OpenUCT :: Browsing by Subject "Applied Marine Science"

Browsing by Subject "Applied Marine Science"

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Open Access
Ancient stonewall fish traps on the south coast of South Africa : documentation, current use, ecological effects and management implications
(2006) Kemp, Lucy Valeska; Branch, George M; Attwood, Colin
Ancient intertidal stonewall fish traps are found world-wide and those along the SouthAfrican south coast are the focus of my thesis. These fish traps, known locally as 'vywers', have recently enjoyed much media attention as interest increases in both South Africa's cultural heritage and its diminishing fish stocks. Two pioneering studies, by Goodwin (1946) and Avery (1975), provided the only documented knowledge of these vywers. My study aimed to locate, survey and document the main concentrations of vywers within a 300-km stretch along the south coast. A total of 43 sets of vywers was located by aerial surveys, 30 of which are only accessible through private land. This affords them some measure of protection, together with five located off reserves, but diminishes their educational and tourism value. Four sets of vywers were mapped in detail using aerial photogrammetry, a method that provided a rapid, extensive, accurate survey record in the form of geo-rectified ortho-images of these sites. The vywers are built in both exposed and sheltered environments, constructed from in situ rock material built into walls with either angular or curved shapes. These walls may occur singularly or in complexes of up to 25 traps. Vywers are prone to decimation by wave action and storm damage and so require maintenance to retain their characteristic form and associated cultural information. Tensions have, however, arisen between those who maintain and fish the vywers, and fisheries managers. Data from a questionnaire survey compared with records from the literature showed that species composition has not changed significantly in the last five decades. The fish are caught most frequently during new-moon spring-tides, especially in the winter months. The vywer fishery, currently active at only two sets of vywers, targets primarily mullet species (mostly Liza richardsonii) but infrequently enjoys 'bonanza' catches of over-exploited linefish stocks such as galjoen Dichistius capensis. It is these latter catches that concern managers, in addition to the noncompliance of fishers in terms of catch composition and size, permits and gear.
Open Access
Application of the sequential t-test algorithm for analysing regime shifts to the southern Benguela ecosystem
(2007) Howard, James A E; Moloney, Coleen; Jarre, Astrid; Clark, Allan
Long-term ecosystem changes, such as regime shifts, have occurred in several marine ecosystems worldwide. Multivariate statistical methods have been used to detect such changes, but they have to date not been applied to the southern Benguela ecosystem. A weakness of many of the methods is that they require long time series data and do not provide robust results at the end of time series. A new method known as the sequential t-test algorithm for analysing regime shifts (STARS) is applied to a set of biological state variables and environmental and anthropogenic forcing variables in the southern Benguela.
Open Access
Are distinct particle spectra an indication of the state of the phytoplankton community in St Helena Bay?
(2012) Crichton, Murray; Hutchings, Larry; Jarre, Astrid
The potential of phytoplankton particle spectra to be used as the basis for an indicator of the suitability of feeding habitat for fish recruits in the Southern Benguela was investigated. Phytoplankton samples collected on regular cruises on the St Helena Bay Monitoring Line (SHBML) off Elands Bay on the west coast of South Africa had been analysed with the Coulter Counter and formed the basis of this study. Chlorophyll a content of phytoplankton samples was also measured on monthly cruises and with total particle concentration (determined by the Coulter Counter) showed that overall phytoplankton cells represented a significant portion (76%) of samples collected. Surface particle spectra were constructed for the 12 stations on the SHBML for each of 15 monthly cruises between September 2000 and February 2007.
Open Access
Assessment of a pond for oyster hatchery development in South Africa
(2015) Simmons, Aron; Jackson, Sue; Bolton, John J
This study assessed a man-made salt-water pond (saltwater pond 1 SP1) as a potential site for the development of an oyster hatchery in Velddrif, South Africa. Over the study period it was observed that the site was not suitable for oyster larvae culture due to the following factors: temperature spikes during the summer months, low dissolved oxygen levels, high salinity levels, and the proliferation of the filamentous green algae (FGA), mainly the sp. Rhizoclonium implexum. Widespread patches of R. implexum were observed within SP1 and increased in biomass over the study period. Biomass patterns were not measured within this study, however microcosm experiments directed at nutrient depletion rates caused by FGA proliferation assessed the effect of the FGA on the system. Within microcosm experiments with and without FGA, nitrite within the system was significantly lower in the FGA inclusion treatment. Pond nutrient dynamics within the system indicated that widespread nutrient depletion occurred between the incoming water and the rest of the pond, and it was clear that the inflow station had significantly higher nutrient concentrations than all the other stations within SP1. Phytoplankton concentrations were extremely low and could be attributed to the FGA dominated state within SP1. Taken together with the fact the water levels within SP1 were not stable, the data suggested that SP1 was not an optimal source of seawater for either algal or larval oyster culture, and an alternative oyster hatchery site should be assessed.
