MASS MORTALITY OF MARINE AND ESTUARINE FISH IN THE SWARTVLEI AND WILDERNESS LAKE SYSTEMS,SOUTHERN CAPE.

Summary

Two incidences of mass mortality of fish were recorded in two saline waterbodies (Swartvlei estuary and Rondevlei) in the Wilderness National Park. Species affected were the Knysna seahorse (Hippocampus capensis) and longsnout pipefish (Syngnathus acus) in the Swartvlei estuary, and Cape stumpnose (Rhabdosargus holubi) and white steenbras (Lithognathus lithognathus) in Rondevlei. Comparison of water quality parameters during fish mortalities to past ranges and reported species tolerances indicated that the probable causes for the mortalities were high water temperature in the Swartvlei estuary, and low dissolved oxygen concentration in Rondevlei.     

THE PLASMA PROTEINS OF SOME FRESHWATER FISH IN THEIR NATURAL ENVIRONMENT

SUMMARY

The plasma proteins of Cyprinus carpio (carp), Barbus holubi (yellowfish), Labeo umbratus (mudfish) and Labeo capensis (mudfish) were electrophoretically separated on polyacrylamide gels from blood samples obtained from specimens sampled during summer and winter in three different localities. Within a species, differences existed in the summer and winter plasma protein electrophoretograms from the different localities. During winter protein fraction concentration differences were found with a displacement of prominence. The results are compared between different experimental conditions and to previous observations. A genetic trait is present, but there were also alterations as a result of environmental factors.     

Reproductive biology of four large riverine fishes (Cyprinidae) in a man-made lake,Orange River,South Africa

The reproductive biology ofBarbus holubi, B. kimberleyensis, Labeo capensis andL. umbratus was examined in a large reservoir on the Orange River, South Africa. The findings are integrated into the existing knowledge on largeBarbus andLabeo species, which coexist in most river systems in Africa and Asia.LargeBarbus spawn on gravel beds within the river channel during floods in spring or summer. In continuously flowing regulated rivers, time of spawning is governed by water temperatures. They have moderate fecundity; large eggs, incubation time of several days and the larvae are initially immobile with large yolk sacs. In the impoundment, they spawn in the inflowing regulated river withB. kimberleyensis spawning four to six weeks later than the more cold-tolerantB. holubi, the dominant largeBarbus. Survival is generally good and the juveniles disperse throughout the lake, but unseasonal release of cold water from an upstream impoundment may cause poor reproductive success.In contrast,Labeo species generally spawn on newly flooded ground, usually leaving the main river channel. Spawning may or may not be preceded by a longitudinal migration. Labeos are relatively fecund with small (30%Barbus size) eggs which hatch quickly and the larvae swim in bursts up into the water column before sinking down again.L. capensis does not require a longitudinal spawning migration and breeds throughout the lake, depending on local conditions. Large temporal variation in gonadal development within the population can result in more than one spawning. Dispersal within the lake is poor.L. umbratus uses larger inflowing tributaries for spawning thanL. capensis and its juveniles have a much greater power of dispersal. Early dependence on external feeding and undependable occurrence of conditions for spawning and juvenile feeding makes for variable reproductive success.     

INFLUENCE OF FRESHWATER FLOW REGIME ON FISH ASSEMBLAGES IN THE GREAT FISH RIVER AND ESTUARY

Summary

Two and a half years of data were collected from the lower Great Fish River, head region and estuary to determine the fish species composition within these areas. Gilchristella aestuaria, Liza dumerilii, Rhabdosargus holubi and Pomadasys commersonnii were the four most abundant species captured, with riverine flow rate having an important effect on both species composition and numbers of fishes in the different regions. Most marine species displayed a strong inverse relationship between catch per unit effort and elevated freshwater inputs. Euryhaline marine species dominated the catches at all sampling sites during low flows but were less common during high flow periods when catadromous species were most abundant. Based on the available evidence it is suggested that for most marine species in the river this decline in abundance is related to low conductivity levels following floods rather than avoidance of elevated flows. The impact of elevated suspensoid concentrations and lowered dissolved oxygen concentrations on freshwater and estuarine fish populations during major river flooding is also discussed.     

Population studies on a South African carrageenophyte: Iridaea capensis (Gigartinaceae,Rhodophyta)

An intertidal population of Iridaea capensis in the south-western Cape Province of South Africa has been studied in detail for a year. The species is generally restricted to sand-inundated rocky shores, which appears not to be the case for Iridaea species in the Pacific. In early winter (June) biomass, plant density and plant size were at a minimum. A small increase in these parameters occurred in August, but there was a massive increase in plant numbers and biomass in October. The largest plants were recorded in summer (February). The population was over 70% sporophytes in April, but switched to almost 80% gametophytes following heavy recruitment between August and October, and remained significantly gametophyte-dominated through April of the following year. Carrageenan levels were high (ca 42% of dry weight) in late winter-spring, and lowest (ca 30–35%) in summer-autumn. Strong offshore wind conditions in early summer caused a reduction in biomass, and it is hypothesized that the associated upwelling of nutrient rich water may be implicated in the lower carrageenan levels at this time.     

PRELIMINARY OBSERVATIONS ON THE FISH POPULATIONS OF THE RECENTLY-IMPOUNDED KATSE RESERVOIR,LESOTHO

Summary

Katse is a new 35 km long impoundment on the Malibamatso River, a highland tributary of the Orange River in Lesotho. Two fishing surveys in 1996 yielded Barbus aeneus, Labeo capensis, Oncorhynchus mykiss and the occasional Austroglanis sclateri. Length frequency data for the first three species show modes which may represent year classes, although gillnet selectivity also plays a role. Barbus aeneus is abundant throughout the reservoir and could support a subsistence fishery. Labeo capensis is segregated by sex in the breeding season, with males remaining on the spawning grounds at the river mouths while females visit the spawning grounds for a short time to shed their eggs. The absence of small-sized Oncorhynchus mykiss in the catch may be due to pollution from mining and construction affecting the spawning grounds. The catches of larger trout and the outstanding scenery suggest that a tourist sport fishery could be developed on the reservoir based on natural recruitment supplemented, if necessary, by stocking hatchery-reared fish. As the three species are potamodromous, subsistence fishing zones will need to be clearly demarcated to prevent fishing in the vulnerable river mouth areas.     

Molecular evidence of conspecificity of South African hares conventionally considered Lepus capensis L., 1758

Conventionally, Lepus capensis is considered to range across large parts of Africa, the Middle East, Central and Far East Asia. However, a recent morphological study restricts cape hares tentatively to a small range in the Western Cape Region of South Africa and groups all other L. capensis-type hares from South Africa into a new species: L. centralis. Here, we studied molecular relationships among L. capensis-type hares from South Africa. Phenotypically and morphologically the individuals matched either the newly described L. capensis or L. centralis. We examined 66 hares for allelic variation at 13 microsatellite loci and for sequence variation of the hypervariable domain 1 of the mitochondrial control region. All tree-generating analyses of the currently obtained sequences and all South African cape hare sequences downloaded from GenBank revealed monophyly when compared to sequences of various other Lepus species. A network analysis indicated close evolutionary relationships between hares of the “L. capensis-phenotype” and the “L. centralis-phenotype” (according to Palacios et al. 2008) from the southwest of the Western Cape, relative to their pronounced evolutionary divergence from all other more central, northern, and north-eastern L. capensis-type hares. F-statistics, a Bayesian admixture STRUCTURE model, as well as a principal coordinate analysis of microsatellite data indicated close genetic relationships among all South African L. capensis-type hares studied presently. A coalescence model-based migration analysis for microsatellite alleles indicated gene flow between most of the considered subspecies of cape hare, including L. capensis capensis and L. capensis centralis, theoretically sufficient to balance stochastic drift effects. Concordantly, AMOVA models revealed only little effects of partitioning microsatellite variation into the two suggested morpho-species “L. capensis” and “L. centralis”. Under an “Interbreeding Species Concept” (e.g. a strict or relaxed Biological Species Concept), the current molecular data demonstrate conspecificity of the two proposed morpho-species “L. capensis” and “L. centralis”. Based on the present molecular data the differentiation of subspecies of cape hares from southern Africa is discussed.     

