Mercury,cadmium, zinc,copper and selenium in harbour porpoise (Phocoena phocoena) from West Greenland

Muscle, liver, kidney and skin samples taken from 78 harbour porpoises (Phocoena phocoena) were analysed for mercury, cadmium, zinc, copper and selenium. The highest concentrations of mercury were found in the liver (geometric mean 4.17 g/g wet weight), whilst the highest concentrations of cadmium were in the kidney (g.m. 13.2 g/g ww). The levels of cadmium were more than ten times higher than in harbour porpoises from the North Sea and the British NW coast, whilst the mercury levels were about the same. The importance of the cadmium content in the prey is discussed, but this attempt did not revealed the differences. Very high levels of zinc (g.m. 359 g/g ww) and selenium (g.m. 28.6 g/g ww) were found in skin samples, respectively seven and ten times more than in liver. A significant correlation was found between age and the level of mercury and cadmium in all organs. The concentration of mercury and selenium in liver and skin samples and of cadmium and zinc in kidney samples were highly correlated.     

Variation in harbour porpoise activity in response to seismic survey noise

Animals exposed to anthropogenic disturbance make trade-offs between perceived risk and the cost of leaving disturbed areas. Impact assessments tend to focus on overt behavioural responses leading to displacement, but trade-offs may also impact individual energy budgets through reduced foraging performance. Previous studies found no evidence for broad-scale displacement of harbour porpoises exposed to impulse noise from a 10 day two-dimensional seismic survey. Here, we used an array of passive acoustic loggers coupled with calibrated noise measurements to test whether the seismic survey influenced the activity patterns of porpoises remaining in the area. We showed that the probability of recording a buzz declined by 15% in the ensonified area and was positively related to distance from the source vessel. We also estimated received levels at the hydrophones and characterized the noise response curve. Our results demonstrate how environmental impact assessments can be developed to assess more subtle effects of noise disturbance on activity patterns and foraging efficiency.     

Modelling spatial patterns in harbour porpoise satellite telemetry data using maximum entropy

The distribution of harbour porpoises in EU waters is poorly understood, and modelled predictions of their distributions could inform the strategic spatial planning of future exploitation of the marine environment to avoid potential conflicts. We analysed satellite telemetry data from 39 harbour porpoises Phocoena phocoena in inner Danish waters using a modelling tool rooted in maximum entropy: Maxent. Maxent does not require absence data and has been shown to be effective for data characterised by small sample size, sampling bias and locational errors. For each season we used an iterative bootstrapping procedure to randomly select among the most precise records from each of the 39 tagged individuals, and ran Maxent on pooled records based on explanatory environmental variables hypothesised to serve as good proxies for harbour porpoise prey abundance. Among our environmental variables, distance to coast and bottom salinity had the most explanatory power, and their response shapes were relatively consistent across most seasons. The predictive power of the models (assessed by ROC‐AUC) ranged from 0.70 to 0.86 within seasons. The southern Kattegat, the Belt Seas, most western part of the Baltic Sea and the Sound were predicted to have relatively high probabilities of occurrence across seasons. In contrast, the central part of Kattegat and the Baltic Sea south and east of Limhamn and Darss Ridge consistently showed low probabilities of occurrence. Areas with the lowest probabilities of occurrence were generally characterised by high predictive uncertainty. Our methods have implications for the analyses of satellite tagged animals in terrestrial and marine environments. By coupling a bootstrapping procedure with Maxent we circumvented some of the statistical challenges presented by satellite telemetry data to generate spatial predictions within the inner Danish waters.     

Granulosa cell tumour in a harbour porpoise (Phocoena phocoena) from German waters

Neoplastic diseases in harbour porpoises Phocoena phocoena have rarely been described, and there are no reported gonadal stromal tumours. A 12 yr old female harbour porpoise was stranded on the North Sea coast of Schleswig-Holstein, Germany. Necropsy findings included a severe granulomatous pneumonia, pregnancy and a left ovarian tumour. Respiratory insufficiency was the likely cause of death. There was a multinodular mass composed of cords with peripherally palisading cells within the left ovary. The histological and cytological appearance of the neoplasm was suggestive of a granulosa cell tumour; supportive immunohistochemical stains, including those for vimentin, cytokeration, carcinoembryonic antigen, c-kit, chromogranin and α-smooth muscle action, were negative.     