Open Access
Baited remote underwater survey of chondrichthyans in False Bay, South Africa
(2013) Watson, Ralph Gareth Andrew; Attwood, Colin
Worldwide, numerous shark populations are in rapid decline due to chronic overfishing. Their slow reproductive capacity make them susceptible to extinction. To monitor the status of chondrichthyan species, the method or combination of methods used should be non-selective, applicable in a variety of habitats and under most environmental conditions. Baited Remote Underwater Video (BRUV) surveys have shown major benefits over traditional capture-based survey methods in multiple areas. They have been shown to be non-extractive, causing no major disturbance to the substrata and its epibenthos. Large, mobile animals that avoid divers and active fishing surveys are detected. The recorded video removes the need for specialist observers to conduct all the fieldwork. The video allows impartial and repeatable measurements and standardizes data collection and training in association with remote taxonomists. The method is also cheaper than alternatives. Ninety-five sites were sampled with 60 minute video recordings across the whole of False Bay during the period of June-July 2012. Fifteen species of chondrichthyans were recorded, of which Haploblepharus edwardsii was the most abundant, being observed at 83 of 95 sites. One hour was sufficient to capture all the chondrichthyans within the observed area as the average time of arrival was about half an hour into the recording. The distribution of the chondrichthyan population was remarkably uniform across the bay. Depth, habitat and substrate type were significant predictors of species composition (P = 0.004, 0.025 and 0.001 respectively). Opportunistic encounters (one individual observed) included Carcharodon carcharias, Squalus megalops, Rhinobatos annulatus and Myliobatis aquila.
Open Access
The biology and macroparasites of the sixgill sawshark Pliotrema warreni
(2017) Foor, Brandon; Attwood, Colin; Reed, Cecile C
Thirty-two specimens of the sixgill sawshark, Pliotrema warreni, were trawled near Bird Island in Algoa Bay on the Eastern coast of South Africa in April and May 2015. The specimens were examined for anatomical proportions, reproductive characteristics, diet, and parasite assemblages. Several external measurements were collected including mass, total length, standard length, girth, rostrum length, interoccular to pre-caudal length, first dorsal origin to second dorsal origin, first dorsal origin to pre-caudal origin, and mouth width. The equation for mass (g) vs. total length (mm) was ln(Mass)=0.2997*ln(TL)+2.0383 for females and ln(Mass)=0.3321*ln(TL)+1.941 for males. 1st Dorsal to 2nd dorsal origin length (DD) to total length equations for females and males were DD=0.2451*TL-26.677 and DD=0.2598*TL-34.535, respectively. Mean lengths and masses were 11.5% greater and 50.3% heavier in females than males, respectively. Females were on average, 994 mm (759 mm – 1283 mm) in length while males were 891.8 mm (763 mm – 1015 mm). Average mass for females was 1702.5 g (602.5 g – 3478.5 g) whereas males it was 1132.6 g (687 g – 1593.5 g). Based on these data both sexes display isometric growth. Males were determined to reach sexually maturity around 850 mm which is similar to that reported by Ebert et al., (2013) around 830 mm. Females were found to reach sexual maturity at 1000 mm which is 100 mm smaller than what is reported by Ebert et al., (2013). Stomach mass increased with total mass and total length regardless of sex (female R² = 0.507; male R² = 0.213 for length and female R² = 0.6123; male R² = 0996 for mass). Females consumed larger prey items in terms of mass and length as well as a higher quantity of prey than males presumably because they are the larger sex and have an increased need for nourishment to provide for pregnancy. Prey items were redeye round herring, Etrumeus whiteheadi (64.96% of the diet), a benthic shrimp species not identified (7.69%), and Cape horse mackerel, Trachurus trachurus capensis (0.85%). Despite strict adherence to the guidelines for age determination for elasmobranchs provided in the literature, the conventional method used which involved extensive cleaning of the vertebral centra with an array of chemicals, setting and cutting in an epoxy resin, and staining for microscopy, did not yield readable results which could be used to determine the ages of these sharks. The highest abundance of parasites were found in the stomachs. Three specimens of a cymothoid isopod was found externally. Two specimens of Ascaris sp. nematode were found in the visceral cavity. The remaining 18 parasites consisted of three Neoechinorhynchidae sp. of acanthocephalan and 15 Proleptus obtusus nematodes all of which were found inside the stomachs. Given the results of the parasite survey, males and females do not have the same parasites as females have four different species while males only have one. More collections from other areas and times of year are necessary to obtain a better description of the species.
