Katrine Borgå

• Jourdain, Eve Marie; McKinney, Melissa A.; Remili, Anaïs; Andvik, Clare Margaret; Fagerlund, Carl Johan Ludwig & Karoliussen, Richard [Show all 8 contributors for this article] (2026). Advancing Amino Acid Isotope‐Inferred Trophic Ecology in an Apex Predator: Insights From a Data‐Rich Killer Whale Population. Ecology and Evolution. 16(8), p. 1–16. doi: 10.1002/ece3.74121. Full text in Research Archive Show summary

  Amino acid‐specific nitrogen isotope analysis (δ 15 N‐AA) is increasingly used to infer trophic ecology, yet remains poorly validated in marine predators. We analyzed bulk tissue δ 15 N ( 15 N/ 14 N) and δ 13 C ( 13 C/ 12 C), and δ 15 N‐AA in 105 skin samples collected from individually identified Norwegian killer whales between 2017 and 2023. Forty‐two individuals with best documented diets in 2010–2023, based on field observations and corroborated by mercury concentrations and bulk tissue δ 15 N values in skin, provided reference diet groups against which δ 15 N‐AA‐derived hypotheses were tested: Fish‐only (100% fish prey; n  = 15), Intermediate mixed diet (~10% mammalian prey in addition to fish; n  = 14), and Top mixed diet (~50% mammals, 50% fish prey; n  = 13). Univariate and multivariate approaches identified diet as the primary driver of δ 15 N variation across individual amino acids and multivariate isotopic space, whereas sex and life stage had little effect. However, substantial inter‐individual variation remained unexplained and appeared to reflect metabolic processes. Metrics δ 15 N ΣTrophic—ΣSource (δ 15 N difference between the sum of trophic amino acids and the sum of source amino acids) and isotopic difference between glutamic acid/glutamine (Glu) and phenylalanine (Phe) (δ 15 N Glu–Phe ) successfully identified Top mixed diet whales but lacked the sensitivity to identify Intermediate mixed diet individuals, whilst δ 15 N values of Threonine showed no relationship with trophic position. Proline (Pro) and Phe used as trophic‐source pair provided the first plausible δ 15 N‐AA‐derived trophic position estimates for killer whales and performed better than bulk isotope‐derived trophic position when a priori knowledge was not available. Multivariate clustering of δ 15 N‐AA data complemented trophic position estimates by resolving finer‐scale dietary variation occurring within trophic levels.

• Nowicki, Robynne; Gabrielsen, Geir W.; Borgå, Katrine; Søreide, Janne & Varpe, Øystein (2026). Seasonality and water masses shape energetics of a high Arctic fish: quantifying energy density and condition indices. Marine Ecology Progress Series. ISSN 0171-8630. 786. doi: 10.3354/meps15150. Full text in Research Archive Show summary

  Seasonal life history decisions and environmental factors shape energetics over annual cycles. We quantified seasonal energy density of polar cod Boreogadus saida , a central predator and prey in the Arctic marine food web. We collected individuals from Atlantic and polar waters in the Barents Sea, to assess the impact of seasonality and water masses on energy density (kJ g -1 wet weight (WW)). Additionally, we compared energy density to 4 condition indices (Fulton’s, residual and hepatosomatic indices, and percent dry weight) to test their accuracy as energetic proxies for polar cod. Energy density varied seasonally and was lower in Atlantic waters. In polar waters, energy density was lowest in April/May, whereas seasonal variation was weaker in Atlantic waters. Energy density was highest in December in both water masses, although not much higher than March in polar water. Differences between water masses were seasonal, greatest in March (Atlantic: 4.07 ± 0.53 kJ g -1 WW; polar: 5.77 ± 0.62 kJ g -1 WW) and negligible in December (5.66 ± 0.83 and 5.86 ± 0.62 kJ g -1 WW, respectively). Percent dry weight best represented energy density, while Fulton’s and residual (derived from WW) indices were poorly correlated to energy density. Our results show that seasonality and environmental factors shape energetics, and that energy proxies must be carefully selected to accurately represent the energetic status of an organism. Our seasonal resolution highlights potential ‘critical windows’, when polar cod may be most vulnerable to stressors, whilst our spatial comparison provides insight into potential impacts of ongoing Atlantification.

