A survey of the fish fauna of Transkei estuaries. Part 1. The Kei River estuary

During the period of survey the 8 km long Kei estuary was subjected to periodic floods which reduced salinities to 0%o and decreased light penetration to a few centimetres. Species composition, and temporal and spatial abundance were determined for fish samples collected by means of gill nets. Twenty-six species of fish were caught with Mugil cephalus, Liza tricuspidens and Argyrosomus hololepidotus predominating, in that order. The family Mugilidae comprised 67,8% of the numbers and 66,6% of the fish biomass caught. Definite seasonal patterns could not be determined for many of the fish although M. cephalus, L. richardsoni and A. hololepidotus were more abundant in summer. The effect of river flooding had unpredictable results on Mugilidae catches which either decreased or increased after floods while catches of P. commersonii and A. hololepidotus usually increased. Largest catches were made in the middle reaches although species diversity was greatest in the lower reaches of the estuary.     

A survey of the fish fauna of Transkei estuaries Part Three: The Mtata River estuary

The species composition, seasonal abundance and spatial distribution of the fish fauna of the Mtata estuary (8,5 km long) was determined by means of gill nets. Nine hundred and ninety fish (462,9 kg) comprising 26 species were caught of which M. cephalus (43,3%), A. hololepldotus (18,9%), P. commersonnii (7,9%), machnata (7,1%) and L. amia (5,45) were most abundant in terms of biomass. Mullet species constituted 48,3% of the biomass caught, representing 25,6% of the numbers. Seasonal patterns were ascertained for M. cephalus, M. capensis, V. buchanani, A. hololepidotus, P. commersonnii, P. kaakan, £ machnata, L. amia, J. dussumieri, T. vitrirostris and L. equula. A mean of 19,4 fish with a mean mass of 9,1 kg were caught per net per station. Numerically the highest catches were made in the upper reaches; gravimetrically in the middle reaches. Temperatures ranged from 10,5-25,5°C; a salinity gradient was usually present in all reaches; oxygen levels and turbidities were high.     

Seasonal abundance,distribution, and catch per unit effort using gill-nets,of fishes in the Sundays estuary

Catch per unit effort was obtained for the fish of the Sundays estuary by means of gill-netting. Fifty-five gill-net catches were made in which 1258 fish were caught in the mouth, middle and upper reaches of the estuary. Sea catfish, Tachysurus feliceps dominated catches numerically and kob Argyrosomus hololepidotus In terms of weight (31% of total). CPUE was 21 kg/standard net. Mean body weight of fish was 894 g. It seems that the food web in the Sundays estuary is based largely upon phytoplankton and dependent zooplankton grazers.     

A survey of the fish fauna of Transkei estuaries Part Four: The Mntafufu and Mzamba River estuaries

The Mntafufu and Mzamba Rivers have small catchment areas (178 and 505 km², respectively) in the forested coastal belt of Transkei and have relatively small estuaries (5 and 2 km long, respectively). Although the annual rainfall is in excess of 1000 mm in this area, the mean annual runoff was less than 70 Mm³ in both cases. Serious floods were not observed during the survey period, while turbidity and sediment loads were usually very low. Salinities were usually high (x? = 30,0-38,0‰) in the bottom water and temperatures in the upper reaches were usually higher than in the lower reaches. The species composition, and seasonal and spatial abundance of the fish fauna of the two estuaries were determined by means of gill nets. A total of 1043 fish (385,8 kg) representing 42 species were caught in the Mntafufu estuary. The orangemouth glassnose Thryssa vitrirostris and V. cunnesius were the most abundant fish in the estuary. Numerically 42% of the catch (46% gravimetrically) belonged to the family Mugilidae (11 species) of which Mugil cephalus, Valamugil buchanani and V. cunnesius were the most important. A total of 389 fish (241,1 kg) were caught in the Mzamba estuary. Twenty-five species were obtained with Hilsa kelee dominating numerically. Seven species of mullet contributed 38,3% of the numbers or 54,2% of the fish biomass. The diamond mullet (Liza alata) and the flathead mullet (Mugil cephalus) were the most abundant in terms of biomass. The highest catches in the two estuaries were taken in the lower reaches. Mean number and biomass of fish taken per net was 20,5 fish and 7,2 kg, and 16,2 fish and 10,1 kg in the Mntafufu and Mzamba estuaries, respectively.     

