Andrew Majewski

Polycyclic aromatic hydrocarbon metabolites in Arctic cod (Boreogadus saida) from the Beaufort Sea and associative fish health effects.

In 2012, Arctic cod (Boreogadus saida) were collected from offshore regions of the Beaufort Sea to determine the concentrations of CYP1A1 phase I metabolites of polycyclic aromatic hydrocarbons (OH-PAHs) in liver and to correlate measured concentrations with (i) morphometric measurements that are known to be indicative of fish health and, (ii) biochemical end points of health including vitamin A/E and metabolites and hepatic deiodinase activity (DI). Four ring OH-PAHs were detected in 90% of our samples with a mean liver concentration of 1829.2 ± 159.2 ng/g (ww). Total (∑) concentrations of 5/6-membered ring OH-PAHs in liver were smaller [mean of 931.6 ± 104.3 ng/g, (ww)] and detected less frequently (75%) than the 4-ring OH-PAHs. Fish length and liver weight were both negatively correlated to ∑ concentrations of 4-ringed OH-PAHs (p < 0.001). Liver somatic index was also negatively correlated to ∑4-OH-PAHs (p < 0.05) but not for ∑5/6-OH-PAHs (p > 0.1). There was a significant positive relationship between DI and 4-ring OH-PAHs (p < 0.05) in liver, suggesting an induction of this enzyme. No such correlation was observed for the 5/6-ring OH-PAHs. Retinyl palmitate (RP) was the only vitamin that could be measured in liver ranging from 0.230 to 26.3 ug/g (ww). No associations between RP and levels of the 4- or 5/6-ringed OH-PAHs were observed. Continued baseline studies are clearly warranted to further understand effects of OH-PAHs on fish health before planned exploration activities begin in this region.

A comparison of the trophic ecology of Beaufort Sea Gadidae using fatty acids and stable isotopes

Polar cod (Boreogadus saida) is one of the most studied Arctic marine fishes given its circumpolar distribution and centralised role in the Arctic marine food web. In contrast, relatively little is known about two other Arctic Gadidae: saffron cod (Eleginus gracilis) and Greenland cod (Gadus ogac). Climate change is expected to have an effect on sea ice-associated species, such as polar cod, but due to our lack of knowledge of other arctic gadid species it remains unclear how climate change will impact them and their interactions within the arctic marine ecosystem. Here, we explored the ecology of three Arctic Gadidae that co-occur in the Canadian Beaufort Sea. Stable isotope (SI) (niche overlap) and fatty acid (FA) (correspondence analysis and linear discriminant analysis) biomarkers were used to assess among- and within-species differences and trophic niche. Despite the close habitat proximity of saffron cod and polar cod while on the shelf, trophic niche characterisation revealed only a marginal overlap. Marginal niche overlaps also occurred for the two coastal species with similar diets, saffron cod and Greenland cod, likely reflecting regional-scale differences between two habitats. Within-species, polar cod collected from three habitats (shelf, upper- and lower-slope habitats) were not differentiated likely due to the movement of individuals between habitats. In contrast, Greenland cod had a narrow trophic niche and differentiation occurred between the two collection sites. The comparison of trophic niches defined by stable isotope and fatty acid proved a promising tool for new insights into the ecology of Arctic fishes.

Osmolyte Adjustments as a Pressure Adaptation in Deep-Sea Chondrichthyan Fishes: An Intraspecific Test in Arctic Skates (Amblyraja hyperborea) along a Depth Gradient

Accumulation of trimethylamine N-oxide (TMAO) by deep-sea animals is proposed to protect proteins against the destabilizing effects of high hydrostatic pressure (the piezolyte hypothesis). Chondrichthyan fishes (sharks, rays, and chimaeras) provide a unique test of this hypothesis because shallow-living species have elevated TMAO levels to counteract the destabilizing effects of high urea levels accumulated for osmoregulation. Limited interspecific studies of chondrichthyans reveal that increasing depth correlates with decreased urea and increased TMAO levels, suggesting a dynamic balance between destabilizing forces on proteins (high urea, hydrostatic pressure) and TMAO to counteract these forces. Indeed, an inability to minimize urea levels or maximize TMAO levels has been proposed to explain why chondrichthyans are absent in the vast abyssal region. An unresolved question is whether the depth-related changes in chondrichthyan osmolytes are a flexible response to depth or whether phylogenetic differences in species-specific physiological set points for osmolytes account for the differences seen with depth. Sampling Arctic skates (Amblyraja hyperborea) across a 1,015-m depth gradient in the Beaufort Sea, we measured organic osmolytes in muscle using spectrophotometry and high-performance liquid chromatography. We found that the urea-to-TMAO ratio decreased linearly with depth, with tighter correlation than that seen in interspecific studies. Minor osmolytes, including betaine, sarcosine, and some α-amino acids, also declined with depth, apparently replaced (as with urea) by TMAO (a stronger piezolyte than those solutes). These data provide the first intraspecific evidence that flexible adjustments of osmolyte combinations are a key response for deep-sea living in individual chondrichthyans, supporting the piezolyte hypothesis.

Isotopic niche overlap between co-occurring capelin (Mallotus villosus) and polar cod (Boreogadus saida) and the effect of lipid extraction on stable isotope ratios

Climate change is expected to drive shifts in abundance and distribution of marine forage fishes and possibly result in dietary overlap among sub-Arctic and Arctic species. Stable isotopes of carbon and nitrogen (δ13C, δ15N) were used as a proxy of dietary niche breadth and overlap between co-occurring, immature capelin (Mallotus villosus) and polar cod (Boreogadus saida) collected in the western Canadian Arctic, Darnley Bay, NT, during August 2013. Stable isotope ratios were determined from muscle tissue to quantify the range of δ13C and δ15N, along with dietary niche breadth metrics (standard area ellipses and total area) and niche overlap between lipid-extracted and nonextracted muscle tissues of capelin and polar cod. Lipid extraction influenced the values of δ13C, δ15N, and C:N ratio in polar cod, but only δ13C in capelin tissue. Lipid extraction influenced the interpretation of dietary niche breadth and extent of overlap between co-occurring species, such that overlap of capelin within the niche of polar cod increased (from 53.0 to 89.7%) when lipids were extracted. We recommend the use of lipid extraction to standardize δ13C values when assessing dietary niches and extent of overlap between co-occurring fishes that differ in lipid content. Species-specific lipid normalization equations for δ13C ratios provided in this study can be used to correct δ13C ratios from nonextracted tissues of polar cod in future research. Overall, the high degree of dietary niche overlap between immature capelin and polar cod in the western Arctic suggests there is a high potential for competition between these fishes while immature.