Influences of selected geophysical and environmental drivers on the movement patterns of <Emphasis Type="Italic">Rhabdosargus holubi</Emphasis> in a southern African estuary

A total of 21 juvenile Cape stumpnose (Rhabdosargus holubi) were tagged with internal acoustic transmitters in the lower, middle and upper reaches of the Kowie Estuary, South Africa. The movements of all fishes were continually monitored for five months using 22 stationary data-logging acoustic receivers, positioned along the length of the estuary. Diel and tidal cycles were identified in the movements of several individual R. holubi; however the lack of extensive movements for most individuals emphasised high residency of the species to particular sections of the estuary. River inflow and water temperature significantly affected the movement behaviour of most tagged R. holubi. Periods of increased freshwater inflow and rising riverine temperatures prompted certain individuals to shift their position downstream, while reduced sea temperatures in the lower reaches prompted certain individuals to shift their position further upstream from the mouth. Given the predicted effects of climate change in the study region, which include increased river inflow due to catchment rainfall and decreased sea temperatures due to ocean upwelling, these results suggest that R. holubi may be sensitive to the environmental effects of global warming and that the distribution and movement behaviour of this species in southern African estuaries is likely to be affected as climate change proceeds.     

New record of Lithodidae (Crustacea Decapoda, Anomura) from the Antarctic (Bellingshausen Sea)

During the Bentart-2003 Cruise, carried out during austral summer 2003 in the Bellingshausen Sea, three species of Lithodidae, Paralomis birsteini, Lithodes murrayi and Neolithodes capensis, were caught from 218 m to 1947 m. With these captures the presence of L. murrayi in Peter I Island is confirmed, the distribution area of N. capensis is greatly increased and the captures of N. capensis and P. birsteini represent the first lithodid record known from the Antarctic continental slope. Also, these records show large and discontinuous distributions, which illustrate that many distribution patterns of Antarctic species are more an artefact of limited studies than representing actual distribution.     

THE DIET AND IMPLICATIONS OF DIETARY CHANGE OF CAPE GANNETS ON BIRD ISLAND,ALGOA BAY

Batchelor, A. L. & Ross, G. J. B. 1984. The diet and implications of dietary change of Cape Gannets on Bird Island, Algoa Bay. Ostrich 55:45-63.

The diet of the Cape Gannet Sula capensis breeding on Bird Island, Algoa Bay, South Africa, was investigated. Approximately 2000 regurgitations representing 13300 prey items were examined. Twenty-three teleost and two cephalopod species were recorded in the diet. More than 90 % of the numerical composition consisted of the three species Pilchard Sardinops ocellata, Anchovy Engraulis capensis and Saury Scomberesox saurus. The proportions of these three species in the diet changed during the sampling periods. These changes were not related to the implied migration patterns of these species. Chick growth rates were investigated in conjunction with the dietary study. These results indicated that Cape Gannet chicks on a diet of Pilchard and/or Anchovy were more likely to fledge successfully than those on a diet of Stockfish Merluccius capensis or Saury. These observations were based on differences in growth rate, and peak and fledgling mass, The data suggest that Pilchard is a preferred prey species and its presence or absence in regurgitationsMayreflect a similar situation on the feeding grounds. The observed increase in the Bird Island gannet populationMaybe related to the availability of high-quality food and consequent reduced pre-breeding mortality. In the absence of historical dietary data, further detailed population dynamics studies are required to support this supposition.     

