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1.
We examined spatial variability in meristic and morphological characteristics of the branchial basket of sardine Sardinops sagax collected from four geographical regions around the southern African coast, namely Namibia and the South African west, south and east coasts. Our analysis tested the hypothesis of three putative sardine stocks off South Africa, one in each of the three geographical regions. We therefore collected fish data from Namibia to compare with South Africa, because sardine from the two countries are considered to be separate stocks. Morphometric measurements (gill arch length and gill raker spacing) and meristic data (number of gill rakers) were collected from the left side of the first gill arch from a total of 377 sardine, approximately equally divided between the regions. A multivariate general linear model with caudal length as covariate was used to assess differences among fish from the four regions and significant differences were observed, although not always consistently across all fish size classes. Small South Coast sardine had shorter gill arches than small West Coast sardine, but adults had gill arches of similar length, longer than those from Namibia and the East Coast. Small sardine from the South Coast had fewer gill rakers than small sardine from the West Coast, but larger fish had similar numbers of gill rakers, significantly more than sardine from Namibia and the East Coast. Sardine from the West and South coasts had similar gill raker spacings, which were smaller than those of fish from the East Coast and Namibia. Despite spatially and particularly temporally unbalanced sampling, we consider that these differences provide evidence of spatial variation in Benguela sardine phenotype and that it would support the hypothesis of discrete sardine stocks off Namibia and South Africa. The results are consistent with the hypothesis of three sardine stocks within the southern Benguela.  相似文献   

2.
The diet of African penguins Spheniscus demersus in Namibia consisted mainly of sardine Sardinops sagax in the 1950s. Since the collapse of pelagic fish stocks in the 1970s, birds fed mainly on bearded (pelagic) goby Sufflogobius bibarbatus, a low-energy prey species. We present diet data for African penguins breeding at Mercury Island, the largest colony for this species in Namibia, between 1996 and 2009. Bearded goby was the main prey item throughout the study period, both in terms of frequency of occurrence (67.8%; SD 31.2) and in terms of mass (59.2%; SD 31.5). Diet composition varied throughout the year as well as between years; birds occasionally fed on a variety of fish species other than bearded goby. In Namibia, poor prey abundance is considered as a major factor contributing to the decline of penguin numbers after the collapse of the sardine stocks. However, bearded goby appears to be relatively abundant along Namibia's southern coast and low prey quality rather than low abundance appears to be a key factor influencing population dynamics of African penguins and other marine top predators in southern Namibia.  相似文献   

3.
Despite much public awareness surrounding the annual migration of sardine Sardinops sagax northward along the east coast of South Africa in winter each year, relatively little research effort has been expended to improve understanding of the ‘sardine run’. For this reason, a dedicated multidisciplinary survey, timed to coincide with the annual sardine run, was conducted off the East Coast in June and July of 2005. The major objective of the survey was to estimate the biomass of sardine off the East Coast during the run, and to compare this with biomass estimates collected during previous surveys conducted in this area during the late 1980s when the South African sardine population was at a considerably smaller size. We also collected data on the distribution of sardine and other small pelagic fish species and their eggs, the biological characteristics of sardine during the run, and data on the hydrography (temperature and currents) and lower trophic levels (phytoplankton and zooplankton) of the region. Results suggest that the biomass of sardine off the East Coast in winter remains relatively small and consistent, regardless of overall sardine population size. The narrow continental shelf to the east of Port Alfred, which is dominated offshore by the fast-flowing warm Agulhas Current, constrains the amount of suitable habitat for sardine and other clupeoids such as anchovy Engraulis encrasicolus, West Coast round herring Etrumeus whiteheadi and East Coast round herring Etrumeus teres, and hence precludes these species from attaining a high biomass in this region. Additionally, primary and secondary productivity levels are much lower than elsewhere on the western and eastern Agulhas Bank off the south coast of South Africa, suggesting that the sardine run is not a feeding migration. A previous hypothesis that the run is mainly a result of an expansion of the distributional range of these fish as conditions become favourable in winter due to sporadic cooling off the East Coast is also not entirely supported by results from the survey. It is suggested that a migration for the purposes of spawning off this coast when conditions become favourable is a more likely incentive for sardine to undertake this arduous journey, despite increased predation and poor feeding conditions.  相似文献   

