Spatial and temporal variability in mercury concentrations in predatory fish in lakes along the and in Marlene Evans1, George Low2, Derek Muir3, Jonathan Keating1, Xiaowa Wang3, Mike Low2, Diane Giroux4, Mike Tollis5, and Shawn Buckley6

1Environment Canada, Saskatoon, SK; 2Dehcho First Nations, , NT; 3Environment Canada, Burlington, ON; 4Akaitcho Territory Government, Fort Resolution, NT; 5Lutsel K'e Dene First Nation, Lutsel K'e, NT; 6Hay River, NT

1.25 1.25 Willow Lake Big Island Lake McGill and Deep lakes 1999 2012  2 Abstract 1.00 2012 1.00 McGill Lake (3.6 km ): average Hg concentrations in 2000 were low in lake whitefish and white suckers, but high in walleye and northern pike. g/g) Our previous research on mercury concentrations in predatory fish in lakes  0.75 0.75 In 2010, Hg concentrations remained high in walleye and increased in Guideline for commercial along the Mackenzie River determined that concentrations tended to be sale of fish northern pike. highest in small lakes, particularly where fish were old (mean age > 10 0.50 0.50 Deep Lake (2.1 km2): average Hg concentrations in 2000 were Mercury ( years), and lowest in large lakes like Great Slave Lake (Evans et al. 2005; 0.25 0.25 moderately low in lake whitefish and walleye, but high in northern pike. Lockhart et al. 2005). Mercury continues to be of concern in northern In 2011, Hg concentrations were higher in walleye and northern pike. environments because of warming trends and increased mercury 0.00 0.00 lake lake northern lake lake northern burbot emissions from Asian sources, which may be reaching the NWT. Climate whitefish trout pike whitefish trout pike Tathlina and Trout lakes 1.25 1.25 2 warming may facilitate the transformation of existing mercury supplies into Mustard Lake Fish Lake Tathlina Lake (574 km ; 1 m deep): there is a long Hg record for walleye in methylmercury, the form which is most readily biomagnified in food webs. 2013 2011 1.00 1.00 this lake because of the periodic commercial fishery. Average Hg This presentation highlights our investigations of 1) current mercury concentrations appeared to increase with time although sample size was concentrations in fish in the smaller lakes along the Mackenzie River, 0.75 0.75 low in most years. comparing current concentrations with previous measurements and 2) our Trout Lake (520 km2): has a relatively long Hg record because of the long-term trend monitoring of mercury in two species of fish in two regions 0.50 0.50 occasional commercial fishery. With the exception of 2008, average Hg of Great Slave Lake. We show an overall trend of increasing mercury 0.25 0.25 concentrations were <0.5 µg/g. Sample size has improved in recent concentrations with highest concentrations in predatory fish in small lakes. years allowing for more rigorous trend detection. 0.00 0.00 lake northern burbot lake lake walleye burbot trout pike whitefish trout Great Slave Lake 1.25 1.25  Introduction Little Doctor Lake Ekali Lake Average mercury concentrations were low (<0.2 μg/g) in lake trout and 1996 1996 burbot; concentrations were slightly higher in West Basin than East Arm  1.00 2013 1.00 2011 Over the past three years, Dehcho community members sampled fish fish.

populations in 12 lakes along the Mackenzie River to determine mercury g/g)  0.75 0.75 There was a significant trend of mercury increase in lake trout and burbot concentrations in fish; these data can be compared with earlier studies. in both regions of Great Slave Lake. The reasons for this increase are  Mercury concentrations have been monitored annually (with some minor 0.50 0.50 being investigated, but do not appear to be directly related to warming exceptions) in lake trout and burbot from the West Basin and East Arm of Mercury ( 0.25 0.25 trends. A paper (Evans et al. 2013) has been published on these Great Slave Lake since 1998; earlier data are available from commercial changes. fisheries records and more recent scientific studies. 0.00 0.00 lake lake walleye northern burbot lake walleye northern burbot whitefish trout pike whitefish pike 0.30 0.30 Fish Burbot Burbot N Wrigley 0 100 kilometers 1.25 West Basin East Arm Sanguez Lake Gargan Lake 0.25 0.25 1996 1.25 1996 2011 2013 1.00 0.20 0.20 1.00 Willow 0.15 0.15 Big Island 0.75 0.75 Little Doctor Fort Simpson Mustard 0.10 0.10

M 0.50 a 0.50 c

k

e

n Jean Marie River 0.05 0.05 z i e Fort Providence 0.25 R McGill Ekali 0.25 g/g) .

