Highland Lake Data - June 4 and June 11

posted Jun 23, 2018, 6:10 PM by Joseph Bickard   [ updated Jun 23, 2018, 6:11 PM ]

Highland Lake is currently experiencing what is called the "clear water phase". The clear water phase happens in most northern lakes, and is characterized by good water clarity, and high populations of Daphnia and other zooplankton who are eating phytoplankton as soon as it appears. However, soon those zooplankton numbers will start to decline, because (1) they start to run out of food - essentially they've become so abundant the phytoplankton production can't keep up, and (2) larval fish get large enough to eat them. These are larval fish of all species - yellow perch, white perch, smelt, bass, sunfish, alewife, you name it.

On June 5th the water quality samplers were on the lake gathering basic water quality data (temperature and dissolved oxygen profiles, secchi depth (a measure of water clarity), and water grabs for nutrients). The secchi depth (a measure of water clarity) was 7 m - excellent! The temperature and dissolved oxygen profiles looked very similar to the previous sampling date (May 23rd).

This summer the water quality team is using a 45 micron mesh filter to capture algae in the water column for analysis- those are very small holes. So even with the small amounts of material in the very clear lake water, filtering still took hours.

During the week of June 11th, we were practicing our fish-sampling techniques, and looking for larval fish. We practiced using our larger purse-seine, but ended up using a larval fish net that we towed in transects across the lake at about a meter depth. We did catch some larval fish (unidentified as of this writing, but probably not alewife, yet), and clogged the net up with zooplankton - Daphnia!  Thus far the larval fish are too small to eat the Daphnia, but soon all manner of larval fish will grow large enough to eat the Daphnia. The larval fish in the photo is approximately 13 mm in length. Mos tof our fish sampling will occur in the evening and early night because larval fish spread out in the dark to feed when they are less likely to be eaten by other fish.

Finally, lake sampling can be unpredictable - we enjoyed the region’s first rain for a couple of weeks while sorting through the Daphnia for tiny larval fish: