Sharks caught in the protective gill nets off Natal,South Africa. 6. The copper shark Carcharhinus brachyurus (Günther)

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.     

Sharks caught in the protective gill nets off Kwazulu-Natal,South Africa. 9. The spinner shark Carcharhinvs brevipinna (Müller and Henle)

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.     

Sharks caught in the protective gill nets off KwaZulu-Natal,South Africa. 11. The scalloped hammerhead shark Sphyrna lewini (Griffith and Smith)

Between 1978 and 1998, a total of 3 385 scalloped hammerhead sharks Sphyrna lewini was caught in the protective nets off KwaZulu-Natal. The mean annual catch was 166 sharks (range 60–279). There was a significant decrease in catch rate with time, but the relationship with the population size in KwaZulu-Natal waters is unknown. Size and sex segregation is indicated. Sizes-at-50% maturity were 161.5cm (males) and 183.1cm (females). Most of the catch (91%) was immature, but neonates are poorly sampled by the 51-cm meshed nets. In small animals (<160cm precaudal length, PCL), males significantly outnumbered females by 2.2:1, and in large animals by 3.6:1. The length-mass relationship differed between sexes. Catches of both small and large animals were highest in summer. Most of the large males were caught in November and December, consistent with an inshore movement of mature animals to breed in summer, but no evidence of recent mating was observed in either sex. Females pregnant with term embryos (median embryo length per litter 30.4–36.2cm) were caught between October and March. These females tended to have maximum ovarian follicle diameters of ≥30mm, indicating that mating would occur shortly after parturition. The median size of 11 litters was 10 embryos. The Tugela Bank to the north of the netted region appears to be a nursery ground. Teleosts, comprising 42 families and 60 identified species, dominated the diet in terms of frequency of occurrence (77%), followed by cephalopods (25%).     

Sharks caught in the KwaZulu-Natal bather protection programme,South Africa. 13. The tiger shark Galeocerdo cuvier

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.     

Sharks caught in the KwaZulu-Natal bather protection programme,South Africa. 14. The smooth hammerhead shark Sphyrna zygaena (Linnaeus)

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.     

Sharks caught in the protective gill nets off Natal,South Africa. 5. The Java shark Carcharhinus amboinensis (müller & Henle)

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.     

Sharks caught in the protective gill nets off KwaZulu-Natal,South Africa. 8. The Great hammerhead shark Sphyrna mokarran (Rüppell)

Between 1978 and 1993, 209 great hammerhead sharks Sphyrna mokarran were caught in the shark nets which protect the swimming beaches of KwaZulu-Natal. This species constituted 0,97% of the total shark catch, with a mean annual catch of 13. Catch rates showed a significant decline during the period under review, from 0,66 to 0,09 sharks·km-net^?1·year^?1. Most sharks were caught in the north of the netted region between January and May. Catches at Mzamba, the southern extremity of the netted region, represent the southernmost records of this species on the east African coast. The males ranged in size from 106 cm precaudal length (18 kg) to 264 cm (220 kg) and females from 140 cm (35 kg) to 326 cm (400 kg). Males matured at about 217 cm and females at 237 cm. Very few sharks were found in mating condition. Elasmobranchs were found in 82% of non-empty stomachs. There was a high incidence of stingrays (Dasyatidae), guitarfish (Rhinobatidae) and other bottom-dwelling fish in the diet.     

Sharks caught in the protective gill nets off Natal,South Africa. 3. The shortfin mako shark Isurus oxyrinchus (Rafinesque)

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.     

Sharks caught in the protective gill nets off Natal,South Africa. 4. The bull shark Carcharhinus leucas Valenciennes

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.     

Influence of the annual sardine run on catches of large sharks in the protective gillnets off KwaZulu-Natal,South Africa,and the occurrence of sardine in shark diet

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.     

Evidence of summer parturition in shortfin mako (Isurus oxyrinchus) sharks from New Zealand waters

A litter of eight near‐term shortfin mako (Isurus oxyrinchus Rafinesque 1810) embryos is described from a 317.5 cm total length (TL) female caught off Hawke Bay, south‐east North Island, New Zealand on 5 February 1999. The embryos (3 males and 5 females) were 67.2–77.0 cm TL. Embryo length, condition, hepato‐somatic indices, and mass of yolk in their stomachs all indicate they were close to birth. This is the first shortfin mako litter reported from New Zealand and is outside the late winter‐early spring parturition period predicted from estimated embryonic and juvenile growth rates. Uterine width data from four mature non‐pregnant females and age‐0+ length‐at‐capture data suggest parturition occurs from September to late February (late winter‐mid summer) but is infrequent after January. We suggest that shortfin makos have an extended parturition period, possibly year‐round, with peak parturition occurring in late winter‐spring.     

