Skeena & Nass Sockeye Lakes Hydroacoustic Surveys 2008

Abstract

Skeena Fisheries Commission conducted hydroacoustic surveys of 4 juvenile sockeye rearing lakes in the Skeena and Nass Watersheds in 2008. Surveys were completed at Lakelse, Damdochax, Wiiminosik, and Bear Lakes. The results of these surveys are contained in this report.

Hydroacoustic sampling was conducted using a DT-X echosounder with a downward-pointing split-beam 199 kHz transducer. Fish samples were captured with mid-water trawl and gillnet gear. The trawl sample was used to determine the species composition of pelagic “small” size fish at each lake.

The overall density of “small” size class fish was highest in Damdochax and lowest in Bear Lake. We captured over 50 juvenile O. nerka in Damdochax and Wiiminosik lakes, and over 100 in Lakelse Lake. We were thus able to provide a fall fry population estimate for O. nerka in these lakes by apportioning the “small” size hydroacoustic estimates by species according to the trawl catch. The trawl catch at Bear Lake was insufficient to determine the species composition in the lake.

The overall “small” size fish estimates are not proportional to the sizes of each lake. Bear lake was the largest of the lakes surveyed in 2008 with a surface area over 1,900 hectares. Wiiminosik was the smallest lake surveyed with a surface area of only 18 hectares. While Wiiminosik is over 100 times smaller than Bear lake, there are only 10 times more “small” size fish in Bear Lake than Wiiminosik. Damdochax Lake covers roughly one tenth of the surface area of Lakelse, but the overall O. nerka population estimates for Damdochax are between 82% and 91% (depending on the method of estimation) of the much larger Lakelse Lake.