Open Access
Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records
(2015) Reed, Jodie Romay; Attwood, Colin; Kerwath Sven
The South African midwater trawl fishery targets adult horse mackerel (Trachurus capensis) on the Agulhas Bank. The bulk of the catch is taken by a single midwater trawler. The bycatch of this fishery is investigated by analysing observer records from 2004 to 2014 to report on bycatch composition, volumes and temporal and spatial patterns. Small fauna were analysed by extrapolation of sample weights and large fauna were counted. The midwater trawl fishery was estimated to have caught 25 415 t annually, with a bycatch rate of 6.9% of the total catch, by weight. Bycatch species with the highest average annual catches were chub mackerel (Scomber japonicus), redeye roundherring (Etrumeus whiteheadi), ribbonfish (Lepidopus caudatus) and hake (Merluccius spp.). Large fauna bycatch species included Cape fur seals (Arctocephalus pusillus), sharks (15 species), sunfish (Mola mola) and cetaceans (two species). Temporal analysis revealed significant differences between day-time and night-time CPUE for nine species, and significant differences in seasonal CPUE for 17 species. Spatial analysis of small fauna species composition and of large fauna species composition identified three groups in each. The 100% observer coverage is high compared to other South African fisheries, and, although the average sampling rate of 1.56% is low, an increase in the sampling rate might not be feasible owing to the size of catches. The bycatch rate in this fishery is low compared to other South African trawl fisheries but similar to global midwater trawl bycatch rates. There are species overlaps with various fisheries, namely the demersal trawl, small pelagic, linefishery, shark longline and squid fisheries, yet the total catch estimates from this fishery are generally small relative to catches taken in the target fisheries.
Open Access
Characteristics of extreme wave events and the correlation between atmospheric conditions along the South African coast
(2004) Van der Borch van Verwolde, Emile; Brundrit, Geoff; Moes, Hans
Characteristics of extreme wave events along the coast of South Africa were researched through a dataset obtained by CSIR wave recording network at four locations. The locations from west to east are Slangkop, FA-Platform (Agulhas bank), East London and Richards Bay. The longest dataset available was the 25-year dataset at Slangkop measured by accelerometer wave buoys. In the subsequent years the wave recording network along the South African coast was expanded to six locations at present.
Open Access
Community composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Ocean
(2015) Annasawmy, Pavanee; Moloney, Coleen L; Menard, Frederic; Ternon Jean-Francois; Potier, Michel
Micronekton fauna was investigated as part of a multi-disciplinary research project carried out in two different bioregions of the South West Indian Ocean: the East African Coastal Province (EAFR) and the Indian South Subtropical Gyre (ISSG). Food web structure was addressed using stable isotopes. Since particulate organic matter had high δ 15 N values in the ISSG province, copepods were chosen as baseline in trophic level estimations. Feeding regime and size were shown to influence the trophic position of micronekon. In the ISSG, carnivores (fishes and squids) and omnivores (crustaceans) had higher δ 15 N values and trophic positions than filter feeder s (gelatinous organisms such as salps and pyrosomes) and detritivores (leptocephali larvae). Fishes and squids encompassed a wide range of overlapping isotopic niches suggesting that organisms across different trophic levels feed on the same resources. Estimated trophic levels ranged from 1.67 to 4.73, showing that micronekton in the ISSG can be tertiary consumers. An average enrichment value of 6.7 ‰ was recorded between the sampled micronekton specimens and swordfish Xiphias gladius in the ISSG. Trawls, being selective in nature, were shown to sa mple smaller - sized micronekton with a lower trophic position than the micronekton being eaten by swordfish. In the EAFR, mean δ 15 N values of micronekton were higher than in the ISSG, exhibiting slightly higher trophic levels. Mesoscale dynamics in the EAFR provide mechanisms that enrich surface layers in nutrients and chlorophyll - a, therefore contributing to a higher abundance and micronekton species richness. In the ISSG, the large - scale wind - driven anticyclonic gyre pushes the nitracline, thermocline and deep chlorophyll maximum deeper in the water column , influencing the diel migration patterns of micronekton , with a significant proportion of micronekton staying in deep layers or slightly above the thermocline at dusk . Regardless of the differences in the ISSG and EAFR in δ 15 N values and trophic positions of micronekton, larger - sized swordfish sampled from these two provinces had similar mean δ 15 N values since swordfish are highly migratory and forage in different p arts of the Indian Ocean. However, smaller - sized swordfish specimens had lower mean δ 15 N values. With a combination of trawl surveys, stable isotope estimates, stomach content and acoustic analyses, this study shed new light on trophic interactions in the oligotrophic ISSG province.
