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PubMed2003

Test for a population expansion after a drastic reduction in population size using DNA sequence data.

Populations may, during their evolutionary history, go through drastic changes in population size due to bottlenecks or founder events upon colonization of new areas. This involves a subsample of haplotypes, causing the allele frequencies to be different from the original population. In addition, the period of recovery after a bottleneck can be of considerable length. If reproduction is unequal among individuals but random with regard to haplotype, large deviations from the patterns expected in a stable population may result. By means of computer simulation, I have analysed the patterns arising when populations undergo bottlenecks and then slowly recover, and used two new statistical tests for the detection of the bottleneck. A test based on the variance of the relative frequency of haplotypes had generally high power even at low sample size (n=25). This statistic was most powerful after very strong bottlenecks and lost power with increasing propagule size. A test based on the variance of the pairwise differences shows slightly less power. As expected, power was reduced when migration into the founder population was allowed from the source population. This suggests that the test is particularly suited for detecting relatively recent and strong bottlenecks, and thus may be a valuable tool for identifying population events on a fine temporal scale, such as colonisations after the last glaciation.

Analysis of Variance↗
PubMed2001

HIV surveillance in complex emergencies.

Many studies have shown a positive association between both migration and temporary expatriation and HIV risk. This association is likely to be similar or even more pronounced for forced migrants. In general, HIV transmission in host-migrant or host-forced-migrant interactions depends on the maturity of the HIV epidemic in both the host and the migrant population, the relative seroprevalence of HIV in the host and the migrant population, the prevalence of other sexually transmitted infections (STIs) that may facilitate transmission, and the level of sexual interaction between the two communities. Complex emergencies are the major cause of mass population movement today. In complex emergencies, additional factors such as sexual interaction between forced-migrant populations and the military; sexual violence; increasing commercial sex work; psychological trauma; and disruption of preventive and curative health services may increase the risk for HIV transmission. Despite recent success in preventing HIV infection in stable populations in selected developing countries, internally displaced persons and refugees (or forced migrants) have not been systematically included in HIV surveillance systems, nor consequently in prevention activities. Standard surveillance systems that rely on functioning health services may not provide useful data in many complex emergency settings. Secondary sources can provide some information in these settings. Little attempt has been made, however, to develop innovative HIV surveillance systems in countries affected by complex emergencies. Consequently, data on the HIV epidemic in these countries are scarce and HIV prevention programs are either not implemented or interventions are not effectively targeted. Second generation surveillance methods such as cross-sectional, population-based surveys can provide rapid information on HIV, STIs, and sexual behavior. The risks for stigmatization and breaches of confidentiality must be recognized. Surveillance, however, is a key component of HIV and STI prevention services for forced migrants. It is required to define the high risk groups, target interventions, and ultimately decrease HIV and STI transmission within countries facing complex emergencies. It is also required to facilitate regional control of HIV epidemics.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Peculiarities of intracranial arachnoid cysts: location, sidedness, and sex distribution in 126 consecutive patients.

OBJECTIVE: To study the distribution of intracranial arachnoid cysts in a large and nonbiased patient population. METHODS: One hundred twenty-six patients with 132 arachnoid cysts were studied. Patients were consecutively referred to our department during a 10-year period from a well-defined geographical area with a stable population. RESULTS: The cysts had a strong predilection for the middle cranial fossa; 86 patients (65.2%) had cysts in this location. Of 106 cysts with clearly unilateral distribution, 64 were located on the left side and 42 on the right side. This significant difference resulted solely from the marked preponderance of middle fossa cysts for the left (left-to-right ratio, 2.1:1). There were significantly more males than females (92 males/34 females). This difference was exclusively due to male preponderance of unilateral middle fossa cysts (66 males/14 females; ratio, 4.7:1). For all other cyst locations, there was no difference between the two sexes (26 males/20 females) or the two sides (10 left, 16 right). The marked left-sidedness for middle fossa cysts was found only in males. Females had an even distribution between the two sides. CONCLUSION: Arachnoid cysts have a strong predilection for the middle cranial fossa that may be explained by a meningeal maldevelopment theory: the arachnoid coverings of the temporal and frontal lobes fail to merge when the sylvian fissure is formed in early fetal life, thereby creating a noncommunicating fluid compartment entirely surrounded by arachnoid membranes. Why males develop more middle fossa cysts on the left side remains a mystery.

Adolescent↗
PubMed1999

Epidemiology of Crohn's disease in Israel: a survey of Israeli kibbutz settlements.