Occurrence of Larval and Early Juvenile Fishes in the Surf Zone Adjacent to two Intermittently Open Estuaries, South Africa

I monitored larval and early juvenile fishes in the surf zone adjacent to two warm temperate, intermittently open estuaries in South Africa. Mugilidae (59–67%) dominated fish assemblages in the surf zones adjacent to the Van Stadens and Kabeljous estuaries. Other dominant families included the Atherinidae, Sparidae and Soleidae. The most abundant species caught during the study were the catadromous mugilid Myxus capensis, in a postflexion or early juvenile stage of development, and the sparid Rhabdosargus holubi, in a postflexion stage of development. Species displaying a degree of dependence on estuaries during the early phase of their life cycle dominated (96–98%) surf zone catches. Most fish encountered were at the postflexion stage of larval development. Larval and early juvenile fishes were more abundant during the summer and autumn months with density peaking several-fold during natural estuary opening events, particularly in the surf zone adjacent to the Kabeljous Estuary. Decreases in salinity showed a significant relationship with increases in fish density during a March opening event in the surf adjacent to the Kabeljous Estuary where catches were concentrated along a current-driven estuarine plume. Catches adjacent to the Van Stadens Estuary also increased considerably during two smaller opening events in March and November although salinity played no statistically significant role in these increased catches. Results from the surf adjacent to the Van Stadens Estuary suggested that either very small amounts of estuarine water entering the surf zone can elicit an accumulation response by estuary-dependent larval and early juvenile fishes or that an additional characteristic of estuary/river water, other than salinity per se, is aiding the cueing process.     

Switching by Lepsiella vinosa (Gastropoda) in South Australian mangroves

Summary In South Australian mangroves Lepsiella vinosa feeds on two species of barnacles, Balanus amphitrite and Elminius modestus, and only attacks other types of prey if no barnacles are available. Laboratory experiments indicate that L. vinosa can be trained to either species and switches in terms of Murdoch's (1969) model.The distribution of barnacles is heterogeneous and distinct prey patches are found in the mangroves. In high density patches, that is over 25 B. amphitrite per metre length of pneumatophore, L. vinosa concentrated its attacks on B. amphitrite irrespective of the relative abundance of the two species. In moderate density patches, that is less than 25 B. amphitrite per metre length of pneumatophore, L. vinosa fed on the two species as expected on the basis of relative abundance. There was, however, also an association between changes in the absolute density of B. amphitrite and the proportion it formed in the diet.Prey selection in the moderate density patches was not random and was influenced by previous feeding history. L. vinosa which fed on the more abundant species, E. modestus, selected this species at a higher rate than expected in subsequent surveys. This result suggests that ingestive conditioning took place in the field, and provides some support for the switching hypothesis.Field cage experiments indicate that L. vinosa shows switching provided that the density of the preferred prey was not too high. L. vinosa had a weak preference for B. amphitrite over E. modestus, c was calculated to be 1.26, when equal numbers of each species were present. The preference appears to be consistent between individual L. vinosa as few individuals fed predominantly on only one prey species.The switching response in L. vinosa was asymmetrical with regard to the two prey species. L. vinosa switched to B. amphitrite when it was more abundant irrespective of prior training. L. vinosa trained to E. modestus, or unfed, prior to the experiment switched to E. modestus when it was more abundant, but, those trained to B. amphitrite did not. L. vinosa also showed asymmetry in its feeding rate. Those trained to E. modestus, or unfed, attacked prey at the average rate observed in the field irrespective of the prey presented. L. vinosa trained to B. amphitrite showed a marked reduction in feeding rate when B. amphitrite was less abundant.Absolute density as well as the relative density of the two prey species influenced prey selection. Higher predation on B. amphitrite was found, despite a fixed relative abundance of one B. amphitrite to five E. modestus, when the barnacle density was increased from 11.2 to 56 per metre of pneumatophore.     

Fish sampling in the marine-dominated Kariega Estuary,South Africa,using a demersal otter trawl: day/night effects

Very few demersal fish assemblage studies using otter trawls in estuaries have been done in South Africa and none of these have tested for the effects of diel period. This study aimed to test whether diel period affects otter trawl catches in the clear, permanently open Kariega Estuary in terms of both species composition and abundance. Fish were sampled by day and night from 30 October to 1 November 2007 at 15 sites using an otter trawl. More species were collected at night, when there were higher catch rates for all key species, with the exception of Rhabdosargus holubi, which was more abundant during the day. Overall assemblages collected by day and by night were similar, with six species accounting for over 90% of the catch in both day and night samples. Both day and night samples reflected differences related to region, with the highest mean CPUE during day and night sampling being recorded in the head region.     

