OpenUCT :: Browsing by Author "Van der Lingen, Carl D"

Browsing by Author "Van der Lingen, Carl D"

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Open Access
Accommodating dynamic oceanographic processes and pelagic biodiversity in marine conservation planning
(Public Library of Science, 2011) Grantham, Hedley S; Game, Edward T; Lombard, Amanda T; Hobday, Alistair J; Richardson, Anthony J; Beckley, Lynnath E; Pressey, Robert L; Huggett, Jenny A; Coetzee, Janet C; Van der Lingen, Carl D
Pelagic ecosystems support a significant and vital component of the ocean's productivity and biodiversity. They are also heavily exploited and, as a result, are the focus of numerous spatial planning initiatives. Over the past decade, there has been increasing enthusiasm for protected areas as a tool for pelagic conservation, however, few have been implemented. Here we demonstrate an approach to plan protected areas that address the physical and biological dynamics typical of the pelagic realm. Specifically, we provide an example of an approach to planning protected areas that integrates pelagic and benthic conservation in the southern Benguela and Agulhas Bank ecosystems off South Africa. Our aim was to represent species of importance to fisheries and species of conservation concern within protected areas. In addition to representation, we ensured that protected areas were designed to consider pelagic dynamics, characterized from time-series data on key oceanographic processes, together with data on the abundance of small pelagic fishes. We found that, to have the highest likelihood of reaching conservation targets, protected area selection should be based on time-specific data rather than data averaged across time. More generally, we argue that innovative methods are needed to conserve ephemeral and dynamic pelagic biodiversity.
Open Access
Assessing the implementation efficacy of an ecosystem approach to Fisheries management in the South African sardine fishery
(2015) McGregor, Emily Skye; Jarre, Astrid; Van der Lingen, Carl D; Wals, Arjen
An Ecosystem Approach to Fisheries management (EAF) offers a holistic approach for sustainable fisheries management by extending the traditional target resources-orientated management (TROM) to include wider social-ecological dimensions of fisheries. An EAF requires balancing of multiple, often conflicting objectives, effectively dealing with complexity and uncertainty, and engaging with diverse groups of stakeholders. Various tools within the field of Multi-criteria Decision Analysis provide a formal approach which takes explicit account of multiple criteria, while effectively dealing with risk and uncertainty. A knowledge-based tool was developed in this thesis to assess the efficacy of EAF implementation for the ecological well-being dimension in the South Africa sardine fishery. An iterative, participatory approach was adopted for its implementation. The modelling philosophy applied a rapid prototyping approach, and an applied research perspective was employed to direct the research. A broad group of stakeholders participated in indicator selection, tool design, and interpretation. The knowledge-based tool provided a hierarchical framework for seven specific management objectives to which eleven ecological indicators were linked. Time series (1987-2009) were collated for each indicator, and a utility approach was used to transform indicators to a common scale. Weights for indicators and objectives were agreed to by stakeholders and combined through the objectives' hierarchy using weighted means. The resulting outputs were discussed in detail during focus group meetings to ensure that the tool was clearly presented and as intended helped improve the stakeholder's understanding of the process. It was confirmed that the 20 knowledge-based tool presents a transparent, repeatable and scientifically defensible approach, suitable to meet management requirements. The tool development process was useful in bringing diverse stakeholder groups together, and through applying the tool as a boundary object, has helped to bridge the boundary between the TROM and EAF research communities. Encouraging stakeholder interaction offers opportunities for social learning, which if carefully facilitated through the tool development process is likely to enhance the outcomes of this process and support more generally in bridging boundaries to EAF implementation. The combined focus on tool development and social processes supports effective implementation of an EAF in the South African small pelagic fishery and provide a model for other fisheries.
