NWT RESEARCH DATABASE

Regions: Dehcho Region

Tags: mercury, biology, fish, subsistence

Objective(s): To establish an estimate of fish mercury concentration in walleye and pike in the Sanguez Lake; and to reduce the number of walleye and pike adults such that predation on walleye recruits decreases.

Project Description: Objectives of this research are to: 1. establish a population estimate of walleye in Sanguez Lake; 2. establish an additional estimate of fish mercury concentrations in walleye and pike. In 2013, mean mercury concentration in walleye was 0.71 mg/kg wet weight, and in pike was 1.09 mg/kg wet weight; 3. reduce the number of walleye and pike adults such that predation on walleye recruits decreases. Re-examine walleye size- and age-structure for walleye after the fish-down. (Note: A suitable number of large walleye adults must remain as spawning stock). The research team will monitor the population size, size structure, and age structure over a ten year period. Test mercury levels every 3 years, and at 10 years post-manipulation (Post study). When stocks have stabilized, establish a safe harvest level for renewed fisheries. 4. determine if data from this study regarding relationship of population structure and mercury concentrations can be used to inform management and manipulation strategies for other lakes in the region (through both data analysis and an extensive literature review); and, 5. Provide a traditional knowledge and science experience for the youth of the Dehcho. The fish down will be done using 50 yard gill nets with 2.5", 3.5", 4.5" and 5.5" mesh sizes, each net will be set over night and checked the following morning using an aluminum boat and kicker. Fish that are of the predetermined size or dead will be pulled from the net and biologically sampled, collecting data on sex, maturity, length, weight and ageing structure. In addition to the biological sampling, a predetermined number of tissue samples will be collected for mercury analysis. Fish that are alive and either too small or big will be removed from the nets and released into the lake. Fish that are being collected will be large and unsuitable for consumption, they will be used as trapping bait or as part of various agricultural projects. Mercury concentrations, and size and age structure of the population will be monitored every 3-5 years, and at 10-years post manipulation. The initial fish-down in September 2017 did not result in the target amount of biomass being removed (the lake was stratified and the fish were not moving much). Thus, additional fish-down activities will be conducted in 2018. This project has been developed with input from the community to ensure full involvement at every level. The project was initiated by a community question of whether or not fishing out certain sized fish species would decrease contaminant concentrations, allowing the lake to be used for increased subsistence. Local community members will be hired as field assistants, camp cooks and helpers, and when the opportunity arises local youth will be transported out to the 5 lakes area to learn about the project, ecology and how to catch and prepare fish. The inclusion of youth in Dehcho Aboriginal Aquatic Resource Oceans Management (AAROM) projects is always a key part of our projects. Presenting all results is a priority for every AAROM project. Community presentations will be given annually and upon completion. As well community camps and cook outs will be used to discuss any results. In addition to community presentations, results will be presented at the annual AAROM meeting and an update given at the Dehcho Assembly. The fieldwork for this study will be conducted from June 28, 2018 to September 30, 2018.