Biogeographical patterns in endoparasite communities of a marine fish (Sebastes capensis Gmelin) with extended range in the Southern Hemisphere

Aim The endoparasites of Sebastes capensis Gmelin are examined over most of its geographical range (coasts of Peru, Chile, Argentina and South Africa) to determine: (1) whether the endoparasite communities of this fish show zoogeographical patterns; and (2) if so, whether there are any relationships between spatial variations in the endoparasite fauna and known zoogeographical patterns for marine free‐living organisms (e.g. prey that are included in the life cycles of endoparasites). Location Fish were captured at nine localities along the Pacific coast of South America, from 11° S in the centre of the Peruvian coast, to 52° S in southern Chile, and also at two localities in the Atlantic Ocean, at 43° S in Argentina, and 34° S in South Africa. Methods From April to September 2003 and April to August 2004, 626 fish were captured. Endoparasites and diet were examined following traditional methods. Cluster analyses were used to evaluate the distribution patterns of the endoparasite communities, and to evaluate similarities in the prey composition per locality. Results The endoparasite fauna of S. capensis consisted of four species widely distributed along the Pacific coast: Ascarophis cf. sebastodis, Anisakis sp., Corynosoma australe, and Pseudopecoelus sp. Other parasites were distributed only in some geographical areas. The species richness of the parasite communities increased with latitude along the Pacific coast, while parasite communities from Argentina and South Africa showed low species richness. Cluster analyses based on endoparasite composition and on prey composition grouped localities in a way consistent with known biogeographical areas for marine free‐living organisms. Main conclusions The endoparasites of S. capensis exhibit a pattern associated with known biogeographical areas for free‐living organisms. The latitudinal increase in endoparasite community richness is associated with changes in prey composition (intermediate hosts) and also possibly with the presence of definitive hosts. Therefore, the biogeographical patterns of prey are considered key determinants of the endoparasite community structure of the host.     

Morphological evidence of species differentiation within Lepus capensis Linnaeus, 1758 (Leporidae,Lagomorpha) in Cape Province,South Africa

A morphological study was carried out of the hares (Lepus) from Cape Province previously assigned to the subspecies L. capensis capensis, L. c. centralis, and L. c. grantii. The purpose of the study was to characterize the species L. capensis Linnaeus, 1758. In doing so, it was possible to distinguish two populations which we consider different species, as each shows homogeneous cranial, dental and pelage features. One of them, defined as L. capensis, is distributed near Cape Town not far from the coast, between Lambert's Bay and Cape Agulhas. The other species, defined as L. centralis, which includes L. grantii as a synonym, is distributed in central and western Cape Province. L. capensis and L. centralis have a parapatric distribution, with a small area of sympatry in a contact zone in Compagnies Drift area, near Lambert's Bay. With respect to cranial differences between the two species, L. capensis has a stronger maxilla and more robust dental series, while L. centralis has larger tympanic bullae. Among dental characters, L. centralis usually has a deeper groove and more abundant cement than L. capensis in the first upper incisor, and its internal lobe is squared, while in L. capensis is rounded. As for pelage color and pattern, L. capensis shows a more extended white ventral area than L. centralis. Our results are of interest for further research on taxonomic problems regarding Old World hare populations in which L. capensis is concerned.     

Ecological investigations on lichen fields of the Central Namib

Number, geographic location, extent and characteristics of lichen fields were recorded within the Central Namib fog desert. Their occurrence is restricted to stable surfaces in the near coastal belt, while percentage cover changes with exposure, elevation and distance from the coastline. Maximum coverage of 70% was found at a distance of 5 km from the coast near Wlotzkas Baken. The highest biomass rate of 400 mg/m² was measured here at a distance of 1 km from the coast, where Teloschistes capensis appears as cushion growth type. Distribution patterns on hills, riverbeds and polygon structures are described. In general, fruticose and foliose lichens dominate on SW-exposed, ocean-facing habitats. Crustose species dominate on NE-E-exposed plots.Species composition and distribution, particularly the distribution of the fruticose species T. capensis (L. f.) Vain. ex Müll. Arg., were investigated in seventysix plots along twenty W-E transects in one lichen field near Wlotzkas Baken. T. capensis occurs in three different growth types: tuft, cushion and mat. Four zones are distinguished within the above lichen field, each dominated by a growth form indicating various influences of different climatic, geomorphic or biogenic parameters.     

