OpenUCT :: Browsing by Author "Moloney, Coleen"

Browsing by Author "Moloney, Coleen"

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Open Access
The abundance, distribution and accumulation of plastic debris in Table Bay, Cape Town, South Africa
(2013) Lamprecht, Annerie; Moloney, Coleen; Ryan, Peter G
Stranded debris and beach litter were examined at two sites in Table Bay, South Africa, repeating a survey made at the same two beaches in 1994. One beach (Milnerton) is a popular recreational beach 12 km from the city centre, whereas the other (Koeberg) is situated in a nature reserve, with limited access by the general public, and is 27 km farther from the city. Daily accumulation rates of manufactured items (>1 cm diameter) were measured at both beaches for ten days in October, November and December 2012. Of the 124,646 items collected, 93% were made of plastic, but these items comprised only 59 % of the total weight. There was generally consistent but large within-site variability in accumulation rate; the within-site coefficients of variation (CVs), which range from 23.7 % to 101.5 %, respond in the same way across months. There was also considerable daily variation (CVs range from 13.6 % to 92.8 %). The mean density of items decreased with distance from Cape Town. Since 1994, the composition, abundance and accumulation rate of debris has changed on these two beaches. The mean (s.e) accumulation rate of plastic articles at Milnerton increased 257 %, from 378 (72.3) plastic items.day-1.100 m-1 of beach to 1350 (126.7) items.day- 1.100m-1. The increase at Koeberg was from 44 (2.7) items.day-1.100 m-1 to 100 (17.3) items.day-1.100 m-1. Evidence of increased input during the peak holiday season (December) was recorded at both beaches. The mean accumulation rates of most materials had increased at Milnerton since 1994 and the composition of the materials had also changed. The non-plastics were numerically dominated by cloth, paper and wood in 1994 but cigarette butts dominated in 2012. In contrast, at Koeberg the accumulation rates of most non-plastic materials decreased since 1994 and there were small differences in composition. No correlation was found between total weights and total counts of plastic items on the beaches. Daily variability (accumulation rate and accumulating weight) was generally not correlated with weather conditions. Since 1994, the accumulation rate of small, unidentified plastic fragments increased by more than 200- fold at Milnerton and by a factor of 80 at Koeberg. To improve our understanding of the vertical distribution, abundance and composition of microplastics (articles < 10 mm), samples were taken at 5 cm depth intervals (0 to 25 cm) on Milnerton. The number of microplastics, sized 2 mm- 10 mm, found in each layer decreased with depth. Smallest plastic items (0.5 - 2 mm) were randomly distributed in the surface layers (top 10 cm) but had low densities in the bottom layers. Plastic pellets had the same decreasing trend with depth. Amounts of plastic litter have increased by two orders of magnitude over an 18-year period, reflecting both accumulation of plastic debris in coastal environments and increased use of plastics during the past decades.
Open Access
Acute and chronic effects of ammonia in the South African abalone, Haliotis midae Linnaeus (Mollusca)
(2006) Reddy-Lopata, Kasturi; Moloney, Coleen; Cook, Peter; Lopata, Andreas
Ammonia is the major end-product of protein catabolism in abalone, and is excreted into the surrounding water. Build-up of ammonia in abalone aquaculture systems can reach high toxic levels and impact negatively on farming operations. Ammonia levels therefore have to be regulated. Accurate estimates of toxic un-ionized ammonia (FAN) from the total ammonia nitrogen (TAN) measured by photometer test kits is crucial as inaccuracies could result in major losses of abalone on the farms. The accuracy and applicability of two frequently used photometer test kits (the Nesslers method and the Palintest method) were compared. The calculated TAN concentrations were regressed against the prepared standard ammonia concentrations in seawater for both methods. The predicted slope (β = 1) if the methods were 100% accurate was compared to observed slopes using the Nesslers (β=0.8327) and Palintest (β = 0.7507) methods. Both these test kits underestimated the TAN concentrations, but the Nesslers method was more accurate. Nitrites and nitrates are toxic to abalone at much larger concentrations than ammonia and exist at low concentrations in natural systems, therefore the sensitivity of their tests was not as important. Nitrites and nitrates were monitored using the Ferrous sulphate method and the Cadmium reduction method, respectively.