Open Access
Comparative age and growth of juvenile dusky kob (Argyrosomus japonicus) in three South African estuaries, with notes on diet and temperature effects
(2003) Mafwila, Samuel Kakambi.; Govender, Anesh; Griffiths, M H
The dusky kob Argyrosomus japonicus is an important commercial and recreational linefish species in South Africa. It has a wide distribution range from Cape Agulhas to the Mozambique border. Juveniles A. japonicus <1070 mm) occur inshore and in estuaries where surf-zone and estuarine anglers target them. Adult A. japonicus (> 1070 mm) are caught beyond the surf zone by line fishermen. In this study, 380 juvenile dusky kob were caught by hook and line from the Breede River, Fish River, and Keiskamma River estuaries. Age of juvenile A. japonicus in these three South African estuaries was estimated by counting growth rings in sectioned sagittal otoliths read under a dissecting microscope using reflected light. The reproducibility of otoliths readings was described by the average percentage error (APE) index and was found to be 0.44% (Breede), 2.78% (Fish), 0.25% (Keiskamma) for an experienced reader and 0.5% (Breede), 4.37% (Fish), 0.53% (Keiskamma) for an inexperienced reader. Comparisons of A. japonicus otoliths by an experienced and an inexperienced reader indicated a reasonable between-reader consistency, however, the otoliths from the Fish River estuary were more difficult to read than from the other two estuaries. The Schnute growth model was used to determine which sub-model would best describe the growth of juvenile A. japonicus. Linear regression lines were fitted to the age-at-length growth curves of juvenile A. japonicus for each estuary to determine whether there were significant differences in growth rate. It was found that growth was the highest in the Breede River estuary (113.7 mm/yr), followed by the Keiskamma River estuary (92.1 mm/yr) and the Fish River estuary (83.9 mm/yr). Variable growth rates of juvenile A. japonicus in the three estuaries may be related to food availability and prey item types and to a lesser extent to water temperature in the estuaries. The comparisons of estuarine diets of A. japonicus indicate that juvenile dusky kob in different estuaries have different dominant prey species. There were one or two taxa dominant in each estuary with Galeichthys feliceps (61.9%), and the mysids (71.8%) being the most important prey items in the Breede River and the Great Fish River estuaries respectively, while teleost Pomadasys commersonnii (73.8%) were the most important prey species in the Keiskamma River estuary.
Open Access
Comparative dietary analysis of four small pelagic fish species from presumed mixed shoals off South Africa's east coast
(2008) Mketsu, Qayiso K; Moloney, Coleen; Van der Lingen, Carl D
Stomach contents of sardine (Sardinops sagax), anchovy (Engraulis encrasicolus), west coast redeye (Etrameus whiteheadi) and east coast redeye (E. teres) were collected from presumed mixed shoals off South Africa's east coast. The stomach contents were analysed to 1) determine the diet composition of each species in terms of dietary carbon, 2) assess whether resource partitioning by prey type and/or prey size occurs amont the four species, 3) compare results with what is known about the diet of these species on the west and south coasts of South Africa and 4) characterize diet of east coast redeye.
