Daylight occurrence of humpback dolphins Sousa chinensis in Algoa Bay, South Africa

This paper describes the pattern of daylight occurrence of humpback dolphins Sousa chinensis in Algoa Bay, the Eastern Cape, South Africa, between May 1991 and May 1994. Two indices, the Sighting Index (SI) and the Total Recorded Dolphin Presence (TRDP), were used to quantify the dolphins' daylight occurrence. Humpback dolphins display a clear pattern of daylight occurrence in Algoa Bay and can be seen mostly in the morning, and, to a lesser extent, in the evening. This pattern varies little between seasons (with possible exception for the evening hours), follows the time of the solar day, is not related to the tidal cycle and is probably governed by the diurnal cycles of dolphins' prey.     

Sixteen years later: Occurrence,group size,and habitat use of humpback dolphins (Sousa plumbea) in Algoa Bay,South Africa

Coastal dolphins are more prone to cumulative impacts of environmental and anthropogenic changes than pelagic species. However, few studies use historical comparisons to evaluate those impacts across a temporal scale. The study presented here describes the pattern of occurrence, group size, behavior, and habitat use of humpback dolphins in Algoa Bay and compares these to a similar study conducted in the early 1990s. Results indicate a considerable change in the frequency of occurrence. Furthermore, the mean group size has decreased from six to three individuals, mainly due to an increase in occurrence of solitary individuals (36.3% vs. 15.4%). Foraging, which was previously the predominant activity (64%), has now been replaced by traveling (49%). Moreover, dolphins showed a negative reaction towards a variety of watercrafts and swimmers. These observed differences could be due to a change in prey abundance, direct anthropogenic disturbance, and/or population decline. We emphasize the need for long‐term environmental and biological data series and long‐term monitoring of the demographics of this population to accurately assess any changes observed in future.     

HABITAT USE AND PREFERENCES OF INDO-PACIFIC HUMPBACK DOLPHINS SOUSA CHINENSIS IN ALGOA BAY, SOUTH AFRICA

This paper examines environmental and behavioral determinants of the habitat use and preferences of Indo-Pacific humpback dolphins inhabiting the Algoa Bay region on the south Eastern Cape coast of South Africa. In order to quantify the habitat use and preference, two indices were used, the Coefficient of Area Use (AU) and the Activity Index (AI). The dolphins inhabit a narrow strip of shallow, inshore waters of Algoa Bay and remain mostly within 400 m of the shore, in water less than 15 m deep, with no apparent preference for clear or turbid water. Water depth is probably the main factor limiting their inshore distribution, and the 25-m isobath seems to represent the critical depth. Within this confined, inshore distribution, dolphin activities concentrate in the vicinity of rocky reefs-their primary feeding grounds. Dolphin dependence on these shallow-water habitats is evident throughout the year and, consequently, the inshore shallow reefs are identified as the "key habitat" which is of primary importance for humpback dolphins in Eastern Cape waters. The dolphins' dependence on this restricted type of habitat within an already restricted inshore distribution makes them particularly vulnerable to alteration or loss of this habitat.     

Whistle characteristics of a newly recorded Indo-Pacific humpback dolphin (Sousa chinensis) population in waters southwest of Hainan Island,China, differ from other humpback dolphin populations

Indo-Pacific humpback dolphins (Sousa chinensis) use whistles to communicate with their conspecifics. Little is known about the acoustic repertoire of Indo-Pacific humpback dolphins in waters southwest of Hainan Island, a newly recorded population in 2014. In this study, whistles of Hainan humpback dolphin population were collected by using autonomous acoustic recorders. The fundamental frequencies and durations of whistles were in ranges of 0.71–21.35 kHz and 0.06–2.22 s, respectively. Significant intraspecific differences in duration and frequency of whistles were found between the Hainan population and the other geographically neighboring populations (in Chinese waters) or the population in Malaysia waters. Compared with other Sousa species, significant interspecific differences were also observed. Based on clustering analysis, the whistle parameters of neighboring populations were likely similar to each other. Significant differences were found between humpback dolphins in waters southwest of Hainan Island and those dolphins in the neighboring areas, supporting the hypothesis that this population may be independent. Ambient noise measurements in waters of Hainan Island, Zhanjiang, and Sanniang Bay showed that humpback dolphin populations may use whistles with longer duration, lower frequency, and fewer inflection points for more effective communication to adapt to a noisier environment.     

