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1.
Fishery-dependent and fishery-independent distribution analyses together reveal four discrete areas of white stumpnose Rhabdosargus globiceps abundance between Port Nolloth and the Kei River off the Cape Province of South Africa: the Western Cape (Saldanha Bay), the South-Western Cape, the Southern Cape and the South-Eastern Cape. On the basis of migratory patterns determined from tagging and catch data, and on differences in growth rate and size-at-maturity, it is concluded that these areas of abundance represent four separate stocks. Each stock apparently disperses offshore in winter (to c. 130 m depth) and concentrates inshore (<60 m depth) in response to ocean ographic patterns during summer. Growth rate and size-at-50% maturity (L 50) increased clinally from the South-Eastern Cape through to the South-Western Cape, and in all three regions males matured at larger size than females. Sizes at maturity for male and female R. globiceps were respectively 18.6 and 15.3 cm (fork length, FL) in the South-Eastern Cape, 22.1 and 18.1 cm in the Southern Cape and 24.3 and 23.6 cm in the South-Western Cape. The fitted Von Bertalanffy growth equations for the three regions were: Lt = 349 (1?e?0.114(t+3.60)) mm for the South-Eastern Cape; Lt = 337 (1?e?0.207(t+1.05)) mm for the Southern Cape; and Lt = 379 (1?e?0.290(t+0.16)) mm for the South-Western Cape. Maximum ages recorded in each region were 21 years for the South-Western Cape, 20 years for the Southern Cape and 10 years for the South-Eastern Cape. Lack of older fish in the South-Eastern Cape sample, attributed to inadequate sample size, has probably resulted in overestimates of both L ∞ and K in this region. Spawning is from August to February, with a peak in spring (September–November). Early juvenile R. globiceps recruit into estuarine and surf-zone marine nursery areas at around 2–5cm (±3 months), but move progressively farther offshore with growth; those trawled deeper than 50 m east of Cape Agulhas were predominantly adults (20–35 cm FL). Because of cooler water temperatures west of Cape Agulhas, adults there are found from the surf zone to depths of only 20 m in summer.  相似文献   

2.
The sparid Dentex macrophthalmus is a widespread, important fishery species along most of the West African coast from southern Namibia to the Mediterranean. In southern Angola it is an important artisanal species targeted predominantly by handline fishers. A biological and fisheries study was conducted on this species in southern Angola between June 2008 and July 2009. It was the dominant species in the artisanal fishery, accounting for 99% of the sparids captured and 67% (by mass) of the total catch. The life history of D. macrophthalmus was characterised by slow growth (females: Lt = 309[1 ? e?0.06(t + 5.43)], males: Lt = 248[1 ? e?0.16(t ? 1.77)]), advanced age at maturity (females: 7.4 years, males: 6.0 years) and high longevity (females: 36 years, males: 38 years). The sex ratio was 1:1 male:female. The length- and age-frequency distributions and macroscopic observations suggested that the species is a late gonochorist. Males and females reached 50% maturity at 151 and 166 mm fork length respectively. Although individuals with ripe gonads were found during most of the year, the peak spawning period appeared to be in December and January. Despite a life history that renders D. macrophthal-mus vulnerable to overexploitation, only 38% of artisanal fishers noticed a decline in the catches of this species. Potential reasons for this include: technology creep; limited pressure on the juvenile portion of the stock as a result of late recruitment (above the length of 50% maturity); the ‘basin affect’, whereby depleted areas are reseeded by areas (e.g. deeper water) inaccessible to the linefishery; and a deep-water reserve of large individuals. It is recommended that precautionary management strategies be implemented until the age estimates are revised by the countries in which this species forms significant fisheries.  相似文献   

3.
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 Lt = 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.  相似文献   

4.
Abstract

Rough and smooth skates (Dipturus nasutus (Banks 1841) and/), innominatus (Garrick &; Paul 1974)) were aged by counting growth bands on X‐rays of thick sections of vertebral centra. Band counts were imprecise, but there was no between‐reader bias. Age estimates were not validated. The oldest rough skate was 9 years old, but few were more than 6 years old. Females may live longer than males. The combined sexes von Bertalanffy growth curve was Lr = 91.3 (1 ‐ e?0.16[t + 1.20]). Half the males matured by c. 52 cm pelvic length (PL) and 4 years, and females by 59 cm PL and 6 years. The oldest smooth skate in the sample was 24 years, but longevity probably exceeds that. Females appear to live longer than males. The combined sexes von Bertalanffy growth curve was: Lt = 150.5 (1 ‐ e?0.095[t + 1.06]). Half the males matured by c. 93 cm PL and 8 years, and females by 112 cm PL and 13 years. Smooth skate are late maturing and long‐lived relative to other skates, whereas rough skate are early maturing with a moderate life span.  相似文献   