Open Access
Comparing estimates of zooplankton abundance from CUFES samples with those from a vertical bongo net
(2008) Sono, Sandisiwe; Moloney, Coleen; Van der Lingen, Carl D
The accuracy of using CUFES (continuous underway fish egg sampler) as an alternative method to vertical bongo nets for sampling zooplankton abundance and distribution is assessed. Analysis is based on 14 taxonomic groups representing a wide variety of organism sizes. Samples were collected in March 2004 in the southern Benguela, South Africa. In total, 64 CUFES samples were collected while the ship was underway and 32 CUFES and vertical bongo net on-station samples were collected along four inshore-offshore transects. The frequencies of obtaining the taxa using the CUFES and vertical bongo net samples were the same for small copepods, amphipod adults and juveniles, and Nannocalanus.
Open Access
Development of a quality index method (QIM) scheme and its implementation in a shelf-life study of kingklip (Genypterus capensis)
(2003) Gebremariam, Thomas W; Graz, Michael; Griffiths, Charles L
In this study Quality Index Method (QIM) schemes for raw headed and gutted (H&G) fish and skinless fillets as well as cooked fillets of kingklip (Genypterus capensis) were developed in a shelf life study. The QIM schemes for raw H&G and skinless fillets are based on six and seven quality attributes respectively, with a scoring system from 1 to 6, where a score of six is best quality (perfect). For the case of cooked fillets the scheme is based on six attributes, with a scoring system from I to 5, where a score of five is best quality. Sensory analysis of cooked fillets was carried out parallel to sensory analysis of raw H&G and skinless fillets as well as microbial count study until 18 days of storage. These were used to decide the maximum storage time in ice and to observe how the different quality attributes of cooked fish, especially odour and flavour, deteriorated with storage time in ice, as they are the best symptoms of fish spoilage. However, the microbial count study alone was continued until 22 days in ice in order to follow the bacterial spoilage pattern with storage time.
Open Access
The diet and foraging ecology of chick-rearing gannets on the Namibian islands in relation to environmental features : a study using telemetry
(2006) Dundee, Benedictus Lissias
GPS telemetry in conjunction with a recent diet time series and historical dietary informationwas used in this study to obtain novel insight into the dietary trends and feeding ecology of Cape gannets Morus capensis on the Namibian islands. particularly Ichaboe and Mercury. The gannet diet has changed substantially since the 1950s. refiecting spatio-temporal changes in the availability of commercially important pelagic prey species. The more recent diet time series for Ichaboe Island (Nov 1995 to Feb 2004) showed that trawler scavenged hakes Merluccius spp and naturally foraged saury Scomberesox saw'us dominated the diet by both contribution to mass (35 and 34 %, respectively) and frequency of occurrence (34 and 25 %, respectively). In a significant contrast, juvenile horse mackerel Trachurus trachurus capensis (40 % mass, 26 % frequency) and juvenile snoek Thyrsites atun (20 % mass, 20 % frequency) were the two main prey species at Mercury Island during Oct 1996 to Feb 2004. Multivariate analysis of data showed significant time and site effects in diet composition between Ichaboe and Mercury for the period Nov 1996 to Mar 1999. Twenty-five and 15 GPS field deployments were made on birds at Ichaboe and Mercury, respectively, during the 2003/4 breeding season. Birds from both locations showed significant differences in their foraging patterns. Birds from Ichaboe had shorter foraging trips (24.3 hrs vs 29.4 hrs),traveled shorter distances away from their island (130 km vs 197 km) and had shorter foraging path lengths (422 km vs 673 km). Birds from Ichaboe foraged in two dominant directions: west. to obtain mainly scavenged fish offal, and north to obtain forage fish. Mercury birds foraged only north, overlapping their foraging zone with birds from Ichaboe in a northerly direction, between 25.8° Sand 24.4° S. Birds at all colonies - especially in the south - appear to be constrained by lower quality food and generally poor feeding conditions which seem to be a limiting factor.