4.
Sardine Sardinops sagax distributed off the west and south coasts of South Africa have traditionally been assumed to comprise a single well-mixed stock for assessment and management purposes. New research, however, lends weight to the possibility of two stocks in this region. A precautionary management approach thus needs to consider the impact of management decisions on the hypothesised two individual stocks as well as on the resource as a whole. As a first step in this process, Bayesian assessments of South African sardine are presented, which compare results for the traditional single-stock hypothesis with those that follow from a new two-mixing-stock hypothesis. Recruits from the west stock are assumed to move to and remain part of the south stock in annual pulses of varying size. This movement is estimated to be appreciable, and to take place from a substantially more productive west stock to the south stock. This immigration makes a greater contribution to the south-stock biomass than do years of above-average south-stock recruitment. Importantly, this two-mixing-stock hypothesis is shown to be consistent with the data available. Further alternative sardine stock-structure hypotheses suggested by the most recent data are discussed.  相似文献   

5.
Catches of sardine Sardinops sagax made by the beach-seine fishery off the KwaZulu-Natal (KZN) coast during the annual winter sardine run have been sampled intermittently since 1951, and a substantial amount of data on various biological characteristics of sardine caught off KZN now exists. Information on length frequency distributions, mean caudal length (CL), length–mass relationships, condition factor (CF), age distributions, sex ratio, gonad maturity and diet have been collated and are presented in this paper. Sardine caught off the KZN coast during the past six decades had a mean CL of 17.4 cm (SD 2.0) and have shown a significant increasing trend in mean CL through time; had substantially lower mass-at-length compared to fish that did not participate in the sardine run; have shown two distinct periods of decrease in CF between 1979 and 2005; ranged in age from 1 to 7 years but were numerically dominated by younger fish (1-, 2- or 3-year-olds); had a 1:1 sex ratio and gonads that were predominantly actively developing and undergoing maturation and vitellogenesis; and had a diet dominated by zooplankton, primarily calanoid and harpactacoid copepods and fish eggs. These characteristics, together with some information on meristic and morphological characteristics of sardine caught off KZN, are compared to characteristics of sardine from elsewhere off South Africa's coast to assess the possibility that the former may be a distinct stock or a functionally discrete adult assemblage. Significant differences in characteristics such as CF, vertebral count and body shape were found, supporting the hypothesis that KZN sardine represent a distinct stock or a functionally discrete adult assemblage. However, small sample sizes and plausible alternative explanations for these differences weaken, but do not invalidate, this hypothesis, and further work is needed to answer this question.  相似文献   

6.
Hydroacoustic surveys off the coast of South Africa over the early years of the 21st century indicated that both the sardine Sardinops sagax and anchovy Engraulis encrasicolus populations had simultaneously reached record abundances. The South African pelagic fishery is regulated using an Operational Management Procedure (OMP). The OMP in use at that time had been developed using data from the two populations prior to this rapid and substantial increase in abundances. This paper documents the revised assessments that were urgently required to provide a basis to update the OMP. These assessments resulted in a changed perception of the status and productivity of these populations. In particular, estimates of the stock-recruitment relationships and the extent of variation about them, which play a key role in evaluating risk when developing OMPs, altered substantially from estimates derived from earlier assessments.  相似文献   

7.
Prevalence of infection with the myxozoan parasite Kudoa thyrsites is not well documented in sardine Sardinops sagax, the Cape hakes Merluccius capensis and M. paradoxus, and kingklip Genypterus capensis. Quantitative polymerase chain reaction assays were used to determine the prevalence of K. thyrsites in wild-caught S. sagax (n?=?296), Merluccius spp. (n?=?162) and G. capensis (n?=?70), harvested in 2015. Sardinops sagax were harvested from the east, south and west coasts of South Africa, whereas M. capensis, M. paradoxus and G. capensis were taken from the west coast only. Relationships between K. thyrsites infection prevalence and fish capture locality, season, sex and size were determined with Chi-square tests. Prevalence was highest in S. sagax (91%), followed by M. capensis and M. paradoxus (87%) and G. capensis (40%). Prevalence was independent of sex of the host for all fish species. In the case of S. sagax only, the prevalence of infection was independent of locality of capture but depended on season, with prevalence lowest during spring and highest during autumn. No significant relationship (p?>?0.05) was found between infection prevalence and host size for any of the fish species.  相似文献   