Gargan  0.00 0.00 Fort Simpson Yellowknife Deep 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010 Sanguez Kakisa 0.00 0.00 lake walleye northern lake northern Trout whitefish pike whitefish pike 0.30 0.30 Great Slave Tathlina Lake Trout Lake Trout (> 600 mm) 100 0 100 200 300 kilometers Mercury ( West Basin East Arm Trout Lake McGill Lake Deep Lake 0.25 0.25 1.5 2000 1.5 2000 2010 2011 0.20 0.20

g/g) 0.15 0.15 Results  1.0 1.0 0.10 0.10 Lakes on the Horne Plateau  2 0.5 0.5 0.05 0.05

Willow Lake (152 km ): average Hg concentrations in 1999 were low Mercury (

(<0.05 g/g) in lake whitefish and moderately low (0.02-0.05 g/g) in lake 0.00 0.00 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010 trout and northern pike. Hg concentrations were slightly higher in 2012. 0.0 0.0  2 lake white walleye northern lake walleye northern Year Big Island and Mustard lakes (each <20 km ): average Hg whitefish sucker pike whitefish pike concentrations were low in lake whitefish (Big Island Lake) and Species moderately low in lake trout, northern pike and burbot from both lakes in 1.25 2012 and 2013, respectively. Tathlina Lake Conclusions walleye 1.00 Fish and Little Doctor lakes   2 Mercury concentrations appear to be increasing in Fish Lake (<20 km ): average Hg concentrations in 2011 were low in lake 0.75 whitefish, moderately low in lake trout and burbot, but high (>0.05 g/g) predatory fish in lakes along the Mackenzie River. in walleye. 0.50 Mercury concentrations are relatively low in predatory Little Doctor Lake (21 km2): average Hg concentrations in 1999 were low fish in Great Slave Lake, with observed increases in lake whitefish, moderately low in lake trout, but high in walleye and 0.25 occurring at a slow rate. g/g)

northern pike. Similar Hg concentrations were observed in lake trout and  0.00 walleye in 2013; burbot Hg concentrations were high. 1981 1990 1991 1993 1994 1998 2012 1.25 References Trout Lake Ekali, Sanguez, and Gargan lakes lake trout 2 Evans, M.S. et al. 2005. Sci. Tot. Environ. 351-352: 479-500.  Mercury ( Ekali Lake (2.0 km ): in 1996 average Hg concentrations were 1.00 Lockhart, W.L. et al. 2005. Sci. Tot. Environ. 351-352: 427-463. moderately high in walleye and northern pike. Hg concentrations Evans, M.S. et al. 2013. Environ. Sci. Technol. 47(22): 12793-12801. increased in 2011 in both species; burbot Hg concentrations were high. 0.75  2 Sanguez Lake (1.8 km ): in 1999 average Hg concentrations were low in 0.50 Acknowledgements lake whitefish, but high in northern pike and walleye. Hg concentrations This research was supported by the Northern Contaminants Program,the were higher in these predators in 2011. 0.25 Dehcho Aboriginal Aquatic Resource and Oceans Management Program, Gargan Lake (1.1 km2): in 1996 average Hg concentrations were low in and the NWT Cumulative Impact Monitoring Program. Special 0.00 lake whitefish, but high in northern pike. Northern pike Hg 1977 1982 1990 1991 2003 2008 2011 2012 appreciation is extended to all community members engaged in the fish concentrations were higher in 2013. Year sampling.