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1.
Grow-out studies of the scallop Pecten sulcicostatus, endemic to the South African coast, contribute to an investigation of the suitability of this species for commercial culture. Hatchery-reared juvenile scallops were placed in a suspended culture system at 5 m depth in Saldanha Bay on the west coast of South Africa. Scallops of 78 days old and ranging in size from 4.5 mm to 11.0 mm shell height (mean 6.9 mm), as measured on 2 February 2010, were deployed in Saldanha Bay on 9 February 2010. Subsequent growth was assessed monthly through increments in shell height in relation to changing environmental conditions as determined through continuous measures of temperature and chlorophyll a. Upon termination of the experiment on 15 February 2011, scallops ranged in size from 42.1 mm to 48.7 mm (mean 45.1 mm), representing an increment in shell height of 38.2 mm over one year. The mean growth rate of 0.10 mm day?1 (mean specific growth rate of 0.0046 day?1) compares favourably with other commercially cultured species and exceeds previous estimates of growth of naturally occurring populations of P. sulcicostatus. Scallop growth was poorly correlated with either temperature or chlorophyll a concentration, but scallop mortality was closely aligned to the temperature regime of Saldanha Bay, exhibiting high mortalities during mid-summer.  相似文献   

2.
It is suggested that Bouvet Island is the surface manifestation of a mantle plume which has resulted in the creation of a chain of seamounts in the South Atlantic and a general shoaling of the region.The strike of two newly defined large fracture zones borth and south of the Bouvet Island pedestal have been utilized to determine a pole of rotation at 12.5°S, 12.5°W for the Africa-Antarctica motion. A pole at 75°S, 13°E has been calculated for the South America-Antarctica motion. At the triple junction the South America-Africa relative motion is 3.3 cm yr-1 (whole rate) at 075°. The Africa-Antarctica motion is 1.7 cm yr-1 at 065° and the South America-Antarctica motion is 1.6 cm yr-1 at 085.  相似文献   

3.
本研究以渤海湾南部(滨州)滩涂为研究区域,设置6个断面共36个采样站位,覆盖潮间带(高潮带-中潮带-低潮带)和潮下带,研究该区域贝类资源群落结构特征及其环境因子相关性。结果表明:整个调查区域常见贝类总共有30种。潮间带共有23种常见贝类,优势种为光滑篮蛤(Potamocorbula laevis Hinds 1843)、四角蛤蜊(Mactra quadrangularis Reeve 1854)、短文蛤(Meretrix petechialis Lamarck 1799);潮下带共有26种常见贝类,优势种为中国蛤蜊(Mactra chinensisi Philippi 1846)、等边浅蛤(Gomphina aequilatera Sowerby 1825)、朝鲜笋螺(Terebra koreana Yoo 1976)、红带织纹螺(Nassarius succinctus A.Adams 1852)、纵肋织纹螺(Nassarius variciferus A.Adams 1851);潮间带贝类多样性指数(H'')和均匀度指数(J'')显著高于潮下带,而丰富度指数(D)则相反;潮间带贝类生物量(710.16 g/m2)和栖息密度(4 523个/m2)远高于潮下带(17.10 g/m2,35个/m2)。群落结构多元统计分析将贝类按照站位划分为5个组群,包括东侧潮下带、西侧潮下带、西侧潮间带、东侧潮间带以及D4站位。冗余分析(RDA)结果表明,对潮间带贝类影响较大的环境因子主要为沉积物的粒径以及砂、粉砂含量,而对潮下带贝类影响较大的主要为浮游植物密度、沉积物的粒径以及砂、粉砂和黏土含量。渤海湾南部(滨州)滩涂贝类资源较为丰富,但应从不同滩涂区域生态特性的角度出发,加强贝类的保护和资源修复,本研究可为该区域贝类的资源养护和可持续利用提供数据基础。  相似文献   

