Strontium in fin whale baleen: A potential tracer of mysticete movements across the oceans?

Strontium is a metal broadly distributed in oceanic waters, where its concentrations follow gradients mainly driven by oceanographic and biological factors. Studies on terrestrial vertebrates show that Sr can accumulate in mammalian hair in amounts mainly related to the external environment, a property that has been scarcely investigated in aquatic mammals. Cetaceans are marine mammals whose skin is generally hairless, but the species belonging to the mysticete group feed through a filtering apparatus made of keratinous baleen plates that, like hair, grow continuously. During their annual latitudinal migrations, mysticetes cross water masses with variable chemo-physical characteristics that may be reflected in these tissues. In the present study, baleen plates were sampled from 10 fin whales obtained from NW Spain (N = 5) and SW Iceland (N = 5) to investigate Sr concentrations along the plates growth axis. Samples were taken longitudinally at regular 1 cm-intervals on each plate. Sr concentrations, determined through mass spectrometry, ranged from 5 to 40 mg kg-1 and increased from proximal to distal positions along plates. These results suggest a progressive adsorption of Sr on the plate surface, a process that also occurs in mammalian hair. Increasing trends were similar in the two regions but overall concentrations were significantly higher in NW Spain, reflecting different Sr baseline concentrations in the two areas and indicating isolation between the two whale populations. Some oscillations in Sr longitudinal trends were also detected, likely indicating that whales migrate across water masses with different Sr baselines. These results suggest that Sr concentrations in keratinous tissues of marine mammals can be used as ecological tracers of their migrations and habitat use.

Fin whales as bioindicators of multi-decadal change in carbon and oxygen stable isotope shifts in the North Atlantic.

Global changes, and particularly the massive release of CO2 to the atmosphere and subsequent global warming, have altered the baselines of carbon and oxygen stable isotopic ratios. Temporal shifts in these baselines can be advantageously monitored through cetacean skin samples because these animals are highly mobile and therefore integrate in their tissues the heterogeneity of local environmental signals. In this study, we examine variation of δ13C and δ18O values in the skin of fin whales sampled over three decades in two different North Atlantic feeding grounds: west Iceland and northwest Spain. These locations are situated about 2700 km apart and thus represent a wide latitudinal range within the North Atlantic Ocean. The δ13C decrease in both areas is attributed to the burning of fossil fuels and increased deforestation worldwide, the so-called Suess effect. The dissimilarity in the magnitude of the shift between the two areas is coincidental with previous information on local shifts and lies within the ranges of variation observed. δ18O values experienced a minimal, yet significant change in fin whales from W Iceland (a decline of -0.44‰ between 1986 and 2013) but not in those from NW Spain. This is in concordance with a higher rise in temperatures in the former area than in the latter. The study validates the use of cetacean skin to monitor temporal and geographical shifts in stable isotopic values and alerts that, when applying this tool to ecological research, comparisons between sample sets should take into account temporal and latitudinal scales.

A genomewide catalogue of single nucleotide polymorphisms in white-beaked and Atlantic white-sided dolphins.

The field of population genetics is rapidly moving into population genomics as the quantity of data generated by high-throughput sequencing platforms increases. In this study, we used restriction-site-associated DNA sequencing (RADSeq) to recover genomewide genotypes from 70 white-beaked (Lagenorhynchus albirostris) and 43 Atlantic white-sided dolphins (L. acutus) gathered throughout their north-east Atlantic distribution range. Both species are at a high risk of being negatively affected by climate change. Here, we provide a resource of 38,240 RAD-tags and 52,981 nuclear SNPs shared between both species. We have estimated overall higher levels of nucleotide diversity in white-sided (π = 0.0492 ± 0.0006%) than in white-beaked dolphins (π = 0.0300 ± 0.0004%). White-sided dolphins sampled in the Faroe Islands, belonging to two pods (N = 7 and N = 11), showed similar levels of diversity (π = 0.0317 ± 0.0007% and 0.0267 ± 0.0006%, respectively) compared to unrelated individuals of the same species sampled elsewhere (e.g. π = 0.0285 ± 0.0007% for 11 Scottish individuals). No evidence of higher levels of kinship within pods can be derived from our analyses. When identifying the most likely number of genetic clusters among our sample set, we obtained an estimate of two to four clusters, corresponding to both species and possibly, two further clusters within each species. A higher diversity and lower population structuring was encountered in white-sided dolphins from the north-east Atlantic, in line with their preference for pelagic waters, as opposed to white-beaked dolphins that have a more patchy distribution, mainly across continental shelves.

