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Stable isotope analysis of baleen plates is a widespread technique for studying baleen whales. Typically, subsamples along the growth axis of the baleen plate are extracted and analysed to examine time-related variation in their stable isotope signals. However, baleen plate tissue is composed of two different tissues: a pair of cortex layers flanking an internal medulla. These two histological components exhibit differential development, and their consolidation as a tissue is therefore likely non-synchronic. This could influence stable isotope results because the stable isotope signal may differ in each subsample according to the proportion of the two histological components extracted from the tissue. In this study, stable isotope analysis was combined with optical microscopy examination of fin whale (Balaenoptera physalus) baleen plates to understand the ontogeny of the two histological components. In both of them, the δ15N values followed a sinewave pattern along the growth axis of the baleen plate. However, the δ15N values of the cortex appeared to be advanced compared to those of the medulla. Additionally, the amplitude of the δ15N values in the oscillations was higher in the cortex than in the medulla. The histological examination revealed that these differences are caused by earlier and faster synthesis of the cortex layer compared to that of the medulla. Because the stable isotope ratios of the two layers differ, we propose that in this type of studies only the outer-most part (closest to the surface) of the cortex should be subsampled and analysed. Additionally, to include the most recently formed tissue, this subsampling should start well below the zwischensubstanz, or baleen "gum". [ABSTRACT FROM AUTHOR]

Stable isotope analysis of baleen plates is a widespread technique for studying baleen whales. Typically, subsamples along the growth axis of the baleen plate are extracted and analysed to examine time-related variation in their stable isotope signals. However, baleen plate tissue is composed of two different tissues: a pair of cortex layers flanking an internal medulla. These two histological components exhibit differential development, and their consolidation as a tissue is therefore likely non-synchronic. This could influence stable isotope results because the stable isotope signal may differ in each subsample according to the proportion of the two histological components extracted from the tissue. In this study, stable isotope analysis was combined with optical microscopy examination of fin whale (Balaenoptera physalus) baleen plates to understand the ontogeny of the two histological components. In both of them, the δ15N values followed a sinewave pattern along the growth axis of the baleen plate. However, the δ15N values of the cortex appeared to be advanced compared to those of the medulla. Additionally, the amplitude of the 815N values in the oscillations was higher in the cortex than in the medulla. The histological examination revealed that these differences are caused by earlier and faster synthesis of the cortex layer compared to that of the medulla. Because the stable isotope ratios of the two layers differ, we propose that in this type of studies only the outer-most part (closest to the surface) of the cortex should be subsampled and analysed. Additionally, to include the most recently formed tissue, this subsampling should start well below the zwischensubstanz, or baleen "gum". [ABSTRACT FROM AUTHOR]

Stable isotope analysis of whale skin has been recurrently used to assess diet and movement patterns. Such studies rely on the untested assumption that the stable isotope ratios in the small skin biopsies analysed are representative of those throughout the skin. In balaenopterids, the ventral skin looks notably different from that of the dorsal region, which is smoother and darker. To investigate possible differences in isotopic ratios throughout the skin, we collected and analysed samples from dorsal and ventral positions in 28 fin whales ( Balaenoptera physalus ). No significant differences were found between these two skin positions, which might suggest that whale skin is likely a homogeneous tissue. Thus, the isotopic ratios determined at a specific point may be representative of the whole skin in whales. [ABSTRACT FROM AUTHOR]

Highly migratory marine species pose a challenge for the identification of management units due to the absence of clear oceanographic barriers. The population structure of North Atlantic fin whales has been investigated since the start of whaling operations but is still the subject of an ongoing scientific debate. Here we measured stable isotopes of carbon, nitrogen and oxygen in skin samples collected from 151 individuals from western Iceland, Galicia (NW Spain), the Azores archipelago and the Strait of Gibraltar (SoG). We found spatiotemporal differences in stable isotope ratios suggesting that fin whales sampled in these four areas may share a common feeding ground within the Northeast Atlantic at different times during the year. Our results also suggest that SoG whales use this common feeding ground in summer but exploit Mediterranean resources during the winter months, further supporting the existence of a limited but current exchange of individuals between these two basins. • δ 13C, δ 15N and δ 18O values were measured in fin whale skin from four North Atlantic areas. • Spatiotemporal differences were found in the stable isotope profiles. • All whales may share a common Atlantic feeding ground at different times during the year. • Gibraltar whales use this common feeding ground in summer but the Mediterranean in winter. [ABSTRACT FROM AUTHOR]

• Mitochondrial monophyly is commonly employed to define evolutionary significant units. • Monophyly may be caused by insufficient sampling or a recent common ancestor. • Mitogenomic studies are generally based on few samples and prone to sampling issues. • Expanded mitogenome sampling negates previous monophyly in fin whales. The advent of massive parallel sequencing technologies has resulted in an increase of studies based upon complete mitochondrial genome DNA sequences that revisit the taxonomic status within and among species. Spatially distinct monophyly in such mitogenomic genealogies, i.e., the sharing of a recent common ancestor among con-specific samples collected in the same region has been viewed as evidence for subspecies. Several recent studies in cetaceans have employed this criterion to suggest subsequent intraspecific taxonomic revisions. We reason that employing intra-specific, spatially distinct monophyly at non-recombining, clonally inherited genomes is an unsatisfactory criterion for defining subspecies based upon theoretical (genetic drift) and practical (sampling effort) arguments. This point was illustrated by a re-analysis of a global mitogenomic assessment of fin whales, Balaenoptera physalus spp., published by Archer et al. (2013), which proposed to further subdivide the Northern Hemisphere fin whale subspecies, B. p. physalus. The proposed revision was based upon the detection of spatially distinct monophyly among North Atlantic and North Pacific fin whales in a genealogy based upon complete mitochondrial genome DNA sequences. The extended analysis conducted in this study (1676 mitochondrial control region, 162 complete mitochondrial genome DNA sequences and 20 microsatellite loci genotyped in 380 samples) revealed that the apparent monophyly among North Atlantic fin whales reported by Archer et al. (2013) to be due to low sample sizes. In conclusion, defining sub-species from monophyly (i.e., the absence of para- or polyphyly) can lead to erroneous conclusions due to relatively "trivial" aspects, such as sampling. Basic population genetic processes (i.e., genetic drift and migration) also affect the time to the most recent common ancestor and hence the probability that individuals in a sample are monophyletic. [ABSTRACT FROM AUTHOR]

In this study we aim to assess the daily ingestion rates of synthetic particles by the fin whales (Balaenoptera physalus) that feed off the western coast of Iceland. To do so, we collected and analysed samples from the stomach content of 25 fin whales, consisting solely of northern krill (Meganyctiphanes norvegica). The particles found consisted of fibres and fragments, mainly blue, black and red, with an average size of 1.2 ± 1.3 mm. To confirm the synthetic nature of these particles, we used Micro-Fourier Transform Infrared Spectroscopy and comparison with a polymer library. The mean concentration of synthetic particles in the krill samples found in the stomachs of whales was 0.057 particles per gram, a value much lower than that previously reported for particle uptake by krill. From this concentration in krill, we estimated that the daily intake of synthetic particles for the North Atlantic fin whale would be ranging from 38,646 ± 43,392 to 77,292 ± 86,784 particles per day. Although at this level it is not possible to assess the impact of synthetic particles and their associated chemicals on the North Atlantic fin whale population, concentrations of these contaminants are likely to increase in the future, potentially causing adverse effects on whales and other marine mammals. [Display omitted] • Stomach content samples from 25 whales from western Iceland were analysed. • The only ingested prey found in the samples was northern krill. • The average concentration in krill was 0.057 synthetic particles (SP) per gram. • The number of SP daily ingested by fin whales was estimated in the tens of thousands. • SP presence in their diet might facilitate the exposure of whale populations to POPs. [ABSTRACT FROM AUTHOR]

Pollution of the marine environment by litter composed of plastics is a growing concern. Chemical additives such as organophosphate flame retardants (OPFRs), which are added to plastics to improve their qualities, are in focus because they allegedly cause adverse effects on marine fauna. Here we analyse OPFR levels in the muscle of fin whales because, as a mysticete, this cetacean obtains its food by filter-feeding and is thus highly vulnerable to marine litter. Moreover, the fin whale performs long-range migrations from low-latitude areas in winter to high-latitude areas in summer, a trait that makes it a potentially good large-scale biomonitor of pollution. We also analyse OPFR levels in its main prey, the krill Meganyctiphanes norvegica , to assess transfer through diet. The samples analysed consisted of muscle tissue from 20 fin whales and whole-body homogenates of 10 krill samples, all collected off West Iceland. From the 19 OPFRs analysed, we detected 7 in the fin whale and 5 in the krill samples. Tri-n-butyl phosphate (TNBP), Isopropylated triphenyl phosphate (IPPP) and Triphenylphosphine oxide (TPPO) were the most abundant compounds found in both species. Mean ∑OPFR concentration, expressed on a lipid weight basis, was 985 (SD = 2239) ng g−1 in fin whale muscle, and 949 (SD = 1090) ng g−1 in krill homogenates. These results constitute the first evidence of the presence of OPFRs in the tissues of fin whales. Furthermore, they seem to support the non-significance of bioaccumulation of OPFRs through lifespan and of biomagnification trough the food web. Unlabelled Image • We provide the first evidence of OPFR presence in the tissues of fin whales. • OPFRs were detected in the fin whale main prey, the krill Meganyctiphanes norvegica. • TNBP, IPPP and TPPO are the most abundant OPFRs in both fin whales and krill. • OPFRs do not seem to bioaccumulate or biomagnify. [ABSTRACT FROM AUTHOR]