OBJECTIVE: The prevalence of Crohn's disease ranges from 10 to 70 cases per 100,000 population, and is 3-8 times more common among Jews. However, this excess risk is not evident in the Jewish population of Israel. Recently we have described a significant increase in the prevalence and incidence of Crohn's disease in the south of Israel. The aim of this study was to confirm this trend in a stable population found in communal (kibbutz) settlements. METHODS: We repeated a community-based survey in 124,400 kibbutz residents, 10 yr after our first study. This population represents 5% of the Jewish population of Israel. All Crohn's disease patients were located by contacting the kibbutz clinics of the 269 kibbutz settlements (100% compliance). Data was updated to December 31st, 1997, which was designated the point prevalence date, and included information on gender, age, origin, education, profession, extent of the inflammatory process, clinical spectrum of the disease, therapy, complications of the disease, and treatment. The average annual incidence for the 10 yr was calculated from the prevalence data. Only cases with a definite diagnosis of Crohn's disease made in a recognized gastroenterology unit were accepted into the study. RESULTS: There were 81 confirmed cases of Crohn's disease and the prevalence rate rose from 25.5/100,000 in 1987 to 65.1/100,000 in 1997 (p < 0.001). The mean annual incidence rate for this period (1987-1997) is 5.0/100,000/yr. Prevalence rates were higher in women than men, and in those born in Israel or Europe/America than in Asia/Africa. The mean age at presentation of the disease was lower in 1997 than in 1987, 37.4 +/- 17.0 and 45.0 +/- 17.0 yr, respectively (p = 0.041). Prevalence was highest in men with > 16 yr of education, and in women with 11-12 yr education, 119.7 and 100.3/100,000, respectively. CONCLUSIONS: During the decade 1987-1997, the prevalence of Crohn's disease has increased in Israel and is approaching the rates in Europe and America.

Adolescent↗
PubMed1986

A population study of severe aplastic anemia in children. Incidence, etiology and course.

The total number of registered cases of severe aplastic anemia in Denmark was 39 among children aged 0-14 years in 1967 to 1982 giving an annual incidence of 2.2 cases per 1 million children in a well defined and stable population. A probable cause of the aplastic anemia was found in 21 cases (54%). Exposure of the population to known etiological factors of aplastic anemia such as chloramphenicol, pesticides and hepatitis was constant in the study period, and accounted for 2, 5, and 2 cases, respectively. Other infections caused 6 cases, other drugs 2 cases, and organic diluents one case. Three children with constitutional aplasia developed severe aplastic anemia among a total of 6 Fanconi's anemias, 3 probable Fanconi's anemias, and 10 cases of erythrogenesis imperfecta diagnosed during the same 16 years. Thirteen patients (33%) died within 3 months after the diagnosis while on supportive treatment and low dose prednisolone supplemented with androgen treatment. Long term survival occurred in 10 patients (26%), of which 5 patients were in complete and 5 in partial remission.

Adolescent↗
PubMed2004

Insight and hopelessness in forensic patients with schizophrenia.

OBJECTIVE: To quantitatively explore the level of insight in forensic patients with schizophrenia, and its relationship to symptoms and to a history of violence. In addition, to test the hypothesis that scores in the insight domains of 'compliance' and 'awareness of illness' are positively correlated with scores on a self-report scale measuring 'hopelessness'. METHOD: The study consisted of a cross-sectional survey. Subjects were inpatients and outpatients in the rehabilitation service of the Victorian Institute of Forensic Mental Health. Twenty-eight patients with a diagnosis of schizophrenia and a history of serious offending consented to take part. Twenty-two of these had committed homicide. Measures were obtained for each on the Schedule for Assessment of Insight, the Positive and Negative Syndrome Scale for Schizophrenia and the Beck Hopelessness Scale. RESULTS: The mean insight score for forensic patients was 8.39 (SD 4.88). Insight scores did not differ significantly between those subjects who had a history of violence prior to their index offence and those who did not. Awareness of illness, but not compliance, was positively correlated with level of hopelessness. A higher level of awareness of having a mental illness was thus related to feeling more hopeless about the future. CONCLUSIONS: Mean insight scores in patients with schizophrenia with a forensic history do not differ significantly from those in non-forensic populations. Being more aware of being mentally ill may be a risk factor for hopelessness about the future. The limitations of the study are the small sample size, and the fact that it is confined to a relatively clinically stable population.

Adult↗
PubMed1976

Effect of adjustment for sex composition in the measurement of fertility on intrinsic rates.