Open Access
Age, growth, reproductive biology and diet of Spondyliosoma emarginatum (Cuvier 1830) in the West Coast National Park, South Africa
(2005) Fairhurst, Lucinda; Moloney, Coleen; Attwood, Colin; Durholtz, Deon
Comprehensive morphometric measurements and counts, external colouration, reproductive behaviour and diet of steentjies (Spondyliosoma emarginatum) in Langebaan Lagoon were recorded between September 2004 and February 2005. Sagittal otoliths were extracted and age estimates recorded from both whole and sectioned otoliths in order to estmate growth and mortality parameters. A total of 302 steentjies (139-312 mm fork length) was sampled of which 243 were females, 55 were males and four were individuals with hermaphroditic gonads. Macroscopic and microscopic examination of gonads and monthly gonadosomtic indices suggest a spring spawning season and that steentjies are protgynous hermaphrodites with males significantly than females (t = 64.75, df = 301, p < 0.001). During the reproductive season, males develop a blue colouration. All males with this colouration had testes classified as either active or ripe and had significantly larger gonad masses than those without mating colours (U = 3.5, Z = 6.48, p $lt; 0.001). The length-at-50%-maturity for females was 171 mm (FL) and for males was 204 mm (FL). The size at 50% sex change was estimted as 250 mm (FL). Analysis of foregut contents showed steentjies to be opportunitistic ominivores, changing from plant to animal food as they age. The average percent error and coefficient of variation values for whole otoliths were 4.59% and 6.00% respectively, and 10.89% and 14.53% for sectioned otoliths. Although the result of the whole otolith study provided more precise age estimates, there was a strong indication of bias so the sectioned otolith results were used for calculating the growth model. Growth (by sex) was modelled using a model developed for sex changing sparids that allows for accelerated growth after sex change. Steentjies appear to have shorter life spans than most sparids; the oldest individuals sampled attaining less than 7 years of age. Growth rates appear to be relatively high. The smallest, youngest fish were all female, with males only present in the larger size classes. The estimated mortality for steentjies was 0.7y[-1]. Such a high mortality rate implies that further increase in fishing pressure on this species may not be sustainable in Langebaan Lagoon.
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
Assessing the effects of internal (trophic structure) and external (fishing and environment) forcing factors on fisheries off central Chile : basis for an ecosystem approach to management
(2008) Alarcón, Sergio Eduardo Neira; Moloney, Coleen; Cury, Philippe; Shannon, Lynne; Jarre, Astrid; Christensen, Villy
Human perception of sea fisheries has evolved from an inexhaustible resource paradigm towards a generalized concern on the degraded state of fish stocks and ecosystems. Accordingly, fisheries science and management are expanding from the traditional single-species approach towards an ecosystem approach to fisheries. Marine communities are organized as webs of interactions that are affected by external natural (climate) and anthropogenic (fishing) forcing, with their relative effects poorly known, but hypothesised to strongly depend on internal food web structure (i.e., who eats and controls whom). This thesis approaches relevant ecological considerations for an ecosystem approach to fisheries in the upwelling ecosystem off central Chile (33ºS-39ºS). The main objective is to assess the effects of internal (trophic structure) and external (fishing and environment) forcing factors at the fish stock and food web level in the study area. The methodology includes i) the construction of snapshot and dynamic food web models to test hypothesis of changes in the food web in the last century, and the relative contribution of fishing, trophic controls and bottom-up environmental variability to those changes, ii) the computation and analysis of a set of ecosystem indicators to test hypotheses of changes in different aspects of the exploited community (mean trophic level, age and length at maturity, network properties and system variability), iii) the analyses of the relationships between time series of abundance of species with known trophic interactions (Chilean hake-red squat lobster and Chilean hake-small pelagic fish) to test hypothesis of top-down and bottom-up