Bluefish Lake Mercury Monitoring

Regions: North Slave Region

Tags: contaminants, mercury, biology, fish sampling, fish, methylmercury, tissue sampling

Principal Investigator: Dewar, David J (1)
Licence Number: 15153
Organization: Northwest Territories Power Corporation
Licenced Year(s): 2012
Issued: Sep 24, 2012

Objective(s): The objectives of this research are:
To gather information in 2012 on the small-bodied and Young of Year fish in Bluefish Lake that may be available for monitoring as well as determine the most suitable methods and locations for their capture in order to finalize the proposed mercury study design; and to finalized the mercury study design to determine if methyl-mercury is generated as a result of flooding to the area between the existing dam and the new primary impoundment dam and, if so, if the methyl-mercury is taken up by fish.

Project Description: The Objectives of this research project are to:
1.) gather information in 2012 on the small-bodied and Young of Year fish in Bluefish Lake that may be available for monitoring as well as determine the most suitable methods and locations for their capture in order to finalize the proposed mercury study design, and 2.) complete monitoring between 2013 and 2015 as described in the finalized mercury study design to determine if methyl-mercury is generated as a result of flooding to the area between the existing dam and the new primary impoundment dam and, if so, if the methyl-mercury is taken up by fish.


This study includes three components:
1.) Determining the target species and sample sport fish for baseline.
2.) The monitoring of two Target species.
3.) The monitoring of game fish caught by anglers in Bluefish Lake using an adaptive management approach.

1.) Attempt to collect both small-bodied and YOY fish in Bluefish Lake during the summer and fall of 2012 to determine a target fish species:
- collect at least 16 Lake Trout (Salvelinus namaycush) and 17 Northern Pike (Esox lucius);
- record the species, age, sex, reproductive status and size of all captured fish and determine an appropriate target fish species;
- collect and submit fish tissue samples to an analytical laboratory for total mercury analysis;
- provide recommendations on the appropriate location, timing and collection methods of target fish species for the annual monitoring program;
- revise the proposed mercury study design, as required, and present the finalized mercury study design to DFO and Environment Canada;
- obtain MVLWB approval on the finalized mercury study design.

2.) Target Species Monitoring:
Monitoring stations for the Target species will be established in two locations in Bluefish Lake, and up to two locations in the newly flooded area (depending upon availability of the Target species). Flooding is anticipated to begin during the fall of 2012. Target species sampling will thus be conducted annually for the first three years after flooding (2013, 2014 and 2015). Specific collection methods (such as the gear type, location and timing) will be provided once the Target species has been determined.

3.) Game Fish Monitoring:
The monitoring of Lake Trout and Northern Pike will follow an adaptive management strategy, and proceed only if the Target fish show an increase in methyl-mercury levels, and there is a risk that methyl-mercury levels in Lake Trout and Northern Pike may meet or exceed safe consumption levels as a result of the Bluefish Hydro Plant.
It was suggested that Lake Trout and Northern Pike be monitored using non-lethal tissue plugs (Environment Canada and Fisheries and Oceans Canada 2012). However, fish age and sex are key to characterizing mercury levels in a fish population (particularly as mercury accumulates with age). Age cannot be as accurately estimated through non-lethal methods (such as fin ray clips) as it can with lethal methods (using the otolith). Use of fin rays tends to under-estimate fish age, possibly leading to an over-estimate of the rate of methyl mercury uptake. Thus, NTPC proposes to collect both otoliths and fin rays from the Lake Trout and Northern Pike in 2012. Age estimates from the two structures will be compared to estimate the accuracy of non-lethal methods before making a determination if non-lethal methods are appropriate for future monitoring.

Sample Collection and Analysis Procedures:
Target species will be lethally sampled. Species, weight and fork length will be recorded in the field. If aging structures cannot be removed in the field (i.e., if a microscope is required), then each fish will be stored in a clean and sealed plastic bag, and kept refrigerated.

Only stainless steel or ceramic blades and tools will be used. Following use, dirt and tissues will be removed from the instruments with distilled water before washing. Processing will be completed on a washable plastic surface covered with a plastic sheet which is changed after each dissection. After removal of the aging structure, each fish will be wrapped in plastic wrap and then placed in a clean and sealed plastic bag with a label containing the appropriate biomarker number and the analyses requested. The entire body (minus the otolith) of the Target species will be tested for mercury. A minimum of 5 grams (g) of tissue is required for the analyses. If the fish weigh less than this, the lab will be contacted and composite samples may be required.

Ageing structures (sagittal otoliths, and fin ray clips from adult Lake Trout and Northern Pike) will be collected from lethally sampled fish.

Studies have indicated that over 90% of the mercury accumulated in fish tissues is methyl mercury. Therefore, analysis of total mercury in fish tissues is proposed, under the assumption that values of total mercury would be in the form of methyl mercury.

A report will be submitted to the Mackenzie Valley Land and Water Board and made available on the public registry.

The fieldwork for this study will be conducted from September 24, 2012 to September 30, 2012.