Population size estimate of Indo-Pacific bottlenose dolphins in the Algoa Bay region, South Africa

This study estimates the population size of Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) in the Algoa Bay region on the Eastern Cape coast of South Africa. Mark-recapture analyses were performed on photo-identification data collected on 54 occasions during a 3-yr-study period. Using a photographic data set of over 10,000 ID-images, 1,569 individuals were identified, 131 of which were photographed on more than one occasion. Using the POPAN formulation in the software program MARK, a total population of approximately 28,482 individuals (95% CI = 16,220–40,744; CV = 0.220), was estimated (estimate corrected for the proportion of distinctive individuals in the population). This is the largest population estimate to date for this species along the South African coast, suggesting that the bottlenose dolphins inhabiting the Algoa Bay region represent part of a substantially larger population that ranges along a considerable length of the South African coast.     

Distribution and abundance of Indo‐Pacific humpback dolphins in Leizhou Bay,China

Abstract

The Indo‐Pacific humpback dolphin (Sousa chinensis) is under severe threat in Chinese waters. Only four small populations of this dolphin are known to survive in the East China Sea and South China Sea. We conducted exploratory surveys from June to September 2005, and found a population of humpback dolphins in Leizhou Bay. Thirty‐eight individuals were identified and catalogued, of which 26 were photographed and re‐identified on more than one occasion, and nine were sighted on five or more occasions each. Our preliminary estimate of the size of the Leizhou population is about 237 individuals, second only to the Pearl River estuary population. We suggest that Leizhou Bay has the potential to serve as a “humpback dolphin sanctuary” in Chinese waters.     

Abundance and residency dynamics of the Indo-Pacific humpback dolphin,Sousa chinensis,in the Dafengjiang River Estuary,China

Robust population size estimates are essential for informing population conservation status. Residency dynamics show population habitat use through time. Population size of Indo-Pacific humpback dolphins (Sousa chinensis) has been extensively investigated in Chinese waters, but their residency dynamics are rarely known. Mark-recapture analysis based on photo-identification records was applied to humpback dolphins in the Dafengjiang River Estuary habitat, one of the key habitats in the northern Beibu Gulf, China. Movement analyses based on lagged identification rate indicated the humpback dolphins spent, on average, 78.5 days inside and 46.9 days outside the survey area. Within the study area, the humpback dolphin abundance was 83 identifiable dolphins. A total of 353–430 humpback dolphins, estimated by POPAN modeling, were involved in this fluid habitat-use dynamic. Robust Design analysis showed strong seasonality in humpback dolphin abundance and emigration probability, implying a movement- and habitat-use pattern likely associated with spatiotemporal distribution of oceanographic characteristics and prey occurrences. Population surveys and conservation measures currently conducted in Chinese waters seldom consider seasonality in movements between habitat patches, which can be addressed by genetic analyses across habitats and cross-matching photo-identification records among neighboring habitats.     

Fine‐scale habitat use in Indo‐Pacific humpback dolphins,Sousa chinensis,may be more influenced by fish rather than vessels in the Pearl River Estuary,China

Shifts in habitat use and distribution patterns in dolphins are often concerns that can result from habitat degradation. We investigated how potential changes to a habitat from human activity may alter dolphin distributions within Lingding Bay in the Pearl River Estuary, China, by studying the relationship between fish choruses, vessel presence and Indo‐Pacific humpback dolphin (Sousa chinensis) detection rates. Analyses revealed temporal and spatial variation within fish choruses, vessel presence and dolphin detection rates. After accounting for any temporal autocorrelation, correlations between fish choruses and dolphin detection rates were also found; however, no relationship between fish choruses and vessel presence or dolphin detection rates and vessel presence were observed. Furthermore, fewer dolphins were detected at sites where fish activity was less intense. Thus fish activity, rather than vessels, may be a key factor influencing the distribution of the dolphins within the estuary. These findings emphasize the risk of potential shifts in habitat use for Indo‐Pacific humpback dolphins due to detrimental changes to prey availability and dolphin feeding grounds from human activity, such as overfishing and coastal developments, within the estuary. This is a critical conservation issue for this dolphin population that is facing intense anthropogenic pressure.     

