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1.
Shark catches in the protective nets set off the beaches of KwaZulu-Natal (KZN), South Africa, are strongly influenced by the sardine run, the winter influx of shoals of Sardinops sagax from the south-west. The effect of the sardine run, which is highly variable from year to year, is greatest in June and July at beaches south of Durban. Total annual shark catch and effort are presented for the period 1952–2005, and total monthly shark catch on the KZN south coast for the period May–August, 1965–2005. Measures to reduce catches of sharks associated with the sardine run have been introduced and have been increasingly successful. Reliable species-specific catch data are available for the period 1978–2005 only. For this period, the spatio-temporal distribution of each of 14 species of shark and the frequency of occurrence of sardine in their diets is documented. Occurrence varies according to species, as does the apparent influence of the sardine run on shark distribution. During June and July on the KZN south coast, sardine were found in the diet of all but two species and frequency of occurrence was 40% or greater in eight species. The presence of copper or bronze whaler sharks Carcharhinus brachyurus in KZN waters appears to be strongly associated with the sardine run, as does that of certain life-history stages of dusky sharks C. obscurus. Spinner sharks C. brevipinna and smooth hammerhead sharks Sphyrna lewini are caught in greater numbers in summer than in winter, but appear to shift their spatial distribution seasonally to feed on sardine.  相似文献   

2.
Data from 36 whale shark (Rhincodon typus Smith, 1828) sightings off north‐east North Island, New Zealand are summarised. Sightings were concentrated over the outer shelf and shelf break in areas influenced by the East Auckland Current at sea surface temperatures (SST) of 21–24°C. Sightings occurred from late spring to early autumn (November‐April) but were most frequent in midsummer (February) when upwelling along the north‐east shelf is weakest. The data indicate whale sharks occur off north‐east New Zealand most summers, including those when SST is colder than usual. A cluster of sightings and three observations of whale sharks feeding on schools of anchovy (Engraulis australis) near Whale Island, Bay of Plenty, suggest whale sharks may aggregate seasonally in this area. Estimated total lengths (TL) of 26 whale sharks ranged from 3.5 to 15 m, with 73% between 6 and 9 m TL.  相似文献   

3.
Shark bite injuries on reef manta rays Manta alfredi off the coast of Inhambane, Mozambique, were examined over a three-year period (2003–2006). The frequency and seasonality of attacks, the rate of wound healing, and the possible identities of attackers were explored. This study presents the first examination of bite wounds on manta rays in the wild and the role sharks may play in the natural mortality of this species. The reported incidence of shark-inflicted injuries is high with over three-quarters of the sampled population affected. In total, 571 bite injuries were observed on 283 identified individuals. The number of bite injuries varied from one to seven, with a mean of 1.54 bite wounds. There was no significant difference in the frequency of bite injuries in male and female rays. The majority (96%) of the observed bite wounds were healed. Fresh wounds occurred throughout the year, with no obvious seasonality. The bull shark Carcharhinus leucas and tiger shark Galeocerdo cuvier are suggested as the primary mediators of attacks, although up to 11 other shark species are listed as potential attackers. The majority of the bite marks (96%) occurred to the most posterior region of the body, specifically the posterior edges of the pectoral and pelvic fins, with many injuries likely having a negative impact on the reproductive abilities and fitness of the rays.  相似文献   

4.
Bull sharks Carcharhinus leucas are common along the coast of Reunion Island (South-West Indian Ocean) and were suspected to aggregate in the vicinity of an aquaculture farm in Saint-Paul Bay on the west coast. In order to understand the behaviour and interaction of bull sharks near aquaculture cages at Saint-Paul Bay, we deployed an experimental unbaited stationary video camera. From 175 hours of recording during daylight hours from March to April 2012, eight individual female bull sharks (seven adults and one immature) were identified based on their natural markings. These sharks were resighted between 3 and 45 times. Residency analysis revealed site attachment under the aquaculture cages for at least three individuals over the course of the study. Recorded behaviours included intraspecific social interactions such as synchronised swimming. Social interactions and relatively strong paired associations for two pairs of females suggest some level of sociality among bull sharks around Reunion Island. Overall, our results demonstrate the utility of unbaited video systems to monitor the behaviour of adult coastal sharks.  相似文献   