Open Access
Assessment of the population structure of the South African sardine Sardinops sagax using a multi-method approach and the morphological and molecular characterization of a stock-discriminating digenean parasite biotag of the genus Cardiocephaloides
(2017) Uzonnah, Nwamaka Mary-Immaculata; Reed, Cecile C; Van der Lingen, Carl D
An understanding of the population structure of commercially exploited species is essential for effective fisheries management. Fish stocks are typically identified based on the observation of differences in genetic and/or phenotypic characteristics between fish from discrete units. Recent deliberations on the management of the South African purse-seine sardine fishery recognises the likely existence of two stocks, one on the west and another on the south coasts, following studies that have documented spatial variability in several phenotypic characteristics of this species around South Africa. Those studies typically examined spatial variability in a single characteristic (e.g. gill raker morphology and meristics, body shape, otolith shape, vertebral count, parasite loads), but the application of multiple stock identification methods to the same individual fish has been recommended in order to maximize the likelihood of correctly inferring and identifying fish stocks. This study seeks to assess the population structure of South African sardine Sardinops sagax using a combination of stock identification methods including meristic, morphometric and parasite markers. Most of the sardine samples used in this study were obtained off the west and south coasts of South Africa during pelagic surveys conducted in 2013 and 2014 by Fisheries Branch of the Department of Agriculture, Forestry and Fisheries, with some additional samples obtained from commercial fisheries. Fish caught from the west and south coasts are presumed to be part of the putative western and southern stocks respectively. The variables examined included body shape, gill arch length, gill raker spacing, number of gill rakers, otolith shape indices (otolith circularity and form factor), the number of vertebrae, and the abundance of a 'tetracotyle' type metacercarian parasite found in the eyes of sardine; these were first analysed individually and then collectively (excluding body shape data) in a multivariate analysis to test their effectiveness in discriminating between sardine from the putative western and southern sardine stocks. Analysis using geometric morphometrics revealed significant differences in body shape between sardine from the putative western and southern stocks. Results of GLM analyses indicated that gill arch length, the number of gill rakers, otolith form factor and circularity, and parasite abundance were effective univariate discriminators of sardine stocks. No significant difference in gill raker spacing and the number of vertebrae was found between individuals from the two stocks. A Stock Identification Index (SDI) of 0.75 derived from the univariate analyses, as well as results of the multivariate analysis of data provided strong evidence for the existence of two mixing stocks, therefore, supporting the two-stock hypothesis. The five multivariate classification models used in the study showed varying degree of allocation success. Overall classification accuracy ranged from a low 47% in the Linear Discriminant Analysis model to highs of 82% and 91% in the Classification Tree Analysis and Random Forest models, respectively. Both CTA and RF revealed the combination of variables with the strongest spatial discriminatory power to be the number of vertebrae and abundance of the 'tetracotyle' type metacercarian parasite. These results agree with those of previous studies and further support the inclusion of sardine population structure into management strategies for the purse-seine fishery for South African sardine. Given the importance of the 'tetracotyle' type metacercaria in the discrimination of South African western and southern sardine stocks, further studies were undertaken to identify and describe this parasite using light and scanning microscopy, as well as molecular tools. Such information will assist in the definitive identification of the first intermediate host of the parasite, presently hypothesized to be a sub-tidal gastropod occurring off the west coast only. Definitive identification of the first intermediate host (or hosts) will enable the full life cycle of this parasite to be determined and the parasite endemic area to be identified; a critical knowledge gap in application of the parasite biotag approach to stock discrimination using this 'tetracotyle' type metacercarian parasite. Metacercariae collected from fresh sardine sampled from a commercial landing in Gans Baai, South Africa, were manually excysted, relaxed in warm water, fixed in 70% ethanol and stained with haematoxylin for light microscopy. The metacercarial body is oval-shaped, measuring 762 - 967 x 512 - 677μm. It is divided by transverse folds into a forebody, midbody and hindbody. Diagnostic features include the unique, large excretory bladder lobes situated on the lateral sides of the body; two large pseudosuckers in the anterior part of the midbody; an acetabulum which is larger than the oral sucker; and a large lobulated holdfast organ in the posterior half of the midbody. These features are those of the metacercariae of the genus Cardiocephaloides, confirming the previous hypothesis regarding the genus of this digenean biotag. Analysis of partial 28S rDNA region sequence data showed that the metacercariae and the adult Cardiocephaloides found in the African penguin Spheniscus demersus are of the same species, likely C. physalis. This study is the first documentation of the morphological and molecular characterization of the stock-discriminating Cardiocephaloides metacercaria found in the eyes of Sardinops sagax in South Africa.