The inconsistencies inherent in the one-sex models created a need for the construction of what are known as marriage functions, especially for the measurement of fertility. But attempts to develop marriage functions have been frustrated by the inability of the proposed functions to meet certain consistency conditions and also by difficulties in empiracally determining function parameters. Among several functions proposed so far, Das Gupta's (1972) "effective population" deserves special mention. He uses both sexes in its formulation, and has shown that the constancy of fertility rates based on such a function together with the constancy of survivorship probabilities of both sexes would result in a stable population. It is suggested in this article that the major source of the problem in a two-sex model seems to be the requirement that the model has to be specific both for sex and age. The ideal of incorporating the relative composition of one sex in the age-specific rates of the other, thereby creating a function dependent on both sexes, is advanced in this article. Such functions, defined explicitly for births, can be easily translated into age-specific birth rates. In addition to simplicity in the definition and form, the conditions leading toward stability can also be established. Interestingly enough, the intrinsic rate for this two-sex model lies in the interval determined by the rates obtained from the two one-sex models.

Birth Rate↗
PubMed2005

Laparoscopic surgery for common surgical emergencies: a population-based study.

BACKGROUND: Despite being controversial in the past, many reports on the safe use of laparoscopic surgery in emergency settings have been published. The aim of this study was to investigate the diffusion of laparoscopic surgery in three common surgical emergency operations, namely, appendectomy, cholecystectomy, and simple repair of perforated peptic ulcer (PPU), in a stable population. METHODS: This was a retrospective analysis of the central database of the Hospital Authority (HA) in Hong Kong. Data for patients managed in 14 HA hospitals from 1998 to 2002 were studied. The operation record and discharge record of each patient were also investigated to verify the data. RESULTS: A total of 12,708 patients underwent appendectomy, 2631 patients underwent cholecystectomy, and 2260 patients had simple repair of PPU performed. During the study period, 37.2% of appendectomies, 46.5% of cholecystectomies, and 23.1% of simple repairs of PPU were performed laparoscopically. More than a two-fold increase in the proportion of laparoscopic surgery was observed in each of these three operations. By the end of 2002, the percentage of laparoscopic surgery had increased to 53.5% for appendectomies, 61.3% for cholecystectomies, and 32.9% for simple repairs of PPU. Significantly lower hospital mortality rates and shorter postoperative hospital stay were consistenty observed in patients with laparoscopic surgery of the three emergencies. A wide variation in the use of laparoscopic surgery, ranging from 3.7% to 73.1%, was observed among the 14 HA hospitals. However, there was no correlation in the use of laparoscopic surgery with the volume of operation performed in each hospital (p = 0.933). CONCLUSION: A high diffusion rate on the use of laparoscopic surgery for common surgical emergency was observed in Hong Kong. However, there was also a wide variation in the diffusion rate among the 14 HA hospitals. Efforts to reduce hospital variation for the better dissemination of safe laparoscopic technique may be warranted.

Acute Disease↗
PubMed2002

Spotlight on a distant mirror - colorectal cancer surgery in a 20-year period at a general hospital.

BACKGROUND: A published audit of the management of colorectal cancer at a general hospital in the 1970s was available for comparison with a later audit at the same hospital in the 1990s. METHODS: Case note analysis. RESULTS: In the later audit, more cases were treated annually by an unchanged surgical team. The incidence of synchronous combined excision of the rectum, for rectal cancers suitable for resection, was halved, and that of anterior resection of the rectum (sphincter sparing, without a permanent stoma) increased almost threefold. The incidence of local recurrence in cases suitable for rectal surgery dropped from 17% to 9%, in spite of the change in the principal operation undertaken for this population. Outcomes associated with critical care improved as resources in this discipline became available. Overall survival figures were only improved by 6% in the20-year period, reflecting a diagnosis of Dukes C tumours or worse in at least 45% of the stable population studied in both audits. CONCLUSION: More resources are necessary in Great Britain to increase survival figures in this common cancer. Earlier diagnosis and more specialist management of the disease may allow us to emulate American and Swedish survival figures.

Journal Article↗
PubMed2003

Heart failure and the aging population: an increasing burden in the 21st century?

