COMERN Project Description
13/02/16
PROJECT DESCRIPTION
1. Identification
Project Manager: Dr. Alain Tremblay
Hydro-Québec, Montréal, Qc
Research Title: Intensive fishing as a mercury contamination mitigation tool
Research Theme: Aquatic food web and wildlife contamination
Theme Leader: Dr. Mike Paterson
Collaborators: Dr Marc Lucotte
Université du Québec à Montréal, Montréal, Qc.
Roger Schetagne.
Hydro-Québec, Montréal, Qc.
Dr. Roger Verdon
Hydro-Québec, Montréal, Qc
2. Project summary
Elevated mercury (Hg) concentrations in fishes of importance for human consumption have been
reported in many natural lakes and large hydroelectric reservoirs of Canada. These concentrations
translate into restrictions for human fish consumption by indigenous communities and sports
fishers and their families and for commercialization of these fishes in urban markets. The
propensity of fish to act as (methylmercury) MeHg accumulators has prompted a number of
experiments to determine whether intensive fishing strategies - which consist in removing a
significant part of the fish biomass from a lake through net fishing - can be used to reduce the
total amount of MeHg within fish communities and to depress the concentration of MeHg in
target species intended for human consumption. In fact, studies done on small lakes in Finland
and Sweden have demonstrated that intensive fishing results in a decrease in the Hg levels in the
fish. However, the mechanisms involved remain unknown. Therefore, in 1997, Hydro-Québec
with the collaboration of Université du Québec à Montréal, initiated a study to evaluate the
feasibility of applying intensive fishing as a mitigation option to reduce Hg levels in fish in lakes
COMERN Head Office: Université du Québec à Montréal, President-Kennedy Bldg – Suite PK-7150 C.P.8888,
Downtown STA (Qc) H3C 3P8. Phone: (514) 987-3601, Fax : (514) 987-3635
www.unites.uqam.ca/comern -- email: comern@uqam.ca
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COMERN Project Description
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and reservoirs. Three hypothesis have been suggested to explain the reduction of Hg levels in
fish: (1) the decrease in fish density leads to a faster growth rate of individuals with lower Hg
accumulation than fish growing slowly (growth dilution); (2) the fishing effort induces a change
in diet favoring less contaminated prey (change in diet); (3) the removal of methylmercury
(MeHg) with fishing leads to a decrease in the amount of MeHg cycling in a lake (mass balance).
3. Research objectives
•
To verify the effectiveness of intensive fishing as a Hg contamination mitigation tool in
lakes.
•
To test the three initial hypotheses (biodilution, change of diet, Hg removal) and eventually
understand how intensive fishing can lead to a decrease of Hg concentration in biota.
•
To extend the conclusion of this study on lakes to larger water plans such as reservoirs.
Details
In 1997, we have characterized the presence of Hg in all environmental compartments of 5
natural lakes of the Nemiscau region Northern Québec (sediments, dissolved and particulate
matter in the water column, benthic invertebrates, plankton and fishes). Biomasses, fish ages and
gut contents have also been determined as well as the physico-chemical conditions of the lakes
and the nature of their drainage basin. An intensive fishing experiment was then conducted
(1998) in 3 of the 5 lakes and 2 were kept as control lakes. The 1998 fishing exercise removed
60%, 50% and 25% of the fish biomass of three experimental lakes with gill nets. Piscivorous
species accounted for at least 35% of the biomass removed from each lake. Plankton and benthic
invertebrate communities, water samples (dissolved and particulates fractions) and sediments
were sampled from 1998 to 2000 in the 3 experimental lakes as well as the 2 reference lakes to
describe and follow the lakes characteristics before and after intensive, as well as to verify the 3
explaining hypothesis.
Further monitoring is now needed to understand the Hg behavior changes truly attributable to
intensive fishing as opposed to those attributable to inter annual environmental fluctuations. Hg
concentrations in fishes must be monitored for a few years (3, 5 and 7 years after the intensive
fishing episode, i.e. 2001, 2003 and 2005) to determine the time lag between the intensive fishing
episode and the response in Hg concentrations. Besides, as the intensity of fishing was variable
from one lake to the next, the monitoring of Hg concentrations in fish over several years may
allow the determining of an optimal intensity and frequency of fishing in order to reduce Hg
concentrations in fishes of socio-economic importance for local communities.