• Andvik, Clare Margaret; Fagerlund, Carl Johan Ludwig; Jourdain, Eve Marie; Yuan, Bo; Haddad-Weiser, Gabrielle & Lyche, Jan Ludvig [Show all 9 contributors for this article] (2026). Comparing polychlorinated n-alkane occurrence and biomagnification with legacy contaminants in a killer whale food web. Environmental Research. ISSN 0013-9351. 306. doi: 10.1016/j.envres.2026.125367. Full text in Research Archive Show summary

  Polychlorinated n-alkanes (PCAs), the largest component of the commercial product chlorinated paraffins, have been used globally in increasing amounts since the regulations of legacy contaminants, such as polychlorinated biphenyls (PCBs). The bioaccumulative potential of PCAs compared to legacy contaminants is inconclusive, with limited data available for PCAs with carbon chain length ≤9 and ≥18, particularly in food webs which include mammalian top predators. Here, we analysed and compared PCAs of different carbon chain length (very-short: PCAs-C6-9 [vSCCPs], short: PCAs-C10-13 [SCCPs], medium: PCAs-C14-17 [MCCPs], and long: PCAs-C18-24 [LCCPs]), 57 legacy contaminants, and total mercury (Hg) in killer whales (Orcinus orca) from northern Norway (n = 59) and a range of fish and marine mammals. We found that legacy organic contaminants dominated in concentration and pattern in marine mammals (54–87%), whereas PCAs and Hg dominated in fishes (58–98%). A species' physiology (poikilotherm or homeotherm) influenced the food web magnification of several contaminants, with estimated trophic magnification factors (TMFs) underestimated in PCAs, and overestimated in PCB-153, p.p’-DDE and Hg, if unaccounted for. PCAs-C6-9 and PCAs-C10-13 had similar and low TMFs for poikilotherms and homeotherms, and similar to PCB-28 (TMF range: 1.9–2.4 [95% confidence interval 0.9–5.7]). PCAs-C14-17 and PCAs-C18-24, had high TMFs in poikilotherms (4.8 [1.3–18] and 4.6 [1.2–18], respectively), and no significant trophic magnification in homeotherms (1.0 [0.5–2.3] and 1.0 [0.4–2.8], respectively), with the opposite pattern for PCB-153 and p.p’-DDE. Our results indicate higher PCA concentrations and biomagnification potential in poikilotherms than homeotherms, which is likely due to lower biotransformation and elimination ability.

• Konestabo, Heidi Sjursen; Leinaas, Hans Petter; Gestel, Cornelis A.M. van & Borgå, Katrine (2026). Prior pesticide exposure reduces drought tolerance in Arctic and temperate springtails—Effects of sequential stressors. Environmental Toxicology and Chemistry. ISSN 0730-7268. 45(6), p. 1460–1469. doi: 10.1093/etojnl/vgag046. Full text in Research Archive
• Giebichenstein, Julia; Warner, Nicholas Alexander; Routti, Heli Anna Irmeli; Harju, Mikael; Varpe, Øystein & Gabrielsen, Geir Wing [Show all 7 contributors for this article] (2026). Accumulation patterns of polychlorinated alkanes in an Arctic marine food web. Environmental Research. ISSN 0013-9351. 299. doi: 10.1016/j.envres.2026.124360. Full text in Research Archive Show summary

  Polychlorinated alkanes (PCAs), otherwise known as chlorinated paraffins, are contaminants of emerging Arctic concern where our understanding of their occurrence and trophic transfer in Arctic food webs remains limited. To investigate biomagnification potential of PCAs, we analyzed short-chain PCAs: C10-C13 and medium-chain PCAs-C14-17 in three Arctic species: polar cod (Boreogadus saida), ringed seal (Pusa hispida), and polar bear (Ursus maritimus) and Subarctic capelin (Mallotus villosus) samples collected from the northern Barents Sea in 2017 and 2021. PCAs-C10-13 concentrations were low, but detectable in all species, while PCAs-C14-17 concentrations were mainly below detection limits in the mammals. PCAs did not biomagnify, as the lowest concentrations were found in polar bear (0.7 ng g−1 lw) and the highest in capelin (56.9 ng g−1 lw). The PCA homologue profiles were similar among Arctic species, with PCAs-C10-13 dominating in polar cod and marine mammals, which may suggest a contribution from long-range atmospheric transport. In contrast, PCAs-C14-17 were most abundant in the Subarctic capelin, likely reflecting a different exposure. Despite differing PCAs-C14-17 concentrations among the two fish species, their PCAs-C14-17 homologue profile was similar, indicating uniform global production trends. Subarctic capelin is increasingly being preyed upon by Arctic predators and may facilitate the biological transport of PCAs-C14-17 into Arctic ecosystems. These findings suggest that climate-driven shifts in species distribution may have the potential to alter contaminant exposure pathways in Arctic marine food webs.

