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1.
During the austral winter, cetaceans and other apex predators follow the annual northeastward movement of shoaling sardines, known as the sardine run, along the southeast coast of South Africa, including a 400-km stretch called the Wild Coast. In total, 131 opportunistic aerial surveys were conducted between May and July, from 1996 to 2014, to monitor sardine movement. Cetacean-sighting data from these surveys were analysed, focusing on long-term trends in frequencies of the cetaceans. In total, 630 sightings involving five cetacean species were recorded: 268 (approximately 32 400 individuals) of Indo-Pacific bottlenose dolphin Tursiops aduncus, 108 (approximately 79 400 individuals) of long-beaked common dolphin Delphinus capensis, 242 (approximately 670 individuals) of humpback whale Megaptera novaeangliae, 1 (two individuals) of southern right whale Eubalaena australis, and 11 (16 individuals) of Bryde’s whale Balaenoptera edeni. The occurrence of common dolphins, typically associated with sardines, decreased significantly in average group size over the study period (p = 0.0343); bottlenose dolphins, considered generalist feeders, demonstrated no such trend (p = 0.916). Humpback whales were most frequently sighted between 2010 and 2014, and with significantly larger groups observed towards the end of the study period (p = 0.0121). For all these species, more sightings were made inside than outside of marine protected areas (>70% of the dolphin species, and >65% of the humpback whales), both pre- and post-2005 (from 2005 the size of the survey area increased). The results indicate that movements of the common dolphin may be employed as a proxy for sardine occurrence. Long-term trends evident in the data also demonstrate the importance of this coastal region for bottlenose dolphins as well as use as a migratory corridor for humpback whales.  相似文献   

2.
The presence and movement of Indo-Pacific bottlenose dolphins Tursiops aduncus were investigated using shore-based observations made during a humpback whale Megaptera novaeangliae migration survey at Cape Vidal, South Africa, undertaken between June and October 1988–1991. Occurrence was analysed as counts of dolphin sightings per hour within a generalised estimating equation framework. Bottlenose dolphin sightings decreased throughout the daily survey period, and there was a small seasonal peak in sightings during August. Data on movement trajectory were collected using a theodolite for 60% of the groups of dolphins sighted. Most groups were observed travelling in a northerly direction, with few groups recorded moving south. A generalised linear model indicated that northward-travelling dolphins were located closer to shore, travelled at higher speeds, and occurred in bigger groups under low-tide conditions, than those seen moving in a southerly direction. The southward-flowing Agulhas Current is close to shore at Cape Vidal, where the continental shelf is particularly narrow. We suggest that bottlenose dolphins in this area have adopted a specific movement regime to cope with the consistent fast-flowing currents that dominate their environment at Cape Vidal.  相似文献   

3.
Records are presented of sightings of 6 cetacean species (15 common dolphins, Delphinus delphis Linnaeus, over 5000 dusky dolphins, Lagenorhynchus obscurus (Gray), approximately 74 bottlenose dolphins, Tursiops truncatus (Montagu), 8 sperm whales, Physeter catodon Linnaeus, 6 southern humpback whales, Megaptera novaeangliae lalandi (Fischer), and 36 southern pilot whales. Globi‐cephala melaena edwardii (Smith)) from m.v. Lloret Lopez II between 8 January and 2 April 1970. A large school of dusky dolphins was observed south of Solander Island. Monthly water temperatures in the summer of 1970 were high and in January ranged from 15.4°c (9.2 km west of Fiordland) and 21.6°c (55 km west of Cape Farewell), in February from 16.2°c (Fiordland) and 20.4°c (Cape Farewell), and in March from 16.0°c (Fiordland) and 20.5°c (Cape Farewell).  相似文献   

4.
中华白海豚(Sousa chinensis)是国家一级重点保护水生哺乳动物,在我国主要分布于东南沿海的近岸及河口水域。厦门湾是中华白海豚重要栖息地之一,同时也是东南沿海经济较为发达的地区。自改革开放以来,厦门进行了高强度的海洋开发活动,对中华白海豚及其栖息地造成了较大影响。为了保护该物种及其栖息地,厦门市制定了一系列的保护措施,如建立自然保护区、跨区域协同管理、鱼类资源管护与增殖放流等,取得了较好成效。本研究总结了厦门湾中华白海豚所面临的主要威胁,以及为保护中华白海豚及其栖息地所采取的保护措施;分析了目前仍然存在的问题并提出改进建议,如保护区优化调整、加强执法监管、开展栖息地生态修复等,可为厦门湾及其他海域中华白海豚的保护与管理提供参考与借鉴。  相似文献   