厦门水域中华白海豚出现于围头湾

厦门海域的中华白海豚是一个受威胁的种群。以往有关该种群的调查范围主要集中在厦门以及邻近的南部漳州海域。为了获得厦门岛东部海域（包括晋江围头湾、小嶝岛以及大嶝岛部分水域）白海豚的分布和数量等信息,本文于2013年6—8月对该水域进行了船基样线法调查和照相识别研究。调查期间共目击到白海豚26群,照相识别白海豚个体27头。所有照相识别的白海豚个体均与厦门中华白海豚个体识别数据库中的个体匹配,表明厦门中华白海豚的分布区至少向东延伸至围头湾。本文白海豚遇见率为5.8群/100km和24.8头/100km,均要高于以往在厦门水域的调查结果,表明大嶝岛—围头湾水域是厦门中华白海豚的重要栖息地之一,值得优先保护和管理。     

厦门湾中华白海豚潜在生态廊道识别及人类活动干扰评估

生态廊道具有维持或恢复生态连通性的功能，对于连接生物栖息地、保护物种多样性具有重要意义。现有的生态廊道研究主要集中于陆地，而海洋生态系统具有水体广泛连通、缺乏直观的景观斑块等特点，导致海洋生态廊道的研究成为长期以来的科学难题。以栖息地位于厦门湾的国家一级保护动物中华白海豚（Sousa chinensis）为对象，尝试基于物种分布模型和最小成本路径分析法建立海洋生态廊道的识别方法。研究采用物种分布模型识别厦门湾内中华白海豚的适宜生境分布区和节点，并利用模型产出的生境适宜性结果生成海洋中的阻力表面，模拟计算节点与节点间在阻力表面上的最小成本路径，从而生成物种扩散网络。研究结果显示，厦门湾中华白海豚的分布主要受到航道距离、到岸线距离和叶绿素浓度三项因素的影响，主要适宜生境位于西海域至九龙江口和大嶝海域。潜在的核心生态廊道面积93.19km²，次级生态廊道面积170.41km²，九龙江口-鼓浪屿南侧-黄厝-大小嶝岛沿线可能是厦门湾中华白海豚的主要迁移路线。在此基础上，从用海空间重叠和桥梁影响两方面开展了人类活动对廊道的干扰评估。评估结果显示旅游活动和航运活动可能是中华白海豚生态廊道的主要影响来源，其中核心廊道受旅游活动影响更大，次级廊道受航运活动的影响更大。此外，厦门岛北部的桥梁亦可能会影响中华白海豚生态廊道的连通性。研究创新性地提出了海洋生态廊道的空间定量化识别方法并成功应用于厦门湾中华白海豚研究，研究结果可为我国海洋生物多样性保护、海洋保护区的空间规划等领域提供新的科学工具。     

Largest reported groups for the Indo‐Pacific bottlenose dolphin (Tursiops aduncus) found in Algoa Bay,South Africa: Trends and potential drivers

This study investigates how group size of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) changes temporally, spatially, and/or with predominant behavior at two discreet sites along the Eastern Cape coastline of South Africa: Algoa Bay and the Wild Coast. The mean group size of bottlenose dolphins was large with an average of 52 animals. Significantly larger groups were observed in Algoa Bay ( = 60, range = 1–600) than off the Wild Coast ( = 32.9, range = 1–250). In Algoa Bay, the mean group size increased significantly over the study period, from an average 18 animals in 2008 to 76 animals in 2016. Additionally, the largest average and maximum group sizes ever reported both in South Africa and worldwide, were recorded in Algoa Bay (maximum group size = 600). Neither season nor behavior had a significant effect on mean group size at both sites. Similarly environmental variables such as the depth and substrate type also had no influence on group size. It remains unclear which ecological drivers, such as predation risk and food availability, are leading to the large groups observed in this area, and further research on abundance and distribution of both predators and prey is necessary.     