8.
Catches of South African sardine Sardinops sagax have declined in recent years from about 200 000 t harvested annually during the period 2002–2006 to less than 100 000 t. Consequently, some companies are now importing sardine from sources elsewhere in the world to meet local demand for canned sardine and bait. This importation has the potential for the introduction of sardine pathogens, in particular the pilchard herpesvirus (PHV), which could have a negative impact on the currently small South African sardine population. The aims of the current study were to determine whether PHV is present in the local sardine population and to assess the extent to which sardine is being imported into the country and whether imported fish are from countries where the virus is known to be endemic. Fish sampled from South Africa’s western (n = 150), southern (n = 182) and eastern (n = 96) putative stocks of S. sagax were analysed for the presence of PHV using real-time quantitative polymerase chain reaction (qPCR). The origin and amount of potentially infected material imported into South Africa during the period 2010–2014 was also assessed. None of the South African sardine collected during this study tested positive for PHV, suggesting that active PHV was not prevalent in the local population of S. sagax at the time of this study. Between 56 000 and 71 000 t of frozen sardine was imported annually into South Africa from countries where S. sagax occurs, including some from areas (Australia and New Zealand) where sardine infection by PHV is known to be endemic. Hence, it is plausible that the PHV pathogen, capable of perpetuating infections in local sardine populations, could be imported into South Africa along with the importation of frozen sardine. Should local sardine be naïve to the virus, as suggested by this study, then the population is at risk of infection and precautions against such must be taken.  相似文献   

9.
Pelagic eggs of marine fish were collected weekly from shelf waters at Park Rynie on the KwaZulu-Natal south coast from 1987 to 2007 to investigate seasonal and annual patterns in the abundance of sardine Sardinops sagax eggs. After a sudden appearance in June each year, sardine eggs were found persistently throughout the winter–spring period before disappearing in early summer. From changes in the cross-shelf distribution of eggs, it is inferred that sardine shoals are close inshore in June, as they arrive in KwaZulu-Natal waters from the south, then the shoals disperse offshore and thereafter return inshore before their return migration southward in early summer. The period 2001–2007 yielded significantly fewer eggs than the previous 14 years of the study.  相似文献   

10.
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   

11.
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12.
Hydro-acoustic surveys have been used to provide annual estimates of May recruitment and November spawner biomass of the South African sardine Sardinops sagax and anchovy Engraulis encrasicolus resources since 1984. These time-series of abundance estimates form the backbone of the assessment of these resources, and consequently the management of the South African sardine and anchovy is critically dependent on them. Upgrades to survey equipment over time have resulted in recent surveys providing more accurate estimates of abundance, yet in order to maintain comparability across the full time-series, estimates of biomass mimicking the old equipment were used for a number of years. In this paper we develop a method to revise the earlier part of the time-series to correct for receiver saturation in the older generation SIMRAD EK400 and EKS-38 echo sounders and to account for attenuation in dense sardine schools. This is applied to provide a revised time-series of biomass estimates for the South African sardine and anchovy resources with associated variance–covariance matrices. Furthermore, the time-series presented here are based on updated acoustic target strength estimates, making this the most reliable time-series currently available for both resources.  相似文献   

13.
Opportunistic observations to determine the relative abundance and distribution of marine mammal and seabird predators of sardine Sardinops sagax were carried out during a dedicated multidisciplinary research survey off the South African east coast in June and July of 2005 that was timed to coincide with the annual sardine run. Associations between different predator species, between predators and clupeoids, and between predators and oceanographic variables, were examined. Species’ distributions were primarily separated by latitude and distance from shore. Bryde's whale Balaenoptera edeni, African penguin Spheniscus demersus, Cape cormorant Phalacrocorax capensis and West Coast round herring Etrumeus whiteheadi were predominantly found in the cool southern part of the survey region. Peak sardine run activity occurred within 4 km of shore at the northward limit of a strip of cool water (<21 °C) stretching along the East Coast. The principal predators associated with this activity were common dolphins Delphinus capensis and Cape gannets Morus capensis, and their nearshore distribution was associated with sardine and East Coast round herring E. teres. Few clupeoids were encountered along the KwaZulu-Natal continental shelf, although patches of high sardine abundance were recorded near the shore immediately south of Durban. It is clear that during the 2005 survey the sardine run terminated in this region, probably as a result of the nearshore intrusion of warm water from the Agulhas Current.  相似文献   

