No abstract

An increasing number of marine mammal studies on physiology, behaviour and ecology rely on data, which have been collected from back-mounted devices, such as bio-logging tags and satellite transmitters. However, external devices may influence an animal's hydrodynamics, behaviour and energy expenditure and, therefore, can impede the individual animal. To investigate the influence of external devices on seals, the water flow along a grey seal was simulated using computational fluid dynamics calculations. The simulations revealed several changes in forces and moments and thus balance, due to this device. The investigated satellite transmitter creates an average 12% increase of the drag coefficient. Additionally, there are significant relative transmitter-induced increases in pitching moment (32%) and lift (240%). The simulations also showed that the transmitter generates areas of decreased wall shear stress on the seal's back. The results of this study demonstrate that external devices can change the hydrodynamics of the seal, which is expected to alter the seal's physiology and behaviour and its use of the ecosystem. Long-term attachment may have adverse effects on the animal's welfare. It is important to take these effects into consideration when studying tagged seals; otherwise, the value of the data obtained will be poor. Therefore, interpretations and extrapolations regarding 'natural behaviour' of animals in their 'natural environment' should only be made with great caution.

Using random PCR in combination with next-generation sequencing, a novel parvovirus was detected in the brain of a young harbor seal (Phoca vitulina) with chronic non-suppurative meningo-encephalitis that was rehabilitated at the Seal Rehabilitation and Research Centre (SRRC) in the Netherlands. In addition, two novel viruses belonging to the family Anelloviridae were detected in the lungs of this animal. Phylogenetic analysis of the coding sequence of the novel parvovirus, tentatively called Seal parvovirus, indicated that this virus belonged to the genus Erythrovirus, to which human parvovirus B19 also belongs. Although no other seals with similar signs were rehabilitated in SRRC in recent years, a prevalence study of tissues of seals from the same area collected in the period 2008-2012 indicated that the Seal parvovirus has circulated in the harbor seal population at least since 2008. The presence of the Seal parvovirus in the brain was confirmed by real-time PCR and in vitro replication. Using in situ hybridization, we showed for the first time that a parvovirus of the genus Erythrovirus was present in the Virchow-Robin space and in cerebral parenchyma adjacent to the meninges. These findings showed that a parvovirus of the genus Erythrovirus can be involved in central nervous system infection and inflammation, as has also been suspected but not proven for human parvovirus B19 infection.

In 1988 and 2002, two major phocine distemper virus (PDV) outbreaks occurred in harbour seals (Phoca vitulina) in north-western European coastal waters, causing the death of tens of thousands seals. Here we investigated whether PDV is still circulating among seals of the Dutch coastal waters and whether seals have protective serum-antibodies against PDV. Therefore seal serum samples, collected from 2002 to 2012, were tested for the presence of PDV-neutralizing antibodies. Antibodies were detected in most seals in 2002 and 2003 while after 2003 antibodies were detected only in seals less than two month-old and adult seals that probably had survived the 2002 PDV-epizootic. We estimated the current proportion of seals with antibodies against PDV at 11%. These findings suggest that at present the vast majority of seals are not immune to PDV infection. PDV re-introduction in this area may cause a major epizootic with infection of >80% and mass-mortality of >50% of the population.

We dedicate this paper to the memory of our colleague Renske Hekman who studied the seals in the Dollard in the summer of 2010. a b s t r a c tThe Dollard area is a core breeding area of common seals, Phoca vitulina, in the Dutch Wadden Sea. Seals mainly use this area in the birth season, and it is at this time that mother and pup pairs are prone to disturbance. Seals in the Dollard lie on sandbanks close to the dyke area which exposes them to various human activities on land and in the coastal waters.The colony of common seals on the sandbanks of the Dollard has increased from 77 individuals in 1993 to 332 in 2010. Observations were made during the pupping and lactation seasons in 2007, 2008, 2009 and 2010. In total, 692 h of observations were made over the last 4 years, and a total of 1329 potential disturbances were recorded. Human activities were more frequent on land than on water or in the air. In total, most disturbances were also recorded as arising from land. Actual disturbances of seals were recorded 344 times; seals were alerted 249 times and seals escaped into the water 95 times. An escape response was observed for 81 of the 1037 (7.8%) recorded land activities, 6 of the 92 (6.5%) recorded water activities, and 8 of the 200 (4%) air activities. These percentages of escape responses did not differ significantly between the land, water and air activities.The construction of a culvert in the dyke in 2001, and the building up of sand ridges along the water flow towards the culvert, provided the seals with an extra place to haul out. Land activities only affected seals resting on these sand ridges which are at a distance of 50-200 m of the dyke. Boats have the potential to disturb seals on all sandbanks of the study area. They affected the highest number of seals per disturbance, with up to 117 animals fleeing into the water. Flying at lower altitudes appeared to cause more disturbances of seals. Therefore, the effect of flying at low altitudes (150-300 m) warrants further investigation.Disturbances which lead to fleeing into the water create the potential risk of separating pups from their mothers. This may contribute to the high incidence of orphaned pups found in the Dollard region. Yearly numbers fluctuated between 13 and 24 orphans representing a substantial proportion of the seals born in this area (with highest pup counts of ca. 100). In addition to separation, disturbances may also impact the condition of pups if they occur repeatedly during suckling.The results of this study demonstrate that disturbance is caused by various human activities to a colony of seals using sandbanks close to the mainland. As these disturbances pose a risk that pups become orphaned or are impacted in terms of their body condition, efforts should be made to minimise the effects of human presence.