Abundance and site fidelity of Indo‐Pacific Humpback dolphins in the Great Sandy Strait,Queensland, Australia

This study examined the population of Indo‐Pacific humpback dolphins, Sousa chinensis, inhabiting the Great Sandy Strait Marine Park, Queensland, Australia. A total of 106 dolphins were identified during 228 boat‐based surveys, completed between April 2004 and April 2007. Based on the distribution of resighted individuals and the pattern of associations, it was established that this population consists of two largely geographically distinct communities, referred to as the Northern Community (NC) and the Southern Community (SC). The only recorded interaction between the two groups was a single pod composed of one member of the NC and 11 dolphins from the SC. Abundance was estimated for the entire population and by geographical area using open population models. Estimates for the Great Sandy Strait indicate that about 150 dolphins (N_GSS= 148.4, SE = 8.3, 95% CI: 132.5–165.2) used this area during the study. The NC and SC total population sizes was estimated to be 76 (N_NGSS= 75.80, SE = 3.88, 95% CI = 71–86) and 75 (N_SGSS= 74.98, SE = 4.43, 95% CI: 66–83), respectively. Analysis of residence patterns indicates that a majority of the identified dolphins are long‐term residents.     

5. Memorandum on Bird Protection

Randall, R. M. &; Randall, B. M. 1980. Status and distribution of the Roseate Tern in South Africa. Ostrich 51:14-20.

The Roseate Tern Sterna dougallii population in Algoa Bay is the largest, and now possibly the only breeding population in southern Africa. The two mainland breeding sites at Cape Recife and Kommetjie have been deserted, and in recent years the last remaining breeding site outside Algoa Bay may have been abandoned. Consequently the present estimate of between 70 and 80 breeding pairs in Algoa Bay may represent the entire southern African population. The decline in numbers from hundreds in 1937 is ascribed to human interference. Although the species is rare and endangered in southern Africa, it has a world wide distribution and is in no immediate danger of extinction.     

POPULATION SIZE, DISTRIBUTION, AND BEHAVIOR OF INDO-PACIFIC BOTTLENOSE (TURSIOPS ADUNCUS) AND HUMPBACK (SOUSA CHINENSIS) DOLPHINS OFF THE SOUTH COAST OF ZANZIBAR

Indo-Pacific bottlenose ( Tursiops aduncus ) and humpback dolphins ( Sousa chinensis ) off the south coast of Zanzibar, East Africa, have been subject to both direct and indirect takes as well as disturbance from local dolphin tourism during the last decade. Meanwhile, little or no information on population parameters exists for these animals. In order to assess the anthropogenic threats, a study was conducted between 1999 and 2002 to determine population sizes, distribution, and behavior of these animals. Population sizes were calculated for each year using mark-recapture methods applied to photo-identification data. The estimates ranged between 136 and 179 for the bottlenose dolphins and between 58 and 65 for the humpback dolphins in the calculated 26 km² study area. Patterns in distribution and behavior were investigated using image and spatial statistic software on data from boat surveys. Analyses of spatial densities showed that both species concentrated their activities to smaller areas (2%–11.5%) within the study area. When the study results were considered in light of the anthropogenic threats, it was clear that immediate conservation measures were needed. This is critical if the negative impact on the species is to be minimized and the dolphins are to continue to represent a socioeconomic resource in the region.     

5. BIRDS ON RIETFONTEIN FARM,LOOP SPRUIT VALLEY

Randall, R. M. &; Randall, B. M. 1981. Roseate Tern breeding biology and factors responsible for low chick production in Algoa Bay, South Africa. Ostrich 52:17-24.

