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1.
Over the last few decades a dramatic decline in the number of Mediterranean monk seals (Monachus monachus) limited scientific studies on the biology, behaviour, and ecology of the species. This lack of information impaired the effectiveness of conservation strategies. Thus, any further information gathered on the monk seal has utmost value in the work to halt and reverse the plight of the species. A hitherto unknown Cilician Basin colony of the Mediterranean monk seal has been investigated during a 6-year period between 1995 and 2001. Results of direct in-cave surveys and land based seal-watch observations enabled the evaluation of habitat use and preliminary demographic information. A total of 39 caves were discovered among which only three were used for breeding. Scarcity of the breeding caves emphasised the importance of breeding habitat in the survival of the colony. Common features of the breeding caves are found as an entrance with a protective barrier against strong waves; a chamber with a wide beach; and a well-sheltered shallow pool. Supplementary data obtained from infrared monitors installed in three actively used caves were used to assess the number of individuals. Throughout the study period, 25 individuals were identified and 11 newborn pups were found. Evaluation of the results suggests the presence of sub-regions inhabited by an individually identified sub-group of monk seals. Recommendations for conservation guided by this information is a Marine Protected Area consisting of two zones; a restricted core zone prohibiting any human activity securing breeding habitat and a restricted fishery zone securing sustainability of the food source.  相似文献   

2.
Cornwall and the Isles of Scilly were explored for grey seal (Halichoerus grypus) breeding localities during the 1973 breeding season. The work invelved investigating many sea caves on the north coast of Cornwall, in addition to open beach and skerry sites. Pup production was determined by relating the number of pups produced in a sample period to the number produced in the same period (in another year) at Ramsey Island, Pembrokeshire. The all-age populations derived from these pup production estimates suggest that the number of grey seals in Cornish waters is about 250 and in Scilly about 120. Haulouts of several hundred animals seen in Scilly outside the breeding season almost certainly breed elsewhere.  相似文献   

3.
An age-structured model of a wandering albatross Diomedea exulans population is developed to stimulate population trends over time, using demographic parameters from the population at Possession Island, Crozets, during 1968–1986. The simulation results portray a population decreasing at a rate of 2·29% per year, which concurs with global population trends. Sensitivity analyses of model parameters indicate that both adult and juvenile mortality are contributing to the decrease. Wandering albatross mortality is presumed to have increased as a result of deaths caused by longline fishing vessels; such deaths are likely to be relatively more frequent among young, naive birds. The model is used to investigate the potential impacts of new longline fisheries such as that for Patagonian toothfish Dissostichus eleginoides in Antarctica. Assuming longline fishing operations affect juveniles more than adults, there is a time lag of 5–10 years before further decreases in population numbers are reflected in the breeding population. Also, because wandering albatrosses are long-lived, population growth rates take approximately 30–50 years to stabilize after a perturbation. Consequently, caution must be exercised when interpreting population trends; short-term (<20 year) estimates may not provide good indications of long-term trends.  相似文献   

4.
《Biological conservation》2003,109(3):417-423
Methods to evaluate population trends have recently received particular attention because of the decreasing patterns shown by several species since the nineteenth century. We have studied demographic traits of the Bonelli's eagle (Hieraaetus fasciatus) population of Andalusia (southern Spain) for 20 years (1980-2000). This species is endangered and is suffering a rapid decline in most of its distribution range. Although our study population has remained stable for the last 10 years, both age at first breeding and productivity have decreased during the last 5 years. We propose that age at first breeding could be used as a potential early warning signal to detect possible future changes in population trends of long-lived species with deferred maturation age. In particular, in this species spatial variation in demographic traits could help to detect whether unnatural events such as shooting are decreasing age at first breeding and productivity. If occupation of territories by non-adults is caused by human persecution, conservation efforts in the particular case of Bonelli's eagle have to be directed to protect those breeding territories where an increase in the percentage of pairs containing at least one non-adult individual would be detected.  相似文献   

5.
Populations of oriental white-backed vultures (Gyps bengalensis) in south Asia have declined over 95% since the mid-1990s due to feeding on livestock carcasses that had been treated with diclofenac, an anti-inflammatory pharmaceutical that is fatal to Gyps vultures. To prevent extinction, captive breeding efforts have been initiated; however, given the overall decline, it is not known to what extent levels of genetic diversity currently exist in the remaining populations. Here we document temporal genetic diversity levels during the 2000-2006 interval for the last remaining breeding colony of oriental white-backed vultures in Pakistan, and show with simulations that a much larger captive population size is required than currently maintained to prevent further loss of genetic diversity. Before this species is extinct in the wild, it is crucial that additional individuals are included in the captive population.  相似文献   