不同气候条件下南海西沙海域鸢乌贼(Sthenoteuthis oualaniensis)渔业生物学比较研究

为探讨不同气候条件对鸢乌贼(Sthenoteuthisoualaniensis)渔业生物学影响,根据2015年8月(厄尔尼诺年)、2016年8月(拉尼娜发生期)和2017年8月(正常时期)我国灯光罩网船在南海采集的1 970尾鸢乌贼样本,对其胴长、体重、性腺成熟度、胃饱满度、初次性成熟胴长进行了比较研究。结果表明:不同年间鸢乌贼雌雄比例不同, 2017年最高, 2015年次之, 2016年最低;优势胴长组不同,2015年最大, 2017年次之, 2016年最小;优势体重组也不同, 2015年最大, 2017年次之, 2016年最小。协方差分析表明不同年间胴长与体重的关系均不存在性别间显著性差异, 2015、2016和2017年分别最适用线性、幂和指数函数表示;不同年间样本性成熟组成存在差异,雌雄样本性成熟样本分别占对应总数的30.96%和25.40%、46.41%和11.15%、7.35%和28.46%;胃饱满度组成也不同。不同年间初次性成熟胴长不同, 2015、2016和2017年雄性初次性成熟胴长分别为184.12、144.41、132.70 mm;雌性分别为192.66、143.68、188.52 mm。结果表明,不同气候变化引起的海洋环境的变化对鸢乌贼渔业生物学产生影响:温度升高导致鸢乌贼个体减小,性成熟胴长减小,雌雄间的个体差异变大。     

Reproductive biology of Mustelus lenticulatus from Kaikoura and Nelson

Mustelus lenticulatus is a non‐placental ovoviviparous shark with a gestation period of about 11 months. Young are born at a total length of 30–32 cm from September to December. Copulation, and ovulation of a further set of eggs, rapidly follows parturition. Fecundity increases with the length of the female; the most eggs found in one female was 24; the mean for all females was 10.73.

Males mature at about 85 cm total length and females at 95 cm at Kaikoura. Nelson males probably mature at a smaller size than do Kaikoura males. Nelson females mature at about 85 cm. Maximum observed lengths were 137 cm for females and 115 cm for males.     

Distribution and movement of scalloped hammerhead Sphryna lewini and smooth hammerhead Sphyrna zygaena sharks along the east coast of southern Africa

Knowledge of population distribution and movement is crucial for the conservation and management of shark species occurring in coastal waters. From 1984 to 2009, 641 scalloped hammerheads Sphyrna lewini, 1 342 smooth hammerheads Sphyrna zygaena and 1 352 unspecified hammerheads Sphyrna spp. were tagged and released along the east coast of South Africa, with recapture rates of 1.9%, 1.5%, and 0.7% respectively. Maximum and average distance moved was 629 km and 147.8 km (95% CI = 33.0–262.7 km) for S. lewini and 384 km and 141.8 km (95% CI = 99.1–184.5 km) for S. Zygaena respectively. The majority of sharks (68% S. lewini, 74.1% S. zygaena and 33.5% Spyrna spp.) were tagged in the Transkei region, with the largest number tagged in Port St Johns. Across regions, most tagged sharks were >50–100 cm precaudal length (PCL), except in Transkei where more sharks >100–150 cm PCL were tagged. In the Western Cape, Southern Cape and Eastern Cape, few sharks were tagged during the autumn/winter months, whereas in KwaZulu-Natal and Transkei sharks were tagged throughout the year. Large-scale directional movements observed may have been migrations in response to seasonal sea surface temperature changes. We identify coastal locations in Transkei that are of importance to juvenile and subadult hammerhead populations year-round.     

Some observations on the reproductive biology of The sixgill shark Hexanchus griseus (Bonnaterre, 1788) from southern African waters

Observations are made of the maturation status of 81 male and 88 female sixgill sharks Hexanchus griseus from southern African waters. Males mature at about 310 cm total length (TL) with the calcification of the terminal cartilage elements of the claspers. Determination of maturity for females was problematic, but most were fully mature by at least 420 cm TL. Newborns were captured at the same location over three consecutive summer seasons, indicating the location of a possible pupping ground.     

Patterns in abundance,population structure and biology of knife prawn Haliporoides triarthrus on deep-water trawl grounds off eastern South Africa

The deep-water trawl fishery along the KwaZulu-Natal coast of South Africa targets several crustacean species, with the knife (or pink) prawn Haliporoides triarthrus contributing most of the catch. Logbook data of fishing effort and catch between 1988 and 2010 were used to assess the distribution and abundance of H. triarthrus on fishing grounds. Generalised linear models were used to quantify the effects of year, month and depth on catch rates. Standardised trends indicated a general decline in abundance between 1990 and 1998, followed by an increase between 2001 and 2008. Catch rates peaked in March, and they were highest between 200 and 499 m depth. Biological samples collected during commercial fishing were used to assess size and sex composition, growth rates and reproductive activity of H. triarthrus. Females became larger than males and mean carapace length (CL) varied by month. The youngest female cohort appeared in November (modal CL of 25 mm), and dissipated after two years (39 mm). Sex ratios were equal for all data combined, but fluctuated by month and CL. Few reproductively active females were recorded. Length-based methods and the standard von Bertalanffy growth function were used to estimate growth parameters (L_∞ and K) of females (40.6 mm CL and 1.06 y^–1) and males (35.2 mm and 1.27 y^–1) respectively. Our findings were compared with information on H. triarthrus from Mozambican waters.     