Shallow-Water Trawling Off the Swartkops Estuary,Algoa Bay

Juvenile fish occurring in Algoa Bay off the mouth of the Swartkops estuary were collected using a 3-m beam trawl. Pomadasys ollvaceum, Engraulis capensis, Caffrogoblus agulhensls, Argyrosomus hololepidotus and Galeichthys feliceps were the most abundant species in the trawl catches. Despite the proximity of the Swartkops estuary the trawls failed to capture species which are abundant as Juveniles in the estuary and it is concluded that the estuary has little influence on the juvenile fish fauna outside the mouth.     

Fish community structures in Zostera and Non-Zostera regions of the Kromme estuary,St Francis Bay

Comparative seine netting for fish was performed quarterly during 1981 in the Zostera and non-Zosfera regions of the upper middle reaches of the Kromme estuary. Twenty-four fish and three crustacean species were recorded. The catches were dominated by the following species: Liza dumerili, Glossogobius glurus and Gilchristella aestuarius (Pisces). Only two fish species (Monodactylus falciformes and Rhabdosargus holubi) were recorded in significantly (P<0,05; P<0,05 respectively) higher numbers in the Zostera than in the non-Zosfera regions and community analyses (comparing numbers, species richness and diversity) revealed no significant (P>0,05) differences between the catches from the two regions. These results are contrary to findings of most other researchers and possible reasons for these differences are discussed.     

Seasonal Abundance Distribution and Catch Per Unit Effort of Fishes in the Swartkops Estuary

Catch per unit effort was obtained for the nekton of the Swartkops estuary near Port Elizabeth by means of gill netting. Fifty gill net catches were made in which 1 269 fish were caught in areas representative of the mouth, middle and upper reaches of the estuary. Pomadasys commersonni, already shown to be the most abundant angling species in the estuary, dominated gill net catches both in terms of mass (29%) and numbers (17%). The family Mugilidae (five species) comprised 25% of the mass and 42% of the numbers caught. Environmental factors and availability of food that might determine distribution offish in the estuary are discussed. The largest mean mass per individual was found in Chanos chanos (4 473 g), Elops machnata (1 656 g) and Valamugil buchanani (1 580 g). Lowest mean masses were recorded for Monodactylus falciformis (63 g), Rhabdosargus holubi (88 g) and Liza dumerili (94 g).     

Seasonal variation in the diet of Cape clawless otters (Aonyx capensis) in a marine habitat

Seasonal changes in the diet of Cape clawless otters Aonyx capensis feeding in the surf zone in False Bay, Western Cape Province, South Africa, were investigated by spraint (faecal) analysis. The most common prey species, during all seasons, was the Cape rock crab, Plagusia chabrus. The next most important prey species was the Cape rock lobster, Jasus lalandii, with the fish species Clinus superciliosus being equally important in winter. Other prey were fresh-water crabs, Potamonautes perlatus, octopus, Octopus granulatus, and 17 other species of fish, frogs and mammals. In winter and autumn the most important prey category was fish while in spring and summer, crustaceans were the most important. Diversity of prey was lowest in winter, increasing through the seasons from spring to autumn.     

Feeding ecology of major carnivorous fish from four eastern Cape estuaries

Stomach content analyses were performed on eight carnivorous fish from four eastern Cape estuaries. Dietary importance was assessed by using three unrelated methods and by combining them to determine the index of relative importance of each food item. It was attempted to relate the percentage of fish with food in the stomach and the feeding intensity to the abundance of the fish in a particular estuary. In general fish consumed more food in estuaries where they were more abundant. The few exceptions that occurred could indicate that a particular estuary was selected for purposes other than food availability eg. Tachysurus feliceps in the Krom estuary for spawning grounds or because of inter- or intraspecific competition for food eg. T. feliceps and Monodactylus falciform is in the Krom and Argyrosomus hololepidotus in the Gamtoos and Sundays estuaries. Similarity analyses showed resource partitioning. Predators such as A. hololepidotus, Elops machnata, Lichia amia and Platycephalus indicus preferred teleost fishes such as mullets and Gilchristella aestuarius, whereas the stomach content of Pomadasys commersonnl, T. feliceps and M. falciform is were dominated by Crustacea, particularly Upogebia africana. Most estuarine predators showed a diverse prey selection, but the food web was characterized by a high energy flow per pathway.     