Open Access
Characterizing and comparing the spawning habitats of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela upwelling ecosystem
(2002) Twatwa, Nandipha M; Field, John G; Van der Lingen, Carl D
The spawmng habitats of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the southern Benguela upwelling ecosystem were characterized by comparing the data on abundance and distribution of eggs of the two species with environmental variables. Data were collected from two different survey programs: (a) 14 SARP (Sardine and Anchovy Recruitment Programme) cruises, conducted monthly for 2 spawning seasons between August 1993 and March 1994, and September 1994 and March 1995, off the west coast of southern Africa from Cape Columbine to Cape Agulhas; (b) annual November/December spawner biomass surveys conducted from 1984-1999 along the South African coast and covering the continental shelf between Hondeklip Bay on the West Coast and Port Alfred on the South Coast. A CalVET net was used to collect fish eggs at stations on a survey grid, and physical and biological data were collected concurrently with egg samples. Physical variables measured included sea surface temperature, nitrate concentration, water depth, salinity, current speed, wind speed and mixed layer depth, whereas biological variables included phytoplankton biomass (as 50m integrated chlorophyll a) and zooplankton biomass and production. The spawning habitats selected by anchovy and sardine were identified by constructing quotient curves derived from egg abundance data and individual environmental variables. Anchovy and sardine spawning probability with reference to the distribution of environmental variables was examined using overlay operation analysis. Relationships between eggs of the two species and the environmental variables were verified using multivariate co inertia analysis. Relationships among the environmental variables were examined through cluster analysis. During SARP surveys, single parameter quotient analysis indicated that the spawning habitats of these two species were most dissimilar in terms of water depth, sea surface temperature, current speed and zooplankton biomass, and most similar in terms of salinity and phytoplankton biomass. Coinertia analysis using all environmental variables as inputs showed a positive association between anchovy eggs and salinity and sea surface temperature, and a negative association between anchovy eggs and secondary production and phytoplankton biomass. Sardine eggs were strongly positively associated with phytoplankton biomass. During spawner biomass surveys, anchovy and sardine spawning habitats appeared to differ with respect to sea surface temperature, wind speed and current speed, and overlapped in terms of water depth, phytoplankton biomass, zooplankton biomass and production. Anchovy eggs were strongly positively associated with SST, salinity, mixed layer depth and zooplanktop production. Sardine eggs were strongly positively associated with current speed and zooplankton biomass.
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
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
Evaluating the implementation efficacy of an ecosystem approach to fisheries in the South African anchovy fishery
(2014) Astor, Nicole; Jarre, Astrid; Van der Lingen, Carl D
A knowledge-based tool was developed to assess the efficacy of the ecosystem approach to fisheries in the South African anchovy fishery. South Africa has agreed to implement an ecosystem approach to fisheries (EAF) management. The EAF management comprises of three dimensions; ecological well-being, human well-being and ability to achieve. The focus for this study was on the ecological well-being dimension. Meetings were held with experts to revise objectives stemming from issues in the anchovy fishery documented earlier and indicators linking to these objectives. A hierarchical tree was constructed using these indicators and objectives. The objectives were divided into pressure and state. The indicators were transformed using piecewise linear transformation on to a common scale from -1 to 1. Thresholds were also decided to assess when the EAF implementation was considered to be 'good' (1), 'ok' (0) and 'bad' (-1). Weighted means were applied through the hierarchy. The overall resulting output, the truth value, was then used to assess how well the ecological dimension of the anchovy fishery had been doing over time. This showed the implementation efficacy of an EAF within the ecological dimension had been doing badly in 1987-1996, and since 1997 the ecological dimension of the EAF has been doing better. Sensitivity tests on the weights also showed that the knowledge based tool was robust to changes in weights. This allowed for experts to have slight differences in opinion over the way the weights should be distributed, but without these differences in opinion affecting the overall truth value. Sensitivity tests on the thresholds of one of the indicators showed that the outcome of the indicator is sensitive to changes in the thresholds. However, when looking at the overall truth values or the objectives, the changes to the thresholds did not affect the resulting objective values or the overall truth value that much. Although the indicator values change with changes in the thresholds, looking at the whole knowledge based tool it is fairly robust to moderate changes in thresholds.