Keeping returns optimal: gain control exerted through sensitivity adjustments in the harbour porpoise auditory system

Animals that use echolocation (biosonar) listen to acoustic signals with a large range of intensities, because echo levels vary with the fourth power of the animal's distance to the target. In man-made sonar, engineers apply automatic gain control to stabilize the echo energy levels, thereby rendering them independent of distance to the target. Both toothed whales and bats vary the level of their echolocation clicks to compensate for the distance-related energy loss. By monitoring the auditory brainstem response (ABR) during a psychophysical task, we found that a harbour porpoise (Phocoena phocoena), in addition to adjusting the sound level of the outgoing signals up to 5.4 dB, also reduces its ABR threshold by 6 dB when the target distance doubles. This self-induced threshold shift increases the dynamic range of the biosonar system and compensates for half of the variation of energy that is caused by changes in the distance to the target. In combination with an increased source level as a function of target range, this helps the porpoise to maintain a stable echo-evoked ABR amplitude irrespective of target range, and is therefore probably an important tool enabling porpoises to efficiently analyse and classify received echoes.     

Stratification and age-related differences in blubber fatty acids of the male harbour porpoise (Phocoena phocoena)

Fatty acid composition of blubber was determined at four body sites of 19 male harbour porpoises. A total of 65 fatty acids were quantified in each sample. The array of fatty acids contained in harbour porpoise blubber was similar to those found in other marine mammals. While chemical composition of total blubber was uniform over the body, with the exception of the caudal peduncle, vertical stratification was evident between the deep (inner) and superficial (outer) blubber layers. Fatty acids with chain lengths shorter than 18 carbons were present in significantly greater amounts in the outer blubber layer, while the longer-chain unsaturated fatty acids were more prevalent in the inner layer. This distribution suggests that the inner blubber layer is more active metabolically than the outer layer in terms of lipid deposition and mobilization. The degree of stratification between the two layers appears to increase with age, indicating a predictable turnover in the blubber layer of male porpoises. Harbour porpoise blubber contained high levels (2–27%) of isovaleric acid in the outer blubber layer, and these levels were positively correlated with age.Abbreviations Caud caudal dorsal body site - GC gas chromatograph - FA fatty acid(s) - IUPAC International Union of Pure and Applied Chemistry - PUFA polyunsaturated fatty acid(s) - II dor II dorsal body site - III dor III Dorsal body site - II Ven II ventral body site     

First indication of gas embolism in a harbour porpoise (Phocoena phocoena) from German waters

In the last decade, a number of cetacean strandings have gas embolic pathology analogous to decompression sickness in man and experimental animals. Acute gas and fat embolic lesions have also been found in mass-stranded beaked whales causally linked to high-intensity anthropogenic mid-frequency sonar activities. Sporadic chronic gas embolic lesions have also been described. This communication describes a first case of numerous gas-filled fibrous cavities in the markedly enlarged liver of a dead adult male harbour porpoise stranded at the North Sea coast of Schleswig-Holstein, Germany. Additional pathological findings consisted of chronic parasitic granulomatous cholangiohepatitis, hepatic vein thrombosis, parasitic infestations of the bronchial tree and pulmonary blood vessels associated with bronchopneumonia and severe parasitic burden in both ear sinuses. The hepatic cavernous lesions are similar to those described in chronic gas bubble disease in other cetaceans, most likely resulting from decompression-related tissue supersaturation with nitrogen.     

Phenotypic and genetic divergence among harbour porpoise populations associated with habitat regions in the North Sea and adjacent seas

Determining the mechanisms that generate population structure is essential to the understanding of speciation and the evolution of biodiversity. Here, we investigate a geographical range that transects two habitat gradients, the North Sea to North Atlantic transition, and the temperate to subpolar regions. We studied the harbour porpoise (Phocoena phocoena), a small odontocete inhabiting both subpolar and temperate waters. To assess differentiation among putative populations, we measured morphological variation at cranial traits (N = 462 individuals) and variation at eight microsatellite loci for 338 of the same individuals from Norwegian, British and Danish waters. Significant morphological differentiation reflected the size of the buccal cavity. Porpoises forage in relatively shallow waters preying mainly on benthic species in British and Danish waters, and on mesopelagic and pelagic fish off the coast of Norway. We suggest that the observed differentiation may be explained by resource specialization and either adaptation or developmental responses to different local habitats.     

Timing of epiphyseal development in the flipper skeleton of the harbour porpoise (Phocoena phocoena) as an indicator of paedomorphosis

Epiphyseal development was investigated on X‐rays of flippers from 158 harbour porpoises from Danish waters. Development followed a proximodistal pattern similar to what is known in other cetacean species. Ossification of epiphyses was rare in the phalanges of the first and fifth digits and in the more distal phalanges of the second, third and fourth digits. Along with the morphology of the first metacarpal and the more distal phalanges this suggested paedomorphosis relative to delphinids. Male and female porpoises showed similar progression of epiphyseal development until approximately the sixth year. From then on, female porpoises showed more progressed development than males. This suggests a higher level of paedomorphosis in the male porpoise. The mechanism behind phocoenid paedomorphosis seems to be progenesis, probably as an adaptation towards a high reproductive rate relative to the delphinids.     

