scholarly journals Continued presence of phocine distemper virus in the Dutch Wadden Sea seal population

1993 ◽  
Vol 133 (13) ◽  
pp. 320-322 ◽  
Author(s):  
I. Visser ◽  
E. Vedder ◽  
H. Vos ◽  
M. van de Bildt ◽  
A. Osterhaus
Keyword(s):  
Wadden Sea ◽  
Phocine Distemper Virus ◽  
Seal Population

scholarly journals Population development and status of harbour seals (Phoca vitulina) in the Wadden Sea

2010 ◽  
Vol 8 ◽  
pp. 95 ◽  
Author(s):  
Peter JH Reijnders ◽  
Sophie MJM Brasseur ◽  
Svend Tougaard ◽  
Ursula Seibert ◽  
Thomas Borchardt ◽  
...  
Keyword(s):  
Health Status ◽  
Wadden Sea ◽  
Conservation Status ◽  
Health Condition ◽  
Harbour Seal ◽  
Population Development ◽  
Sex Structure ◽  
Phocine Distemper Virus ◽  
Favourable Conservation Status ◽  
Seal Population

An index for the condition of a population should include a measure of the recuperative power or resilience of the population in question. This measure needs to cover both the demographic and physiological condition of the population. Applied to the harbour seal population in the Wadden Sea we therefore address respectively the population development and distribution, and its health condition, and relate these to environmental conditions. The harbour seal population has been severely depleted by hunting in the first half of the 20th century. After hunting was stopped in the mid-1970s the population recovered gradually. This recovery was twice interrupted by Phocine Distemper Virus (PDV) outbreaks in 1988 and 2002. These PDV-epizootics reduced the population by 57% and 50% respectively. They also lead to changes in age and sex structure of the population, which gradually returned to a stable age-structure. Despite the reduction in population size by respectively 57% and 50%, the population showed a strong recovery with a growth rate close to the considered maximum possible for this species. The observed changes in the distribution of the population over the 4 sub-regions indicate that distribution is not a static phenomenon. Long term field and pathological investigations point out that the general health status of the population has improved, particularly that of newborn seals (0-6months old). The increasing prevalence of parasites in lungs and intestine warrants continued monitoring of the health status of seals. This is especially relevant in view of the exponential increase of the population, which may finally approach the carrying capacity of the area. Concluding, we canstate that the condition of the population in terms of demographic and health parameters is satisfactory. The best guarantee for maintaining such a favourable conservation status is to abstain from human interferences (e.g. rescue, rehabilitation and release) with natural population processes. However, in practice there is increasing exploitation of marine waters. This requires a continuous monitoring of the potential impacts on the population, particularly of the effect on foraging and migratory behaviour.

Sources and Fate of PCBs in the North Sea: A Review of Available Data

1991 ◽  
Vol 24 (10) ◽  
pp. 77-85 ◽  
Author(s):  
J. Klamer ◽  
R. W. P. M. Laane ◽  
J. M. Marquenie
Keyword(s):  
Adverse Effects ◽  
North Sea ◽  
German Bight ◽  
Marine Mammals ◽  
Wadden Sea ◽  
Annual Basis ◽  
The North ◽  
Total Input ◽  
Seal Population ◽  
The North Sea

From literature data it is calculated that on an annual basis, 11 to 17 tonnes of PCBs enter the North Sea. Largest sources are the Atlantic Ocean and the atmosphere: together they account for 60-79% of the total input. Sources with greatest impact are the rivers, sewers and sludge. Highest concentrations are found close to the Dutch shore and in the German Bight. The PCB levels result in adverse effects on the seal population in the Wadden Sea. Of the total world PCB production, at least 57% is still in use and their future dispersal into the oceans cannot easily be controlled. If the increase in ocean PCB concentration continues, it may ultimately result in the extinction of fish-eating marine mammals.

scholarly journals Harbour seals (Phoca vitulina) and rehabilitation

2010 ◽  
Vol 8 ◽  
pp. 355 ◽  
Author(s):  
Nynke Osinga ◽  
Pieter ‘t Hart
Keyword(s):  
Social Support ◽  
Anthropogenic Impact ◽  
Wadden Sea ◽  
Quality Standards ◽  
Phoca Vitulina ◽  
The Past ◽  
Harbour Seals ◽  
Seal Population ◽  
One Year ◽  
Ecosystem Changes

