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1.
Estimating numbers of whales present in an area from recorded call rates could be a useful conservation tool. We recorded southern right whale Eubalaena australis vocalisations and presence in Walker Bay on the south coast of South Africa. In all, 45 sessions with synchronous acoustic and visual data were analysed to determine call rates directly (overall call rate, OCR) and in relation to the number of whales sighted (call rate per whale, CPW) and number of groups sighted (call rate per group, CPG). The OCRs were examined in the presence of varying numbers of whales, using a log-linear model to investigate the dependence of the call rate on whale density. The number of whales present exerted a strong quadratic effect on the OCR, which peaked at around 15 whales and decreased to a low rate as whale presence approached a maximum, for all calls combined and for four of their constituent 13 call types: a quadratic trend was present to varying degrees among the remaining call types. Both quadratic and linear trends were absent when OCR was assessed against number of groups present, possibly because group size increased with increasing density of whales. A linear regression on the CPW and CPG suggested that there was a negative inverse relationship with the number of whales and groups present respectively. These findings are important in that, while they preclude the estimation of absolute numbers from call rates, they imply that, under the conditions prevailing in Walker Bay, southern right whales were aware of the presence, arrival and departure of other animals in their vicinity and adjusted their vocal behaviour accordingly.  相似文献   

2.
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   

3.
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   

4.
ABSTRACT

The length-frequency distribution of sperm whales (Physeter macrocephalus) was studied on the east coast of NZ using passive acoustic recorders moored offshore of Kaikoura, Cape Palliser and Castlepoint. Sperm whale’s echolocation signals are unique among odontocete species. Their clicks are composed by multiple pulses resulting from the sound transmission within the whale head. The total length of the whales can be estimated by measuring the time delay between these pulses. A total of 997 length measurements were obtained from click trains using cepstral analysis (mean?=?14.6?m; min?=?9.6?m; max?=?18.3?m; std?=?1?m). The size-frequency distributions at all three locations were similar, although animals smaller than 12?m were not present offshore of Kaikoura. Animals of various sizes appeared to be present all year round, with no apparent seasonality in the occurrence of any size class.  相似文献   

5.
Observations of blue whales were made in Kenyan offshore waters during a seismic survey from September 2014 to January 2015. These represent the first live at-sea sightings of blue whales reported from Kenyan waters. All 30 sightings occurred between September and October in waters ranging from 2 990 to 4 705?m depth. It is unknown to which of the three possible subspecies the animals sighted belong. Based on timing and geographical location, they are likely to have been either Antarctic blue whales Balaenoptera musculus intermedia, Madagascar pygmy blue whales B. m. brevicauda or northern Indian Ocean blue whales B. m. indica.  相似文献   

6.
The Sainte Marie Channel on the northeast coast of Madagascar is an important breeding ground for humpback whales; the first observation of birth was documented there, yet it has never been investigated for phenology and habitat use of humpback whales. The present study was aimed at examining temporal and spatial distribution patterns and the encounter rate of different social groups of humpback whales during the breeding season. We used a large set of opportunistic sightings data collected from whale-watching boats. A total of 3 247 sightings were collected during 897 whale-watching trips conducted between June and September from 2009 to 2013. Our study complements previous information on the seasonal presence of humpback whale social groups by demonstrating a persistent and well-structured temporal pattern in the succession of the different groups. Over the different years of the study period, groups without calves consistently dominated the first 30 days of the breeding season, followed by an increase in groups with calves. Interannual differences were observed in the encounter rates, with significantly higher global encounter rates in 2009, 2011 and 2013 (2.2, 2.3 and 2.3 sightings h–1, respectively), and likewise for the mean encounter rates for groups with calves. In contrast, the encounter rate of groups without calves was similar over the study period. Although our study area exhibits a narrow configuration and poorly contrasting physiographic features due to its restricted spatial extent, we report a spatially segregated pattern of humpback whale social groups in the Sainte Marie Channel. A general linear model showed that groups with calves were influenced by water depth and distance from shore, being observed mostly in shallow waters (to 20 m depth) and close to the coastline (6 km). Our findings will be useful for the development of strategic sustained management plans by providing baseline information on humpback whale distribution at an important but poorly documented breeding site.  相似文献   