The fish community of the berg river estuary and an assessment of the likely effects of reduced freshwater inflows

Data concerning the species composition, abundance and distribution of fishes inhabiting the Berg River estuary are presented and used to assess the value of the estuary to fish, and the likely eflects of reduced freshwater inflows. A total of 31 species was recorded, eight of which were classified as estuarine residents, 11 as marine estuarine-opportunists, six as marine stragglers and six were freshwater species. Liza richard- sonii, an opportunist, was the most abundant (54% N) and widely distributed species encountered during the winter and summer seine-net surveys. Three other species (all residents) contributed more than 10% of the total catch; Atherina breviceps and Caffrogobius nudiceps occurring most abundantly in the lower estuary, and Gilchristella aestuaria in the middle estuary. The low number of species compared with estuaries in other regions of the South African coast reflect a well-established marine biogeographical trend. The higher proportions ol resident species, entirely dependent species and partially dependent species suggest, however, that west coast estuaries may be more important to the fish that inhabit them than are estuaries in other regions. It is concluded that the fish community of the estuary is already suffering the effects of habitat degradation and that further reductions in freshwater inllows are not desirable.     

Abundance,Distribution and Species Composition of Fish Larvae in the Swartkops Estuary

A two-year quantitative survey of the ichthyoplankton of the Swartkops estuary has resulted in the identification of 17 larval fish. The ichthyoplankton was present through all months of the year, but was only abundant during the summer months (November-February). During both years sampled, thehighest densities were recorded in December. An attemptwas made to correlate the data with environmental parameters such as temperature, salinity and rainfall. The ichthyoplankton of the Swartkops is dominated by few species. The family Gobiidae (59,44%) and a clupeid species, Gilchristella aestuarius (31,12%), accounted for 90,56% of all the fish larvae sampled. The family Gobiidae were most common in the mouth and lower reaches of the estuary, while G. aestuarius dominated the mid- and upper estuary.     

Ecology of southern African estuaries Part XI. Mngazana: a mangrove estuary in Transkei

Mngazana is a rich estuary dominated by mangroves and containing a diversity of both invertebrates and fish. Its richness is mainly due to favourable physical conditions. The invertebrate fauna includes temperate, tropical, and subtropical species, predominating in the lower reaches, middle reaches and head respectively. The fish have affinities with the tropics in summer, while in winter many warm-temperate species increase in numbers. In comparison with the fauna of soft substrates, that of rocks has a higher percentage of stenohaline and estuarine forms, and a more restricted distribution. The rocky habitat in estuaries favours greater specialization with respect to salinity tolerance. A high percentage of the biomass of invertebrates in soft substrates consists of detritivores, and the biomass is related to the organic content of the substrate. Mangrove mud has the hlghest organic content and supports the highest biomass, but few species can tolerate the conditions there. Mangroves are probably the major primary producers in the system.     

Turbidity-induced changes in feeding strategies of fish in estuaries

The aim of this study was to determine the effect of turbidity on the feeding strategies of fish in estuaries. Three species representing different feeding guilds were selected for the investigation. These were Elops machnata (representative piscivore), Pomadasys commersonnii (a macrobenthivore) and Atherina breviceps (a planktivore). The stomach contents of these fish were examined from a clear and a turbid estuary and some experimental work was carried out on A breviceps to test the hypothesis that turbidity affects feeding behaviour. Turbidity was found to have no effect on size selection of prey, but feeding rate, particularly of visual predators, was reduced at higher turbidity levels. This was caused by a decrease in the reactive distance of the fish. It would appear that in order to optimize the aquisition of food under different turbidity conditions fishes have the ability to change their feeding strategies. Visual predators are more affected by turbidity than are macrobenthic feeders.     