5.
Recent studies have provided evidence that the Cape horse mackerel Trachurus trachwus capensis in South African waters is a unit stock. Therefore, an age and growth study of the entire stock throughout its distributional range was undertaken in 1988/89. Growth is described by the equation

Lt = 487,989 (1 – e?0.556(t – 0,229)) mm.  相似文献   

6.
The growth of hottentot is described by the relationship Lf (mm) = 538,015 (1?e?0,097(t + 0,431)). By determining the otolith growth rate and validating it with counts of daily rings identified on scanning electron micrographs of otolith sections, it was found that previous growth curves underestimated the age of the fish by one year. Differences in growth rate between sexes and over geographical regions were negligible. The ratio of males to females in sampled catches was 1:1,383 and 50-per-cent sexual maturity was attained at 220 mm fork length. There are two main spawning seasons, late autumn and summer, although some breeding activity continues throughout the year. Spatial differences in mean gonadosomatic indices were minimal.  相似文献   

7.
Growth of the red gurnard, Chelidonichthys kumu (Lesson and Garnot), from Pegasus Bay, Canterbury, was measured during 1966–67. Otoliths were used as an indicator of fish growth; mean length‐at‐age data were obtained from back‐calculated fish lengths at the time of formation of successive annual rings in the otoliths. Growth in length was found to be adequately expressed by the von Bertalanffy growth equation :

lt = 52.0 [1 ‐ e‐0.406 (t‐o.291)]

(where lt is the fork length in cm at age t). The length: weight relationship was:

w = 78.56 × 10‐4 l 3.072

(where w is the weight in grams). From this relationship, growth in weight was described by the equation:

wt = 1469 [1 ‐ e‐0.406 (t‐0.291)]3.  相似文献   

8.
The age and growth of filefish, Thamnaconus modestus (Günther 1877) in the southern waters of Korea were investigated. Samples were collected with commercial trawl catches during the period from May 2009 to December 2011. Of the 2,626 specimens collected, the sex ratio was not significantly different from 1:1 (P > 0.05). The total length ranged from 11.3 to 42.1 cm. The gonadosomatic index for both sexes was the highest in May to June, indicating that May to June is the main spawning period. The length of females at sexual maturity was 25.92 cm. The length-weight relationship of the filefish was TW = 0.0121TL3.0536 (n = 1,692, r2 = 0.9034, P < 0.001). The age of the sampled individuals was estimated by counting growth rings recorded on the 5th vertebrae; ages ranged from 0 to 9 years. The filefish of the same age displayed a high individual variation in total length. Length-at-age data were fitted by using the Von Bertalanffy growth model. The estimated Von Bertalanffy growth parameters were L∞ = 42.04 cm, k = 0.21 year?1 and t0 = ?1.56 for females, L∞ = 41.20 cm, k = 0.18 year?1 and t0 = ?2.36 for males, and L∞ = 43.16 cm, k = 0.17 year?1 and t0 = ?2.18 for the combination of both male and female. These data can be used as useful biological information for the future fishery management of filefish resources in Korean waters.  相似文献   

9.
Ages of redeye round herring Etrumeus whiteheadi were estimated with associated errors and used to infer life-history information, such as age composition, age-at-maturity and instantaneous mortality rate. Samples were collected in November 2005 during a research survey aimed at estimating the biomass of spawning pelagic fish off South Africa’s west and south coasts. Replicate age estimates obtained from sagittal otoliths were collected with slight bias and relatively high precision. A von Bertalanffy model describing growth of the combined sexes, including juveniles, was Lt = 20.41(1 ? e?0.41(t ? 1.92)). Kimura’s likelihood ratio test revealed no statistically significant differences between growth parameters of males and females. Results suggested that otolith length is a better predictor of age than otolith weight. Maturity estimates for E. whiteheadi were similar to those previously documented.  相似文献   