control versus alternative hypotheses of fishing and/or environmental control in the same populations, and iv) simulation experiments to test hypotheses of ecosystem change and recovery under fishing and environmental forcing. Models and indicators are constructed using data series of abundance, catches, production, consumption and diets of the main functional groups in the study area. Snapshot and dynamic food web models are constructed and analyzed using the Ecopath with Ecosim software version 5.1 and routines therein. The observed trends in indicators and model results are in accordance with what is theoretically expected in stressed ecosystems (shift towards a food web dominated by short-lived, low trophic level and high turnover rate species), and suggest that the food web could be in a state that is more susceptible to external forcing. Fishing and the environment (bottom-up anomaly in PP) may have affected the upwelling ecosystem off central Chile both at the stock and at the food web level between 1970 and 2004. The effects of these forcing factors may have been mediated by trophic controls operating in the food web. There is also evidence to support the hypothesis that trophic controls beyond fishing, e.g., trophic (internal) and environment (external) may operate in the analysed populations and this information should be considered in their assessment and management. While target objectives are set and agreed, it is proposed that the main objective for the ecosystem approach to fisheries should be to avoid fishing-induced regime shifts, since results from simulation experiments suggest that fishing can induce ecosystem changes of lower recovery than bottom-up forcing.
Open Access
Characterizing and comparing the spawning habitats of sardine (Sardinops sagax) and anchovy (Engraulis encrasicolus) in the northern Benguela region
(2008) Tjizoo, Mbeurora Beau; Moloney, Coleen; Van der Lingen, Carl D; Kreiner, A
Spawning habitats of sardine and anchovy in eastern boundary systems are characterized in an attempt to understand the fluctuations observed in their abundance. These species have developed mechanisms that enable them to survive in these turbulent conditions. Spawning habitats were characterized by investigating the relationships between egg abundance and environmental data collected through two different survey programmes: SW APEL surveys (1978 -1985) and Nansen surveys (1999 - 2004). Single factor quotient techniques were used to define the selection of environmental conditions by these species for spawning.
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
Comparing in situ and satellite temperature data on the Agulhas Bank to understand changes in anchovy (Engroulis encrasicolus) distribution
(2014) Schlegel, Robert William; Moloney, Coleen; Roberts, Mike; Van der Lingen, Carl D
Satellite data have high spatial/ temporal resolution, extensive coverage and are easily accessible, making them a common part of many studies on the oceans. One such important study to use satellite data found a relationship between the cross-shelf SST difference on the Agulhas Bank and the relative distribution of anchovy (Engraulis encrasicolus) spawner biomass east of Cape Agulhas. However, other studies have shown that nearshore satellite data may not be as accurate as originally believed. Using the relationship observed in the aforementioned study as a test, I compared time series' from two types of in situ temperature data to satellite SST data. A combined CTD/CalVET (PISCTD) data set was used for in situ data on the coastal and offshore regions of the Agulhas bank whereas a data set with two UTRs was used for inshore in situ data. None of the data sets correlated significantly with each other, save the two UTRs. Both in situ data sets showed a negative relationship between the size of the cross-shelf temperature difference on the Agulhas bank and the increase in anchovy biomass there, whereas the satellite data showed a positive relationship. This was largely due to the pattern of decadal warming observed in the in situ data whereas the satellite data showed decadal cooling. Even though it was found that the difference in sampling methodology between the satellite and in situ data sets prevented them from being accurately compared, the difference in the annual and decadal patterns between these two types of data do support other findings showing discrepancies between remotely-sensed and in situ data for nearshore environments.