14.
Numbers of Cape cormorants Phalacrocorax capensis breeding in South Africa decreased by nearly 50% from approximately 107 000 pairs in 1977–1981 to 57 000 pairs in 2010–2014. Although four colonies had >10 000 pairs in 1977–1981, there was just one such colony in 2010–2014. Almost all the decrease occurred after the early 1990s off north-west South Africa, between the Orange River estuary and Dassen Island. South of this, the number breeding in the two periods was stable, with some colonies being formed or growing rapidly in the 2000s. The proportion of South Africa’s Cape cormorants that bred south of Dassen Island increased from 35% in 1977–1981 to 66% in 2010–2014, with the opposite situation observed in the north-west. This matched a shift to the south and east in the distributions of two of the Cape cormorant’s main prey species, anchovy Engraulis encrasicolus and sardine Sardinops sagax. In 2014, an apparent scarcity of prey in the north-west resulted in Cape cormorants attempting to take bait from hooks of fishing lines over an extended period, a behaviour not previously recorded. The number of Cape cormorants breeding in the south may be constrained by the absence of large islands between Dyer Island in the west and Algoa Bay in the east. If so, it may be possible to bolster the southern population through the provision of appropriate breeding habitat, such as platforms, or restricting human disturbance at suitable mainland cliff breeding sites.  相似文献   

15.
The annual winter sardine run along the South African east coast impacts the KwaZulu-Natal (KZN) coastal system in a variety of ways. These include ecological impacts, such as enrichment of a largely oligotrophic environment, competition between migrant sardine Sardinops sagax, other migrant and resident small pelagic fish species, and interactions with predators, as well as the socio-economic impacts of the sardine run on the local people. Enrichment of KZN coastal waters with organic nitrogen contained within the sardine is compared with alternative sources of nitrogen such as upwelling, river, sewage and stormwater runoff, and groundwater discharge. The sardine run appears to contribute most nitrogen to this system—96 000 t compared to 500–3 300 t for each of the other significant sources at trophic level 2, although upwelling estimates are extremely wide. Nonetheless, the majority of surviving sardine, their young and predators return southwards, suggesting that the nett export of nitrogen to KZN waters during the run is likely to be of a similar order of magnitude as that from other sources. Further, whereas the sardine supply of nitrogen is exclusively during winter, the bulk of the riverine input is in summer, thus ensuring that nitrogen supply in the region is maintained at fairly constant levels throughout the year. Competition for food between small pelagic fish is minimised by resource partitioning, but further dietary data are needed for resident species. Although interactions between sardine and top predators must exist, further studies are needed to confirm links between top predator life cycles and the sardine run. The estimated value of sardine as a tourist spectacle is compared to that from a seasonal beach-seine or boat-based purse-seine fishery for this species. Whereas the estimated value of the sardine as a tourist attraction appears substantially higher than could be derived from catching them, the small-scale beach-seine fishery itself draws tourists and also provides limited, seasonal employment opportunities.  相似文献   

16.
The annual movement of South African sardine Sardinops sagax up the east coast of South Africa, known as the ‘sardine run’, was investigated using data from aerial surveys for the period 1988–2005 and compared with remotely sensed sea surface temperature (SST) and chlorophyll a data. Sardine sighting rates were highest within the Waterfall Bluff Bight off the Eastern Cape Coast, where conditions appeared to be most favourable. Sardine and predator sightings decreased significantly northwards of Mdoni on the KwaZulu-Natal (KZN) coast, whereas the proportion of nearshore sightings increased. The causal mechanism for this inshore concentration is suggested to be the influx of warm Agulhas Current water from the Durban Eddy that forces sardine shoreward. Cape gannet Morus capensis, common dolphin Delphinus capensis and sardine distributions were associated, and there was an association between SST and sardine and predator distributions. There was a marked increase in bottlenose dolphin Tursiops aduncus sightings upon commencement of the sardine run, with these dolphins being consid-ered to be a ‘migratory’ stock that enters KZN waters every winter.  相似文献   

17.
Stomach content analyses and measurements of gillraker morphology were used to assess the diet and feeding ecology of the East Coast redeye round herring Etrumeus wongratanai and provide data for comparisons with other small pelagic fishes off South Africa. Samples were collected by jigging from a kayak off Scottburgh, KwaZulu-Natal (KZN), over the period July 2013–May 2014. In total, 66 stomachs (containing 4 407 prey items) and 66 gill arches were examined. Stomach content analyses indicated that East Coast redeye round herring, at the time of sampling, fed on large (1 500–2 500?µm) particles, with ～2 500?µm particles making the greatest contribution to dietary carbon. The species feeds on larger particles than do anchovy Engraulis encrasicolus and sardine Sardinops sagax, but on particles of a similar size to those consumed by West Coast redeye round herring Etrumeus whiteheadi. There were significant differences in mean gillraker gaps between East Coast redeye round herring and both sardine and anchovy, but not between East Coast and West Coast redeye round herring. The differences in gillraker gaps between East Coast redeye round herring, sardine and anchovy are indicative of resource partitioning through differential feeding, based on zooplankton size. The data suggest that there is no resource partitioning between East and West coast redeye round herring, indicating that competition is likely to occur between them. However, such competition is minimised by limited spatial overlap between these two species.  相似文献   