Roseate Terns Sterna dougallii were studied in 1977 on St Croix Island, Algoa Bay, South Africa. They are winter breeders in Algoa Bay and remain away from the breeding islands until about three weeks before the first eggs are laid. Full breeding dress is usually attained by the time the chicks hatch, when red appears on the culmen. Reasons are given for regarding the red culmen as an intraspecific aggressive signal. Nest density was 0,2/m² with a mean nearest neighbour distance of 0,66 m ± 0,27 m. Mean size of first clutches was 1,32 eggs, of replacement clutches was 1,03 eggs. Eggs measured 42,1 mm (39,8-44,5 mm) x 30,1 mm (28,6-31,5 mm). In clutches of two eggs, first eggs had significantly larger volumes than second eggs. Incubation took about 25 days and one of the pair did most of the incubating. Rearing took less than 28 days and all the terns had left the island a week after the last chick first flew. Human disturbance, gull predation, intraspecific aggression, and rain were factors contributing to the low production of 33 flying young in 1977. An estimated production of 79 flying young was calculated as necessary to maintain the population of 74 breeding pairs.     

北部湾沙田水域中华白海豚和江豚的同域分布格局及时空变化

北部湾是中华白海豚和江豚的重要分布区,但是对该水域两物种的分布格局及时空变化的研究却比较少,也不清楚这两个物种分布区是否有重叠。2003 ～ 2004 年与2011 ～2012 年期间,我们在北部湾沙田水域进行了船只调查,总计航程4 876.8 km,收集了两个物种空间分布的数据。结果表明,2003 ～ 2004 年仅发现中华白海豚,2011 ～2012 年则同时发现了中华白海豚和江豚。与2003 ～ 2004 年4 ～ 5 月相比,中华白海豚在2011 年4 ～ 5 月份的遇见率明显增加(0.152 vs 0. 028 头次/km)。中华白海豚的MCP、95% FK 家域和50% FK 核心域面积分别为162. 6 km² 、271. 35 km² 和56.78 km² ,2011 ～ 2012 年50% FK 核心家域有所扩大且东移。江豚的MCP、95% FK家域和50% FK 核心域面积分别为97.21 km² 、318.72 km² 和38.18 km² 。江豚主要分布于中华白海豚的外围远岸水域,同时两个物种的分布区有小部分重叠。基于多种因素的分析,我们推测,江豚可能存在季节性迁移以及中华白海豚对河口区有明显的偏好,可能是造成它们分布格局不同的原因。     

Larval fish variability in response to oceanographic features in a nearshore nursery area

The influence of oceanographic features on ichthyoplankton assemblages in the warm temperate nearshore region of Algoa Bay, South Africa, was assessed. The nearshore ichthyoplankton comprised 88 taxa from 34 families. Samples were collected at six stations between August 2010 and July 2012 using a plankton ring net of 750 mm diameter and 500 µm mesh aperture. The majority of larvae collected were in a preflexion stage, indicating the potential importance of the nearshore for newly hatched larvae. Engraulidae dominated the catch (38·4%), followed by Cynoglossidae (28·1%) and Sparidae (8·4%). Larval fish abundance was highest during austral spring and summer (September to February). Unique patterns in responses of each dominant fish species to oceanographic features in the nearshore indicate the sensitivity of the early developmental stage to environmental variables. Using generalized linear models, ichthyoplankton abundance responded positively to upwelling and when warm water plumes originating from an Agulhas Current meander entered Algoa Bay. Highest abundances of Engraulis encrasicolus and Sardinops sagax were observed during Agulhas Plume intrusions into Algoa Bay. When a mixed and stratified water column persisted in the nearshore region of Algoa Bay, larval fish abundance decreased. The nearshore region of Algoa Bay appears to serve as a favourable environment for the accumulation of ichthyoplankton.     

Area utilization patterns of humpback dolphins (Sousa plumbea) in Richards Bay, KwaZulu-Natal, South Africa

Geographically referenced data on humpback dolphin (Sousa plumbea) distribution and behaviour were collected in Richards Bay, South Africa, between 1998 and 2006. Utilization distributions presented a clear pattern in the distribution of dolphin activities and use of various locations within the study area. The 50 % kernel density estimate (core area) for foraging/feeding (2.1 km²) was clustered around the harbour mouth (including the shark net installation). The core areas for resting, socialising and travelling were more widespread (>2.95 km²). A mixed effects model indicated that location (longitude and latitude), distance from shore, year and group size are important variables in predicting foraging/feeding behaviour as opposed to other behaviours. The resting core was found in the southern part of study area and socialising was less clustered. This indicates preferential use of certain areas for specific behaviours. The overlap of foraging/feeding areas with stationary fishing gear (shark nets) and boat traffic are a major concern due to the risk of human-induced incidental mortalities. Any future alteration of the coastal area of Richards Bay, particularly development in the harbour, should be considered carefully, as further intrusion into areas critical to humpback dolphins, such as their foraging grounds, will inevitably carry negative implications for this already severely impacted population.     