4.
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   

5.
Data from the first systematic survey of inorganic carbon parameters on a global scale, the GEOSECS program, are compared with those collected during WOCE/JGOFS to study the changes in carbon and other geochemical properties, and anthropogenic CO2 increase in the Atlantic Ocean from the 1970s to the early 1990s. This first data-based estimate of CO2 increase over this period was accomplished by adjusting the GEOSECS data set to be consistent with recent high-quality carbon data. Multiple Linear Regression (MLR) and extended Multiple Linear Regression (eMLR) analyses to these carbon data are applied by regressing DIC with potential temperature, salinity, AOU, silica, and PO4 in three latitudinal regions for the western and eastern basins in the Atlantic Ocean. The results from MLR (and eMLR provided in parentheses) indicate that the mean anthropogenic CO2 uptake rate in the western basin is 0.70 (0.53) mol m?2 yr?1 for the region north of 15°N; 0.53 (0.36) mol m?2 yr?1 for the equatorial region between 15°N and 15°S; and 0.83 (0.35) mol m?2 yr?1 in the South Atlantic south of 15°S. For the eastern basin an estimate of 0.57 (0.45) mol m?2 yr?1 is obtained for the equatorial region, and 0.28 (0.34) mol m?2 yr?1 for the South Atlantic south of 15°S. The results of using eMLR are systematically lower than those from MLR method in the western basin. The anthropogenic CO2 increase is also estimated in the upper thermocline from salinity normalized DIC after correction for AOU along the isopycnal surfaces. For these depths the results are consistent with the CO2 uptake rates derived from both MLR and eMLR methods.  相似文献   

6.
The San Juan River has one of the most extensive and best developed deltas on the Pacific coast of South America, measuring 800 km2. The river drainage basin measures 16?465 km2 and is located in one of the areas with the highest precipitation in the western hemisphere. The annual rainfall varies from 7000 to 11?000 mm, and as a result the San Juan River has the highest water discharge (2550 m3 s−1), sediment load (16×106 t yr−1), and basin-wide sediment yield (1150 t km−2 yr−1) on the west coast of South America. The San Juan delta growth began approximately 5000 years BP. The structure of the delta is determined by the interactions between fluvial deposition and the effect of 1.7-m significant swells, mostly from the SW, and strong tidal currents. Analysis of delta progradation indicates that during 1848-1992 the morphology of the delta was characterized by beach ridge accretion, spit growth, narrowing of inlets, and a general advance of the delta shoreline. During the past decade processes such as rapid erosion of the delta shore, narrowing of barrier islands, and breaching of a new inlet, are the result of a long-term relative sea-level rise of 2.6 mm yr−1 due to tectonically induced subsidence coupled with a eustatic rise of sea-level. The delta also experiences strong oceanographic manifestations associated with the El Niño-La Niña cycle, causing regional sea-level elevation of 20-30 cm during El Niño years. Recent coastal subsidence in the delta is evidenced by: (1) increased occurrence of non-storm washover events; (2) increased erosion of barrier islands with average loss of 11 m yr−1 during 1993-1997; and (3) a relative sea-level rise of 3.4 mm yr−1 during 1991-1999. The morphology and recent evolution of the San Juan delta are unique when compared to other deltas of South America because of the singular combination of extreme climatic, geologic, and oceanographic conditions under which the delta has formed and the absence of human-induced impact in the drainage basin.  相似文献   