Open Access
Comparing the coarse- and high-resolution horizontal and vertical egg distribution patterns of three clupeiform species in the southern Benguela ecosystem
(2003) Dopolo, Mbulelo Tomie; Moloney, Coleen; Van der Lingen, Carl D
Three fish species, anchovy Engraulis encrasicolus, sardine Sardinops sagax and round herring Etrumeus whiteheadi, co-exist over the western Agulhas Bank (W AB) in the southern Benguela upwelling ecosystem. To date, data on high-resolution distributions in ichthyoplankton in the region is lacking. To address this need, coarse and high-resolution ichthyoplankton data were collected using a California vertical egg tow (CalVET) net and a continuous, underway fish egg sampler (CUFES) for horizontal data, respectively, and plankton pump and a closing WP II net for vertical data. Simultaneous measurements of temperature were recorded during the CalVET net hauls. Eggs from vertically stratified samples were grouped into three categories based on their developmental stage using established protocols. Volumetric estimates of egg density (eggs.m-3) from on-station CUFES samples were significantly correlated with normalized areal (eggs.m-2) estimates of egg density from CalVET net samples at these stations for sardine (r 0.91), round herring (r=0.80) and anchovy (r = 0.73), demonstrating the validity of the CUFES sampling technique. Underway sample collection reduced the survey coefficient of variation for sardine and round herring eggs but not for anchovy eggs. Horizontal egg distribution patterns for anchovy showed that high egg densities were centered at two specific regions: midshelf (east of Cape Point) and offshore in the southern region of the study area, whereas those of sardines and round herring were more continuously distributed above and beyond the 200m isobath. Egg abundances for all species generally increased from inshore towards offshore. The mean egg densities for all three species were found to be spatially associated, whereas the station by station distribution patterns of anchovy eggs were spatially distinct from sardine and round herring. Eggs of all three species were concentrated near the surface (0-20 m), although proportions varied among species. All developmental stages of anchovy egg were confined close to the surface indicating that this species spawns near the surface. Sardine and round herring vertical egg profiles varied ontogenetically, even though all developmental stages were concentrated near the surface. A significant (> 50%) proportion of early egg stages were widely distributed between 0-60 and 0-80 m for sardine and round herring, respectively. These results therefore show that the spawning depths of these three c1upeiforms overlap to a large extent, but the intensity of spawning varied at depth for each species. In general the vertical thermal structure seemed to affect only how deeply the eggs are distributed rather than the mean egg abundance. The differences in vertical egg profiles among and within (with respect to ontogenetic variation) species were found to be statistically significant (Chi-squared test, P < 0.05). Investigations of spawning patterns in relation to temperature, longitude and latitude were used to compare the spawning habitats of the three species. Quotient rule analysis was used to distinguish the preferred temperature ranges of all three species. Round herring spawn over a wider temperature range (16.5-18.1°C) than anchovy (17.4-17.8° C and sardine (17-18.1 °C). Two spawning peaks were apparent for round herring (main peak at 17.2°C and secondary peak at 17.8°C), whereas only one peak at 18.0°C was apparent for anchovy and sardine. Anchovy spawning showed a domed-shape relationship with geographic location and the relationship was viewed to be more informative (r2 = 0.13 longitude, ~ = 0.11 latitude) compared to sardine (r2 = 0.08 longitude, r2 = 0.07 latitude) and round herring (r2 = 0.04 longitude, r2 = 0.06 latitude). These results indicate that anchovy were more specific in their selection of spawning habitat than sardine and round herring. Generally, these results suggest that the overall spawning habitats of anchovy, sardine and round herring on the W AB overlap to a large extent, but their exact locations of the point of spawning are spatially distinct.