5.
Public perception has been that an apparent increase in the nearshore occurrence of white sharks Carcharodon carcharias in False Bay, on the south coast of South Africa, can at least be partly attributed to beach-seine (treknet) operations attracting sharks into this coastal area. To assess the merit of these concerns, all available beach-seine catch-and-effort data from the False Bay fishery over a 32-year period were analysed. A total of 27 cartilaginous species from 15 families was recorded in around 11 400 hauls from 1974 to 2006. Most (98%) of these comprised small benthic invertebrate feeders such as smooth houndshark Mustelus mustelus and lesser guitarfish Rhinobatos annulatus. Large sharks such as C. carcharias and ragged-tooth shark Carcharias taurus were rare, occurring in <0.2% of hauls. The only medium to large sharks that occurred frequently (15% of hauls) in any appreciable numbers (0.3 per haul) were bronze whalers Carcharhinus brachyurus. The relatively high numbers of C. brachyurus compared with C. carcharias, their overlapping size distributions and the difficulty of identifying sharks from a distance, suggests that many of the sharks observed following beach-seine nets are the bronze whalers. Overall, the frequency of occurrence of C. carcharias in the nets is much lower than would be predicted from the high number of observations in the nearshore region. Furthermore, beach-seine fishing rights in False Bay have been reduced from around 170 in the 1970s to five at present. There has been no corresponding decrease in shark incidents. On the contrary, shark incidents have increased from two in the 1970s to six during the period 2000–2005. Overall, there appears to be no strong link between beach-seine activity and human incidents with white sharks in False Bay.  相似文献   

6.
Between 1978 and 1990,1 800 copper sharks Carcharhinus brachyurus were caught in the shark nets that protect the swimming beaches of Natal. The species constituted 9,6 per cent of the total shark catch. Annual catches and catch rates fluctuated widely about a mean of 138 sharks and 3,5 sharks·km net?1 respectively. Most sharks were caught at the southern beaches during the annual Natal sardine run in June and July, when shoals of pilchard Sardinops ocellatus move into the waters off southern Natal. Catches were dominated by sharks >140 cm pre-caudal length PCL. Mature males (generally ≥ 175 cm PCL) were present for much of the year, but mature females (generally ≥ 190 cm) and immature sharks were only abundant in June and July. Gonad indices in males were highest in March and April, whereas high gonad indices and large ova were recorded in females in June and July. Mating appears to take place after July and parturition about 12 months later, both occur south of the netted region. The smallest of 50 pregnant females caught was 178 cm. Mean embryo length within a litter ranged from 17 to 54 cm. Teleosts were found in 92 per cent and pilchard in 84 per cent of stomachs containing food.  相似文献   

7.
我国在中西太平洋(Western and Central Pacific Ocean,WCPO)金枪鱼围网渔业作业的方式主要分为捕捞自由鱼群(free swimming school,FSC)和人工集鱼群(fish aggregation devices,FAD),镰状真鲨(Carcharhinus falciformis)是这两种作业方式中主要的兼捕鲨鱼。本研究根据2018—2019年我国围网渔业渔船在中西太平洋区域(15°S—15°N,140°E—180°E)共20个作业航次记录的渔捞日志,对FSC和FAD两种状态的捕捞作业下兼捕到的镰状真鲨渔获率、生存状态等进行比较分析,结果表明:(1) FAD作业相比FSC作业兼捕到的镰状真鲨分布范围更广,两种作业方式兼捕到的镰状真鲨单位捕捞努力量渔获(catch per unit effort,CPUE)主要分布区域均集中在基里巴斯和瑙鲁专属经济区;(2) FAD和FSC兼捕镰状真鲨CPUE出现较高月份均在5—9月,FAD兼捕镰状真鲨CPUE显著高于FSC (P 0.05);(3) FSC和FAD兼捕镰状真鲨的死亡率范围分别为0.00%～92.86%和20.26%～76.71%,经检验两种作业方式下镰状真鲨死亡率间无显著性差异(P 0.05)。研究结果有助于了解不同作业方式对鲨鱼兼捕的影响,以实现提高目标鱼种渔获率、降低鲨鱼兼捕率的目的。  相似文献   

