Patterns of Stranding and Mortality in Common Seals (Phoca vitulina) and Grey Seals (Halichoerus grypus) in The Netherlands between 1979 and 2008

Pathological examination of stranded marine mammals provides information on the causes of mortality in their populations. Patterns of stranding and causes of death of dead-stranded seals on the Dutch coast were analyzed over a 30-year period (1979-2008). Stranding data (n = 1,286) and post-mortem data (n = 379) from common seals (Phoca vitulina) and grey seals (Halichoerus grypus) found dead, or that died before admission to rehabilitation, were obtained from the Seal Rehabilitation and Research Centre database. Data for the years 1988 and 2002, when mass mortality occurred due to phocine distemper virus epidemics, were excluded. Common seal stranding increased from one to nearly 100 per year over this period. This coincides with the increase in the number of common seals in Dutch waters over recent decades. Grey seal stranding increased gradually from one to about 40 per year over the period, reflecting recolonization of Dutch waters by this species. For both species, the trend in stranding of dead seals was found to be in line with that of seals observed in Dutch waters during aerial surveys and did not provide any indications of a relative change in the stranding rate of dead seals. The total monthly stranding rates peaked at more than 120 in June and July for common seals and at nearly 60 in January for grey seals. This coincides with the pupping periods of the two species. Besides phocine distemper, the most common causes of death in investigated common seals (n = 286) were by-catch (confirmed and inferred) (19%), pup starvation (7%), intestinal volvulus (7%) and parasitic bronchopneumonia (6%). The most common causes of death in investigated grey seals (n = 93) were by-catch (confirmed and inferred) (15%), pup starvation (11%) and trauma (5%). The relative occurrence of by-catch significantly decreased over time for grey seals, but not for common seals. Common seals were affected by infectious disease significantly more often than grey seals, mainly because of a higher occurrence of parasitic pneumonia. Phocine distemper caused mass mortalities among common seals, but not among grey seals. These findings in dead-stranded seals differ in part from those reported elsewhere in live-stranded seals, for which pup starvation and parasitic bronchopneumonia were the main causes of stranding. A substantial proportion of seals in Dutch waters die from causes related to human activity. Continued monitoring of stranding patterns and causes of death is warranted for early detection of changes and the possibility of taking timely management actions. (c) 2012 Elsevier Ltd. All rights reserved

Wet dune slacks: decline and new opportunities

For a number of infiltrated coastal dune areas it is discussed to what extent artificial infiltration for the public water supply affects the quality of soil, groundwater and vegetation around pools and ponds, and what its effect is on the vegetation. Further, the results of investigations into the quality of vegetation, soil and water of a number of non-infiltrated, less affected dune areas are presented. The emphasis is on changes in groundwater flow pattern and on changes in the chemical composition of groundwater on the vegetation of wet dune slacks. Finally, recommendations for the management of wet dune slacks are presented. It can be concluded that the introduction of nutrients through infiltration causes an abundance of nitrophilous herbaceous vegetation along the banks of all infiltration ponds and most dune pools. Of the three investigated macro-nutrients, nitrate, potassium and phosphate, the latter shows the most significant correlation with the composition, cover and biomass of the vegetation. The moist biotopes of non-infiltrated dunes have largely disappeared because of desiccation, mainly as a consequence of water withdrawal, afforestation and coastal erosion. Relatively unaffected dune slacks can be found in the dunes on the Dutch Wadden Sea islands and a small number of dune areas on the mainland. In most areas, however, a serious decline in many rare species has been observed during the past twenty years because of eutrophic and acid precipitation, often in combination with disturbances of the groundwater regime.