• Dulgheriu, Daniela; Andvik, Clare Margaret; Jourdain, Eve Marie; Borgå, Katrine; Ruus, Anders & Haug, Tore [Show all 9 contributors for this article] (2026). A sensitive liquid chromatography–tandem mass spectrometry analytical method of steroid hormones in small blubber samples from four whale species. Conservation Physiology. 14(1). doi: 10.1093/conphys/coag023. Full text in Research Archive Show summary

  Steroid hormones can give an indication of stress, physiological health and reproductive status in whales; however, analysis is often limited by sample mass. We developed a sensitive analytical method using solid phase extraction–liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS/MS) for the identification and quantification of eight steroid hormones (cortisol, cortisone, testosterone, androstenedione, progesterone, 11-deoxycortisol, 11-deoxycorticosterone and 17-hydroxyprogesterone) in small amounts of whale blubber (≤50 mg). Blubber biopsies were collected from stranded killer whales (Orcinus orca; n = 7), harbour porpoises (Phocoena phocoena; n = 3) and sperm whales (Physeter macrocephalus; n = 4), harvested common minke whales (n = 10; Balaenoptera acutorostrata) and free-living killer whales (n = 2) in Norway and the Barents Sea. Steroid hormones were separated using pentafluorophenyl propyl stationary phase and an optimized gradient programme with a total 20-min run. All samples (n = 26) were analysed at 50-mg sample mass, and a subset (n = 11) at 25 mg or lower. Low limit of detection and limit of quantification values resulted in high detection rates of hormones, and we found similar hormone concentrations between parallel samples and at the lowest tested sample mass (14 mg). Cortisol concentrations in sperm whales (4.3 ± 1.6 ng/g) were four times higher than stranded killer whales (1.1 ± 0.96 ng/g), which in turn were up to four times higher than free-living killer whales (0.23 ± 0.12 ng/g), harbour porpoise (0.64 ± 0.38 ng/g) and harvested minke whales (0.22 ± 0.13), possibly due to fatality type and duration of stress prior to death. We provide the first quantification of blubber steroid hormones in killer whale, minke whale, sperm whale and harbour porpoise, and in less than 50-mg sample mass. By minimizing sample mass without compromising precision or sensitivity, our method allows for steroid hormone analysis even on samples with limited availability, strengthening our ability to monitor and conserve marine mammal populations.

• Graves, Stephanie D.; Kidd, Karen A.; Arts, Michael T.; Braaten, Hans Fredrik Veiteberg; Wit, Heleen de & Borgå, Katrine [Show all 8 contributors for this article] (2025). Terrestrial carbon inputs drive methylmercury accumulation in zooplankton of boreal and subarctic lakes. Limnology and Oceanography. ISSN 0024-3590. 70(10), p. 2910–2923. doi: 10.1002/lno.70185. Full text in Research Archive Show summary

  Boreal and subarctic lakes are subject to the climate‐sensitive process of browning, whereby transport of terrestrial dissolved organic matter (tDOM) to lakes results in greater dissolved organic carbon (DOC) concentrations and associated darker water color. Increasing tDOM will increase mercury (Hg) transport to these lakes, but whether this leads to greater methylHg (MeHg) bioaccumulation in food webs remains unclear. We determined whether increasing DOC increased MeHg bioaccumulation in the lower food web (i.e., zooplankton) by measuring a suite of water chemistry characteristics (including aqueous MeHg and DOC) along with stable isotopes of C (δ 13 C) and N (δ 15 N), fatty acid (FA) profiles, and MeHg content of zooplankton from 16 Scandinavian boreal and subarctic lakes along a DOC gradient in the Fall of 2016. We found that both aqueous and zooplankton MeHg were positively correlated with DOC concentration, and that DOC and zooplankton MeHg both increased with the bacterial FA marker 18:1n‐7 and decreased with docosahexaenoic acid (DHA) : arachidonic acid and DHA : eicosapentaenoic acid ratios in zooplankton, which are indicators of diet or taxonomic composition. Zooplankton MeHg content was best predicted by δ 13 C and the FA 18:1n‐7, indicating that zooplankton MeHg bioaccumulation in zooplankton was associated with changes in their resource use along a DOC gradient. Our results suggest that lake browning will likely lead to an increase in MeHg bioaccumulation in zooplankton by affecting aqueous MeHg exposure and lower food web dynamics. In turn, this may lead to increased MeHg contamination in fish and other wildlife.

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• Giebichenstein, Julia; Warner, Nicholas Alexander; Harju, Mikael; Routti, Heli Anna Irmeli; Varpe, Øystein & Gabrielsen, Geir W. [Show all 7 contributors for this article] (2025). SHORT- AND MEDIUM-CHAIN CHLORINATED PARAFFINS IN AN ARCTIC MARINE FOOD CHAIN. Full text in Research Archive
• Giebichenstein, Julia; Dupont, Nicolas; Harju, Mikael; Varpe, Øystein; Gabrielsen, Geir W. & Andersen, Tom [Show all 7 contributors for this article] (2025). Seasonal Insights into Pollutant Accumulation and Biomagnification in an Arctic Marine Food Web. Full text in Research Archive
• Andvik, Clare Margaret; Jourdain, Eve Marie; Borgen, Anders; Lyche, Jan Ludvig; Karoliussen, Richard & Haug, Tore [Show all 7 contributors for this article] (2025). Intercorrelations of short-, medium- and long-chain chlorinated paraffins, dechloranes and legacy POPs in 10 species of marine mammals from Norway, in light of dietary niche. Full text in Research Archive

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