6.
The world population of Dalmatian pelicans Pelicanus crispus, the largest pelican species of the genus Pelicanus, has decreased drastically since the last century. Its breeding range has diminished in relationship to agricultural and industrial development and draining of wetlands, and is now limited to the eastern part of the Old World. The present status of P. crispus is reviewed, and the number of breeding pairs in the world is estimated to be between 700–1100 in 16–24 different breeding sites. Migration and wintering are poorly known. Data on the food (strictly fish), the impact of P. crispus on fisheries and a peculiar feeding behaviour of Dalmatian pelicans is distinct association with the great cormorant Phalacrocorax carbo are discussed. New contributions on reproduction and predation are presented, and suggestions are made for conservation, monitoring and management.  相似文献   

7.
The dehesa (oak woodland) is an extensive agro-pastoral ecosystem characteristic of the Western Mediterranean countries which is suffering a great transformation process since 1950. Although its distribution largely overlaps with several endangered species, there is scarce information on how they use this human-transformed habitat. We studied the foraging habitat selection of one of them, the cinereous vulture Aegypius monachus. We radio-tracked 14 cinereous vultures in one of the largest European colonies from 1998 to 2000. Used and available habitats were compared at two scales using compositional analysis. Moreover, we developed a distance-based GLMM for assessing habitat selection in this central-place forager species, by taking into account the spatial distribution of habitat patches in relation to the location of the colony. Home ranges overlapped over a total surface of 592,527 ha around the colony, and both individual home ranges and travel foraging distances (mean 27.86 km, maximum 86 km) were larger during the breeding season. All cinereous vultures avoided agricultural lands within their home ranges throughout the year. Habitat use in relation to the distance to the colony pointed out that dehesas were positively selected in spite of being on average far away from the colony than other habitats, a result that was consistent among individuals and seasons. The cinereous vulture thus depends for its conservation not only on the protection of breeding areas, as has been so far considered, but also on the maintenance of well-conserved dehesas close to the colonies. Preserving the cinereous vultures could contribute to the economic sustainability of dehesas by attracting PAC funds for their traditional low-intensity exploitation. Although other species may also benefit from this study since cinereous vulture could be a “flagship” for the large-scale conservation of Mediterranean oak woodlands and associated biodiversity, more fine local management guidelines should be performed on the basis of studies on more sensitive species.  相似文献   

8.
The flesh-footed shearwater (Puffinus carneipes) is a migratory seabird that ranges widely across the Pacific and Indian Oceans. The principal breeding populations are in Australia and New Zealand. The only breeding site in eastern Australia is on Lord Howe Island. Despite it being afforded a high level of legislative protection, the population on Lord Howe Island has declined substantially during the last few decades. The total extent of nesting habitat in 2002 was 24.3 ha, a reduction of 13.4 ha (35.6%) since 1978. Loss of nesting habitat was associated with increased urbanisation, the adverse impact of which extended beyond the footprint of buildings and gardens. In 2002, overall burrow density was 0.123 per m2 and the total number of burrows was estimated to be 29,853 ± 5867, a decline of about 19.0% since 1978. A substantial decline in burrow density was evident in the colony where loss of habitat to urbanisation had been greatest. In 2002, 58% of burrows were occupied by breeding birds, and the total population size was estimated to be 17,462 breeding pairs. Breeding success (the proportion of eggs that produced fledglings) was 50%, but was lowest in the most urbanised colony. To avert further declines in the population of flesh-footed shearwaters on Lord Howe Island major changes in land use practices, enforced through appropriate legislation, are needed, together with reductions in the level of seabird bycatch in fisheries operations and in the amount of plastics that litter the world’s oceans.  相似文献   

9.
We investigated the status of the grey seal in the Molène archipelago, western Brittany, where a Marine National Park is planned. We combined regular censuses, photo-identification and satellite telemetry to investigate trends in grey seal abundance, site fidelity, individual movements and haulout site use. Individual movements and seasonal variations in abundance suggest that the seals used the Molène archipelago alternatively with other haulout sites of the South-west British Isles during their annual cycle. Nine out of 16 seals fitted with Satellite Relay Data Loggers (SRDLs) moved to the Isles of Scilly, English Cornwall, Wales or the Channel islands. On average the seals spent 85% of their time Near Haulout, 56.8% of which in the Molène archipelago. Overall the seals spent 66% of their tracking time within the boundaries of the Marine National Park. From 1997 to 2000 in the Molène archipelago, we observed a peak in number during the moulting season (mean = 49.8 seals) and a lower abundance during the breeding season (mean = 38.3 seals). The sex ratio was strongly skewed towards males during the moult (between 3.1 and 5.3-1), and was close to 1:1 during the summer. Inter-annual site fidelity outside the breeding season was very high, varying from 70% to 95% of identified seals, suggesting that the observed movements constitute rotations rather than random dispersion. From 1991/1994 to 1997/2000, the mean number of seals counted at haulout sites increased by 7%, close to the rates of increase observed in the core population of the British Isles at the same period. The Marine National Park may be too restricted for the overall conservation of the population but management plans should be aimed at preserving the characteristics of the habitat for the grey seal.  相似文献   