THE DISTRIBUTION AND ECOLOGY OF TWO MULLET SPECIES IN SOME FRESH WATER RIVERS IN THE EASTERN CAPE,SOUTH AFRICA

SUMMARY

Data on the relative abundance, penetration and breeding biology of the freshwater mullet Mugil cephalus and the flathead mullet Mugil cephalus in the freshwater reaches of some Eastern Cape coastal rivers are described. The differences found between the two species indicate that Myxus capensis is more specialized for a catadromous life history in an unstable riverine environment. Evidence showing the importance of the freshwater phase for the latter species is given and the disastrous effects of the erection of barriers to fish movement are stressed.     

FISH SPECIES IN STEIUTONTEIN DAN,TUGELA-VAAI SYSTEM,SOUTH AFRICA

SUMMARY

Two alien species and seven indigenous species, including two minnow species, were present in Sterkfontein Dam. Of the larger species, Barbus aeneus and Labco capensis were the dominant in terms of numbers.     

Causes and consequences of human induced impacts on a ubiquitous estuary-dependent marine fish species

Decreasing populations of common estuary-associated marine fishes are being documented globally and red flags associated with such declines are often ignored due to the high relative abundance of these species when compared to more rare and threatened taxa. The Cape stumpnose Rhabdosargus holubi (Steindachner 1881) is an abundant and widespread southern African sparid that is dependent on estuaries as a primary nursery area. Historical and current information on the species is comprehensive and the accumulated evidence strongly suggests that this ubiquitous fish is under pressure, mainly due to degradation of estuaries and associated catchments, increasing fishing pressures from recreational and subsistence anglers, habitat loss relating to reduced submerged macrophyte areas in many systems, industrial and agricultural pollution, infrastructural developments in and around estuaries, and climate change. In particular, the temporary loss of Lake St Lucia, which accounts for approximately 50% of the estuarine surface area in South Africa, has drastically reduced the nursery area availability for R. holubi on the subcontinent. Overall we present strong evidence to support the hypothesis that present-day stocks of R. holubi are much smaller than those in the pristine state and that urgent management measures need to be considered and implemented to prevent current depleted populations of the species from declining further.     

Analysis of the Brassica oleracea genome by the generation of B. campestris-oleracea chromosome addition lines: characterization by isozymes and rDNA genes

Summary This study aimed at generating chromosome addition lines and disclosing genome specific markers in Brassica. These stocks will be used to study genome evolution in Brassica oleracea L., B. campestris L. and the derived amphidiploid species B. napus L. B. campestris-oleracea monosomic and disomic chromosome addition plants were generated by crossing and backcrossing the natural amphidiploid B. napus to the diploid parental species B. campestris. The pollen viability of the derived sesquidiploid and hyperploid ranged from 63% to 88%, while the monosomic and disomic addition plants had an average pollen fertility of 94% and 91%, respectively. The addition lines were genetically characterized by genome specific markers. The isozymes for 6PGD, LAP, PGI and PGM, and rDNA Eco RI restriction fragments were found to possess the desired genome specificity. Duplicated loci for several of these markers were observed in B. campestris and B. oleracea, supporting the hypothesis that these diploid species are actually secondary polyploids. A total of eight monosomic and eight disomic addition plants were identified and characterized on the basis of these markers. Another 51 plants remained uncharacterized due to the lack of additional markers. rDNA genes were found to be distributed in more than one chromosome, differing in its restriction sites. Intergenomic recombination for some of the markers was detected at frequencies between 6% and 20%, revealing the feasibility of intergenomic gene transfer.