COMERN Head Office: Université du Québec à Montréal, President-Kennedy Bldg – Suite PK-7150 C.P.8888,
Downtown STA (Qc) H3C 3P8. Phone: (514) 987-3601, Fax : (514) 987-3635
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COMERN Project Description
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1. Biogeochemical processes responsible for the decrease of Hg concentrations in fish
following intensive fishing
It is of prime importance to understand the mechanisms of Hg reduction in the biota in order to
maximize the proposed remedial method of intensive fishing. To do so, the following three
hypotheses will be tested in the years to come:
By harvesting a fair share of the lake biomass, a significant fraction of MeHg in circulation in a
given fish community of a lake may simultaneously be physically removed. But it is not clear yet
to which extent the ongoing releases of Hg from the largest Hg reservoir in a lake, i.e. the surface
sediments will mask this physical removal of Hg from the lake. Preliminary results from the
mass balance approach before fishing, showed that lake sediments (first cm only) represent 85%
to 95% of the total mercury budget and the dissolved fraction (<0.45 m) represent and another
5% to 15%. Benthic and plankton organisms account for less than 1% while the fish contribute
from 0.5% to 3%. As for MeHg, fish represent 40% to 74% of the methylmercury budget found
in lake ecosystems. Sediments, dissolved fraction, benthic and plankton organisms account for
respectively 10-40%, 12-32% and 1-12%. The removal of 25-60% of the fish biomass in a lake
represents the removal of around 40% of the MeHg budget, and more if sediment MeHg content
is not considered as part of the lake cycle.
Intensive fishing may also influence the age distribution in a given fish community and as such
the growth rates of the remaining fishes. Consequently, MeHg levels may decrease in fish tissues
as a consequence of biodilution in faster growing organisms. In this study, we shall use
information on the age, length and weight of both predatory fishes and smaller species.
The preferential removal of certain species (such as dominant predators) through fishing
activities may affect the community structure, and in particular the fish diet. As the main source
of MeHg for a fish comes solely from its food, MeHg body burdens in fish may be significantly
altered if the fish communities modify their diet after the intensive fishing episode. Stable
isotopic analyses (13C and 15N) in all major compartments of the food web will be used to
determine its overall structure. Preliminary results show that intensive fishing does not
significantly affect zooplankton biomass or size structure. The results, however, show changes in
dominance of macro-zooplankton species (>500 m, from Holopedium gibberum to Daphnia) in
the fished lakes as opposed to reference lakes. Lakes dominated by Daphnia presented lower
concentrations of total Hg and MeHg in zooplankton than lakes dominated by Holopedium
gibberum.
2. Extrapolation of the intensive fishing experiment to larger water bodies using
bioenergetic models
Basic data on the evolution of Hg behavior and identification of key biogeochemical processes
triggered by the intensive fishing experiment in the five experimental lakes will be used as tests
COMERN Head Office: Université du Québec à Montréal, President-Kennedy Bldg – Suite PK-7150 C.P.8888,
Downtown STA (Qc) H3C 3P8. Phone: (514) 987-3601, Fax : (514) 987-3635
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COMERN Project Description
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against existing bioenergetic models of Hg accumulation in fishes. Both models define Hg
burdens in fish as the difference between accumulation through food (and to a minor extent
through gills), and losses attributable to metabolism.
In a second step, we intend to apply the models to lakes of great fishing importance for the
Nemaska (Northern Québec) community. We shall choose the lakes to be tested in agreement
with the interest expressed by local Cree community (through the Cree Regional Authority).
Two years will be dedicated to test the mitigation model and to investigate harvesting tool
improvements for Hg management. In close collaboration with local users of the lakes, we shall
investigate the role of fishery practices on MeHg abundance in fish communities, on Hg
concentrations in selected species and size ranges of target fish species. In order to successfully
apply the scientific results to lakes harvested by local communities, we shall emphasize the
introduction into our bioenergetics model of traditional knowledge of the Cree community about
the lakes they use for fishing (species present, fish abundance, nature of the drainage basin, inter
annual fluctuations, etc.).
The results of this program should have important feedback on the local Cree communities as
well as on the sports-fishing industry. From the perspective of Canadian First Nation
communities reliant on domestic (subsistence) fisheries and in the context of sports or
recreational fisheries, it is important to know to what extent, and in what circumstances, different
harvesting strategies can be used to influence MeHg body burdens in the fish harvest.
COMERN Head Office: Université du Québec à Montréal, President-Kennedy Bldg – Suite PK-7150 C.P.8888,
Downtown STA (Qc) H3C 3P8. Phone: (514) 987-3601, Fax : (514) 987-3635
www.unites.uqam.ca/comern -- email: comern@uqam.ca
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