10.
We evaluated the persistence and possible recovery of two depleted marine mollusks, the red (Haliotis rufescens) and black abalone (H. cracherodii), in central California, USA. Monitoring over 32-years did not reveal increasing or decreasing trends in red abalone abundances and sizes over the past three decades, in the absence of harvesting. Comparisons between marine reserves protected for at least 25 years and sites with open public access showed significant difference in size structure for black abalone, with individuals greater than 8 cm in shell length comprising 14–37% of animals in reserves and 2–11% at open-access sites, and a trend for greater abundances of red abalone within reserves. Despite no increasing trends, protection in one of the no-take reserves, the Hopkins marine life refuge (HMLR), has led to persistence of red abalone populations over multiple generations, at average densities of 0.2 individuals/m2. At other locations, both within the HMLR and elsewhere, red abalone densities are lower than at the location where long-term studies were conducted (av. 0.03 animals/m2), and an order of magnitude lower than for black abalone (av. 0.4 animals/m2). These results suggest that continued fishery closure and protection in no-take reserves are effective tools for allowing persistence of abalone populations, though there are no signs of recovery to levels comparable to those preceding fisheries collapse. Such failure to recover is most likely associated with high natural mortality and possibly continued illegal take, but not with processes underlying low abalone population levels elsewhere, including food or habitat limitation, recruitment failure, or disease. Linking current structure and trends to specific processes is a crucial first step towards devising focused strategies for conserving and re-building depleted marine populations.  相似文献   

11.
Australian fur seals are known to interact directly (i.e. operational interactions) with trawlers fishing in the winter blue grenadier trawl fishery of western Tasmania, Australia. The purpose of this study was to identify the environmental and operational aspects of the fishery that were associated with increased numbers of seals observed at the surface. The incidence of net entry was determined in order to establish the effectiveness of the currently used Seal Exclusion Device (SED) at reducing by-catch and mortalities. In addition, the stage and depth at which seals were at greatest risk of entering the net at depth and becoming by-catch were also identified.

An increase in seal numbers observed at the surface is assumed to be proportional to the increased risk of by-catch and mortality incidences at trawlers. The most important subset of environmental and operational factors for predicting the number of seals observed at the surface both in the fishing ground in general and during fishing operations were identified using Generalised Linear Modelling. The final model yielded a significant result (R2 = 0.63, P < 0.01, n = 149) and indicated that the number of seals observed increased when weather conditions deteriorated, particularly when barometric pressure decreased and when swell height and visibility increased. Vessel operations also influenced the number of seals observed; seal numbers increased when the number of nearby vessels and trawl frequency increased, but decreased when vessel speed increased. Seal numbers also increased as the distance from the nearest breeding colony and haul-out site decreased.

Seal numbers at the surface generally increased steadily during trawling operations (n = 475), although brief declines were noted during shooting and hauling phases. Sub-surface net interactions were also examined using a submersible video camera unit. Seal activity at depth was converse to that observed at the surface, with increased seal numbers noted during shooting and hauling, suggesting that seals dived to forage on fish in the submerged net.

All seal by-catch occurred during the day and almost half occurred during shooting. Mortalities were significantly higher during shooting compared with hauling (Fishers exact test: coef. = 0.65, P < 0.05). However, mortality rates were similar between tows with the Seal Exclusion Device (SED) attached and those without (Fishers exact test: coef. = 0.07, P < 0.99). Only one seal was detected entering and exiting the net mouth during monitored tows, suggesting that the recently observed reduction in by-catch levels (and mortalities) may not necessarily be attributed to the introduction of the Seal Exclusion Device. Seal by-catch recorded during hauling typically occurred when haul speeds exceeded minimum average swimming speeds for fur seals.