8.
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   

9.
Identifying nearshore waters that serve as important habitats for neonate and juvenile sharks is crucial for effective fisheries management. This study examined the abundance of neonate and juvenile dusky sharks Carcharhinus obscurus within the Port of Ngqura, on the south-east coast of South Africa, between September 2006 and August 2007 using a combination of shore-angling catches and mark-recapture data. During this period, the port was non-operational and still undergoing construction. A total of 480 dusky sharks, ranging in size from 50 to 123 cm (precaudal length), was captured. Catch per unit effort was greatest between October and February, peaking in November at 0.51 sharks angler–1 h–1. Of the 219 C. obscurus tagged and released during the study period, 37 (16.9%) were recaptured. Sharks were at liberty from 0 to 409 days with the majority (89.2%) recaptured within the port. Using a Jolly-Seber open population model, the abundance of sharks within the port was estimated at 552 (95% CI: 422–765). Annual apparent survival probability was 0.38 (95% CI: 0.30–0.46), with an average annual recapture probability of 0.28 (95% CI: 0.19–0.39). This study demonstrates that the Port of Ngqura is an important summer habitat and core activity zone for both neonate and juvenile dusky sharks.  相似文献   

10.
The current study provides long-term catch-rate, biological and feeding data for smooth hammerhead sharks, Sphyrna zygaena, caught in South Africa’s KwaZulu-Natal bather protection programme. In total, 2 512 S. zygaena were caught in net installations between 1978 and 2014, and 72 S. zygaena were caught on drumlines between 2007 and 2014. There was no significant log-linear year trend in the net catch rate over time (slope = 0.0054, t = 1.808, p = 0.07). However, there was a significant temporal increase in mean size of the captured sharks (slope = 0.0012, t = 3.502, p < 0.001). A quasi-Poisson generalised additive mixed model showed that increasing latitude, winter months, colder sea temperatures and the deployment of drumlines all had a significant positive effect on the catch rate of sharks in nets. The size frequency of the catch was unimodal, with significantly more females caught in the nets and more males on the drumlines. The majority (93.1%) of all sharks caught were immature and measured between 80 and 120 cm precaudal length. Teleosts and cephalopods dominated the sharks’ diet in terms of all dietary indices. The prey species consumed indicate that immature S. zygaena are feeding primarily within the pelagic zone of shallow coastal habitats.  相似文献   

11.
The first detailed elasmobranch fisheries data for the Kingdom of Bahrain are presented, based on surveys of fish markets in April 2012. At least 25 species were recorded, including undescribed taxa. The milk shark Rhizoprionodon acutus was the most frequently recorded species; together with the Arabian smoothhound Mustelus mosis and banded eagle ray Aetomylaeus nichofii, these species comprised 53% of individual abundance. Sharks were almost entirely small individuals <1 m total length (TL). Males of small shark species were largely mature, whereas nearly all individuals of larger sharks were immature. For several elasmobranch species, landings were significantly biased towards males, which were largely mature. The species assemblage showed some notable differences in composition to that of adjacent Qatar, sampled at the same time of year, highlighting the importance of local data collection.  相似文献   

12.
Between 1978 and 1990, 209 Java sharks Carcharhinus amboinensis were caught in the shark nets that protect the swimming beaches of Natal, thereby constituting 0,5 per cent of the total shark catch. The catch rate was relatively constant at about 0,4 sharks·km net?1·year?1. Catches were highest at the northernmost beaches in summer and autumn and they consisted mostly of juvenile, but not newborn, and adolescent sharks. Specimens ranged from 99 to 176 cm PCL, with a mode of 131–135 cm for males and 131–145 cm for females. Males matured at 150 cm and females at 160 cm. Of the eight mature females caught, five were pregnant. Mating takes place in late summer and gestation is thought to last approximately 12 months. The largest embryo found was 53 cm. Teleosts were identified in 62,1 per cent of the 103 stomachs that contained food. Elasmobranchs (44,7%), crustaceans (12,6%) and cephalopods (11,6%) were the other major prey groups. Most of the fish prey were demersal, associated with soft bottoms.  相似文献   