Open Access
Diet of the Tristan rock lobster Jasus tristani following the 2011 soya spill at Nightingale Island
(2017) Jones, Luke; Blamey, Laura K; Branch, George M; De Lecea, Ander M
The spiny lobster Jasus tristani inhabits the Tristan da Cunha Island archipelago in the South Atlantic Ocean 2,400km from the West coast of South Africa. It is commercially exploited across the archipelago and is the main economic source of income for the local government as it accounts for nearly 80% of the local gross domestic product. The commercial rock lobster industry was established in 1949, and the fishery is currently recognised as sustainable, and as a result was awarded a Marine Stewardship Council Certification in 2011. That same year however, the sinking of the OLIVA at Nightingale Island spilt 60,000 tonnes of soya beans (Glycine max), greatly affecting the local benthic environment, and with probable consequences for the local food web, including the diet of J. tristani. It is still unclear whether the soya beans are still on the seafloor at Nightingale Island as there have been no scientific surveys conducted since the spill. Using samples from 2015, I assessed whether the diet of the lobsters from Nightingale Island differs from that of lobsters from the unaffected Tristan and Inaccessible Islands, and whether there is any evidence of soya in the diet of the lobsters from Nightingale Island. In addition, I examined whether diet differed between lobsters of small or large size, and between shallow and deep depths. In total, 540 lobsters were sampled across the three islands, and a combination of gut content and stable isotope (SI) analysis was conducted to assess the dietary components of the lobsters. Gut fullness was significantly less at Nightingale Island suggesting there may be less food available on the reef. Statistical analyses showed that diet differed between all islands, depths and sizes, although this was difficult to ascertain from visual multidimensional scaling plots as diet showed considerable overlap and variability both within and between islands, depths and sizes. The stable isotope analysis showed significant differences in nitrogen levels among the three
Open Access
Distribution and predictors of non-indigenous marine species within South Africa's MPA network
(2016) Brooker, Ben; Robinson, Tamara; Moloney, Coleen L
Considering the continual dissemination of marine non-indigenous (NIS) species across biogeographic borders, little is known about the status of these species within the network of South African marine protected areas (MPAs). Using the most recent data, a target list of NIS was set up for each MPA. Nineteen of the 23 South African MPAs were surveyed intertidally for alien and invasive species. The intertidal zone was divided into high-, mid- and low-shore and surveys were conducted during spring low tide. The presence and location in the intertidal zone of alien and invasive species were recorded. Additionally, invasive species' biomasses were quantified at sites at which they were found. Classification and regression tree (CART) analysis was used to assess which factors result in high numbers of NISs within MPAs. The invasive Mediterranean mussel, Mytilus galloprovincialis, was the most widespread species, occurring in 13 of the 19 sampled MPAs. It was most prominent on the island MPAs of the West Coast National Parks and had an overall highest biomass in the mid-shore. The bryozoan, Bugula dentata, was also widespread - present in MPAs across all three ecoregions. The invasive acorn barnacle, Balanus glandula, and bisexual mussel, Semimytilus algosus, both exhibited high levels of invasion in MPAs on the west coast. Extensions of known ranges were recorded for a number of species: the bryozoans Bugula dentata, Watersipora subtorquata and Cryptosula pallasiana, the polychaete Neodexiospira brasiliensis, the amphipod Orchestia gammarellus and the hydrozoan Obelia dichotoma. Certain species were recorded outside of harbours for the first time: the hydrozoans Obelia dichotoma and Obelia geniculata, the bryozoan Cryptosula pallasiana and the ascidians Microcosmus squamgiger and Diplosoma listerianum. CART analysis indicated that the size of the nearest port was an important indicator of the number of alien species in an MPA. When the nearest port is bigger than 0.4 km², more alien species are likely to occur within that MPA. For invasive species, the distance to the nearest yacht marina was the most important factor, with MPAs within 3.7 km of a yacht marina being more likely to have more invasive species in their borders. For all NISs, the highest numbers in an MPA were expected when the nearest port was greater than 2.1 km² and the nearest yacht marina was within 3.7 km of that MPA. Using these findings, spatial planning of future MPAs can further be prioritised to minimise the risk of introduction and spread of NIS therein. MPAs at risk as defined by these findings require structured monitoring regimes. A proactive measure would be establishing an interdisciplinary forum between relevant management authorities in order to enable dissemination of information on NIS. While controlling established NIS is difficult, the creation of task groups to act as rapid response teams for NIS, and the possibility of small-scale fisheries from edible invasive species are practical avenues that could be explored as mitigation efforts.