Sexual dimorphism of Dall's porpoise and harbor porpoise skulls

To evaluate and quantify sexual dimorphism of skull shape and assess the ontogenetic background for differences, samples of 134 harbor porpoise (Phocoena phocoena) and 85 Dall's porpoise (Phocoenoides dalli) were compared in terms of cranial shape and shape ontogeny using three-dimensional geometric morphometrics. After correction for allometry, no sexual differences were detected in harbor porpoise, while Dall's porpoise showed statistically significant sexual dimorphism of skull shape. Since no sex-specific differences were detected in the directionalities of the ontogenetic vectors, we cannot reject that the dimorphism is innate. Based on the different mating systems of the two species and the lack of sexual dimorphism in the harbor porpoise, the dimorphism in Dall's porpoise is most likely a result of sexual selection in relation physical competition for mates given that male skulls provide room for larger neck muscles with a more favorable lever arm.     

Mitochondrial Control Region and microsatellite analyses on harbour porpoise (Phocoena phocoena) unravel population differentiation in the Baltic Sea and adjacent waters

The population status of the harbour porpoise (Phocoena phocoena) in the Baltic area has been a continuous matter of debate. Here we present the by far most comprehensive genetic population structure assessment to date for this region, both with regard to geographic coverage and sample size: 497 porpoise samples from North Sea, Skagerrak, Kattegat, Belt Sea, and Inner Baltic Sea were sequenced at the mitochondrial Control Region and 305 of these specimens were typed at 15 polymorphic microsatellite loci. Samples were stratified according to sample type (stranding vs. by-caught), sex, and season (breeding vs. non-breeding season). Our data provide ample evidence for a population split between the Skagerrak and the Belt Sea, with a transition zone in the Kattegat area. Among other measures, this was particularly visible in significant frequency shifts of the most abundant mitochondrial haplotypes. A particular haplotype almost absent in the North Sea was the most abundant in Belt Sea and Inner Baltic Sea. Microsatellites yielded a similar pattern (i.e., turnover in occurrence of clusters identified by STRUCTURE). Moreover, a highly significant association between microsatellite assignment and unlinked mitochondrial haplotypes further indicates a split between North Sea and Baltic porpoises. For the Inner Baltic Sea, we consistently recovered a small, but significant separation from the Belt Sea population. Despite recent arguments that separation should exceed a predefined threshold before populations shall be managed separately, we argue in favour of precautionary acknowledging the Inner Baltic porpoises as a separate management unit, which should receive particular attention, as it is threatened by various factors, in particular local fishery measures.     

Rhizopusmycosis in a harbor porpoise from the Baltic Sea.

A case of systemic mycosis due to a Rhizopus sp. infection is described in a dead-stranded, 10-yr-old, male harbor porpoise (Phocoena phocoena) found on the beach of Neustadt, Schleswig-Holstein on the Baltic Sea (Germany). At necropsy, granulomatous mycotic lesions in brain, lung, kidneys, testis, and draining lymph nodes were found. In addition, a focal ulcerative gastritis of the first stomach, due to a nematode infection, was present and is suspected to be the portal of entry for the fungus.     

Role of isovaleroyl lipids in channeling of sound in the porpoise melon

Physical properties (e.g. specific gravity, adiabatic compressibility and sound velocity) of lipids isolated from tissues from contiguous areas of the fatty melon of an echo-locating porpoise (Delphinus delphis) were determined to elucidate relations between lipid composition and structure, and sound transmission in the head. Lipid content varied greatly within the melon (13.6–77.6% of the tissue weight) and triacylglycerols (80–100%) were the major lipid components. This lipid class was composed of diisovaleroylglycerides (triacylglycerols containing two isovaleroyl moieties and a long-chain acyl moiety), monoisovaleroyldiacylglycerols and triacylglycerols consisting of long-chain acids. The lipid-rich (>45%) areas in the melon contained a high proportion (>45% of total triacylglycerols) of diisovaleroylglycerides. There were gradations of sound velocities within the melon; the lowest sound velocities were associated with high concentrations of diisovaleroylglycerides (<1400 m/s) and the highest with high concentrations of long-chain triacylglycerols. Assuming an average sound frequency of 75 kHz, and considering dimensions of melon (path length and width of 12–14 cm and 5 cm, respectively), a forward radiating lobe of 15–25 degrees is produced. Thus, the deposition of lipids of different acoustic properties in a three-dimensional matrix within the porpoise melon results in a lens for the projection of sound into the marine environment.