13.
The first documented recapture of a South African-tagged juvenile blue shark Prionace glauca off Uruguay lends weight to the hypothesis of a single blue shark population in the South Atlantic. The presence of neonate blue sharks with umbilical scars and females with post-parturition scars, as well as the high frequency of small juveniles in research longline catches, confirm the existence of a parturition and nursery area off South Africa. The final positions of three tagged sharks suggest that large-scale movement patterns in the South Atlantic are a mirror image of movements in the North Atlantic, with sharks using the north-westerly Benguela Drift to migrate into the tropics and ultimately across into South American waters. The confirmed existence of a parturition and nursery area off the south coast of South Africa and the movement of sharks into both adjacent ocean basins suggest that the southern African blue sharks are part of a single stock that straddles the South Atlantic and Indian oceans, and possibly the entire Southern Hemisphere.  相似文献   

14.
A total of 2 728 spinner sharks Carcharhinus brevipinna was caught in nets that protect the swimming beaches of KwaZulu-Natal between 1978 and 1997. The species constituted 10.3% of the total shark catch during that period. An average of 136 spinner sharks was caught annually, with no trend in catch rate over the study period. The species was caught throughout the year, predominantly in the south and mainly from February to July. Males matured at approximately 150 cm precaudal length and females at 154 cm. Gonad indices in mature males were highest during December and January and in females during February and March. Mating takes place between January and March. The hepatosomic index of pregnant females was highest at the onset of pregnancy and lowest at parturition. Evidence suggests a two-year reproductive cycle in females, with a gestation period of 13–18 months. The average litter size was nine, with an estimated length at birth of between 50 and 60 cm. Near-term pregnant females were caught mainly in the north, indicating the possibility of a nursery there. Both large and small pregnant females produce pups of the same length, but larger females general1y have larger litters. Regional, seasonal and size variations were evident in the diet, with teleosts being the most frequently eaten prey.  相似文献   

15.
Landing site and market surveys of sharks landed along the Arabian Gulf coast of the United Arab Emirates were undertaken between October 2010 and September 2012 to obtain biological data from this artisanal fishery. Data were collected on the size and sex of 12 482 individuals representing 30 species. Maximum sizes of Carcharhinus sorrah, C. amblyrhynchoides and Hemipristis elongata were extended by at least 300?mm total length (TL) compared with published global maxima. The size at 50% maturity was determined for males of five species and this indicated that the males of smaller shark species (<1 000 mm maximum TL) in the fishery were largely mature. For many species, including Loxodon macrorhinus and Mustelus mosis, overall sex ratios were male-biased, indicating that sexual segregation is likely in those species. Furthermore, sex ratios for several species, such as Rhizoprionodon acutus, showed differences across seasons. Overall, the landings contained a high proportion of juveniles, causing concerns about the sustainability of this fishery. Biological parameters of a number of species differed from those recorded earlier for the region, demonstrating a need for additional local data collection to support the development of management measures.  相似文献   

16.
The current study provides long-term catch rate and biological data for tiger sharks Galeocerdo cuvier caught in the KwaZulu-Natal bather protection programme. Between 1978 and 2014, 1 760 G. cuvier were caught in nets and between 2007 and 2014, 108 G. cuvier were caught on drumlines. Standardised catch rates increased significantly over time (p < 0.001) for both small (≤180 cm precaudal length, PCL) and large sharks (>180 cm). There was also a significant temporal increase in the mean size of sharks across gear types (p < 0.001). A quasi-Poisson generalised additive mixed model showed that the deployment of drumlines had no significant effect on the catch rate of sharks in nets. The nets, however, caught significantly larger sharks (mean 184.5 cm, SD 39) than did drumlines (mean 138.6 cm, SD 36.5; p < 0.001). The size frequency of the catch was unimodal and females significantly outnumbered males in both gear types. Few young-of-the-year (0.8%) or mature sharks (1.8%) were caught. Only 23 (4.7%) of the 486 sharks tagged and released were recaptured, with the majority (87.0%) of those recaptured <150 km from their original tagging locality. The results from this study suggest an increasing local population trend in G. cuvier along the KwaZulu-Natal coast.  相似文献   

