Changes in mercury and cadmium concentrations and the feeding behaviour of beluga (Delphinapterus leucas) near Somerset Island, Canada, during the 20th century

Beluga (Delphinapterus leucas) continues to be an important food species for Arctic communities, despite concerns about its high mercury (Hg) content. We investigated whether Hg and cadmium (Cd) concentrations had changed during the 20th century in beluga near Somerset Island in the central Canadian Arctic, using well-preserved teeth collected from historical sites (dating to the late 19th century and 1926-1947) and during subsistence hunts in the late 1990s. Mercury concentrations in both historical and modern teeth were correlated with animal age, but 1990s beluga exhibited a significantly more rapid accumulation with age than late 19th century animals, indicating that Hg concentrations or bioavailability in their food chain had increased during the last century. The geometric mean tooth Hg concentration in modern 30 year old animals was 7.7 times higher than in the late 19th century, which corresponds to threefold higher concentrations in muktuk and muscle. Teeth from 1926 to 1947 were similar in Hg content to the late 19th century, suggesting that the increase had occurred sometime after the 1940s. In contrast, tooth Cd was not correlated with animal age and decreased during the last 100 years, indicating that anthropogenic Cd was negligible in this population. Late 19th century beluga displayed a greater range of prey selection (tooth delta15N values: 15.6-20.5 per thousand) than modern animals (delta15N: 17.2-21.1 per thousand). To prevent this difference from confounding the temporal Hg comparison, the Hg-age relationships discussed above were based on historical animals, which overlapped isotopically with the modern group. Tooth delta13C also changed to isotopically more depleted values in modern animals, with the most likely explanation being a significant shift to more pelagic-based feeding. Industrial Hg pollution is a plausible explanation for the recent Hg increase. However, without further investigation of the relationship between the range exploitation of modern beluga and their possible exposure to regional marine food chains with (naturally) higher Hg contents than their historical counterparts, we cannot unequivocally conclude that the increase was anthropogenically driven.     

An evaluation of teeth of ringed seals (Phoca hispida) from Greenland as a matrix to monitor spatial and temporal trends of mercury and stable isotopes

Total mercury (Hg) concentrations were measured in teeth of ringed seals from Qeqertarsuaq, central West Greenland (1982 to 2006) and Ittoqqortoormiit, central East Greenland (1986 to 2006). Stable isotopic ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) were determined as well to provide insights into diet variations between regions or through time. Mercury concentrations decreased the first years of life of the animals suggesting that Hg had been transferred from the mother to the foetus and newborn. The Hg concentrations in teeth were significantly lesser in ringed seals from central West Greenland compared to those from central East Greenland. Carbon and nitrogen stable isotopic values measured in the animals differed also significantly between the two regions. Increasing temporal trends of dental Hg concentrations between 1994 and 2006 were observed in ringed seals from both central West Greenland and central East Greenland. These increases were attributed to global changes in environmental Hg levels since no temporal trends in δ¹⁵N values were found to support the hypothesis of a diet shift over time. Furthermore, a decreasing temporal trend in δ¹³C values was observed in the teeth of seals from central East Greenland, and explained by a likely change over time towards more pelagic feeding habits; alternatively, the so-known Seuss effect was thought to be responsible for this decrease. Finally, it was concluded that the tooth of ringed seal was a good monitoring tissue to assess Hg trends.     

Hexachlorocyclohexanes (HCH) in ringed seal (Phoca hispida) from Ulukhaktok (Holman), NT: Trends from 1978 to 2006

Trends in α-, β-, and γ-hexachlorocyclohexane (HCH) concentrations were examined in blubber lipid of ringed seals (Phoca hispida) from Ulukhaktok (Holman), NT (Canada) sampled at intervals between 1978 and 2006. α-HCH usually represented approximately 90% of the total HCH isomers. α-HCH and γ-HCH concentrations showed no change over the sampling interval, but β-HCH concentrations increased significantly, about 8-10-fold in females and 4-5-fold in males. Residue concentrations showed no dependence on age. Concentrations (all data as ng/g lipid, GM (range)) of α-HCH were significantly higher (P < 0.001 by t-test) in males (217 (93.9-517), n = 37) than those in females (138 (40.9-402), n = 38). β-HCH concentrations did not differ between the sexes. Concentrations of γ-HCH were significantly higher (P < 0.05) in males (6.74 (0-46.7)) than in females (4.35 (0-19.0)). Although global emissions of both α-HCH and β-HCH have declined since the early 1980's, the “signal” of HCH emission changes has not yet resulted in a “response” in ringed seal residue concentrations. In the light of our current understanding of the dynamics of HCH in the Arctic, we conclude that any such response may not be detected by retrospective analyses of the sort describe here at least for another decade or so, because of the longevity of the seals.     

Modeling spatially explicit population dynamics of Pterostichus melanarius I11. (Coleoptera: Carabidae) in response to changes in the composition and configuration of agricultural landscapes

The intensification of agricultural practices has induced the local, national and regional extinction of many species and also affected ecosystem services provided by biodiversity such as biological control of agricultural pests. We model the population dynamics of Pterostichus melanarius (Coleoptera: Carabidae), a carabid beetle often used as indicator species of habitat changes, by a joint model that combined a matrix model of population dynamics including local dispersal with an explicit model of the patchy landscape of the polders of the Bay of Mont St. Michel (Brittany, France). We used this model to evaluate the effects of landscape composition and configuration on the spatial population dynamics of this carabid beetle, and also investigated the consequences that different management strategies of the structure and composition of an agricultural landscape can have on its abundance and spatial distribution. The results of this study highlight that semi-habitats (field edges, dykes, hedgerows) usually considered as shelters for wintering play a key role as well for summer recruitment. We find that there is an optimal cluster size of patches for population viability that is induced by the seasonal movement of P. melanarius. However, the effect of increasing the amount of semi-natural habitats patches on the viability of this population critically depend on the spatial arrangement, connectivity and spatial alternation of the network of semi-natural habitats, a feature that should be considered in the conservation and management actions in the landscape context.     

Influence of sex, maturity and reproduction on PCB and p,p′DDE concentrations and repartitions in the European hake (Merluccius merluccius, L.) from the Gulf of Lions (N.W. Mediterranean)

The main objective of this work was to establish the influence of sex, maturity and reproduction on the contamination of the demersal fish Merluccius merluccius by organochlorine compounds. Polychlorinated biphenyls (PCBs) and p,p′DDE were quantified in muscle, liver and gonads of female and male hakes collected in the Gulf of Lions in 2004 and 2005. Observed levels appeared higher than the population of the Bay of Biscay and lower than the population of the Thyrrenian Sea. Contaminant fingerprints were roughly constant whatever the studied organ and the hake biological condition. Concentrations varied significantly according to the sex and maturity of hakes. Mature specimens were more contaminated than immature, and males presented higher levels than females. This sex effect can be linked to a lower growth rate of males, and a contaminant elimination during female spawning. Gonadal contamination depends on the importance of lipid content and increases with the maturation degree. Although the main organ of energy and PCB storage is the liver, muscle appears as the main contributor to the gonad contamination.