7.
Rhodoliths are important marine carbonate producers that provide habitat for several marine organisms, and are threatened by ongoing global climate change. Meter‐sized sedimentary patches rich in living rhodoliths, interspersed among corals, were discovered in the back reef of Ras Ghamila lagoon, Southern Sinai, at less than 1 m water depth. In this shallow and relatively sheltered subtropical environment, rhodoliths were found to be monospecific or oligospecific, spheroidal, 3.5 to 9.4 cm in maximum diameter, with warty/lumpy or fruticose (protuberance degree IV) growth forms, and corresponded to the unattached branches or praline type. They grew in bright light under seasonal, moderate, wind‐driven water motion. The dominant rhodolith‐forming species recorded were: Lithophyllum kotschyanum, Porolithon onkodes, Hydrolithon sp. and three species of Neogoniolithon: Neogoniolithon fosliei, Neogoniolithon brassica‐florida, and an undescribed species noted in the text as Neogoniolithon sp. A total of 38 Alizarin‐stained rhodoliths was released in the field and collected after 1 year. They showed different banding patterns (alternating long and short cells) that revealed seasonal growth, with the lowest rates occurring in winter for all species, and an additional summer growth slackening in Neogoniolithon fosliei. Lithophyllum kotschyanum presented evidence of occasional growth cessation, possibly due to temporary burial. The observed annual growth rate of rhodoliths was unrelated to their size. The mean accretion rates were 1.08 mm · year?1 in L. kotschyanum, 0.75 mm · year?1 in P. onkodes, 0.49 mm · year?1 in Hydrolithon sp., 0.85 mm mm · year?1 in N. fosliei, 0.63 mm · year?1 in N. brassica‐florida and 0.57 mm · year?1 in Neogoniolithon sp. The annual mean marginal elongation rate for these taxa was respectively 8.74, 13.92, 3.59, 9.40 and 9.25 mm · year?1, with the exception of Neogoniolithon sp., for which this parameter was not recorded. Maximum marginal elongation occurred in P. onkodes pointing out its greater ability as a space competitor in comparison with the other rhodolith species. The highest accretion rate and common presence of L. kotschyanum indicate its importance as carbonate producer in tropical reef.  相似文献   

8.
Abstract

Thirty sites were sampled in three New Zealand rivers (Waikato, Maitai, and Wakapuaka) during late summer 1977. Samples were collected from just below the surface at mid river or in the tailraces below hydro‐electric dams.

Parameters measured included bacterial numbers (direct counts), heterotrophic potential (Vmax ), adenosine triphosphate (ATP), chlorophyll a (Chi a), and concentrations of nitrogen and phosphorus compounds.

Bacterial populations per millilitre fluctuated threefold (6.4–19.4 × 105) along the Waikato River and were lower and more consistent in the two South Island rivers (1.46–2.55 × 105). In contrast, Vmax varied 5000‐fold in the Waikato River, from a characteristically oligotrophic value of 0.0035 μg. l?1·h?1 (Lake Taupo outlet) to a eutrophic value of 18.4 μg. l?1·h?1 at the Mihi bridge. Vmax for the two South Island rivers ranged from 0.0091 to 0.189 μg. l?1 · h?1.

ATP, Chi a, Kjeldahl nitrogen, nitrate nitrogen, and total phosphorus concentrations for the 20 sites on the Waikato River varied in a similar way to the Vmax and bacterial data. There were large peaks at the Mihi bridge, lower values for the dam tailraces and significant increases for the sites below Hamilton. Concentrations for these parameters were lower and more consistent along the lengths of the two South Island rivers.

Most parameters were significantly correlated with each other for the Waikato River samples. The strongest correlations were between Vmax and bacterial numbers and between Vmax and nitrate nitrogen. In the Maitai and Wakapuaka River series these correlations were also significant, but the only other significant correlations recorded there were between ATP and nitrate nitrogen, and between ATP and bacterial numbers.  相似文献   

9.
Porites panamensis is a hermatypic coral present in the eastern Pacific Ocean. Skeletal growth parameters have been reported, but studies of the relationship between annual calcification rates and environmental controls are scarce. In this study, we investigated three aspects of the annual calcification rates of P. panamensis: growth parameters among three P. panamensis populations; the sea surface temperature as a calcification rate control spanning a latitudinal gradient; and calcium carbonate production among three sites. Growth parameters varied among the sites due to the colony growth form. Massive colonies in the north showed a higher calcification rate than encrusting colonies in the south (mean: 1.22–0.49 g CaCO3 · cm?2 · yr?1), where variations in calcification rates were related to growth rate (0.91–0.38 cm · yr?1) rather than to skeletal density differences (overall mean ± SD, 1.31 ± 0.04 g CaCO3 · cm?3). Our results showed a positive linear relationship between annual calcification rates and sea surface temperatures within these P. panamensis populations. Differences were related to distinct oceanographic environments (within and at the entrance of the Gulf of California) with different sea surface temperature regimes and other chemical properties. Different populations calcified under different environmental conditions. Calcium carbonate production was dependent upon the calcification rate and coral cover and so carbonate production was higher in the north (coral cover 12%) than in the south (coral cover 3.5). Thus, the studied sites showed low calcium carbonate production (0.25–0.43 kg CaCO3 · m?2 · yr?1). Our results showed reduced calcification rates, regional temperature regime control over calcification rates, different growth forms, low coral cover and low calcium carbonate production rates in P. panamensis.  相似文献   