18.
The Humboldt Current System (HCS) is dominated by two pelagic species; Peruvian anchovy or anchoveta (Engraulis ringens) and sardine (Sardinops sagax). Using data from 43 acoustic surveys conducted from 1983 through 2005 by the Peruvian Marine Institute (IMARPE), we examined the distribution of these two species relative to water masses. We tested the hypothesis that anchovy was found more frequently in upwelled cold coastal water (CCW) and mixed waters (MCW) than in other water types and that sardine was more associated with more offshore oceanic surface subtropical water (SSW). Surface temperature, salinity, latitude, season and distance to the coast data were used to define water masses. Results using generalized additive models (GAM), modelling sardine and anchovy presence–absence as a function of year, water body, bottom depth and latitude, showed that anchovy were primarily found in CCW and MCS, while sardine were more ubiquitous relative to water masses with some predilection for SSW. These results were supported by various indexes of anchovy and sardine distribution versus water mass as well as temporal and location variables.  相似文献   

19.
From 1987 to 2005, numbers of African penguins Spheniscus demersus breeding in South Africa's Western Cape Province increased by about 50%. Numbers decreased at the four northernmost colonies in the region: Lambert's Bay and the three colonies in Saldanha Bay, although at Jutten Island the decrease is inferred from an estimate for 1987, derived from interpolation. Numbers also decreased at Geyser Rock and Dyer Island on the South Coast. At five colonies between Saldanha Bay and Dyer Island there were large increases. At a sixth colony in that region, Seal Island, where Cape fur seals Arctocephalus pusillus pusillus limit breeding space, numbers remained stable. At two colonies that were initiated in the early 1980s, Robben Island and Boulders, increases were initially rapid (>20% per annum) and matched growth of the South African stock of sardine Sardinops sagax. Strong growth at Dassen and Vondeling islands, between Robben Island and Saldanha Bay, was observed from about 1996–2002, when there was a large increase in the biomass of pelagic fish off South Africa. Increases at colonies between Saldanha Bay and Boulders slowed after 2002, whereas the colony at Dyer Island stabilised at that time. In 2003, a new colony was initiated east of Dyer Island at De Hoop Nature Reserve. These latter trends followed an eastward shift in the distribution of sardine. Small penguin colonies may act as foci for growth in a period when the distribution of prey is changing. Hence, it is important that they be maintained, especially those that, if lost, would increase the isolation of regional populations. Some of the small colonies are less susceptible to oil spills than colonies in the proximity of harbours, and for that reason also are important.  相似文献   

20.
African penguins Spheniscus demersus live in the Benguela and western Agulhas ecosystems off southern Africa. Their numbers decreased throughout the 20th century from at least 1.5 million to about 0.18 million adults, although different regional trends were apparent. They feed to a large extent on shoaling epipelagic fish, notably anchovy Engraulis capensis and sardine Sardinops sagax, and regional trends in the abundance of penguins are associated with trends in the abundance and distribution of these prey fish. Many first-time breeders emigrate from colonies where feeding or other conditions at the time are unfavourable to more favourable breeding localities. This has led to both the extinction and formation of colonies. Food now may limit colonies at relatively small sizes, a fact attributable to industrial fisheries reducing the densities of forage fish. African penguins share their habitat with several other predators, with which they compete for food and breeding space. One of these, the Cape fur seal Arctocephalus p. pusillus, increased through the 20th century to 1.5 – 2 million animals at its close. Reported observations of predation by fur seals on seabirds have increased in recent decades and threaten the continued existence of small colonies of penguins. Stochastic modelling suggests that colonies of 10 000 pairs have a 9% probability of extinction in 100 years, so smaller populations should be regarded as "Vulnerable". However, in a period of prolonged food scarcity off southern Namibia, the regional population decreased from more than 40 000 pairs in 1956 to about 1 000 pairs in 2000, and many colonies numbering less than 1 000 pairs became extinct. The minimum viable population for African penguins is currently considered to be >40 000 pairs, likely of the order of 50 000 pairs, a figure equivalent to its level in 2000. The chance of survival of the species through the 21st century is tenuous.  相似文献   

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