Open Access
Developing an individual based model of phytoplankton using a size-based approach
(2005) Tobi, Nontsasa Princess; Moloney, Coleen
Open Access
Drivers of short-term variability in phytoplankton production in an embayment of the southern Benguela upwelling system: an observational and modelling study
(2018) Burger, Jessica; Fawcett, Sarah; Moloney, Coleen
In the southern Benguela upwelling system (SBUS), the wind-driven supply of nutrient-rich water from depth sustains elevated levels of primary productivity. St Helena Bay (SHB), a coastal embayment in the SBUS positioned north of an upwelling centre, is an area of water mass retention. In addition to supporting 40-50% of total SBUS productivity, SHB often experiences harmful algal blooms (HABs) and hypoxic conditions that are difficult to predict given the high sub-seasonal variability that characterises this region. To better understand this variability, net primary production (NPP), nitrate and ammonium uptake, and phytoplankton community composition were measured for ten days during the upwelling season at an anchor station in SHB. A period of active upwelling (days 1-5) was followed by one of relaxation (day 6-10), together constituting an “upwelling cycle”. During upwelling, the mixed layer was deeper than the euphotic zone and phytoplankton were light-limited, evidenced by high ambient nutrient concentrations and relatively low rates of NPP and nitrate uptake. During relaxation, water column stratification increased, restricting phytoplankton production to a shallow, well-lit surface layer in which nitrate was exhausted after three days. The subsequent decline in NPP and nitrate uptake rates confirms that nutrient availability succeeded light as the ultimate control on productivity during the relaxation phase. Of the three phytoplankton size classes investigated (0.7-2.7 µm, 2.7-10 µm, >10 µm), the 2.7-10 µm fraction contributed most to the measured increases in biomass and nutrient uptake rates. This was unexpected given that large (>10 µm) diatoms typically dominate in upwelling systems; however, the 2.7-10 µm size fraction achieved a faster growth rate and sustained it for longer than the other size classes. The success of this size fraction may be partly due to a capacity for luxury nitrate uptake, evidenced by a low biomass C:N ratio and a nitrate uptake rate that was decoupled from NPP. Throughout the experiment, the phytoplankton community comprised mainly Chaetoceros spp. and Skeletonema costatum. These diatoms occupy a large size range (2-80 µm), although it is likely that they mainly occurred in the 2.7-10 µm size class during the experiment. They also produce resting spores that may provide a selective advantage during seeding in highly variable upwelling systems, increasing their chances of proliferating when conditions become favourable. Once the water column stratified, the phytoplankton community diversified, with dinoflagellates and the large diatom, Coscinodiscus gigas (200-500 µm), becoming more abundant. The contribution of C. gigas to biomass and productivity was not fully accounted for in the measurements because collected seawater was screened (200 µm mesh) prior to incubation. However, a simple N₃P₃ ecological model parameterized with the observations suggests that their contribution would have been minimal. The hydrographic data indicate that another upwelling cycle commenced by day 10 of the experiment. This likely prevented the further proliferation of dinoflagellates, some of which are HAB species, that may have succeeded the small diatoms given a longer period of quiescence. One implication of this is that understanding the rapid cycling between light and nutrient limitation, as induced by an actively upwelling versus stratified water column, may advance our capacity to predict the occurrence of HABs in SHB.
Open Access
Effects of sea surface temperature, adult size and adult condition on spatial variability in egg volumes of three pelagic species from the southern Benguela
(2007) Duthie, Tarryn-Lee; Moloney, Coleen; Van der Lingen, Carl D
Spatial variability in egg volume was investigated for anchovy, sardine and round herring in the southern Benguela in 1998, 2000 and 200 l. The relationship between sea surface temperature (SST) and egg volume was determined and the parental condition hypothesis was investigated through the relationships of adult size and condition with egg volume. General linear models for each species were used to determine the factors that were significantly related to egg volume at the scale of sample collection. Visual interpretation of the effects of adult size and condition on egg volumes was done on a large scale.