10.
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   

11.
We used an oxygen microsensor for high-resolution measurements of pore water oxygen concentration in semi-closed coastal bays of the South Sea of Korea during summer. The oxygen penetration depths ranged from 0.60 to 3.65 mm. Oxygen consumption rates were estimated to be 9.1 to 59 mmol m?2 d?1 (average: 22.8 mmol m?2 d?1). At the sediment-water interface, the oxidation rates of organic carbon were estimated to be 84–545 mg C m?2 d?1 (average: 211 mg C m?2 d?1). Approximately 38% (～211 mg C m?2 d?1) of pelagic primary production was regenerated in the surface sediment, indicating the tight benthic-pelagic coupling in the coastal sea of the South Sea of Korea.  相似文献   

12.
At Park Rynie Beach on the KwaZulu-Natal coast, South Africa, four species of zoanthids were invaded by a sand-tube building polychaete Mesochaetopterus minutus. It is a small polychaete about 15 mm long, which occurs gregariously in dense masses of sandy tubes. M. minutus is an opportunistic species that exploits zoanthid colonies mainly for support and protection from heavy wave action because of the inability of the fragile sandy tube to survive in exposed habitats. Population density studies of the polychaete were undertaken to quantify the degree of invasion of the different zoanthid species. Highest polychaete density was recorded for Zoanthus sansibaricus, the number of polychaetes exceeding 3 500 m?2, followed by Palythoa nelliae, with a density of 2 200 m?2. Polychaete densities were comparatively low in Z. durbanensis and Z. natalensis (<1 000 m?2). No polychaete tubes, however, were seen among the polyps of Isaurus spongiosus.  相似文献   

13.
The fauna and flora of two sublittoral communities situated in close proximity on the west coast of South Africa are described and shown to be radically different, despite the fact that both experience similar physical conditions. One of these communities, at Marcus Island, has prolific beds of the black mussel Choromytilus meridionalis (35 954 g wet weight·m?2) accompanied by a large number of other species, notably sea urchins, holothurians, brittle stars, whelks and barnacles. In contrast, the other site, Malgas Island, is dominated by a large population of rock lobsters Jasus lalandii together with a dense seaweed flora (3 866 and 4 402 g wet weight·m?2 respectively). The numbers of species are similar at both sites (102 at Malgas Island and 107 at Marcus Island) but only 34 per cent are common to both localities. Although preliminary research indicates that the two sites have fairly similar physical conditions and bottom topography, they maintained their contrasting communities for the whole research period (1983–1986) and have probably done so for at least nine years, suggesting that they represent two stable alternative states of the same ecosystem. In the absence of rock lobsters at Marcus Island, wave action and inter/intraspecific competition are the main forces structuring the benthic community. Stability is maintained here by the resilience and rapid recovery of the mussel population after disturbance by storms. Where rock lobsters are abundant, as at Malgas Island, intense predation pressure is the main force controlling the structure of the benthos, and it is continually maintained because the rock lobsters are resistant to the effect of storms. Therefore, the presence or absence of high densities of rock lobsters is fundamental to the maintenance of these two contrasting communities.  相似文献   

14.
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   

15.
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   

16.
Abstract

In September 1986, dense concentrations of freshly spawned hoki (Macruronus novaezelandiae) eggs were located in eastern Cook Strait. A follow‐up exploratory trawl survey of Cook Strait and the east coast of the South Island, in August and September 1987, located concentrations of spawning hoki in canyon features in Cook Strait, off the Kaikoura coast, and off Banks Peninsula. The largest concentration, 14 km long, 4 km wide, and up to 150 m thick occurred in Cook Strait Canyon, with catch rates of hoki up to 48 t h?1. Gonad conditions of male and female hoki showed they were actively spawning. Catch rates in Cook Strait Canyon were comparable to the main fishery on the west coast of the South Island but were much lower off Kaikoura and Banks Peninsula. Hoki associated with spawning concentrations were not feeding. Bycatch species were mostly ling (Genypterus blacodes) and spiny dogfish (Squalus acanthias), and both were preying on hoki. Spiny dogfish were also feeding on spawned fish eggs. The possible stock structure of hoki is discussed.  相似文献   