10.
Rhabdosargus holubi is a small (maximum weight=2.4?kg) yet important fishery species in the estuaries of the south-east coast of South Africa. Little is known of its biology and specifically its growth rate, which is essential for sustainable management of the fishery. We examined and counted the opaque zones in the sectioned otoliths of 134 R. holubi to determine its age and growth parameters. The otoliths from two recaptured fish marked with oxytetracycline confirmed that one opaque zone was deposited annually. The species reached a maximum age of 18 years and growth was adequately described by a von Bertalanffy growth function of the form: Lt = 358.1 (1 – e?0.24(t+0.77)) mm fork length. There were no significant differences between any of the male and female growth parameters (likelihood ratio test: p = 0.3). The growth was slow (omega index: ω = 86.56); however, despite this, the unique life history of R. holubi may provide a degree of resilience to heavy fishing pressure in estuaries.  相似文献   

11.
The West Coast dusky kob Argyrosomus coronus is an understudied yet important fishery species in Angola. During a five-year study (2005–2009), the species was recorded in all fishery sectors, but was most important in the inshore recreational fishery in southern Angola (Cunene Estuary to Namibe). Early juveniles (<300 mm total length, TL) were captured in the offshore artisanal fishery at Praia Pinda, whereas juveniles (300–600 mm TL), subadults (600–870 mm TL) and adults (>870 mm TL) were captured in all fisheries as far north as Namibe, and shoals of large adult fish (>1 000 mm TL) were occasionally captured in the offshore purse-seine commercial fishery between the Cunene Estuary and Lucira. Because some Argyrosomus species are morphologically cryptic, a DNA barcoding method was used to confirm the taxonomic status of the biological samples used in this study. The male:female sex ratio of examined samples was 1:1.4 (n = 225). The length-at-50% maturity was 823 mm and 904 mm TL for males and females respectively. Age-at-50% maturity was 4.4 and 4.3 years for males and females respectively. The periodicity of otolith ring formation was confirmed to be one year using a marginal zone and a chemical marking analysis. Growth (in mm TL) was best described by: Lt = 1 826(1—e?0.12(t + 1.60)). Argyrosomus coronus fed predominantly on fish, mainly Sardinella aurita (62% frequency of occurrence). Early juveniles appeared to frequent the offshore zone (50–100 m depth), moving into the inshore region at approximately 300 mm TL. Juveniles and subadults were resident (57% recaptured at the same site) and were particularly abundant around the mouth of the Cunene Estuary as well as in central and northern Namibia. Adults undertake migrations that correspond with the movement of the Angola–Benguela frontal zone, moving north as far as Gabon in winter and returning to southern Angola in spring, when spawning appeared to take place offshore. There are currently no catch restrictions on A. coronus in Angolan waters. However, declining catches and increasing fishing effort suggest that some management intervention is required, commencing with a proposed closure of the Cunene Estuary mouth region to fishing.  相似文献   

12.
The hottentot seabream Pachymetopon blochii is a small-sized (maximum 2.67 kg) sparid endemic to southern Africa. It is an important target in South Africa's Western Cape traditional linefishery, particularly in the absence of more valuable pelagic species (such as Thyrsites atun and Seriola lalandi). In 2000, South Africa's linefishery was declared to be in a state of emergency, and commercial fishing effort was consequently reduced by 70%. A subsequent increase in stock biomass and intraspecific competition, coupled with environmental changes, were hypothesised to have thereafter altered the growth rate of hottentot, from 2000 to 2010. This study aimed to revise outdated age–growth models for the hottentot by using modern techniques (sectioned otoliths), and to compare age–growth relationships before and after the declared linefish state of emergency. The maximum age observed was 19 years, with no difference in the growth rate between sexes (p = 0.39–0.43) or time-periods (p = 0.96). Although the growth rate did not change, there is evidence that the age structure of the stock changed between time-periods as a result of changes in fishing pressure between 2000 and 2010. The enhanced recent growth model for hottentot, described as Lt = 418.063 (1 – e?0.104(t – [?4.709])) (pooled sexes; n = 206), indicates a considerably slower growth rate for this species than was proposed previously using whole otoliths and has major implications for effective stock management.  相似文献   

13.
Eight spotted ragged-tooth sharks Carcharias taurus (95–248,4 cm total length TL), ranging in known age from 0 to 16,6 years, were used to investigate the growth of the species in captivity. Total length was measured by a standard technique in some cases and estimated from photographs in others. The accuracy of the photographic technique was evaluated and found adequate for captive growth studies in sharks. Parameters of various growth models were estimated by non-linear regression and the special Von Bertalanffy growth model provided the best fit to the age-length data of the combined sexes. The parameters of the special Von Bertalanffy model are L ∞ = 249,8 cm TL, K = 0,233·year?1, t 0 = ?2,238 years. Longevity of captive C. taurus is greater than 16,6 years.  相似文献   

