The highlight of the Cedar Lake SPIN project was the successful partnership between the A/OFRC and Ontario Ministry of Natural Resources (OMNR) Harkness Laboratory for Fisheries Research. Like A/OFRC intern Jenna MacLaurin said, “We sure know how to make an entrance,” as the cavalry of 4 boats and 5 trucks made their way down the Brent Algonquin Park access road. With rotating crews, Algonquins of Pikwakanagan Fisheries Technician Peter Meness was able to experience many different aspects of the project. In three days, three crews set a total of 104 summer profundal index nets that fished for two hours in different depth strata (5-10m, 10 – 20m, 20 – 30m, 40-60m and >60m). Later that week, sculpin traps and pelagic nets (nets that float in the water column as opposed to sitting on the ground) were set at night. The netting program was accompanied by hydroacoustics transects that were completed during the day and night. The purpose of the intensive study will give an estimate of lake trout and pelagic fish abundance.
Fisheries hydroacoustics uses sound to detect fish (like a large depth sounder but more accurate). A sound pulse is transmitted and when it encounters objects that are of different density than water, such as fish or zooplankton, the sound is reflected back toward the receiver on the boat, creating an echo. These echoes provide information on fish size, location, and abundance. For example, during the day you can see the fish congregated in schools, with a cloud of Daphnia and other zooplankton at the top of the water column (Figure 1), and the Mysis zooplankton cloud floating around the 20 m zone, where light does not penetrate. After sunset, you can see the Mysis cloud rising and the fish disperse from the schools (Figure 2). This allows for a more accurate count of how many individual fish there are in the lake. These images are processed by a computer program to give estimates of biomass and number of fish broken into different size classes. These values partnered up with the index netting data can give estimates of abundance of different fish species present.
Figure 1: Daytime hydroacoustics image.
Figure 2: Night time hydroacoustics image.
Interestingly, one of the fish species caught in abundance was the Blackfin Cisco, previously considered to be extinct provincially, with the exception of Lake Nipigon (ROM 2008 www.rom.on.ca). Scientist, Dr. Mark Ridgway, at the Harkness Laboratory for Fisheries Research had previously discovered Blackfin Cisco in Hogan and Radiant Lake. So, he was excited to also find them in Cedar Lake, which is connected to Radiant Lake by the Petawawa River.
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