17.
Abstract

The age of pufferfish Uranostoma richei (Freminville) in Lyttelton Harbour, South Island, New Zealand is described from analyses of length‐frequency distributions and growth zones in otoliths. Length‐frequency analysis is adequate only for aging smaller fish. The validity of using growth zones in otoliths is checked by examining the pattern and time of zone formation. Length‐weight relationships are established and growth rates calculated. Compared with males, females grow faster (2.4cm·y?1; 2.1 for males), attain a larger size (to 18 cm and 120 g; 12 cm and 40 g for males) and live longer (to 7 y; 5 for males).  相似文献   

18.
During November 1978, Cape cormorants Phalacrocorax capensis at Mercury Island, off South West Africa (Namibia), consumed practically exclusively pelagic gobies Sufflogobius bibarbalus. The mean number of fish per regurgitation was 52 with a mean caudal length of 48 mm and an estimated mean mass of 1.7 g. The estimated mean original mass of stomach contents was 75 g. These Cape cormorants took significantly smaller pelagic gobies than did bank cormorants P. neglectus sampled concurrently at the same locality.  相似文献   

19.
An integrated telephone and on-site questionnaire survey was used to estimate total shark fishing effort and specific catch of the ragged-tooth shark Carcharias taurus by coastal club-affiliated shore-anglers, primarily along the east coast of South Africa. Mean total shark fishing effort was estimated to be 37 820 fisher-days year?1 (95% CI = 28 281–47 359 fisher-days year?1) with a mean cpue of 0.073 C. taurus fisher?1 day?1 (95% CI = 0.068–0.078 fisher?1 day?1). Cpue for C. taurus varied significantly along the coast and ranged from a high of 0.260 fisher?1 day?1 in the Eastern Cape to zero fisher?1 day?1 on the West Coast. The total number of C. taurus caught annually by coastal club anglers was estimated at 1 764 fish year?1 (95% CI = 321–3 207 fish year?1). The majority (92.1%) of young-of-the-year sharks (<1.2m total length, TL) were recorded between East London and Jeffreys Bay, suggesting that this may be the primary nursery area for C. taurus. Post-release mortality ranged from 3.8% for young-of-the-year sharks to 18.5% for adult sharks (>2.4m TL). The majority (76.2%) of anglers interviewed stated that they now fished less for sharks since the banning of vehicles on beaches in December 2001. As a result of this ban, almost half (49.2%) of interviewed anglers stated that they now fished more for non-cartilaginous species.  相似文献   

20.
Survival and reproductive rates in fish are often a function of body size. Consequently, spatial‐ and sex‐specific variation in somatic growth rates can have important consequences for population growth and resilience. We used otolith‐based approaches to estimate geographic‐ and sex‐specific growth rates of yellow‐eyed mullet (Aldrichetta forsteri) collected from 14 estuaries and harbours around New Zealand. Aldrichetta forsteri is an abundant and dominant component of New Zealand's estuarine fish fauna. We extracted otoliths from 511 fish, validated daily and annual increments, and prepared transverse thin sections of otoliths to determine age. “Size‐at‐age” relationships were estimated using both linear‐ and non‐linear (von Bertalanffy) growth models, and model performance was evaluated using Akaike's Information Criterion. Because growth rates of sampled fish were best approximated by linear functions, we used ANCOVA to test the null hypothesis that growth rates of A. forsteri were homogeneous between sexes and among geographic locations around New Zealand. Our analyses suggest heterogeneous growth rates between sexes and among locations. Interestingly, relative growth rates between sexes appeared to vary across separate latitudinal gradients for North Island and South Island. Within each island (but not across islands), female A. forsteri generally grew faster than males at the lowest latitudes; relative growth rates of females declined progressively below males with increasing latitude.  相似文献   

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