Shipboard measurements of the hearing of the white-beaked dolphin Lagenorhynchus albirostris.

This is the first report of an underwater audiogram from a dolphin in a capture-and-release scenario. Two bow-riding white-beaked dolphins Lagenorhynchus albirostris (a female and a male) were captured using the hoop-net technique in Faxaflói Bay, Iceland. The dolphins were transferred to a stretcher and hoisted into a plastic research tank on board a small fishing vessel. Two underwater transducers were used to cover the frequency range from 16 to 215 kHz. Two human EEG electrodes mounted in suction cups, one placed near the blow hole and the other on the dorsal fin, picked up bioelectrical responses to acoustic stimuli. Responses to about 1000 sinusoidal amplitude modulated stimuli for each amplitude/frequency combination were averaged and analyzed using a fast Fourier transform to obtain an evoked auditory response. Threshold was defined as the zero crossing of the response using linear regression. Two threshold frequencies at 50 kHz and 64 kHz were obtained from the female. An audiogram ranging from 16 to 181 kHz was obtained from an adult male and showed the typical ;U' shaped curve for odontocetes. The thresholds for both white-beaks were comparable and demonstrated the most sensitive high frequency hearing of any known dolphin and were as sensitive as the harbor porpoise.

Pathological findings in harbour porpoises (Phocoena phocoena) from Norwegian and Icelandic waters.

A study of 37 by-caught harbour porpoises from Icelandic and Norwegian waters showed that most were in good or moderate nutritional condition and none was severely emaciated. Mild infection with lungworms (Halocercus invaginatus, Pseudalius inflexus, Torynurus convolutus) was found in 84% of the Icelandic and 91% of the Norwegian animals, usually associated with bronchopneumonia which was rarely severe. Most (91%) of the animals had parasites in the stomach and intestine (Anisakis simplex, Contracaecum osculatum, Pholeter gastrophilus), and Campula oblonga was present in the liver and pancreas of 88 and 21%, respectively. Oesophagitis, gastritis, cholangitis, pericholangitis, pancreatitis and lymphadenitis were almost exclusively associated with parasitic infection and usually mild. Bacterial isolates were obtained from 50 to 55% of the animals but were not considered to be clinically significant. There was no indication of morbillivirus infection. Icelandic and Norwegian animals showed a thicker blubber layer and a lower incidence of severe lesions, especially in the respiratory tract, as compared with reports of by-caught animals from the Baltic Sea.

Populations genetic analysis of nuclear and mitochondrial loci in skin biopsies collected from central and northeastern North Atlantic humpback whales (Megaptera novaeangliae): population identity and migratory destinations.

It has been speculated that humpback whales, Megaptera novaeangliae, from the northeastern North Atlantic breed in tropical waters off the coast of West Africa and therefore that they represent a separate breeding population from that which winters in the West Indies. We determined the genotype at six microsatellite loci as well as the sequence of the first 288 nucleotides in the mitochondrial control region of 133 skin biopsies collected from humpback whales in the central North Atlantic (Iceland and Jan Mayen) and the northeastern North Atlantic (Bear Island and the northern coast of Norway). We detected no significant deviations from Hardy-Weinberg proportions nor any differences in genotype frequencies between localities at the nuclear loci. However, the mitochondrial analyses revealed two distinct matrilineal aggregations: the central and the northeastern North Atlantic. Our findings were not compatible with the idea of a separate eastern North Atlantic breeding ground unless one has been established recently. The proposed alternative hypothesis of a common North Atlantic panmictic population (wintering primarily in the West Indies) in which individual whales display maternally directed site-fidelity to specific feeding grounds was supported by re-sightings of two northeastern North Atlantic humpback whales in the West Indies.

Species hybridization between a female blue whale (Balaenoptera musculus) and a male fin whale (B. physalus): molecular and morphological documentation.

In 1986 a large, pregnant, female balaenopterid whale was caught in Icelandic waters. The animal had morphological characteristics of both the blue and the fin whale. Molecular analyses of the whale showed that it was a hybrid between a female blue whale and a male fin whale. The descent of the species hybrid was established without access to either parental specimen. Analysis of the fetus showed that it had a blue whale father. The present report of species hybridization between the two largest cetacean species, the blue and the fin whale, documents the occurrence of cetacean species hybridization in the wild. It is also the first example of any cetacean hybridization giving rise to a fertile offspring.