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Summary
Arctic charr in Lake Ellasjøen, Bear Island,
possesses one of the highest muscle concentrations of PCBs observed so
far in freshwater fish in remote Arctic areas. Thus, the aim of this
study was to reveal possible effects from accumulation of PCBs on the
individual and/or the population level on the sympatric Arctic charr
population in Lake Ellasjøen. This was accomplished by 1) comparing
the charr population structure in 1998 with the one in 1978 (population
level), and 2) by correlating the individual variation in PCB level
with life history traits as size, age, growth rate, sex, maturity
stage and parasite burden (individual level). Individual contamination
was also correlated with habitat/food choice.
PCB-concentrations (å
PCB) in muscle tissue from 132 charr, varying in length from 10 to 67
cm, varied from 55 to 2 500 ng/g ww. For smaller charr (< 30 cm),
slow growing individuals were significant more contaminated than fast
growing ones, in accordance with the "growth dilution"
phenomena. For larger fish (> 30 cm), å
PCB increased strongly with fish size/age, probably due to cannibalism.
We found no significant correlation between contamination of PCB and
fish sex, maturity stage or parasite burden.
No clear cut changes in the charr population
structure between 1978 and 1998 was found.
Scientific results
Background
Within freshwater ecosystems, PCBs reach predatory
fish mainly through their prey, and high levels have especially been
recorded in long-lived predators such as northern pike (Esox lucius),
burbot (Lota lota) and lake trout (Salvelinus namaycush).
In some lakes in the Yukon Territories and in high mountain lakes in
Canadian Rocky Mountains, high concentrations of the pesticide
toxaphene in lake trout flesh has made it necessary (for Health and
Welfare Canada) to limit consumption of these foods.
Based upon a pilot study, in which a few fish (1-3
individuals) charr were analyzed for PCB in several lakes in the
western Arctic, the only charr caught and analyzed from Ellasjøen,
displayed a contamination level of PCB fish of more than 5 000 ng/g ww.
Under a joint venturing in 1996, NINA and Akvaplan-niva sampled and
analyzed a few more fish from Ellasjøen and Øyangen, and the earlier
findings were confirmed, i.e. that the muscle concentrations of PCBs
in Ellasjøen charr was very high.
Aim of this study
Thus, the aim of this study was to reveal possible
effects from accumulation of PCBs on the individual and/or the
population level on the sympatric Arctic charr population in Lake
Ellasjøen. This was accomplished by 1) comparing the charr population
structure in 1998 with the one in 1978 (population level), and 2) by
correlating the individual variation in PCB level with life history
traits as size, age, growth rate, sex, maturity stage and parasite
burden (individual level). Individual contamination was also
correlated with habitat/food choice.
Sampling and analyzes
Most charr were sampled by gillnetting and by
electrofishing in autumn 1998 (some from 1996 were also used). A
subsample of 487 charr from Ellasjøen and 65 charr from Øyangen were
analysed regarding length, weight, age, sex, maturity status, parasite
burden (Diphyllobothrium spp.), flesh colour and diet. Of these
162 and 13 charr from Ellasjøen and Øyangen, respectively, were
analyzed for PCB by Natalia Plotitsyna, at the Polar Research
Institute of Marine Fisheries and Oceanography (PINRO-Murmansk). A
signed contract was made between Norwegian institute for nature
research (NINA-Tromsø) and Polar Research Institute of Marine
Fisheries and Oceanography (PINRO-Murmansk) beforehand. Some time was
spent to prepare the contract, and in addition a few problems arise
when analyzing the fish. Some fish had to be reanalyzed, and the last
results was not ready before last week (14. November 2000). A total of
11 congeners were analyzed: PCB (28, 31, 52, 99, 101, 105, 118, 138,
153, 156 and 180). During the results, the "å
PCB" is the summation of all 11 congeners.
Results
Our investigation on Bear Island confirm earlier
findings that the Arctic charr population in Lake Ellasjøen,
Bear Island, probably possesses the highest muscle concentrations of
PCBs observed so far in freshwater fish in remote Arctic areas. Charr
captured in a nearby lake, Øyangen, however, possessed levels of PCBs
far lower than those found in Ellasjøen. Of the 11 congeners, PCB153
constituted as much as 45 % of the total PCB, while PCB138 and PCB 152
constituted 25 and 12 % respectively.
The å PCB in muscle tissue from the 132
charr analyzed from Ellasjøen (varying in length from 10 to 67 cm)
varied from 55 to 2 500 ng/g ww. For smaller charr (< 30 cm), slow
growing individuals were significant more contaminated than fast
growing ones, which is in accordance with the "growth dilution"
phenomena (Jensen 1982). For larger fish (> 30 cm), å
PCB increased strongly with fish size/age, probably due to cannibalism.
We found no significant correlation between contamination of PCB and
fish sex, maturity stage or parasite burden. No clear cut changes in
the charr population structure between 1978 and 1998 was found.