5.
Ecological data for the Atlantic humpback dolphin Sousa teuszii are scant. Six on-effort Sousa teuszii sightings were recorded during 817.6?km of boat-based effort in the Río Nuñez region of Guinea during October and November 2013. Two incidental sightings were also reported. Groups comprised 1–25 animals. Photo-identification produced a minimum population estimate of 47 animals. Most sightings (n = 5) were located close (<1?km) to shore along a 5.7?km stretch of coast on the west side of Île de Taïdi, primarily over shallow, sand–mud habitat. Two very distinctive individuals were present in all four Taïdi photo-identification encounters, suggesting high site fidelity and stable associations. Two sightings occurred in the outer Río Nuñez Estuary much farther from the coast (5–12?km) but in relatively shallow water (≤15?m) over sand–mud sediment. Focal follows (n = 5: 0.2–3.8?h duration) produced 9.02?h of behavioural data. Travel (51%), foraging (39%) and feeding (9.2%) dominated, with Taïdi dolphins spending more time foraging and feeding than the outer estuary groups. Three individuals had linear-severed dorsal fins consistent with injuries from fishing line. Some management implications of variation in habitat, site fidelity and movements of Sousa teuszii groups are discussed.  相似文献   

6.
Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140?km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population.  相似文献   

7.
The abundance of Indo-Pacific bottlenose dolphins Tursiops aduncus off the south-west coast of Mauritius was estimated using capture-mark-recapture modelling. Over the past two decades this population has been subjected to ongoing anthropogenic disturbance in the form of extensive coastal development. Furthermore, daily dolphin tourism, which started in 1998, has rapidly increased in intensity. Identification photographs were collected between April 2008 and June 2010 from dolphins occurring along a 30 km length of coast where a dolphin tourism industry is concentrated. A total of 137 groups were encountered over 229 survey days. Over 5 000 photographs were taken, from which 35 individuals were considered to be sufficiently distinctively marked to use in mark-recapture analyses. The majority (85.7%) were seen more than once and resighting frequencies indicated a resident population. Three newborn calves were recorded during the study. Open population models produced abundance estimates of <100 individuals in the population. These results will be used to make recommendations for the conservation and management of this small, resident population, which is a valuable economic resource for the island but is currently under threat from high levels of human activity.  相似文献   

8.
During October and November 2015, the first systematic survey of Sousa teuszii was carried out in the Saloum Delta (Senegal, West Africa), comprising 1 617.5 km of boat-based survey coverage. Thirty sightings were recorded in the Saloum and Diomboss rivers, and along the southern coastline. Dolphins were also observed entering the Bandiala and Djinack channels, and travelling across the border into Gambia. The initial sighting locations were 0.043–1.192 km from shore, and tracked dolphins did not move more than 2.082 km from shore. Groups comprised 1–29 animals (mean 9.3 animals), and at least three neonate calves were observed during November. The overall relative abundance was 0.018 sight. km?1 and 0.175 ind. km?1. Sightings were concentrated in the Diomboss where relative abundance reached 0.037 sight. km?1 and 0.331 ind. km?1. Non-intensive photo-identification produced a minimum population size of 103 animals, the highest recorded for S. teuszii anywhere in its range. Photo-identification also confirmed a movement of individuals between different parts of the Saloum Delta. Combined travel–forage dominated the behaviour. Dolphins were photographed capturing mullet (Mugil sp.) on three occasions. The distribution, population size and movements of S. teuszii are discussed in relation to management.  相似文献   

9.
Spinner dolphins Stenella longirostris longirostris off the south-west coast of Mauritius are subject to ongoing anthropogenic disturbance in the form of daily dolphin tourism, which has intensified since 1998. Abundance of this species was estimated using photo-identification data and mark-recapture analysis. Between April 2008 and June 2010, identification photographs were collected from dolphins occurring along a 30 km length of the coast of south-west Mauritius. A total of 250 groups were encountered over 229 survey days. Mark-recapture analyses were performed on a photographic dataset of more than 8 000 good- and excellent-quality images and 83 animals were identified as distinctively marked individuals. The majority (85.5%) were seen more than once and resightings indicated a resident population. The compiled version of SOCPROG 2.4 was used to investigate the lagged identification rate. The fitted model supported a mostly resident population with additional animals moving in and out of the study area. The estimated abundance of the total population in the study area ranged between 138 and 399 individuals. Our results can be used for monitoring the population for fluctuations and for encouraging both the enforcement of laws regarding dolphin watching and the development of further means of management needed to ensure the long-term presence of this population.  相似文献   