Open Access
Establishing a baseline for evaluating changes in fish body condition and population dynamics of Cape hake (Merluccius capensis and M. paradoxus) in South Africa
(2014) Boyd, Danielle Winona; Moloney, Coleen; Ndjaula, Hilkka O N; Fairweather, Tracey
Standard weight (Ws) equations were developed and relative weight (Wr) indices calculated for both shallow-water (Merluccius capensis) and deep-water (M . paradoxus) Cape hake. The aim was to provide fixed baselines and Wr indices to aid understanding of temporal and spatial variability in fish condition . Baselines were calculated using the empirical percentiles (EmP) method applied to length (L) – weight (W) data collected by research surveys on the South African west and south coasts, from 1983 to 2013 . Four quadratic Ws equations for each species were generated, based on the following weight statistics for each size class j : first quartile, median, third quartile and mean. Median Ws equations were chosen for the baseline for shallow-water hake (log₁₀ Ws=-2.491 + 3.33 8 *(log₁₀ L)-0.065 *(log₁₀ Lj)²) and deep-water hake (log₁₀ Ws =- 2.161 + 2.930*(log₁₀ L) + 0.0456 *(log 10Lj)²). Shallow-water hake was found to be the heavier of the two species at the same length. Wr indices display good condition values (>100%) for both species throughout all analyses . Fish condition for both species was best between 1988-2009, ranging from 50-1 65% for individual fish and 100 – 109% for annual averages. Monthly mean Wr indices peaked in June and October for shallow-water hake and July and October for deep-water hake. Mean Wr values were different for shallow-water hake on the south (105%) and west (103%) coasts. Deep-water hake showed no spatial variability in mean Wr values. There were no differences between mean Wr values of males and females between, and within, species. Future hake data may be compared to these Ws equation baselines and Wr indices to show changes in body condition for this commercially important stock.
Open Access
Establishing a weight-length baseline for evaluating changes in yellowfin tuna (Thunnus albacores) body condition in the Western Indian Ocean
(2013) Harikishun, Ameil; Moloney, Coleen; Marsac, Francis; Ndjaula, Hilkka O N
Standard weight (Ws) equations were established for yellowfin tuna (Thunnus albacares) in the Western Indian Ocean and used as a baseline for calculating relative weight (Wr) indices. Length-weight data for yellowfin tuna were obtained from the Indian Ocean Tuna Commission (IOTC) for 1984 to 1991 and 2003 to 2013. Four quadratic standard weight equations were established (based on mean, median, first and third quartile statistics for each length class) using log10-transformed weight (W, in grams) and fork length (FL, in mm) data. The median Ws equation (log10(W) = -3.903 + 2.425(FL) + 0.103(FL)2) was the preferred baseline for the Wr analysis. Relative weight estimates for individual fish ranged from 92 to 110. Annual and monthly Wr estimates ranged from 99 to 101 and 99.9 to 100.5 respectively. A GLM was fitted to separate the effects of year, month and sex on the response variable Wr. Year, month, sex and the interaction terms Year:Sex and Month:Sex all contributed significantly to the variability in Wr explained. Correlations between environmental variability and yellowfin tuna condition were observed. Concentrations of suitable prey in 2003 and 2004 correlated to above average condition, although 2005 and 2006 were below average condition during similar prey availability and environmental conditions. Relative weight followed an increasing trend from 2008 to 2013 despite lower biological enrichment. Mechanisms such as a shallower thermocline and reduced fishing pressure are proposed explanations. This study provided a reference study for body condition studies of yellowfin tuna in the Indian Ocean. It also provided support for the application of the Wr index to other tuna species in the Indian Ocean managed by the IOTC.
Open Access
Feeding habits of sardine (Sardinops sagax) in relation to their spawning activities
(2011) Mashifane_TB; Moloney, Coleen; Ndjaula, Hilkka O.N.