Euryhaline zooplankton of the Sundays estuary and notes on trophic relationships

The euryhaline component of the Zooplankton in the Sundays River estuary was sampled monthly at 10 stations from August 1979 to April 1981. In deeper regions surface and near-bottom samples were taken (Stations 1-7) using WP2 nets. Shallow (< 2,0 m) stations were sampled in surface waters only. Water temperature ranged between 14-27 °C. A full salinity gradient was present and salinity stratification was well developed. Acartia longipatella was most abundant during winter and spring (maximum 73 300 m^-3) in the lower estuary. The interaction of temperature and salinity as factors regulating temporal and spatial distribution was evident, these factors also interacting in the water column owing to stratification. The pioneer copepod species, seudodiaptomus hessei, attained high abundance following floods or increased river inflow. Three species of mysid shrimps were common in the plankton in summer, each species showing clear zones of maximum distribution. Zooplankton standing stock (dry mass) ranged from < 10 mg m^-3 to 1 450 mg m^-3 In surface samples and < 10 mg m ^-3 to 8 275 mg m ^-3 in bottom samples. Contribution of mysids to standing stock was rarely less than 70% and often exceeded 90%. Differences in standing stock between surface and bottom samples were owing to behavioural differences between the Zooplankton species, particularly the mysids. Behavioural adaptations play an important role in the retention of the indigenous Zooplankton in the estuary. Aspects of trophic relationships are discussed and demonstrate the significance of the Zooplankton in the transfer of energy to higher trophic levels In this estuary.     

Ecology of southern African estuaries: Part XIII. The Palmiet River estuary in the south-western Cape

The Palmiet estuary is only 1,67 km in length, but has a relatively large catchment of 539 km². Rain falls largely during winter when it scours the estuary and widens the mouth, but by late summer the mouth narrows and, in some years, may close. The estuary never closes for more than a few months, and salinities are normal. The entire estuary has clear bottom water and high bottom salinities, but the surface waters are usually fresh and darkly stained with humic acid. This permanent stratification allows many marine species to penetrate the estuary.

Owing to the scouring in winter, the sediments are coarse, >98% consisting of sand and gravel, with a low organic content. In situ primary production is low, contributing only about one fifth of the organic material in the system, the rest being imported from the river and the sea. Species richness is low, only 28 species of invertebrates being recorded, but many of these occur in enormous numbers. Callianassa kraussi plays a crucial role, trapping fine particles around its burrows and locally enhancing the organic content of the sediments. Its faeces are an important vehicle for the concentration and turnover of organic matter.

Four of the 19 species of fish recorded breed in the estuary, the rest being represented largely by juveniles or small adults. Only three species occurred in the estuary year-round, the other species being absent during the period that the estuary is in flood.

Floods and a relatively high flow of river water are critical to keeping the estuary open. If, as proposed, a dam is built on the river, steps will have to be taken to ensure that the mouth is kept open. A related problem will be the reduction of organic material entering the estuary from the river and the sea.     

Prédation and prey selectivity by Argyrosomus hololepidotus (Osteichthyes: Sciaenidae) in south-eastern Cape waters of South Africa

Argyrosomus hololepidotus (kob) is a top predator in the shallow marine environment of the south-eastern Cape. There is considerable change in prey taken over the size range of predators examined (256-1701 mm). Young A. hololepidotus are planktivorous taking swarming mysids, but as they grow they become piscivorous, feeding on both pelagic and demersal prey associated with soft sediments. The pelagic cephalopod Loligo reynaudi is also taken by large specimens. Prey selection varies with locality and time of year. A field experiment in which the prey were compared with fish caught in a small-mesh net revealed a preference for some slow-moving demersal species. The length distributions of dominant prey species are given and these clearly show that larger prey are preferred by larger predators.     

Marine connectivity and fish length frequencies of selected species in two adjacent temporarily open/closed estuaries in the Eastern Cape Province,South Africa

The effects of timing, frequency and duration of mouth opening and marine overwash events on fish assemblages in two, adjacent temporarily open/closed estuaries were investigated. Sampling was conducted biannually over two years during summer and winter, using selective sampling gear to target estuarine-associated marine species. During this period the East Kleinemonde Estuary opened more frequently than the West Kleinemonde Estuary and it also experienced a greater number of bar overwash events when larval recruitment can occur. The timing of mouth opening and the frequency of marine overwash events did not influence species richness of marine-spawning species but had a pronounced effect on abundances (catch-per-unit-effort) of species. The species composition of both estuaries was similar, but the catch-per-unit-effort in the East Kleinemonde Estuary was more than three times greater than that of the West Kleinemonde Estuary. The East Kleinemonde also supported a greater proportion of immature individuals of Rhabdosargus holubi and Monodactylus falciformis, and the length frequency distributions of both these species differed significantly between the two estuaries. The larger fish sizes in the West Kleinemonde Estuary were attributed to the prolonged mouth closure that resulted in the trapping of larger juveniles and mature fish within the estuary.     

