Results update: Delving deeper into understanding Lake Trout
Understanding the potential competitive interactions between Lake Trout and bluelisted Bull Trout in the Peace Reach of Williston Reservoir is at the crux of a project led by Diversified Environmental Services (DES). Now, two years into a proposed four-year project, important data gaps are being filled.
Lake Trout are a freshwater char, native to many lakes in northern B.C. In Williston Reservoir there has been a dramatic increase in numbers, and knowing more about their seasonal movements, spawning areas and potential interactions with Bull Trout is a priority in our Reservoirs Action Plan.
In 2016, 40 Lake Trout were fitted with acoustic transmitters and hydrophones were positioned throughout the Peace Reach. The hydrophones are managed by Carleton University for a concurrent Bull Trout movement study. With 2017 data, the study team has been able to document for the first time, potential spawning areas in Williston Reservoir.
“In natural systems, they typically spawn on cobble shoals and shorelines,” says DES biologist, Ted Euchner. “While not unusual, Lake Trout in Williston Reservoir must spawn deeper than the 15 m drawdown depth, in order to reproduce successfully. Potential spawning sites identified in 2017 appear to coincide with rocky slopes that are now inundated.”
At one location, fish were frequently recorded at depths between 22 and 32 metres. An October 2017 temperature profile found an abrupt thermocline between 20 and 22 metres, where the water temperature dropped from nine to three degrees Celsius.
The research also found that the reservoir’s Lake Trout appear to form a single, wide-ranging population that move extensively throughout the entire reservoir. After transmitter deployment in June 2016, more than two thirds (68 per cent) of the tagged fish left the Peace Reach and returned by May 2017.
In 2018, more fish are being fitted with transmitters in the Parsnip and Finlay Arms, and more hydrophones are being deployed outside of the Peace Arm. When all the work is completed and the data analysed, the knowledge gained about Lake Trout will help inform future fisheries management strategies in Williston Reservoir.
Peace Reach Lake Trout movements
In Year one (2016-2017) of this project, 66 adult Lake Trout were sampled and acoustic transmitters were implanted in 40. In Year two (2017-2018), data from 27 data-logging hydrophone receivers (maintained by Carleton University and BC Hydro as part of a concurrent study) and four additional hydrophones deployed in the Finlay and Parsnip reaches, were used to focus field sampling in fall 2017. In Year three (2018-2019), acoustic transmitters will be implanted on 20 additional Lake Trout, additional receivers will be placed in the Finlay and Parsnip reaches, a second year of movement data will be recovered and fall survey work will focus on potential Lake Trout spawning or fall congregation areas, identified in 2017.