10.
The Norwegian Sea is a migration and feeding ground for fin whales (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) in summer. During the last decade, significant structural changes in the prey community, including northerly expansion and movement in the distribution of pelagic fish species, have been reported from this ecosystem. However, little information on whale feeding ecology exists in the Norwegian Sea and surrounding waters. A total of 59 fin whales and 48 humpback whales were sighted during 864 h of observation over an observation distance of about 8200 nmi (15,200 km) in the Norwegian Sea from 15 July to 6 August 2006 and 2007. The fin whale group size, as mean (±SD), varied between one and five individuals (2.1 ± 1.2 ind.) and humpback whale group size varied between one and six individuals (2.5 ± 1.7 ind.). Fin‐ and humpback whales were observed mainly in the northern part of the study area, and were only found correlated with the presence of macro‐zooplankton in cold Arctic water. Humpback whales were not correlated with the occurrence of adult Norwegian spring‐spawning herring (Clupea harengus) except for the northernmost areas. Despite changes in the whale prey communities in the Norwegian Sea, no apparent changes in fin‐ or humpback whale distribution pattern could be found in our study compared to their observed summer distribution 10–15 years ago.  相似文献   

11.
鲸豚类是大型的海洋哺乳动物,是海洋中的重点保护生物。在制定相应的保护政策前,应较为充分地了解其种群特征。而分析一个地区的鲸豚搁浅等信息,则能够为该地区提供其组成和物种多样性等基本信息。本研究收集了2010-2015年台湾海峡西岸发生的鲸豚类的搁浅、误捕和救护等资料和样本。结果共记录了48例事件,其中包括37例搁浅事件,8例误捕事件和3例救护事件,共涵盖了13个鲸豚物种。其中,中华白海豚和江豚占较大比例,分别为31.3%和25%。值得注意的是,其中10起事件（20.8%）发生在平潭岛,而且包含了3种须鲸和4种齿鲸。另外,我们还比较了台湾海峡东西两侧鲸豚物种的组成,发现共有31种鲸豚物种生活在台湾海峡,说明该地区的鲸豚物种丰富度较高。通过这些信息的收集和分析,我们基本摸清了台湾海峡的鲸豚物种分布。今后,我们将通过开展野外调查来系统地分析台湾海峡的鲸类物种组成,种群大小和栖息地状况等基础资料,为提供更好的保护管理打下良好基础。  相似文献   

12.
Photo‐identification has been established as a helpful tool in cetacean research. However, no study to date has attempted to apply this method to short‐beaked common dolphins (Delphinus delphis L.). We present here the results of two studies that were conducted concurrently in Mercury Bay and the Hauraki Gulf on the north‐east coast of New Zealand's North Island. Methods for distinguishing between individual dolphins are discussed. Sighting records of recognisable individuals indicate that some common dolphins move between Mercury Bay and the Hauraki Gulf (100 km distance), as well as between Mercury Bay and Whakatane (200 km distance). Common dolphin abundance and site fidelity appeared to be greater in the Hauraki Gulf than in Mercury Bay. A selection of photographs of distinct individuals is presented to allow future studies to compare their sighting records to ours, which may help establish the extent of home ranges, site fidelity, and possibly even longevity for common dolphins.  相似文献   

13.
A series of land-based surveys were conducted at two vantage points of known dolphin abundance in Hong Kong. The purpose of this study was to determine the behavioral response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic. Results indicated that dolphins dove for a longer duration in areas of heavy vessel traffic or when there was the presence of an oncoming vessel. Dependent upon the type of vessel and the relative distance, dolphins might flee, continue their ongoing activity, perform a new activity, or approach the vessel. Whilst slow-moving vessels appeared not to cause immediate stress on the dolphin community, fast-moving vessels often cause disruption of behavior and social life. In order to ensure a better environment for the animals, we suggest that proactive conservation measures such as the creation of a marine park, rules and regulations for dolphin watching activities, and regional control of vessel speed should be implemented.  相似文献   