BACKGROUND: Despite an overall decline in age adjusted mortality from coronary heart disease in developed countries, the number of patients with heart failure may be increasing. OBJECTIVE: To project the future burden of heart failure in Scotland from contemporary epidemiological data. METHODS: Scotland, like many industrialised countries, has an aging though numerically stable population (5.1 million). Current estimates of prevalence, general practice (GP) consultation rates, and hospital admission rates related to heart failure were applied to the whole Scottish population. These estimates were then projected over the period 2000 to 2020, on an age and sex specific basis, using expected changes in the age structure of the Scottish population. RESULTS: There are currently estimated to be 40 000 men and 45 000 women aged > or = 45 years with heart failure in Scotland. On the basis of population changes alone, these figures will rise in men and women by 2300 (6%) and 1500 (3%) by year 2005, and by 12 300 (31%) and 7800 (17%) in the longer term (2020), respectively. On the same basis, the annual number of male and female GP visits is likely to rise by 6400 (6%) and 2500 (2%) by year 2005, and by 35 200 (40%) and 17 300 (16%) in the longer term (124 000 and 126 000 visits), respectively. In the year 2000 about 3500 men and 4300 women in Scotland had an incident hospital admission for heart failure. By the year 2020 these figures are likely to increase by 52% (1800 more) and 16% (717 more) in men and women, respectively. If recent trends in short term case fatality rates continue to improve, the number of men who survive this event will increase by 59% (1700 more). Overall, by 2020 the annual number of male and female hospital admissions associated with a principal diagnosis of heart failure is expected to increase by 34% (from 5500 to 7500) and by 12% (from 7800 to 8500), respectively. CONCLUSIONS: Unless rapid and major changes occur in the incidence of heart failure, the burden of this disorder will continue to increase in both primary and secondary care over the next two decades. The greatest increase is likely to occur in men. Future health service planning must take this into account.

Age Distribution↗
PubMed2006

Integral projection models for species with complex demography.

Matrix projection models occupy a central role in population and conservation biology. Matrix models divide a population into discrete classes, even if the structuring trait exhibits continuous variation (e.g., body size). The integral projection model (IPM) avoids discrete classes and potential artifacts from arbitrary class divisions, facilitates parsimonious modeling based on smooth relationships between individual state and demographic performance, and can be implemented with standard matrix software. Here, we extend the IPM to species with complex demographic attributes, including dormant and active life stages, cross-classification by several attributes (e.g., size, age, and condition), and changes between discrete and continuous structure over the life cycle. We present a general model encompassing these cases, numerical methods, and theoretical results, including stable population growth and sensitivity/elasticity analysis for density-independent models, local stability analysis in density-dependent models, and optimal/evolutionarily stable strategy life-history analysis. Our presentation centers on an IPM for the thistle Onopordum illyricum based on a 6-year field study. Flowering and death probabilities are size and age dependent, and individuals also vary in a latent attribute affecting survival, but a predictively accurate IPM is completely parameterized by fitting a few regression equations. The online edition of the American Naturalist includes a zip archive of R scripts illustrating our suggested methods.A zip archive of R scripts illustrating our suggested methods is also provided.

Biological Evolution↗
PubMed2005

Stable isotope and band-encounter analyses delineate migratory patterns and catchment areas of white-throated sparrows at a migration monitoring station.

The Canadian Migration Monitoring Network consists of several fixed migration monitoring stations (MMS) that apply constant-effort protocols to track changes in the abundance of migratory birds. Such monitoring will be important for tracking long-term population trends of songbirds, especially for species breeding in remote areas such as the North American boreal forest. The geographical catchment sampled by individual MMS, however, remains largely unknown. Here, we used hydrogen isotope measurements (deltaD) of feathers of white-throated sparrows (Zonotrichia albicollis) moving through Delta Marsh MMS in Manitoba, Canada, to determine both wintering and breeding ground catchment areas monitored by this station. The deltaD of tail feathers, collected from spring and fall migrants delineated previous breeding or natal latitudes, ranging from the northern to the southern extremes of the western boreal forest. The deltaD values of head feathers grown on the wintering grounds and collected during spring migration revealed that individuals wintered in a broad region of the southeastern United States. The isotope data showed no relationship between estimated breeding/natal and wintering latitudes of white-throated sparrow populations. Stable isotope data provided little information on longitude. Band-encounter analyses, however, indicated a clear east-west segregation of these sparrows across Canada, supporting connectivity among breeding/natal and wintering longitudes over the entire scale of this species' range. Isotope analyses of multiple feather types representing different periods and geographic regions of the annual cycle can provide key information on migratory connectivity for species moving through dedicated MMS.

Animal Migration↗
PubMed1994

Cycles in the two-sex problem: an investigation of a nonlinear demographic model.