Feeding activity of sardine (Sardinops sagax) from St Helena Bay and Gans Bay in the Southern Benguela was studied between February and April 2011 and related to reproduction. Feeding intensity of 373 sardine was calculated and correlated with caudal length across different gonad maturity and fat stages. Feeding intensity tended to be higher in small than large sardine (r = -0.14, n = 373, p = 0.005) and similar for both sexes (t = 1.567, df = 371, p = 0.12). Feeding intensity was high in St Helena Bay, possibly because of food availability. Gonad maturity and GSI were highest in February and were greater in St Helena Bay than in Gans Bay. Fat staging and the relative weight index were used to represent fish condition. Fat reserves varied, being low in February during the spawning season and peaking thereafter in March and April. A GLM indicated that feeding intensity in sardine was affected by time of year and gonad maturity state. Sardine fed throughout the study period but feeding intensity was highest in periods before- and after- spawning. With the observed continuous feeding and the accumulation of fat reserves before spawning, it appears S. sagax in the Southern Benguela employs both capital and income breeding strategies.
Open Access
Feeding habits of sardine (Sardinops sagax) in relation to their spawning activities
(2011) Mashifane_TB; Moloney, Coleen; Ndjaula, Hilkka O.N.
Feeding activity of sardine (Sardinops sagax) from St Helena Bay and Gans Bay in the Southern Benguela was studied between February and April 2011 and related to reproduction. Feeding intensity of 373 sardine was calculated and correlated with caudal length across different gonad maturity and fat stages. Feeding intensity tended to be higher in small than large sardine (r = -0.14, n = 373, p = 0.005) and similar for both sexes (t = 1.567, df = 371, p = 0.12). Feeding intensity was high in St Helena Bay, possibly because of food availability. Gonad maturity and GSI were highest in February and were greater in St Helena Bay than in Gans Bay. Fat staging and the relative weight index were used to represent fish condition. Fat reserves varied, being low in February during the spawning season and peaking thereafter in March and April. A GLM indicated that feeding intensity in sardine was affected by time of year and gonad maturity state. Sardine fed throughout the study period but feeding intensity was highest in periods before- and after- spawning. With the observed continuous feeding and the accumulation of fat reserves before spawning, it appears S. sagax in the Southern Benguela employs both capital and income breeding strategies.
Open Access
Fishing patterns around the Cape Peninsula National Park : implications for a fisheries monitoring program
(2002) Duffell-Canham, Alana; Moloney, Coleen; Attwood, Colin
The aims of this study are to analyse the extent and distribution of boat and shore based fishing along the Cape Peninsula for the purpose of designing a comprehensive fisheries monitoring program. The focus of this study is the non-quota regulated fisheries, which have thus far eluded monitoring attempts. A fishery monitoring program should be able to detect biologically significant shifts in resource abundance in the Marine Protected Areas and to provide data that are relevant to stock assessment models. Personnel and cost implications of the monitoring program will be estimated.
Open Access
An individual-based modelling approach to examine life history strategies of sardine Sardinops sagax in the southern Benguela ecosystem
(2006) Miller, David Charles Moorcroft; Moloney, Coleen; Van der Lingen, Carl D; Lett, Christophe
Hypotheses regarding the spawning strategy and recruitment of sardine (Sardinops sagax) in the southern Benguela ecosystem are tested using an individual-based Lagrangian particle tracking model linked with a 3-D hydrodynamic model of the region. Experiments focus on the dispersion of eggs and larvae among possible spawning and nursery areas. The two main areas of interest were the west coast upwelling region and the south coast shelf region (Agulhas Bank). A stage-based temperature-dependent development model is incorporated and vertical positioning schemes are tested. The spatial distribution and size structure of the sardine spawning stock for the period 1991-1999 are presented and a simple size-based fecundity model, combined with modelled recruitment, is used to determine the relative importance of each spawning and nursery area. The area of spawning plays a fundamental role in determining the destination of spawned eggs, and recruitment of sardine in the southern Benguela ecosystem appears to be divided into three recruitment systems by the circulation of the region: eggs spawned west of Cape Agulhas recruiting on the west coast (the WAB/WC-WC system), eggs spawned east of Cape Agulhas recruiting on the west coast (the CAB-WC system), and eggs spawned east of Cape Agulhas recruiting