Eve Jourdain

Climate change and other anthropogenic pressures are rapidly reshaping marine ecosystems, altering prey availability and predator interactions. Yet empirical evidence of how these relationships shift under changing conditions remains scarce. Drawing on over a decade of monitoring in a subarctic fjord system, we provide a rare insight into these dynamics. In northern Norway, the winter aggregation of herring (Clupea harengus) and their primary predator, the killer whale (Orcinus orca), has shifted northward under the combined influence of climate change and fishing pressure. This redistribution has brought baleen whales into the same foraging grounds, leading to direct interference competition. Humpback (Megaptera novaeangliae) and fin whales (Balaenoptera physalus) frequently intrude into killer whale carousel feeding events, exploiting dense, shallow prey patches optimized for lunge feeding. Such intrusions often end hunts prematurely, imposing energetic costs on killer whales. Meanwhile, the rapid growth of whale-watching tourism in these fjords further disrupts foraging activity. Integrating unpublished data and existing literature, this article highlights the asymmetric energetic costs and benefits arising from these emerging interactions; processes likely widespread, yet still largely undetected in other marine ecosystems. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.

Many of the key dynamics that shape predator–prey interactions are governed by the physical and physiological principles which determine how animals move and perform in their environments. This opinion paper outlines the foundations underlying marine vertebrate predator–prey encounters within the context of pelagic habitats. Variables, such as maximum swimming speed, acceleration and manoeuvrability, play crucial roles in dictating the outcome of predator–prey encounters. In pelagic areas, sustainable swimming speed is an additional factor that can play an important role when chases occur. These locomotor traits are, in turn, influenced by body size, morphology and physiology. For predator–prey size ratio between 10 and 100, predators resort to a number of alternative strategies in order to overcome the elusiveness of the prey resulting from their higher manoeuvrability. These include pursuit leading to prey exhaustion, group hunting and the use of weapons. The framework of how physiological, physical and scaling rules affect pelagic predator–prey systems is a useful tool for investigating multi-predator feeding aggregations, where the relative success and potential competition between each predator species will be dictated by the potential strategies available to them within the scope of their performance limits. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.

Knowledge of killer whale (Orcinus orca) diets is essential for assessing their ecological role, resilience to habitat change, and contaminant exposure risk. Previous dietary studies of...

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.

Genetic studies of killer whales ( Orcinus orca ) historically relied on markers from mitochondrial DNA or microsatellites, which are cost‐effective, but the difficulties in cross‐laboratory standardization have limited global data integration. Transitioning to whole genome sequencing (WGS) has advanced our understanding of killer whale population structure and demographic histories; however, the costs of WGS remain a limiting factor for studying many individuals. Targeted Single Nucleotide Polymorphism (SNP) genotyping provides a cost‐effective, reproducible alternative, yet it can be susceptible to ascertainment bias whereby markers discovered in a limited set of reference populations may fail to capture genetic diversity in unrepresented populations. Here, we evaluate ascertainment bias in a custom RNA bait enrichment kit targeting 1346 SNPs, originally identified in a dataset of North Pacific, Icelandic, and Southern Ocean killer whales. Specifically, we compare the relationships among 25 killer whales representing the species' global range inferred from 225,281 unlinked genome‐wide SNPs to the same relationships inferred from the 1346 SNPs targeted by the capture baits, with both sets subsampled from WGS data. Comparing principal component analyses (PCAs), the targeted subset recapitulated broad‐scale global population structure and clustering patterns consistent with the larger WGS dataset. We found a high correlation between the targeted bait PCA and the WGS PCA ( r = 0.961). However, the observed value fell below expectations based on random sampling ( p < 0.01). This deviation was likely driven by samples belonging to lineages not included in the original SNP discovery panel, suggesting a small level of ascertainment bias. Consequently, some unique genetic variation in these excluded lineages remains unrepresented, specifically impacting inference of the relationships to and among lower‐latitude populations. While this targeted enrichment panel is a robust tool for elucidating major evolutionary differentiation and facilitating cross‐laboratory comparisons, it is less reliable for detecting fine‐scale structure in unrepresented, genetically divergent populations.

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.