‘n Vergelyking van wei‐ en voergewasse vir die produksie van slaglammers in die Pretoria‐ Witwatersrand‐Vereeniging(PWV)‐gebied

A comparison of pasture and fodder crops for the production of slaughter lambs in the Pretoria‐Witwatersrand‐Vereeniging (PWV) area. A number of pasture and fodder species were evaluated for the production of mutton with weancr lambs. Animal performance and meat production under three stocking rates, which were classified as light, medium, and heavy, were obtained with the aim of identifying best pasture/fodder for every season. The pastures/fodders included were Lolium multiflorum cv. Midmar and Triticum X Secale pastures under irrigation, Avena sativa and Vicia dasycarpa pasture mixture and maize crop residues under rainfed conditions, and Medicago sativa and Digitaria eriantha hay for the winter months. The spring pastures were L. multiflorum cv. Midmar, Lolium perenne cv. Nui and Dactylis glomerata cv. Hera under irrigation, while the summer pastures included Digitaria eriantha var. eriantha and M. sativa cv. Cuf 101 pastures under rainfed conditions and Cynodon dactylon cv. NK37 under irrigation. Of these, the midmar pasture for the winter and spring, maize crop residues for the winter, Hera for the spring and Cuf 101 for the summer seemed to be the best pasture of those tested in their season of use, from an animal production point of view.     

Habitat use and demography of Mus musculus in a rural landscape of Argentina

The main goal of the paper was to determine the habitat distribution of the house mouse (Mus musculus) within a rural landscape of Buenos Aires province, Argentina. We also studied the seasonal variation in abundance and reproductive activity. The habitats studied were poultry farms, human houses in a small village, cropfields, pastures, cropfield and pasture edges, riparian habitats (streams), railway embankments and woodlots. We captured 817 M. musculus and 690 individuals of 5 native rodent species. M. musculus was captured in poultry farms, houses, riparian habitats, cropfield and borders, but it showed a significantly higher abundance in poultry farms compared to the other habitats. Its presence outside poultry farms was significantly related to the distance to streams and poultry farms. The mean trapping success index of M. musculus did not show significant variations between periods, but the proportion of active males was significantly higher in the spring–summer period than in the autumn–winter period. All captures of M. musculus in cropfields, borders and riparian habitats occurred in the spring–summer period. The capture of M. musculus in many types of habitats suggests that it can disperse outside poultry farms, and streams may be used as corridors.     

Seasonal changes in digestibility, passage rate and rumen fermentation of alfalfa hay in sika deer (Cervus nippon) under restricted feeding

To investigate seasonal variations in the digestive functions of sika deer, five female sika deer were provided with an amount of alfalfa hay cubes equivalent to voluntary food intake during winter. We measured the rate at which the food passed through the digestive tract, digestibility and rumen fermentation during the summer (August), autumn (November), winter (February) and spring (May). Total mean retention time in the digestive tract during summer and autumn was numerically longer than that in winter and spring, but the difference did not reach significance. Organic matter and fiber were less digestible in summer and autumn than in winter and spring (P < 0.05), whereas the digestibility of the dry matter tended to vary with the seasons (P < 0.1). Ruminal pH values seasonally changed (P < 0.01), and were the lowest in autumn. The concentration of ruminal ammonia‐nitrogen differed significantly among the seasons (P < 0.05), increasing in winter and decreasing during spring and summer. The numbers of protozoa changed significantly among the seasons (P < 0.05), being higher in autumn than in winter and spring, and intermediate in summer. The concentration of total volatile fatty acids was not seasonally affected, but the molar percentages of propionic acid and butyric acid significantly changed according to season (P < 0.05 and P < 0.01, respectively), and the ratio of acetic to propionic acid tended to change with the seasons (P < 0.1). The results of this study suggested that the digestive functions in sika deer, fed a commercial diet at a restricted level, differed notably among the seasons and these variations might partially be due to environmental effects.