fluorometer (Benthotorch, www.bbe-oldaenke.de). Water column chlorophyll-a was obtained by filtering 500 ml of water onto glass fiber filters (0.7 μm pore size), extracting chlorophyll-a in 90% acetone for 24 h, and then measuring the fluorescence of the sample. Samples were collected at the beginning, middle, and end of the experiment each year. Dissolved oxygen was measured in situ every 10-min with an archival probe (miniDOT logger, Precision Measurement Engineering Inc., California, USA) at a depth of approximately 0.5 m . Continuous temperature was recorded every 15 minutes using TidbiT v2, HOBO Water Temp Pro v2 (Onset Computer Corporation). Two temperature loggers were put into each limnocorral with one logger approximately 0.25 m below the surface and one logger at a depth of approximately 1 m.

We measured fork length (mm) and marked their otoliths by immersing fish in 50 ppm alizarin complexone for 4 h following methods of Zimmerman (2005). Marking the fish otoliths with alizarin complexone verifies the presence of fish in the limnocorral at the start of the experiment and provides a mark to estimate growth more accurately. In the laboratory, otoliths were removed and one sagittal otolith from each fish was mounted sulcus side down with Crystal Bond 509 on a microscope cover slip attached on one edge to a standard microscope slide. The otolith was then ground with 1200-grit sandpaper in the sagittal plane to the level of the nucleus (Zimmerman 2005). Using a fluorescent light (Leica EL 6000; Leica Microsystems (Switzerland) Limited) images of the otolith were taken using Leica camera (Model: DMC6200; Leica Microsystems (Switzerland) Limited) mounted on Leica microscope (Model: M60; Leica Microsystems (Switzerland) Limited). Using Image-Pro Premier (Version: 9.2 Build 6156, 64-bit. Media Cybernetics, Inc.), two independent technicians measured the distance from the nucleus of the otolith to the alizarin complexone marking and to the edge of the otolith. Aging transects occurred in the dorsal plane of the otolith approximately 135 degrees from the anterior-posterior axis.