7.
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   

8.
The North Atlantic right whale, a seriously endangered species, is found in Cape Cod Bay (Massachusetts, USA) during the winter and early spring. During their residency in these waters, these whales are frequently observed feeding. This study evaluated spatial and temporal changes in the chemical composition (carbon weight and C/N ratio) of the food resource targeted by the right whales in Cape Cod Bay. The three taxa measured (Centropages typicus, Pseudocalanus spp., and Calanus finmarchicus) had highly variable chemical compositions resulting from the different life strategies and from fluctuations in their surrounding environment. The impact of seasonal variability in the energy densities of the food resource of right whales was calculated and compared to the energetic requirements of these whales. Calculations indicated that differences in the nutritional content of the zooplankton prey in Cape Cod Bay could have a considerable effect on the nutrition available to the right whales. Therefore, it is likely that using more precise estimates of the energetic densities of the prey of right whales would lead to a re‐evaluation of the adequacy of the food resource available to these whales in the North Atlantic.  相似文献   

9.
The distribution, seasonality and schooling behaviour of killer whales Orcinus orca in South African waters have been investigated from 785 records compiled between 1963 and 2009, and their size, morphometrics, growth, reproduction, food and feeding behaviour described from the examination of 54 individuals, 36 of which were landed at the Durban whaling station between 1971 and 1975. Qualitatively, the species appears to be more frequently encountered offshore, where it forms small schools of generally less than six animals. Seasonality of occurrence is not marked, although circumstantial evidence indicates that some individuals migrate from higher latitudes. Males reach 8.81 m and females 7.9 m, with 16.2% of males exceeding the size of the largest female. Stomach content and observational data suggest that the species can be characterised locally as an opportunistic predator of megavertebrates, rather than as the fish-feeding ecotype previously described. A stranded adult male with extreme tooth wear that was 1.5–2 m shorter than other males of equivalent age may be representative of a separate ‘offshore’ ecotype. Apparent differences between features of the popu lation's life history and those of resident killer whales in the north-eastern Pacific might be attributed to either uncertainties in age determination using dentinal growth layer groups or sampling bias. The basis for the suggestion that killer whales in South African waters should be reclassified as Vulnerable (rather than Data Deficient) is challenged.  相似文献   

10.
Seasonal fluctuations in the occurrence of inshore South African Bryde's whales Balaenoptera edeni were investigated between November 2005 and June 2008. Sighting data were collected in Plettenberg Bay on the south-east coast of South Africa. Bryde's whale occurrence was modelled in relation to the following environmental covariates: sea surface temperature, chlorophyll a concentrations and wind speed. Seasonal increases in encounter rates (sightings per day) were observed during summer and autumn, with a peak in April that corresponded to increased feeding activity and above average aggregation sizes. All three environmental covariates were significant factors in terms of explaining variability in the occurrence of whales. Multispecies associations with common dolphins Delphinus capensis and Cape gannets Morus capensis were most common in summer and autumn, when feeding activity was highest.  相似文献   

11.
Southern Resident killer whales (SRKWs) (Orcinus orca) are an endangered population in the United States and Canada, partly due to declines of their primary prey species, Chinook salmon. Prey availability influences various aspects of SRKW behavior, including distribution patterns and social structure. Yet, it is unclear to what extent a limited prey source influences the frequency of surface‐active behaviors (SABs), behaviors with important ecological implications. Here, we used long‐term datasets (1996–2019) to examine the relationships between the abundance of Chinook salmon, vessel presence, and the frequency with which SRKWs perform SABs. Salmon abundance was a significant predictor of SAB frequency, with fewer SABs performed in times of lower salmon abundance. SRKWs displayed more SABs when more whale watching vessels were present, and the whales spent a greater amount of time in the study area, performing more milling as opposed to traveling behavior, when vessel numbers were higher. Lastly, we found pod‐specific differences, such that K pod displayed significantly fewer SABs than either J or L pods. The observed relationships between SRKW behavior and both salmon abundance and vessel presence have implications for social network cohesion and foraging success. Our study adds to a growing body of literature highlighting factors affecting SRKW behavior as they experience increased threats from decreased prey availability, habitat loss, and anthropogenic disturbance, with implications for trans‐boundary management and conservation efforts.  相似文献   