Throughout the past few decades, rehabilitation of seals has become an activity that is anchored in the present day society of many countries. Seals are primarily rehabilitated to help individual animals in distress. At the same time, the release of seals which would have otherwise died can be considered as a contribution to the population. Most rehabilitated seals are animals under one year of age. They are mainly orphans, weaned seals with complications and seals with a parasiticbronchopneumonia. For the optimal handling of seals and their diseases, centralised operations with quality standards are essential. Rehabilitation provides an instrument to monitor the health of the seal population and its ecosystem. Changes in stranding trends or the appearance of new diseases can be monitored. Moreover, rehabilitation is important to show the general public thestate of the marine environment. In the Netherlands there is significant social support for the rehabilitation of seals. Experience obtained with seal care is of importance in countries where urgent help of threatened seal species is required. Here individual seals are also ambassadors to raise support for the protection of this species in general. Given that the anthropogenic impact on the seals and their environment is extensive in the Wadden Sea, rehabilitation centres can compensate the consequences of this impact on individual seals as well as the population as a whole.

scholarly journals Harbour seals are regaining top-down control in a coastal ecosystem

2018 ◽  
Author(s):  
Geert Aarts ◽  
Sophie Brasseur ◽  
Jan Jaap Poos ◽  
Jessica Schop ◽  
Roger Kirkwood ◽  
...  
Keyword(s):  
North Sea ◽  
Marine Mammal ◽  
Wadden Sea ◽  
Demersal Fish ◽  
Fish Growth ◽  
Harbour Seal ◽  
Top Down ◽  
Harbour Seals ◽  
Seal Population ◽  
The Impact

ABSTRACTHistoric hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels, and may again act as a top-down regulatory force on marine ecosystems. Also the harbour seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960’s, and the current number ∼38,000 is close to the historic population size. Here we estimate the impact of the harbour seal predation on the fish community in the Wadden Sea and nearby coastal waters.Fish remains in faecal samples and published estimates on the seal’s daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey.Harbour seals from the Dutch Wadden Sea fed predominantly on demersal fish, e.g. flatfish species (flounder, sole, plaice, dab), but also sandeel, cod and whiting. Total fish biomass in the Wadden Sea was insufficient to sustain the estimated prey consumption of the entire seal population year-round. This probably explains why seals also acquire prey further offshore in the adjacent North Sea, only spending 13% of their diving time in the Wadden Sea. Still, seal predation was estimated to cause an average annual mortality of 43% and 60% on fish in the Wadden Sea and adjacent coastal zone, respectively. There were however large sources of uncertainty in the estimate, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species.Our estimate suggested a considerable top-down control by harbour seals on demersal fish. However predation by seals may also alleviate density-dependent competition between the remaining fish, increasing fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could potentially become an important component in the functioning of shallow coastal systems.

scholarly journals Phylogeography in an “oyster” shell provides first insights into the genetic structure of an extinct Ostrea edulis population

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sarah Hayer ◽  
Dirk Brandis ◽  
Alexander Immel ◽  
Julian Susat ◽  
Montserrat Torres-Oliva ◽  
...  
Keyword(s):  
Large Scale ◽  
Wadden Sea ◽  
Atlantic Coast ◽  
Phylogenetic Reconstruction ◽  
Oyster Shell ◽  
Glacial Refugia ◽  
Late Nineteenth Century ◽  
Ostrea Edulis ◽  
Geographic Ranges ◽  
The North

AbstractThe historical phylogeography of Ostrea edulis was successfully depicted in its native range for the first time using ancient DNA methods on dry shells from museum collections. This research reconstructed the historical population structure of the European flat oyster across Europe in the 1870s—including the now extinct population in the Wadden Sea. In total, four haplogroups were identified with one haplogroup having a patchy distribution from the North Sea to the Atlantic coast of France. This irregular distribution could be the result of translocations. The other three haplogroups are restricted to narrow geographic ranges, which may indicate adaptation to local environmental conditions or geographical barriers to gene flow. The phylogenetic reconstruction of the four haplogroups suggests the signatures of glacial refugia and postglacial expansion. The comparison with present-day O. edulis populations revealed a temporally stable population genetic pattern over the past 150 years despite large-scale translocations. This historical phylogeographic reconstruction was able to discover an autochthonous population in the German and Danish Wadden Sea in the late nineteenth century, where O. edulis is extinct today. The genetic distinctiveness of a now-extinct population hints at a connection between the genetic background of O. edulis in the Wadden Sea and for its absence until today.

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