14.
A total of 639 pink dentex Dentex gibbosus was collected in Canary Islands waters between April 1991 and September 1993. Total lengths ranged from 14,2 to 95,2 cm. Females dominated smaller size-classes and males the larger ones. The species was characterized by protogynous hermaphroditism. The overall ratio of males to females was 1 : 1,45. The reproductive period extended from April to September, spawning peaking in June/July. The total lengths at 50% maturity were 34,7 cm for females and 38,6 cm for males. The length-mass relationship for the whole sample can be described by the parameters a = 0,01014 and b = 3,0812. Fish aged 0–16 years were present in the samples. The parameters of the Von Bertalanffy growth equation were: L ∞ = 101,2 cm, k = 0,149·year?1, and t 0 = ?0,111 years. The rates of total mortality Z and natural mortality M were 0,57 and 0,28·year?1 respectively. Rates of fishing mortality F and exploitation E were 0,29 and 0,51·year?1 respectively. The estimated length at first capture (LC 50) was 17,8 cm total length.  相似文献   

15.
Kingklip Genypterus capensis inhabit deep continental shelf and slope waters off southern Africa and are now largely harvested as a bycatch in trawl and longline fisheries for Cape hakes Merluccius spp. Regional differences in growth, vertebral count and otolith morphology indicate that kingklip may consist of three stocks. In this study, allozyme markers are used to test whether the two southern stocks, the putative Cape and South Coast stocks, are genetically distinguishable. Standard electrophoretic methods detected Mendelian polymorphisms at six (23%) of 26 enzyme-encoding loci in five samples extending from about 29°S on the West Coast to about 25°E on the South Coast. No deviations from Hardy-Weinberg proportions were observed in the samples or in the pooled sample. Gene diversities (heterozygosity) ranged from HS = 0.039 to 0.042 among samples, and averaged 0.041. Genetic differentiation among localities was remarkably small, FST = 0.003, and did not differ significantly from zero. A Bayesian analysis of population structure, based on detecting departures from Hardy-Weinberg proportions and gametic phase equilibria between loci, indicated with a high likelihood that the five samples were drawn from a single genetic population. In combination, these results are consistent with the occurrence of a single population off South Africa. However, the most conservative management strategy is to set harvest quotas individually on the Cape and South Coast stocks.  相似文献   

16.
During deposition in the Palaeogene, the Pearl River Mouth Basin (Enping Sag) was filled by sediments derived from northern and southern source regions. The northern sources are the fold belt Caledonian and Hercynian metamorphic rocks that are widely exposed along the South China block and stacked with Mesozoic igneous rocks, and the southern sources are Mesozoic igneous rocks from the southern Panyu lower uplift. We analysed the characteristics of the provenance and sediment-dispersal patterns of the beach and bar systems in the Palaeogene third-order sequence framework on the basis of detritus, thin section, zircon and the geophysical response test data. The source and deposition areas were distinguished based on their palaeogeomorphology. The sedimentary material composition of the deposition area was determined based on the characteristics of the detrital assemblage and cathode luminescence, and the characteristics of the age distribution were determined in detail using detrital zircon U–Pb dating. This study suggests that the provenance system in the Palaeogene mainly consisted of Palaeozoic metamorphic rocks and Mesozoic igneous rocks, with a supplement of Proterozoic metamorphic rocks. The transport capacity of three large fault troughs that delivered the northern provenances gradually increased from the Wenchang Formation (E2w) to the Enping Formation (E3e), whereas the southern provenances were transported by four or five incised valleys in E2w and then submerged in E3e. In the 3D seismic area, the features of the beach and bar sedimentary systems were described and interpreted based an analysis of the well-based sedimentary facies, seismic reflection characteristics and multiple attribute clustering. The results show that the beach and bar systems by the short-axis braided deltas mainly developed in the upper member of E2w and that the beach and bar systems on the subaqueous high in E3e developed during the Palaeogene. In addition, the bedrock-beach bar sedimentary system in the lower member (E3eL) was transferred to the braided delta–beach bar sedimentary system in the upper member (E3eU).  相似文献   