Recommendations based on these findings have been made to assist with the future management of fur seal populations that interact with trawl fisheries.  相似文献   


12.
Common seals Phoca vitulina vitulina Linnaeus 1758 were surveyed throughout Ireland during the 1978 breeding season. Compared with the abundance of the species in Great Britain, the Irish stock is small. The results are discussed in relation to the activities of man, particularly bounty hunting to protect fisheries, and the availability of suitable breeding localities. Problems relating to stock management, not least of which is that the species is subject to legislation in the south but not in the north, are discussed.  相似文献   

13.
Methods to evaluate population trends have recently received particular attention because of perceived declines in several species during the 20th century. We investigated whether age at first breeding could be used as an “early warning signal” to detect possible changes in population trends in long-lived species with deferred maturity using data from the Spanish imperial eagle (Aquila adalberti) population in Doñana National Park (Spain). This bird of prey is an endangered species that has suffered a rapid decline in this population during the last 10 years. As a result of our 27-year monitoring (1976-2002) study, we detected that an increase in immature breeding birds occurred before population decline became evident. The proportion of immature-plumaged breeders in the population was significantly higher during the period of decline than during the period of stability. In our case, more than 10% of immature breeders can be considered as an “early warning signal” that anticipates population decline. Owing to the ignorance of this warning signal, urgent actions for the recovery of this eagle population started 10 years later than necessary, and when population size had been reduced.  相似文献   

14.
1961-2013年新疆潜在蒸散量变化特征及趋势   总被引：2，自引：4，他引：2  
准确地评估潜在蒸散量的时空变化趋势对新疆水资源合理利用及气候变化下水文变化研究具有重要意义。该文采用Penman-Monteith公式以及55个气象站的气象资料计算了新疆1961-2013年潜在蒸散量,运用年代距平、M-K检验、Cramer’s突变检验,相关分析及贡献率分析方法,分析了新疆潜在蒸散量的时间、空间变化特征及变化原因。结果表明:1995年为ET0突变点。年ET0在1961-1994年处于明显减少趋势,平均递减率为-3.21 mm/a;在1995-2013年转为明显上升趋势,平均递增率为3.51 mm/a。空间上,75%以上的气象站在1961-1994年处于降低趋势,在1995-2013年转为增加趋势。在全区范围及天山北坡、天山南坡、昆仑山北麓3个分区,风速具有最大的相对贡献率。阿尔泰区则是相对湿度具有最大的相对贡献率。天山山区在两个时段分别是日照时数、温度具有最大贡献率。  相似文献   

15.
Management plans for threatened or recovering large vertebrate species that are increasing in population size and range focus on the establishment of viable populations within set temporal limits. New Zealand (Hookers) sea lions (Phocarctos hookeri) were declared a threatened species in 1997, and New Zealand legislation requires that threatened species of marine mammals must be managed to reduce human-induced mortality and achieve a non-threatened status within 20 years. The present breeding distribution of P. hookeri is highly localised, with over 95% of total annual pup production located at Auckland Islands and almost all of the remainder at Campbell Island. Breeding elsewhere has been ephemeral or restricted to <10 adult females. The only recorded sustainable breeding at a new location has been at Otago, South Island, New Zealand. This breeding population consisted of a total of four breeding females in 2002 and is derived from one immigrant female that gave birth to her first pup in the 1993/1994 breeding season. The New Zealand Department of Conservation management plan specifies that to achieve a non-threatened status P. hookeri (1) at Otago must increase in the number of breeding females to ?10, and (2) must establish ?two new breeding locations within the 20-year time frame, each with ?10 breeding females. This study 1) projects the population growth trends at a new location (Otago) to see if it will achieve ?10 breeding females within the legislated time frame, and (2) examines the likelihood that other breeding locations will establish elsewhere given the demographic information available for this species. We present 20 deterministic and three stochastic Leslie matrix model scenarios for female population growth for the initial years following the start of breeding at a new location. Our results indicate that (1) a new breeding population derived from one immigrant female is unlikely to reach 10 breeding females in 20 years; this duration is more likely to be 23-41 years (deterministic models) or 23-26 years (stochastic model), (2) the likelihood of two new sites establishing within 20 years is unquantifiable, but the probability is low, and (3) if the legislated outcome and time limit are not revised in the population management plan, the feasibility and effectiveness of re-locating young females could be investigated.  相似文献   