Biology of the redspotted tonguesole Cynoglossus zanzibarensis (Pleuronectiformes: Cynoglossidae) on the Agulhas Bank,South Africa

The biology of the redspotted tonguesole Cynoglossus zanzibarensis, a common African cynoglossid inhabiting the Agulhas Bank, South Africa, is described. Growth studies based on sectioned sagittal otoliths revealed that C. zanzibarensis is relatively fast-growing and long-lived, attaining ages >8 years. Growth in length was rapid in immature fish, fish attaining 56% of their maximum size within their first year. By sexual maturity, fish had attained 28% of their maximum age and 68% of their maximum length. Total length-at-age was best described by the Von Bertalanffy growth model with combined-sex growth described as L_t = 354.78(1?e^{?0.43 (t+1.17)}) mm TL. Sexually dimorphic growth patterns were evident, females attaining larger lengths, but at a slower growth rate than males. Despite the similar mean size of adult fish, the trawl-sampled adult population was dominated by females, with a sex ratio of 1 male:2.4 females. Female C. zanzibarensis mature in their second year of life (275 mm TL), after which they spawn small, pelagic eggs throughout the year. Approximations of the rates of total, natural and fishing mortality were estimated to be 0.62, 0.48 and 0.14 year^?1 respectively.     

Composition of elasmobranch landings in Bahrain

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.     

Spatial and seasonal distribution patterns of the ragged-tooth shark Carcharias taurus along the coast of South Africa

Catches from competitive shore-anglers, inshore boat-based anglers and sightings by spearfishers and divers were used to infer the spatial and seasonal movement patterns of young-of-the-year (<1.2m TL), juvenile (1.2–1.8m TL), sub-adult (1.8–2.4m TL) and adult (>2.4m TL) ragged-tooth sharks Carcharias taurus along the coast of South Africa. Adult sharks inhabited the entire coast between Maputaland in the east and St Helena Bay on the West Coast. The geographical range of sharks at earlier life-history stages decreased with size. The vast majority (93.8%) of young-of-the-year sharks recorded from competitive shore-angling club records were between East London and St Francis Bay on the East Coast, suggesting this region to be the primary nursery area for C. taurus. Estuarine systems, although utilised by young-of-the-year and juvenile C. taurus, do not form an important component of their nursery area in South Africa. Catches of pregnant and post partum females taken during the same time of year and in different areas indicated a biennial reproductive cycle. C. taurus appears to display a high degree of affinity for particular reefs. The reason some reefs are chosen over others, despite having similar physical characteristics, remains unclear. A significant increase in the number of C. taurus caught in competitions held by the Border Rock and Surf Angling Association between 1984 and 2004 suggests an increase in the abundance of C. taurus.     

The life history of the giant octopus Octopus magnificus in South African waters

Octopus magnificus is a regular bycatch of traps set for spiny lobsters and bottom trawls for Cape hakes Merluccius spp. on the continental shelf of South Africa. Octopuses were collected from rocky substrata (traps) and soft sediments (research trawls) during a three-year period (2002–2005) and over a wide geographical and depth range to investigate their basic biological and life-history characteristics. Octopuses collected from trawl nets were smaller than those from traps. Males from traps and trawl nets were larger than females, with males being more frequently caught in traps than females. Size distributions were seasonally cyclical, increasing from a small mean size in the austral winter to a peak in summer, and receding during autumn. No mature females were found on soft sediments. The female gonadosomatic index peaked during summer, and sperm were found in oviducts year-round. Males reached 50% maturity at a weight of 4.6kg compared with 5.8kg in females. Mature females produced up to 10 000 medium-to-large (4–9mm maximum length) eggs, and potential fecundity was positively related to female body and ovary weight. Feeding rates were highest in trap-caught octopuses and gut contents consisted mainly of bait, spiny lobsters and teleosts (mainly jacopever Helicolenus dactylopterus). The gut contents of trawl-caught octopuses consisted mainly of crustaceans (84%), mostly portunid crabs but no spiny lobsters, teleosts (15%) and molluscs (1%). The results suggest that O. magnificus has a short (c. 1 year) lifespan, with winter/spring recruitment, a summer spawning peak, and post-spawning mortality in autumn. Alternatively, the species may have a longer lifespan with seasonal migrations between rocky and soft substrata.