"A fundamental shortcoming of classic stable population theory is its failure to handle populations differentiated by sex. The classic theory is linear while the two-sex problem is inherently nonlinear. Previous two-sex investigations have focused on equilibrium conditions rather than dynamics, and ignored competition between age groups for marriage partners. This study makes a start at analyzing dynamics and models that incorporate competition, which can play an important role in any realistic marriage model and can turn a model with a stable equilibrium sex ratio into one with a cycling equilibrium." This is a revised version of a paper originally presented at the 1990 Annual Meeting of the Population Association of America. (SUMMARY IN FRE)

Demography↗
PubMed1983

Dissemination of yeasts after gastrointestinal inoculation in antibiotic-treated mice.

Mice pretreated with antibiotics were inoculated intragastrically with different yeast isolates to determine whether the resulting disruption of the normal flora ecology would allow certain fungi to colonize and disseminate from the gastrointestinal tract. Antibiotic treatment decreased the total population levels of the indigenous bacterial flora, and predisposed mice to gastrointestinal overgrowth and subsequent dissemination by Candida albicans, C. parapsilosis, C. pseudotropicalis, C. tropicalis, and Torulopsis glabrata. A clinical isolate of Rhodotorula rubra, on the other hand, was unable to maintain a stable population in the gut of similar mice and could not be isolated from systemic organs. Control animals not receiving antibiotic therapy, challenged with C. albicans, showed significantly lower gut population levels of yeasts, and Candida organisms could not be grown from visceral organs. It is suggested that suppression of fungi within the gastrointestinal tract by members of the normal bacterial flora may be an important mechanism whereby fungi are confined to the alimentary tract.

Animals↗
PubMed2000

Competition for glucose between Candida albicans and oral bacteria grown in mixed culture in a chemostat.

The competition for glucose as a growth-limiting substrate between Candida albicans and a mixed community of oral bacteria was investigated. A chemostat was operated under glucose-limiting and glucose excess conditions at a dilution rate of 0.05/h. A mixed population of oral bacteria was established and after a steady state had been reached the chemostat was inoculated with C. albicans. Seven bacterial species Streptococcus sanguis, S. sobrinus, S. mitis, Lactobacillus casei, Veillonella dispar, Eubacterium saburreum and Fusobacterium nucleatum - were able to establish stable populations under glucose-limiting conditions. The yeast was unable to grow with the bacteria under glucose limitation. Only three bacterial species, S. sobrinus, L. casei and E. saburreum, became established under glucose-excess conditions. C. albicans was also able to become established in the glucose-excess chemostat and could grow and maintain a steady state in a mixed culture with these organisms. L. casei, S. mitis and S. sobrinus had faster glucose consumption rates than C. albicans. All the bacteria, except for E nucleatum, had maximum specific growth rates higher than C. albicans. The results suggest that glucose may act as a growth-limiting substrate for C. albicans in the establishment and growth of the yeast in a mixed community of oral bacteria.

Bacteria↗
PubMed1984

Immunity after treatment of human schistosomiasis mansoni. I. Study design, pretreatment observations and the results of treatment.

This paper describes the design of a study on immunity to reinfection after treatment of children with Schistosoma mansoni infections, the initial observations on transmission that led to the selection of the study population, the effects of treatment, and the results of immunological tests carried out before and at five weeks after treatment. Iietune village in Machakos District, Kenya, was selected on the basis of high prevalence and intensities of infection in a small preliminary survey, a stable population living in a small area amenable to detailed study, and a lack of previous intervention in the area. Subsequent observations over a pretreatment period of one year confirmed that prevalence and intensities of infection among children attending the local primary school were high. This was associated with extensive contact of members of the community with water-bodies shown to contain large numbers of infected snails. Analysis of pretreatment intensities of infection and water contact patterns in the schoolchildren allowed the selection of 129 children showing a broad scatter between: (a) high intensity, low water contact, and predicted to be non-immune, and (b) low intensity, high water contact, and predicted to be immune. These children were treated with oxamniquine, 30 mg/kg in divided doses. Five weeks after treatment, 70% of children showed apparent complete cure, and the over-all reduction in geometric mean egg output was 98.9%. Since these children represented only a small proportion of the whole community, there was no obvious reduction in transmission, as reflected by snail infection rates, during the following five-month period. Thus, we are in a position to determine whether successfully treated children do or do not become reinfected in a high transmission environment in which it will be possible to make direct estimates of exposure. Immunological tests carried out immediately before treatment were consistent with a pattern of high exposure leading to the early expression of immune responses in most infected children. Eosinophil levels were elevated in 61% of the children, all of whom showed detectable levels of antibodies against adult worm and egg antigens, as measured by ELISA. In addition, all patients showed antibodies capable of mediating eosinophil-dependent killing of schistosomula. At five weeks after treatment, eosinophil counts and anti-adult worm antibody levels had risen, whereas anti-egg antibodies remained grossly unchanged. The wide variation in the levels of responses shown by different individuals will allow us to test whether such responses are associated with resistance to reinfection during the follow-up period.