12.
Cetacean research, in terms of the number of papers, and areas for which data are available, has expanded considerably in the southern African subregion in the past decade, especially in the South-West Indian Ocean. We review cetacean research within this subregion from the 1800s to the present to provide an overview of findings, investigate trends and identify knowledge gaps. Data are presented separately for large whales (those subject to commercial whaling) and smaller cetaceans, and are separated by era and ocean basin. Over 550 peer-reviewed papers and books were identified relating to research on cetaceans within the subregion. More than half (284) have been produced since 1990 and 193 relate specifically to South African waters. The most-studied species are those that are most accessible due to their coastal distributions (southern right whale Eubalaena australis: 45 papers, humpback whale Megaptera novaeangliae: 31 papers, killer whales Orcinus orca: 27 papers, Indo-Pacific bottlenose dolphin Tursiops aduncus: 30 papers, Indo-Pacific humpback dolphin Sousa chinensis (plumbea form): 25 papers) and/or were hunted commercially (sperm whale Physeter macrocephalus: 25 papers). Identified conservation concerns vary throughout the subregion, but include bycatch and directed hunts, oil and gas development, ecotourism activities, shifts in prey resources, and noise and chemical pollution. The inshore stocks of Bryde's whales Balaenoptera edeni, the Indo-Pacific humpback dolphin and the Atlantic humpback dolphin S. teuszii were identified as the populations of highest conservation concern, although there are considerable knowledge gaps relating to deep-water species and almost no data (even on species occurrence) are available for several areas and countries.  相似文献   

13.
A total of 772 bull sharks Carcharhinus leucas was caught in Natal's protective "shark nets" between 1978 and 1990. Confusion in distinguishing C. leucas from C. amboinensis resulted in their catch data being combined from 1966, when data collection began, to 1977. The catch rate of the species pair declined until 1977, recovered until the mid 1980s, but subsequently declined again. The trend in catch rate of C. leucas alone for the period 1978–1990 was similar, with minima of 0,70 sharks·km-net?1·year?1 in 1978 and 0,95 in 1990, and a maximum of 2,08 in 1986. Recaptures of six tagged sharks suggest that the species is not highly migratory. Catches, particularly of immature sharks, were highest at the northernmost beaches. Most bull sharks were caught in summer and in turbid water (mean water clarity 2,0 m). The sex ratio of the catch was 1 male to 1,3 females. Sizes ranged from 74 to 213 cm precaudal length, with modes of 141–145 cm (males) and 171–175 cm (females). Size at maturity for both sexes was between 180 and 190 cm. The mating season was prolonged but with a summer peak. Seven gravid females were examined; the mean litter size was 8,7 embryos and size at birth was approximately 55 cm. Fluke infections were observed on 9 per cent of animals examined. As size increased there was a shift in diet, in terms of frequency of occurrence, from teleost to elasmobranch predominance. There was a high incidence of benthic and demersal species in the stomachs. Minor prey groups included mammals, birds, turtles, molluscs and crustaceans. Scavenging appeared to be important.  相似文献   

14.
The composition and social structure of schools of sperm whales Physeter catodon Linn, in temperate latitudes east of New Zealand to longitude 150° W are examined and discussed. The study is based on sightings of about 1,572 animals supplemented by catch data from among this number.

Six major social categories were recognised: solitary males, male pairs, schools of bachelor males, mixed‐sex schools consisting almost entirely of immature animals, harems, and nursery schools. Male pairs probably represent the final stage in the break‐up of bachelor male schools into solitary animals, but the possibility that they could be temporary homosexual associations is considered. The schools of immature animals of both sexes are probably very temporary.

An inverse relationship in male schools between school size and mean body length is demonstrated. Mean testis weights of solitary males and bachelor school males are shown to be significantly different at P < 0.001. No relationship between seminiferous tubule diameter and body length was found for pubertal and mature males, as had been demonstrated by a previous worker.

Some data are presented which support the contention by Best (1969) that sexual maturity in the male sperm whale is attained at body length of about 45 ft (12.6 m), rather than at 36.6–41.0 ft (10.3–11.3 m) as suggested by earlier authors.  相似文献   

15.
The concentration of DDTs and PCBs was determined in two strata (inner and outer) of the blubber of fin and sei whales from the eastern North Atlantic. In the two species residue levels of all organochlorines in the outer layer were significantly higher than in the inner one. The DDE/tDDT ratio did not show significant variation between strata, but the tDDT/PCB ratio was higher in the outer layer than in the inner one. Such differences between strata cannot be explained by variation in the quantity of lipids present in the blubber and probably indicate a constant organochlorine distribution pattern in the blubber of large whales. The differential role of the blubber strata in the fattening cycle, the heterogeneous lipid composition of blubber throughout its depth and the different turnover rates of pollutants in the layers are the probable factors responsible for these observed differences in pollutant distribution between blubber strata. Because of this heterogeneous distribution, blubber samples collected from cetaceans for pollutant analyses should include equal representation of all layers in order to be representative of the individual's pollutant load. This is especially important when sampling stranded specimens or taking biopsy samples from large free-ranging whales.  相似文献   