Relevance for monitoring (only in
Norwegian)
Dette økologiske studiet har vist at røye i Ellasjøen er utsatt
for en særdeles høy PCB- belastning. Akkumuleringen eller
fordelingen av PCB varierer imidlertid stort mellom individer, og kan
blant annet relateres til variasjon i livshistorieparametre som vekst
og kannibalisme. Hos fisk mindre enn 30 cm er PCB-nivået relativt
høyt, men det avtar likevel frem til fisken blir om lag 25 cm. Hos
større fisk, dvs. fra 30 til 65 cm øker PCB-nivået igjen kraftig.
Det viktige her er at PCB-belastningen hos den mest utsatte delen av
bestanden, dvs. de største og eldste fiskene (kannibalene), trolig er
direkte bestemt av kontamineringsnivået hos små fisk (byttefisken).
Ved en ytterligere økning av PCB innhold hos byttefisken vil nivået
hos kannibalene mangedobles.
Resultatene viser derfor at en vurdering av et habitats eller en
populasjons belastning av PCB, forutsetter at bestandens struktur og
livsstrategier er kjent. Det viktige hos røyebestanden i Ellasjøen
er forholdet byttefisk:kannibaler. En økning av PCB til
innsjøsystemet vil øke kontamineringen blant småfisk som igjen vil
mangedoble nivået hos stor fisk og eventuelt øke dødeligheten.
Forholdet mellom små- og storvokste individer kan derfor representere
en økologisk "helsefaktor" i (kontaminerte) bestanden.
Vi fant ingen klare endringer i populasjonsstrukturen i bestanden
mellom 1978 og 1998. Det er imidlertid uvisst hvorvidt PCB-nivået var
høyere eller lavere i røyebestanden for 20 år siden. Dersom det
etableres en (eller flere) referansebestander (-sjøer), bør denne
inneha sympatrisk røye med lignende livshistorie som i Ellasjøen.
Bestanden i Øyangen viser en helt annen livshistorie. Bestanden lever
i stor grad på skjoldkreps. Kannibalisme er ikke (lite) påvist og
transmisjonen fra kontaminert småfisk til større fisk finnes ikke.
Det finnes neppe sammenlignbare innsjøer på Bjørnøya, mens det på
Svalbard (Spitsbergen) finnes flere bestander med tilsvarende
livshistorie, men med "normalt" lav PCB akkumulering. Det
bør derfor vurderes å benytte eventuelle referansebestander på
Svalbard.
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Summary
Arctic populations inhabiting high
latitudes suffer a high risk of being exposed to various persistant, lipophilic pollutants
(e.g. polychlorinated biphenyls, PCBs) from atmospheric deposition. These compounds are
stored in body fats and increasingly concentrated as it passes up the food chain
(biomagnification). PCBs have been found in high levels in the top predators in marine
systems and have also been traced in landlocked fish.
Within freshwater ecosystems, PCBs reach predatory fish mainly through
their prey, and high levels have especially been recorded in long-lived predators such as
northern pike (Esox lucius), burbot (Lota lota) and lake trout (Salvelinus
namaycush). In some lakes in the Yukon Territories and in high mountain lakes in
Canadian Rocky Mountains, high concentrations of the pesticide toxaphene in lake trout
flesh has made it necessary (for Health and Welfare Canada) to limit consumption of these
foods.
In this project, an ecological study will be performed on wild
landlocked Arctic Charr from two neighbouring lakes at Bjørnøya, Lake Ellasjøen and
lake Øyangen. Arctic charr is the only fish species in these lakes, and in both lakes
charr exists in two forms: a slow growing "dwarf" and a fast growing
"normal" charr.
Based upon a few charr collected on the Bjørnøya in 1996, it was
shown that landlocked Arctic charr from Ellasjøen, possessed one of the highest muscle
concentrations of PCBs observed so far in freshwater fish in remote Arctic areas. Charr
captured in a nearby lake, Øyangen, however, possessed levels of PCBs far lower than
those found in Ellasjøen. It was also documented that the levels of PCBs in Ellasjøen
charr varied tremendously, from less than 100 up to more than 5 000 ng/g muscle w.w.
Differences in food preferences and life strategy within the fish
population in the lake probably explain most of the variations found between individuals.
There were some indications that slow growing individuals were more contaminated than fast
growing ones, probably due to the "growth dilution" phenomena. On the other hand
the largest charr is suspected to contain high levels, due to cannibalism, i.e. that the
large fast growing individuals become highly contaminated by eating dwarf charr.
Differences in age structure and sexual maturity cycles may also contribute to differences
in body burdens of PCB. The biomagnification of PCB in Ellasjøen may thus have an effect
upon the proportion of dwarfs compared to the amount of fast growing individuals, which in
turn would have great management influences.
The aim of this study is to reveal possible effects from accumulation
of PCBs on the individual and/or the population level on the sympatric Arctic charr
population in Ellasjøen and Øyangen, Bjørnøya. This will be accomplished by:
- Comparing the charr population structure in 1978 with the one in 1998 (population
level),
- Correlating the individual variation in PCB level with growth, growth rate (size at age
and back-calculated yearly increase), parasite burden, fecundity (gonado-somatic index,
fecundity, energy content), immune parameters, sex and maturity stage. Individual
contamination will also be correlated with habitat/food choice. The project was
initialized in 1998.
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