Adolescent↗
PubMedDate not supplied

Biocontrol strain Pseudomonas sp. W34: specific detection and quantification in the rhizosphere of Cucumis sativus with a DNA probe and genotypic characterization by DNA fingerprinting.

A DNA probe specific for biocontrol strains of Pseudomonas was produced by screening randomly amplified polymorphic DNA (RAPD) PCR fragments. Specificity of the probe was assessed by dot blot and colony hybridization. It was used to specifically determine the population of these strains on roots of Cucumis sativus cv. Delikatess. Two polymorphic RAPD fragments of 750 bp, and 550 bp showed identical specificity. The biocontrol strain Pseudomonas sp. W34 was shown to be competitive in the rhizosphere of cucumber and to maintain a stable population for at least 10 days when inoculated on the seed. The phylogenetic relationships between the biocontrol and reference strains were analyzed at the strain level by means of RAPD and repetitive sequence-based PCR genomic fingerprinting (rep-PCR), and at higher taxonomic levels by means of amplified 16S ribosomal DNA restriction analysis ARDRA. It was shown that the antagonistic strains are closely related, forming a separate cluster from other non-antagonistic and reference Pseudomonas strains, their taxonomic placement remaining uncertain.

Cucumis sativus↗
PubMed1982

On the ecology of the harbour seal Phoca vitulina in the Wadden Sea: population dynamics, residue levels, and management .

The harbour seal population in the Dutch Wadden Sea decreased significantly during the last decades. Calculations based on bounty data revealed that the population decreased from about 2700 in 1950 to about 900 in 1959. Annual aerial surveys--which were carried out since that time--showed a slight increase due to the stop of hunting. However, after 1964 a new decline occurred and since 1974 the population stays at a level of about 450 specimens. During 1974 to 1978 the population dynamics of the population have been studied Frequent aerial surveys provided data on the size of the population. These data have been used in a simulation model and the birth rate and the initial juvenile mortality were calculated. During boat trips an indication of the age composition was obtained by measuring track widths. By comparing these results with similar results from a stable population in Schleswig Holstein it appeared: (1) that juvenile mortality in the first weeks in the Dutch population is higher than that in Schleswig Holstein but the overall mortality of pups in both areas in their first three months of life is of the same order; (2) that pup production in the Dutch population is low compared to the population in Schleswig Holstein; (3) that apparently immigration from elsewhere occurs. To investigate the contribution of environmental pollution to the decline of the Dutch seal population tissues of dead, stranded animals originating from Schleswig Holstein, Denmark and the Netherlands were collected and analyzed for PCBs, o,p'-DDT, p,p'-(DDT, DDE, TDE), dieldrin, aldrin, endrin, endosulfan, alpha, beta, gamma,-HCH, HCB, QCB (pentachlorobenzene), HEPO, total mercury, methyl-mercury, selenium and bromium. Considering epidemiological and experimental data on the effects of PCBs on mammalian reproduction, strong support is obtained for the hypothesis that PCBs are responsible for the decreased reproduction in seals from the Dutch Wadden Sea. if PBCs are responsible for the decrease of the Dutch seal population, measure of all North Sea countries are urgently required because these PCBs may not only be a hazard to seals but also to other animals and even man. Production and use of PCBs should be limited and used PCBs should be collected and destroyed. However, even if an immediate ban on PCB's would be effected, the effects of PCBs because of their persistent character are likely to last many years. For that reason it may be assumed that the seal population in the western Wadden Sea still faces a difficult period in the years to come. In order to lead this population through this difficult period, all possible measures enhancing its continued existence should be taken. Since the seals in the Wadden Sea form one population maximum result may be expected from measures applying to all seals in the Wadden Sea. Thus international cooperation is necessary. The following measures are proposed: Continued interdiction of hunting in order to obtain a maximum number of animals taking part in reproduction. Establishment of seal reserves and, additionally supporting seal nursery stations in order to guarantee a maximum reproductive output. However, it has to be stressed that these measures are not effective if at the same time the main cause of the decrease is not found and brought under control.

Animals↗