Resource partitioning in sympatric delphinids: space use and habitat preferences of Australian snubfin and Indo-Pacific humpback dolphins

1. Many species of delphinids co-occur in space and time. However, little is known of their ecological interactions and the underlying mechanisms that mediate their coexistence. 2. Snubfin Orcaella heinsohni, and Indo-Pacific humpback dolphins Sousa chinensis, live in sympatry throughout most of their range in Australian waters. I conducted boat-based surveys in Cleveland Bay, north-east Queensland, to collect data on the space and habitat use of both species. Using Geographic Information Systems, kernel methods and Euclidean distances I investigated interspecific differences in their space use patterns, behaviour and habitat preferences. 3. Core areas of use (50% kernel range) for both species were located close to river mouths and modified habitat such as dredged channels and breakwaters close to the Port of Townsville. Foraging and travelling activities were the dominant behavioural activities of snubfin and humpback dolphins within and outside their core areas. 4. Their representative ranges (95% kernel range) overlapped considerably, with shared areas showing strong concordance in the space use by both species. Nevertheless, snubfin dolphins preferred slightly shallower (1-2 m) waters than humpback dolphins (2-5 m). Additionally, shallow areas with seagrass ranked high in the habitat preferences of snubfin dolphins, whereas humpback dolphins favoured dredged channels. 5. Slight differences in habitat preferences appear to be one of the principal factors maintaining the coexistence of snubfin and humpback dolphins. I suggest diet partitioning and interspecific aggression as the major forces determining habitat selection in these sympatric species.     

Population Differentiation and Hybridisation of Australian Snubfin (Orcaella heinsohni) and Indo-Pacific Humpback (Sousa chinensis) Dolphins in North-Western Australia

Little is known about the Australian snubfin (Orcaella heinsohni) and Indo-Pacific humpback (Sousa chinensis) dolphins (‘snubfin’ and ‘humpback dolphins’, hereafter) of north-western Australia. While both species are listed as ‘near threatened’ by the IUCN, data deficiencies are impeding rigorous assessment of their conservation status across Australia. Understanding the genetic structure of populations, including levels of gene flow among populations, is important for the assessment of conservation status and the effective management of a species. Using nuclear and mitochondrial DNA markers, we assessed population genetic diversity and differentiation between snubfin dolphins from Cygnet (n = 32) and Roebuck Bays (n = 25), and humpback dolphins from the Dampier Archipelago (n = 19) and the North West Cape (n = 18). All sampling locations were separated by geographic distances >200 km. For each species, we found significant genetic differentiation between sampling locations based on 12 (for snubfin dolphins) and 13 (for humpback dolphins) microsatellite loci (F _ST = 0.05–0.09; P<0.001) and a 422 bp sequence of the mitochondrial control region (F _ST = 0.50–0.70; P<0.001). The estimated proportion of migrants in a population ranged from 0.01 (95% CI 0.00–0.06) to 0.13 (0.03–0.24). These are the first estimates of genetic diversity and differentiation for snubfin and humpback dolphins in Western Australia, providing valuable information towards the assessment of their conservation status in this rapidly developing region. Our results suggest that north-western Australian snubfin and humpback dolphins may exist as metapopulations of small, largely isolated population fragments, and should be managed accordingly. Management plans should seek to maintain effective population size and gene flow. Additionally, while interactions of a socio-sexual nature between these two species have been observed previously, here we provide strong evidence for the first documented case of hybridisation between a female snubfin dolphin and a male humpback dolphin.