16.
American white pelicans (Pelecanus erythrorhynchos) are colonial-nesting birds and their breeding sites are concentrated in a few small areas, making this species especially vulnerable to factors that can influence productivity, such as disease, disturbance, predation, weather events and loss of nesting habitat. Nearly half of the American white pelican population breeds at four colonies in the northern plains: Chase Lake National Wildlife Refuge (NWR) in North Dakota, Bitter Lake (Waubay NWR) in South Dakota, Medicine Lake NWR in Montana, and Marsh Lake in Minnesota. Thus, sustained productivity at these colonies is crucial to the health of the entire species. During the latter half of the 2002 and 2003 breeding seasons, unusually high mortality of pelican chicks was observed at these colonies. West Nile virus (WNv) was identified as one source of these losses. In 2004–2007 we monitored three major colonies in the northern plains to assess mortality of chicks during the late breeding season. We documented severe weather events, disturbance, and WNv as factors contributing to chick mortality. Before WNv arrived in the region in 2002, chick mortality after mid-July was 4%, and then jumped to as high as 44% in the years since WNv arrived. WNv kills older chicks that are no longer vulnerable to other common mortality factors (e.g., severe weather, gull predation) and typically would have survived to fledge; thus WNv appears to be an additive mortality factor. Persistence of lower productivity at American white pelican colonies in the northern plains might reduce the adult breeding population of this species in the region.  相似文献   

17.
The New Zealand fairy tern Sterna nereis davisae has only one small population of c.30 individuals and its conservation is a priority. The population was declining prior to the mid 1980s. Management of the three remaining breeding sites was initiated during 1983/84 and intensified from 1991 onwards. We have collated historic data and reviewed the changes in the population since 1991. Our results illustrate that the number of chicks fledged increased since 1991. Fifty-five chicks fledged between 1991/92 and 2002/03. Demographic modelling based on productivity and age-specific survival estimates predicted that the population should increase at c.1.5% per annum. The predicted results from the demographic model contrasted against the observation of a stable resident population. This difference could have resulted from the movement of individuals out of our study area. Demographic modelling also indicated that the population may have continued to decline at a rate of c.1.4% per annum if management was not initiated. Extinction risk within 50 years has decreased from 0.52 to 0.39.  相似文献   

18.
The hen harrier (Circus cyaneus) population on the Scottish Orkney Islands has declined dramatically since the end of the 1970s. We postulate that the cause of this decline was due to a reduction in the amount of available prey and predict that if this was the case the population would currently be limited by food. The evidence for this hypothesis is explored by examining the rates at which males deliver prey to their females in relation to breeding performance both among individuals within the declining population and also between this declining population and another, non-declining population in southern Scotland. Breeding performance within the Orkney population was related to male provisioning rates: males that provided more food to their females were more likely to initiate a breeding attempt and there was a tendency for males with the highest provisioning rates to breed with more females. Comparisons between the two populations revealed that harriers on Orkney had a lower breeding performance and also a lower rate of food provision. Changes in agriculture, in particular decreases in rough grazing and increases in sheep densities are thought to be the most likely cause for a reduction in food supply. Conservation measures should be aimed toward increasing the areas of rough grass habitat.  相似文献   

19.
The roseate tern Sterna dougallii Montagu (Aves, Laridae) has a nearly cosmopolitan breeding distribution. The North American and European populations, the only ones which have been well-documented, have both declined drastically in the past decade, raising grave concern over the species' future. Literature search and correspondence reveal that the species currently maintains substantial breeding populations in the Indian Ocean, Caribbean, and Australasian regions. Most old reports provide no quantitative population estimates, while even many recent reports provide only vague estimates of population size. Nonetheless it has been possible to estimate regional populations in most cases to within one order of magnitude. The North American and Caribbean populations total about 10 000 pairs, while the European population is about 1500 pairs. The African population, including the Seychelles and the western Indian Ocean, may have 15 000 to 22 000 pairs. The documented world population is between 20 000 and 30 000 pairs, but the breeding populations of many areas are not yet documented. Substantial variation within and between regions in appearance and breeding biology indicates that each of the five named forms, at least, should be studied and managed separately.  相似文献   

20.
This is the first assessment of the status of cheetahs, Acinonyx jubatus, in Tanzania since 1965. It completes a series of recent studies in Kenya, Uganda, and Malawi to provide an overall understanding of the species’ status in East Africa. Interviews with 370 informants yielded 1050 cheetah sightings. Eighty nine percent of all sightings were made in 1990-1994, and 39% of all sightings occurred in protected areas. All-adult groups contained 1.92±0.04 S.D. individuals; the average number of dependent cubs was 2.63±0.08 S.D.; and the cub-to-adult ratio was 0.34. Since the 1960s, the distribution has remained stable overall with possible reductions in central Tanzania. No definite population trends were detected. With an estimated 569-1007 cheetahs, Tanzania emerges as a sanctuary for the species worldwide. However rangelands, which may hold half of Tanzania’s cheetahs, are undergoing rapid degradation. This precarious situation calls for the establishment of a nationwide monitoring program. Distribution map and population sizes from this study could serve as a baseline for monitoring the species’ status.  相似文献   

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