to the south coast (the SC-SC system). There is a slight increase in retention in the two nursery areas during winter, but the transport of eggs and larvae from the Agulhas Bank to the west coast is optimal during spring to early summer. Slow development arising from cold temperatures on the west coast could negatively impact recruitment by increasing offshore loss of individuals before they develop to a stage when they are able to actively avoid offshore currents and through its effect on mortality rate. This could explain the spatial separation of spawning and nursery areas in this system. The vertical position of individuals has an effect on the level of modelled recruitment and mortality rate, but observed vertical distributions of sardine egg and larvae do not signiﬁcantly increase the level of modelled recruitment to optimal nursery areas. This suggests that efficient transport and retention are traded-off against other factors such as predator avoidance or prey abundance. Observed size structure and spatial distribution of the sardine spawning stock for 1991-1999 ﬂuctuated greatly with most spawning centred on the western Agulhas Bank. When spawning was centred east of Cape Agulhas, recruitment was poor. No signiﬁcant relationship could be established between potential reproductive output reaching the west coast and estimated recruitment, but positive recruitment anomalies required good transport to, and retention on, the west coast. A conceptual model of the early life history of sardine is proposed in light of limitations imposed by transport and retention of individuals. Lower primary production and the possibility of higher predation on the Agulhas Bank suggest that the south coast supports less recruitment than the west coast. The hypotheses tested using available data and model results could improve the understanding of recruitment of sardine in this complex ecosystem. These need to be validated by ﬁeld observations. Additionally, further avenues for research that could help in developing a better understanding of the sardine life history in the southern Benguela ecosystem are suggested.
Open Access
Modelling South African cold-water coral habitats
(2019) De Haast, James Andrew; Moloney, Coleen
Cold-water corals are found globally but little is known about energy flows associated with these habitats. The degree to which the benthic ecosystems containing cold-water corals are linked to the overlying pelagic ecosystems is also poorly understood. Observational studies have indicated that fish abundance is greater in the waters surrounding coldwater coral reefs compared to nearby waters over barren seafloor, implying enhanced productivity in the cold-water coral ecosystems. Support for this hypothesis is tested in this study using a customised Ecopath with Ecosim model. The model is applied to Childs Bank, a region on the west coast of South Africa located in the southern Benguela eastern boundary ecosystem. A previously constructed Ecopath model of the southern Benguela was modified to represent the main groups of organisms found on Childs Bank and additional groups were added to better represent the main groups associated with cold-water coral. In total, including the additional compartments, the model ecosystem consisted of 34 living compartments and three non-living compartments. Three novel living compartments were considered in the model: Cold-water corals, Sponges and Tube-worms. Two additional non-living compartments comprised Coral skeleton and Coral mucus. The Ecopath model was balanced by assuming that the three additional living groups had the same production to biomass ratios as the Macrobenthos group. The production to consumption ratio of Sponges and Cold-water corals were sourced from literature. An unconstrained non-linear minimisation function was used to solve for the biomass of the Sponge and Cold-water coral groups as their production was needed for the Ecopath model to balance; thus a biomass estimate was required for both these groups. The balanced Ecopath model was used in an Ecosim model, which was applied to three scenarios designed to investigate whether trophic links in the cold-water coral ecosystems could account for increased fish abundance: scenario 1, the removal of both cold-water coral and cold-water coral skeleton; scenario 2, changes in fishing pressure on small pelagic fish; scenario 3, the removal of coldwater coral skeleton without damage to the living coral. Scenario 3 is an artificial scenario designed to isolate the effects of cold-water coral skeleton loss from the trophic interactions from the living cold-water corals. None of the scenarios produced results with notable changes in biomasses of groups in the wider ecosystem. It is thus hypothesised that enhanced fish production results from cold-water corals changing the local oceanographic conditions through their physical structure rather than primarily by their trophic interactions.