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Some modifications in the vascular system of marine mammals provide adaptive advantages for diving. This study analyses the organisation of the aortic wall in dolphins, observing artery changes in volume and blood pressure for diving behaviour. Samples of three aortic segments (ascending, thoracic and abdominal) of three dolphin species were processed for histological and morphometric studies. The three dolphin species used, striped dolphin (Stenella coeruleoalba), Atlantic spotted dolphin (Stenella frontalis) and common dolphin (Delphinus delphis), have shallow or intermediate diving habits. Our results indicated that the components of the aortic wall of the dolphins had different dispositions in the three selected segments. The aortic wall decreased in thickness along its length due to a loss of the lamellar units in the tunica media and a thinning of the main elements of the lamellar units along the artery. The life stage had little influence on the thickness of the aortic wall except for the ascending aorta. The weight, body length, species or sex of the specimen did not significantly influence the thickness of the wall or the lamellar units. In summary, the histological and morphometric aortic structure in dolphins, in relation to the studied parameters, seems to be similar to that previously described of terrestrial mammals such as pigs, except for a larger difference in the proportion of lamellar units between the ascending and thoracic segments.

An adult female Sowerby’s beaked whale was found floating dead in Hermigua (La Gomera, Canary Islands, Spain) on 7 December 2016. Severe traumas of unknown aetiology were attributed, and the gross and microscopic findings are consistent with catastrophic trauma as a cause of death. Rib fractures affected the intercostals, transverse thoracis skeletal muscles, and thoracic rete mirabile. Degenerated muscle fibres were extruded to flow into vascular and lymphatic vessels travelling to several anatomic locations into the thoracic cavity, including the lungs, where they occluded the small lumen of pulmonary microvasculature. A pulmonary and systemic skeletal muscle embolism was diagnosed, constituting the first description of this kind of embolism in an animal. The only previous description has been reported in a woman after peritoneal dialysis. Skeletal pulmonary embolism should be considered a valuable diagnostic for different types of trauma in vivo in wild animals. This is especially valuable when working with decomposed carcasses, as in those cases, it is not always feasible to assess other traumatic evidence.

Fat embolism is the mechanical blockage of blood vessels by circulating fat particles. It is frequently related to traumas involving soft tissues and fat-containing bones. Different techniques have been used for decades to demonstrate histologically fat emboli, being the extremely toxic post-fixation with osmium tetroxide one of the most used techniques in the last decades. In the present study, the osmium tetroxide technique was compared qualitatively and quantitatively, for the first time, with chromic acid and Oil Red O frozen techniques for histological fat emboli detection in the lungs of eight sperm whales that died due to ship strikes. This was also the first time that chromic acid technique was tested in cetaceans. Results showed that the three techniques were valuable for the histological detection of fat embolism in cetaceans, even when tissues presented advanced autolysis and had been stored in formaldehyde for years. Although quantitative differences could not be established, the Oil Red O frozen technique showed the lowest quality for fat emboli staining. On the contrary, the chromic acid technique was proven to be a good alternative to osmium tetroxide due to its slightly lower toxicity, its equivalent or even superior capacity of fat emboli detection, and its significantly lower economic cost.

Mass stranding events (MSEs) of beaked whales (BWs) were extremely rare prior to the 1960s but increased markedly after the development of naval mid-frequency active sonar (MFAS). The temporal and spatial associations between atypical BW MSEs and naval exercises were first observed in the Canary Islands, Spain, in the mid-1980s. Further research on BWs stranded in association with naval exercises demonstrated pathological findings consistent with decompression sickness (DCS). A 2004 ban on MFASs around the Canary Islands successfully prevented additional BW MSEs in the region, but atypical MSEs have continued in other places of the world, especially in the Mediterranean Sea, with examined individuals showing DCS. A workshop held in Fuerteventura, Canary Islands, in September 2017 reviewed current knowledge on BW atypical MSEs associated with MFAS. Our review suggests that the effects of MFAS on BWs vary among individuals or populations, and predisposing factors may contribute to individual outcomes. Spatial management specific to BW habitat, such as the MFAS ban in the Canary Islands, has proven to be an effective mitigation tool and mitigation measures should be established in other areas taking into consideration known population-level information.

Rationale: Isotope ratios from skin samples have been widely used to study cetacean trophic ecology. Usually, isotopic skin uniformity has been assumed, despite the heterogeneity of this tissue. This study aims to investigate (1) regional isotopic variation within the skin in cetaceans, and (2) isotopic variation among internal tissues.Methods: Stable carbon (delta C-13 values) and nitrogen (delta N-15 values) isotope ratios were measured in 11 skin positions in 10 common dolphins (Delphinus delphis) and 9 striped dolphins (Stenella coeruleoalba). In addition, the isotope ratios in the muscle, liver and kidney of both species were determined and compared with those from the skin and from all tissues combined. The signatures were determined by means of elemental analyser/isotope ratio mass spectrometry (EA/IRMS).Results: In both species, no differences between isotope ratios of the skin positions were found. Moreover, the isotope ratios of skin were similar to those of muscle. In contrast, liver and kidney showed higher isotope ratios than muscle and skin.Conclusions: Isotopic homogeneity within the skin suggests that the isotope ratios of a sample from a specific skin position can be considered representative of the ratios from the entire skin tissue in dolphins. This conclusion validates the results of previous stable isotope analyses in dolphins that used skin samples as representative of the whole skin tissue. Isotopic similarities or dissimilarities among tissues should be considered when analysing different tissues and comparing results from the same or different species.