14.
Understanding and characterising movement and area-use patterns of fishes within estuaries, as well as understanding the degree of connectivity between estuaries and the marine environment, can provide important insights into a species’ ecology, which is fundamental for effective management and conservation. Mark-and-recapture data obtained from the 082 TAG FISH Project, a dart-tagging programme, were used to describe movement patterns of juvenile leervis Lichia amia in the permanently open Swartkops Estuary, South Africa, as well as the degree of connectivity with the adjacent marine environment. A total of 628 juvenile leervis were tagged from 2008 to 2015, of which 77 fish (12.3%) were recaptured, with juveniles comprising 85.7% of all measured recaptures. The majority of recaptures (75.3%) were made within the Swartkops Estuary, indicating estuarine philopatry, with 23.4% having moved less than 1 km, revealing site fidelity, but most (51.9%) displaying estuarine roaming. A smaller portion of recaptures (27.7%) had dispersed to other habitats; 16 (20.8%) displayed multiple-habitat connectivity, while only 3 (3.9%) had undertaken long-distance movements (>100 km) and were recaptured up to 825 km northeast of the Swartkops Estuary. Lichia amia that had moved greater distances were characterised by a greater mean size and age at the time of recapture. This study provides valuable information on the philopatry and dispersal of juvenile L. amia.  相似文献   

15.
Common bottlenose dolphins, Tursiops truncatus, were surveyed in offshore gas fields off Ravenna, Italy, between Spring and Autumn, 2001–2005. These visual surveys provide the first density estimates of bottlenose dolphins in the Northwestern Adriatic Sea south of the Po River. Since no study has examined the distribution of bottlenose dolphins relative to gas platforms, when dolphins were encountered, their distance from the nearest gas platform was estimated and behaviour was assessed. Dolphins were sighted on ca. 36% of survey trips, which varied in duration from 1 to 6 h. Group size ranged from 1 to ~50 individuals, with no seasonal trend evident in the likelihood of encounter. Dolphin density was estimated to be approximately 80% higher within 750 m of gas platforms, relative to densities >750 m from platforms, although variability around the estimates was high. From a limited number of behavioural observations, slightly higher frequencies of feeding and milling behaviour were observed closer to gas platforms, whereas dolphins observed further away exhibited higher frequencies of socialising and travelling. Gas platforms are known to provide habitat for demersal fishes and act as aggregation points for pelagic fishes, and these data provide some support for the idea that bottlenose dolphins may utilise gas platforms opportunistically as feeding sites.  相似文献   

16.
The major causes of large whale entanglement in South Africa are static fishing gear, especially the type associated with the West Coast rock lobster Jasus lalandii industry, and large-mesh gillnets that are set off the coast of KwaZulu-Natal (KZN) to reduce shark attacks (shark nets). The prevalence of entanglements is seasonal with the peaks in activity coinciding with the breeding migrations of humpback whales Megaptera novaeangliae and southern right whales Eubalaena australis, the two large whale species that are the most prone to entanglement. Generalised linear models with a Poisson or quasi-Poisson distribution were used to describe the relationship between the number of incidents and time. Taking into account the combined length of shark-net installations per year as an offset variable, entanglement of humpback whales in shark nets increased at 15.1% per year (95% CI = 9.5–21.6%) from 1990 to 2009. This is comparable to the rate of increase in the numbers of this species migrating past the KZN coast, between 1988 and 2002 (9–11%). The number of reported incidents of southern right whales entangled in gear other than shark nets also increased between 1990 and 2009. This was accounted for by the increase in numbers of this species in South Africa (7% per year), so in neither case are the two species at increasing risk of individual entanglement, and anthropogenic factors including entanglement do not seem to be affecting the recovery of these whale populations. Nevertheless, there is concern regarding the vulnerability to entanglement of a small assemblage of humpback whales that habitually visits the West Coast in spring and summer. The continued recovery of whale populations is likely to lead to greater levels of anthropogenic interaction and heighten the need for adequate mitigation measures. The KZN Sharks Board and the South African Whale Disentanglement Network (since 2006) have respectively released (disentangled) 81% and 23% of confirmed entangled individuals, and recorded relevant information on entanglement incidents. Such information is critical for developing mitigation measures and monitoring the prevalence of entanglement.  相似文献   

17.
Atlantic humpback dolphins Sousa teuszii are a priority for research due to their restricted geographic range, narrow ecological niche and the paucity of existing information. The distribution and behaviour of S. teuszii off Flamingos, southern Angola, was investigated during summer and winter 2008 using boat- and shore-based surveys. In all, 71 S. teuszii sightings were recorded, ranging from one to eight animals. Sousa teuszii inhabited shallow, nearshore waters throughout the region, with the exception of southern areas adjacent to fishing villages. Small bays, sheltered waters behind reef-breaks and areas off dry river mouths were used for foraging/feeding behaviour, whereas most travelling occurred along exposed coast. Ten individual S. teuszii were photo-identified. Multiple resightings (and absence of unmarked animals) indicate that all individuals present at the time of the surveys were photocaptured, exhibited high site fidelity and had year-round occurrence. Association indices of 0.77-1.0 indicated strong social affiliation between eight individuals, particularly in winter. Off Flamingos, S. teuszii occurs in small numbers and exhibits high site fidelity to a relatively small stretch of nearshore habitat, making the species vulnerable to local extirpation. Wider-scale surveys and development of a management plan are crucial to ensuring the long-term conservation of S. teuszii off Flamingos.  相似文献   