17.
用深海鲨鱼制备角鲨烯,角鲨烷   总被引：3，自引：0，他引：3  
探讨了７种深海鲨鱼的角鲨烯含量。这几种深海鲨鱼的肝脏约占体重的２０％,肝脏中油脂含量大部分超过５０％,有些达到８０％以上。肝油中角鲨烯的含量与鱼种及个体特性有关,但一般超过５０％。介绍了角鲨烯、角鲨烷的制备方法。  相似文献   

18.
This study provides one of the first quantitative assessments of a fish community within a pre-operational deep-water port system. Between September 2006 and September 2007 a total of 4 559 fish, representing 47 species and 27 different families, were caught within the Port of Ngqura, Africa's deepest port, in 1 713 h of shore-angling (2.3 fish angler?1 h?1) and 239 h of boat-based angling (2.8 fish angler?1 h?1). Catches included species representative of both estuarine and shore fisheries. The majority (83.0%) of species caught were marine and most were less than size-at-50% maturity (71.4%). The most abundantly caught species were dusky kob Argyrosomus japonicus (25.5%), elf Pomatomus saltatrix (24.9%), garrick Lichia amia (17.7%) and dusky sharks Carcharhinus obscurus (10.7%). Fish assemblages differed significantly (p < 0.05) between three habitats within the port: Dolosse, Quay Wall and Sandy Shore. The Dolosse habitat supported the greatest abundance (3.1 fish angler?1 h?1) and diversity (43) of fish species. The Port of Ngqura is thus functioning as an important habitat for both juvenile and adult fish. The diversity and abundance of fish suggests the potential use of ports and other artificial structures for enhancing local fisheries in South Africa.  相似文献   

19.
Between 1966 and 1989,255 shortfin mako sharks Isurus oxyrinchus were caught in the gill nets which protect the tourist beaches of Natal. The catch rate showed no trend, fluctuating about a mean of 0,34 sharks·km-net?1·year?1. Catches were highest between May and November, when the water tends to be cooler. The sex ratio was 1,4 males to 1 female. Specimens ranged in size from 84 to 276 cm precaudal length, with a mode of 191–195 cm for males and 251–255 cm for females. Males matured at 160-170 cm and females at approximately 220 cm. Catches included two recently fertilized females and two with well-developed embryos. External injuries were found on 14 per cent of males examined and 41 per cent of females. Elasmobranchs were the most common prey category, occurring in 60 per cent of stomachs containing food, followed by teleosts at 40 per cent. Most of the elasmobranch prey were sharks shorter than 1 m.  相似文献   

20.
The distributions of the nematode parasites Paraquimperia sp., Spirocamallanus sp., and Cucullanus sp. in the intestines and recta of Anguilla dieffenbachii and A. australis from Lake Ellesmere and the South Branch of the Waimakariri River were studied over two years. Peak occurrence of Paraquimperia was in the anterior intestine of A. australis and mid intestine of A. dieffenbachii. Male and female Spirocamallanus sp. established in the mid intestine, but as female worms grew they attached more anteriorly and thus maintained the mid body in the mid intestine, prevented the tail end entering the rectum, and maintained the vulvae close to male worms. Cucullanus sp. was most often found in the mid intestine, but occurred throughout the intestine, possibly because of migration with food. Paraquimperia and Spirocamallanus extended their range with crowding; Cucullanus increased in density in the mid intestine. Posteriad movement, with or without subsequent evacuation, was a general feature of all species in both hosts, held live or examined after death. Chilling and freezing slowed or arrested loss from dead hosts. Larger worms (Spirocamallanus sp.) moved and were lost more rapidly than small worms (Paraquimperia sp.); worm loss was more rapid from A. dieffenbachii than from A. australis.  相似文献   

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