16.
Shore-based surveys of migrating humpback whales Megaptera novaeangliae were undertaken from Cape Vidal, northern KwaZulu-Natal, South Africa, each year between 1988 and 1991, and in 2002. Daily observations of migrating whale groups were carried out from an approx. 60 m-high platform during all surveys. Whale groups were tracked by position-fixing on surfacing bouts using survey theodolites, to determine swimming speeds and headings and distance offshore, while group size estimation was carried out at each theodolite measurement. Numbers of whales observed or projected (at tracked speeds) to cross the midline of the survey area within the observation period each day were tallied in each of three distance bins. These counts were adjusted to account for daily sighting effort and for proportions that were likely to have been missed on account of their distance offshore or poor sighting conditions to produce daily sighting rates. Such daily tallies were summed over the survey period to estimate the number of whales passing Cape Vidal each year, with counts from days of <2.5 h of observation effort (due to weather or sighting condition restraints) replaced by the mean of the previous and following days. The numbers passing to the north of Cape Vidal during coincident periods of 17 days over the 1988–2002 surveys (6–22 July) and 25 days over the 1990, 1991 and 2002 surveys (6–30 July) provide statistically significant increase rates of 11.5% (SE 2.8) and 9.0% (SE 2.7) per annum respectively.  相似文献   

17.
The feeding habits of the mud shrimp Solenocera melantho were studied in the East China Sea by analysing 720 stomach contents and comparing diet composition and prey diversity among seasons, sexes and size classes. Feeding activity was linked to season and ovarian condition. The stomach fullness was high during spring and summer and low in fall. Females with advanced ovaries also displayed low stomach fullness, which suggests that feeding activity is affected by the reproductive cycle. The diet of S. melantho consisted of 42 different prey categories, primarily smaller crustaceans, Foraminifera, polychaetes, mollusks and fishes (larvae and eggs). Crustacea,Foraminifera and polychaetes together constituted the dominant prey groups, accounting for 75% of total prey abundance and >50% of total prey occurrence. Diet composition differed among seasons between sexes and size classes. Females and males consumed the same prey items but with different orders of importance. In terms of body size, the small shrimps preferred relatively small food items, such as Foraminifera and algae, whereas larger shrimps preferred polychaetes and crustaceans. Trophic diversity varied among the seasons within both sexes and size classes, with the highest values being observed in fall. Niche overlap was high within both sexes and size classes among seasons (0.6051–0.8740).  相似文献   

18.
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19.
Long-finned pilot whales (Globicephala melas), Risso's dolphins (Grampus griseus), melon-headed whales (Peponocephala electra), Cuvier's beaked whales (Ziphius cavirostris), Sowerby's beaked whales (Mesoplodon bidens), northern bottlenose whales (Hyperoodon ampullatus), sperm whales (Physeter macrocephalus), dwarf sperm whales (Kogia sima) and pygmy sperm whales (Kogia breviceps) make up the large community of deep-diving odontocetes occurring off the Bay of Biscay, northeast Atlantic. The ecology of these toothed cetaceans is poorly documented worldwide. The present study described their prey preferences from stomach content analysis and showed resource partitioning within the assemblage. The majority of the species appeared to be mostly teutophageous. Fish was an important food source only for the Sowerby's beaked whale and, to a lesser extent, for the long-finned pilot whale. In terms of foraging habitats inferred from prey composition, either pelagic oceanic or demersal neritic habitats were exploited by toothed whales in the Bay of Biscay, with only the long-finned pilot whale foraging in the two habitats. Finally, with more than 14,000 identified cephalopods from 39 species, the present study highlighted also the poorly known deep-sea cephalopod community off the Bay of Biscay using top predators as biological samplers.  相似文献   

20.
Southern right whales (Eubalaena australis) were widespread in New Zealand waters before commercial whaling in the nineteenth century caused drastic declines in their abundance and distribution. Following the cessation of whaling, the population has been recovering and is now slowly recolonising its former range. Estimates of population demographics, including reproductive output, are essential for predicting the trajectory of this population. We gathered photo-identification data on female southern right whales during annual field trips to the Auckland Islands, the principal calving area in New Zealand waters. Forty-five calving intervals were observed between 2006 and 2013 (mean interval?=?3.31 years, 95% CI?=?3.06–3.57). Incorporating the effects of possible missed calving events produced a plausible range of mean calving intervals from 3.17 to 3.31 years. Our results suggest that the calving interval of New Zealand southern right whales is similar to that found in populations elsewhere.  相似文献   

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