17.
Status assessment of exploited fish populations is a general requirement to ensure sustainability of fisheries in both global and local contexts. The blue jack mackerel Trachurus picturatus (Bowdich, 1825) remains unassessed in a data-limited fishery in the eastern central Atlantic, within the waters of the Canary Islands (Spain) off the coast of northwest Africa. This is the most southwestern targeted fishery in the species’ distributional range. To obtain basic life-history information, a total of 2 472 specimens were analysed, ranging from 10.2 to 31.9 cm total length, from samples collected monthly between March 2005 and March 2006. Length–weight relationships (a = 0.0023; b = 3.418; R 2 = 0.97) showed no significant difference between sexes. Deposition periodicity and coherence of the ageing criteria were verified by analysis of the monthly evolution of the otolith edge. Ages were estimated by counting annual growth rings on whole otoliths, with these fish ranging from age 0 to 6 years. The von Bertalanffy growth model, which was used to estimate growth parameters from both direct readings and back-calculated length-at-age data, gave good statistical fits. The parameters from the direct readings were: L∞ = 34.9 cm; k = 0.214 y–1; t 0 = ?2.545 y (R 2 = 0.84), and the natural mortality rates estimated from empirical methods varied between 0.20 and 0.55 y–1.  相似文献   

18.
The sagittal otoliths of Lophius upsicephalus, although extremely variable in shape, were found to be the only structures suitable for age estimation. The annuli are multi-ringed zones separated by "wider than normal" opaque zones. They are difficult to interpret, especially those of fish older than nine years. Periodicity of annulus formation could not be determined by standard methods. By inference, annulus formation could be related to feeding habits and reproductive seasonality. The growth in length (sexes combined) is best described by

Length-at-age = 733,7 (1 – e?0,1054 (t + 1,879))mm.

There is a significant difference in growth by mass between the sexes. The respective equations describing growth by mass (in g) for males and females are:

Weight-at-age = 8616 (1 – e?0,1054 (t + 1,879))2,805 and

Weight-at-age = 9499 (1 – e?0,1054 (t + 1,879))2,890.  相似文献   

19.
Abstract

Growth rates of five species of surf clam were estimated on the Kapiti Coast, southern North Island, New Zealand. Length‐frequencies of sequential population samples were analysed by the computer program, MULTIFAN. Incremental growth of marked individuals was analysed by the computer program, GROTAG. The von Bertalanffy growth parameters k and L 8 estimated by MULTIFAN for Spisula aequilatera (Deshayes in Reeve, 1854) were 0.80 yr?1 and 52.1 mm; for Mactra murchisoni Deshayes in Reeve, 1854 were 0.60 yr?1 and 72.3 mm; and for M. discors Gray, 1837 were 0.35 yr?1 and 60.1 mm. MULTIFAN could not model growth of Paphies donacina (Spengler, 1793) and Dosinia anus (Philippi, 1848) from the population samples. The growth parameters estimated by GROTAG for D. anus were 0.53 yr?1 and 53.0 mm and for M. murchisoni 1.84 yr?1 and 72.4 mm. The growth rates of P. donacina, S. aequilatera, and M. discors were estimated for the size range of their incremental growth data and the estimates are usable for this limited size range only. Growth rates of each species varied with depth in the surf zone in the same way in the North and the South Island. The growth rate of two species was faster in the South Island and asymptotic size of all species was greater in the South Island.  相似文献   

20.
长牡蛎F3 代快速生长选育群体生长特性的研究   总被引：1，自引：0，他引：1  
采用模型拟合方法研究了长牡蛎(Crassostrea gigas)F3代快速生长选育群体不同时期各生长性状的发育规律。结果表明,长牡蛎幼虫期壳高(SH)、壳长(SL)对日龄(t)的回归遵循Logistic模型,生长方程分别为SH=455.612/(1+9.500e-0.142t),R2=0.999;SL=462.476/(1+8.026e-0.108t),R2=0.996。幼虫期壳高与壳长成直线相关,回归方程为SL=0.76SH+18.82,R2=0.994。长牡蛎养成期各生长性状呈现明显的季节变化,壳高(SH)、壳长(SL)、壳宽(SW)和总质量(TW)对月龄(X)的多项式回归方程分别为SH=-0.0297X4+1.0365X3-12.0220X2+57.6500X-68.9260,R2=0.985;SL=-0.0173X4+0.5893X3-6.5702X2+30.2420X-34.4150,R2=0.986;SW=-0.0068X4+0.2620X3-3.2806X2+16.9170X-22.1410,R2=0.956;TW=-0.0219X4+0.8234X3-10.1680X2+50.7040X-85.4110,R2=0.972。壳高、壳长、壳宽与总质量均呈幂函数相关,回归方程分别为SH=23.645TW0.3213,R2=0.998;SL=12.337TW0.3776,R2=0.995;SW=6.611TW0.3589,R2=0.981。  相似文献   

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