Open Access
Ectoparasites of the southern mullet Liza Richardsonii in the Berg Estuary, South Africa
(2004) Van Praag, Alex; Smit, N J; Griffiths, Charles L
The aims of this study were to observe changes in ectoparasite abundance and diversity on fish in relation to salinity gradients in the Berg Estuary. The host species studied was the commercially important, euryhaline southern mullet Liza richardsonii that is superabundant in estuaries of the Western Cape. A total of 210 fishes were sampled by using a single haul with a beach seine net at each of seven localities along a salinity gradient from the mouth to the upper reaches. Seven species of parasite were found. These included five species of Copepoda; a member of the family Caligidae, an Ergasilus species, a Dermoergasilus species, a Brachiella species and an unidentified caudal fin parasite. Two representatives of the Monogenea were found, one from the family Microcotylidae and another that was not identified.
Open Access
The effect of quick freezing and fast thawing on stored seawater nutrient concentrations of dissolved inorganic phosphate, nitrate and ammonium
(2004) Wedeinge, Josef; Brundrit, Geoff; Waldron, Howard
In an attempt to improve the quality of preserving seawater nutrients for delayed analyses, a sample of unfiltered and aged nutrient-depleted seawater was obtained from Marine and Coastal Management (M&CM) and spiked with small different volumes of standard nutrient solutions. These were prepared into 100 mL glass bottles to constitute the lowest, intermediate and highest levels of dissolved inorganic phosphate (0.5, 1.5, 3.0 μM), nitrate (5, 15 and 30 μM) and ammonium (0.5, 1.5, 2.5 μM) that are found in the southern Benguela region. After spiking, the samples were analysed to determine their "true" initial concentrations and immediately quick frozen using liquid nitrogen. A time series analysis (up to seven weeks) was performed by first fast-thawing the samples using a microwave oven and fixing up the nutrients within 20 minutes. Variations in nutrient concentrations did not exceed 7% for phosphate, 4.0% for nitrate at all levels and 8% for ammonium at the intermediate and highest levels, but varied by 19.2% at the lowest level. Statistical tests for significance of the means were made at a = 0.05 level and no difference was found at any level for the nitrate, and the lowest level phosphate. The higher levels of phosphate, and all ammonium were found to be significantly different. Hence, the experimental conditions employed in this paper would not be recommended for the all ammonium and the higher levels of phosphate concentrations. These variations were however not large or regular in pattern but erratic, which suggested that they were not due to microorganisms and optimizing those conditions may well to yield improved results.
Open Access
Effects of cannibalism, maternal age and varying fish selectivity in age structured models of deep water hake populations
(2011) Koch, Erich; Moloney, Coleen L
An Age Structured Model (ASM) was develop in which dynamic and density-dependent cannibalism was included as a top-down control on a modeled population of M. paradoxus which used spawner biomass and maternal based recruitment. The ASM was used to evaluate the effects cannibalism had on age structure, recruitment and spawner biomass of the modeled population. The development of the model was described and evaluated with special emphasis on incorporating cannibalism and maternal based recruitment.
Open Access
The effects of the macroalga Gracilaria gracilis and increasing temperatures on the performance of the endemic Cape eelgrass Zostera capensis
(2017) Beltrand, Maeva Mereana Marion; Pillay, Deena
Rising temperature caused by global warming alters physiology, phenology and/or distribution in a wide array of plant and animal species, which has dramatic knock-on effects at different levels of organisation. This study investigates the individual and interactive effects of temperature (18ᵒC, 22ᵒC and 30ᵒC) and additions of the macroalga Gracilaria gracilis (high and low) on the performance of the seagrass Zostera capensis, which occurs in Langebaan Lagoon, South Africa over a seven-week period. Results from the laboratory experiment revealed that G. gracilis did not significantly affect the performance of Z. capensis although temperature did result in greater leaf width, fouling and senescent biomass, as well as marginally greater leaf area and lower below-ground biomass at 30ᵒC. Increasing temperature also increased G. gracilis biomass, percent cover and fouling by microalgae. In addition, there was no interaction between temperature and the additions of Gracilaria. The overall findings of this study indicate that Z. capensis abundance is likely to decrease while G. gracilis will conversely increase in abundance in response to warming. Changes in abundance of those two ecosystem engineers highlight the possibility of a phase shift from a seagrass- to macroalgal-dominated state in Langebaan Lagoon.