18.
Daily charts of the aerial search effort (432 206 nautical miles) of the Union Whaling Company and 1 099 sightings of 10 497 whales were available from 628 flights off Durban between 1972 and 1975. Densities of whales were analysed by month and water depth distribution over the four-year period. Low observed densities of blue Balaenoptera musculus, right Eubalaena australis, sei B. borealis and humpback Megaptera novaeangliae whales most likely resulted from earlier whaling pressure. Seasonality of blue, sei and humpback whales was bimodal, indicative of winter migrations to the north of the Durban whaling grounds, whereas the unimodal seasonality of fin whales B. physalus and minke whales B. bonaerensis or B. acutorostrata suggest the offshore region as the northern terminus of their migrations. Sperm whales Physeter macrocephalus migrate northwards offshore of the KwaZulu-Natal coast in autumn/early winter and southwards in late winter/spring, with larger males migrating later than the smaller males and females. Killer whale Orcinus orca presence was coincident with that of offshore minke whales and the southward migrations of other baleen whales, whereas densities of animals deemed as bottlenose whale Hyperoodon planifrons suggest strong early and late summer seasonal abundance in the offshore region. Such extensive surveys offshore of the KwaZulu-Natal coast are unlikely to be repeated; hence, data-extraction of whaling records provides a valuable source of seasonal and distributional information for marine management.  相似文献   

19.
Marine Protected Areas (MPAs) are increasingly used to protect marine mammals from anthropogenic threats despite limited studies that assess their efficacy. The small population of Burrunan dolphins (Tursiops australis) that inhabit Port Phillip Bay (PPB), Australia, are genetically isolated, listed as threatened and are exposed to dolphin-swim tourism. This study aimed to identify areas within PPB where dolphins are most likely to rest, forage and socialise, and whether these behaviours occur frequently within Ticonderoga Bay Sanctuary Zone (TBSZ), the only protected area designated for dolphins within PPB. Here, a comprehensive activity budget for Burrunan dolphins was established and critical habitat identified. Behavioural data were collected from 51 independent dolphin groups during 67 boat-based surveys conducted in southern PPB between December 2009 and May 2013. Travel (63.9%) and rest (1.8%) were the most and least frequently observed behaviours, respectively. Forage (16.4%), mill (10.8%) and social (7.2%) accounted for the remainder of the activity budget. Results indicate that the broader PPB region is important for foraging, socialising and nursing dolphins, while TBSZ has proven importance for foraging dolphins. Thus, the implementation of TBSZ was a correct management decision and MPAs developed without baseline data can be effective for marine mammal conservation. Three candidate MPAs were objectively identified in areas that are hotspots for foraging and socialising Burrunan dolphins in southern PPB. The findings of this study will be used to inform current conservation management strategies. If implemented, the aim of the proposed MPAs will be to reduce impacts from anthropogenic disturbance, namely dolphin-swim tour vessels.  相似文献   

20.
万山群岛海域生态环境日益恶化、渔业资源持续衰退,因此建设万山群岛海洋牧场,修复海域生态环境、实现渔业资源可持续利用迫在眉睫。针对现阶段基于海洋生物资源的海洋牧场适宜性评估的研究较少,本研究利用渔业资源调查和全球物种数据库记录数据及13个环境因素数据,采用物种分布模型MaxEnt对选择的白姑鱼、日本金线鱼、红星梭子蟹和浅缝骨螺潜在分布区进行预测,探讨海洋生物地理分布与海洋环境因素之间的关系进而进行万山海洋牧场生境适宜性评估,结果表明:(1)各模型AUC值均大于0.9,说明构建的模型对这些物种潜在分布的模拟效果较好,后续可采用MaxEnt模型对4种生物的栖息地分布区进行预测;(2)海底浮游植物密度、海底温度以及海底硅酸盐浓度是影响这4种海洋生物栖息地分布的关键环境因子;(3)基于该4种海洋物种MaxEnt模型的HSI分布区所存在重叠区域来看,海洋牧场拟建设区域应为纬度21.85°N~22.15°N,经度113.6°E~114.2°E。研究结果可为万山海洋牧场规划和建设提供科学依据。  相似文献   

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