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
Investigating trophic interactions between parasites and their marine fish hosts using stable isotope analysis
(2018) Weston, Mark Jonathan; Reed, Cecile C; Van der Lingen, Carl D
Parasitism is accepted as being an essential driver in the organization of biological communities. However, although there are estimated to be more parasitic than free-living organisms, parasites have been largely neglected from ecological studies and we have a relatively limited understanding of their trophic ecology. Hence, in order to incorporate parasites into food-web models and ecological studies, basic trophic interactions between parasites and their hosts need to be assessed. Here, I investigated host-parasite interactions using stable isotope analyses on a broad range of marine fish hosts and their associated copepod and monogenean gill parasites. The study also provides insight into the gill parasite diversity of a number of host species from South African marine waters. Seventeen species of fish hosts, ranging from lower to upper trophic levels, were collected from South African waters in 2015 and 2016 during surveys conducted by the Department of Agriculture, Forestry and Fisheries from South African waters. These host species were; Thunnus albacares, Thunnus maccoyii, Thunnus alalunga, Thunnus obesus, Isurus oxyrinchus, Prionace glauca, Xiphius gladius, Brama brama, Thyrsites atun, Seriola lalandi, Sarda sarda, Genypterus capensis, Merluccius paradoxus, Merluccius capensis, Lampanyctodes hectoris, Sardinops sagax and Trachurus capensis. The head region, gills and operculae from a total of 1513 fish were examined and any ectoparasites removed, identified down to the lowest taxonomic level possible, and counted. A total of 32 parasite taxa, comprising 20 copepods and 12 monogenean species, were recorded. Two new host records and 15 new geographic records for South Africa were catalogued. The new host records are Mazocraes sp. infecting T. atun, and Caligus dakari infecting T. capensis. The new locality records consist of Euryphorus brachypterus recovered from T. alalunga and T. obesus, Pseudocycnus appendiculatus recovered from T. albacares, T. alalunga and T. obesus, Hexostoma sp. recovered from T. albacares and T. obesus, Nasicola klawei recovered from T. albacares and T. obesus, Tristoma adcoccineum recovered from X. gladius, Eobrachiella elegans and two species from the genus Parabrachiella recovered from S. lalandi and Anthocotyle merlucci recovered from M. paradoxus and M. capensis. These new records have substantially contributed to the known parasite biodiversity within the South African marine environment. Host-parasite interactions between 15 species of fish host and their copepod and monogenean gill parasites were investigated by means of stable isotope analysis. Host white muscle tissue, host gill tissue and parasite samples were analysed for their carbon and nitrogen isotopic signatures. Results indicated that δ¹⁵N is tissue-specific, with host white muscle tissue showing significantly greater enrichment in ¹⁵N compared to host gill tissue (n =60; Z=5.66843; p<0.00001), and as gill tissue is what the parasites are presumably feeding on, host gill tissue was therefore selected as the most appropriate proxy.
Open Access
Laboratory studies on the feeding behaviour of juvenile Cape horse mackerel, Trachurus trachurus capensis
(2002) Mapukata, Tembela; Van der Lingen, Carl D; Field, John G
Laboratory studies were conducted on juvenile horse mackerel to examine feeding selectivity and rates of zooplankton consumption of two size classes of fish. Fish were fed a variety of natural zooplankton assemblages and sequential subsampling of water in the experimental tanks provided estimates of prey concentration. Video observations were used to examine feeding behaviour and to investigate the feeding response of horse mackerel to various food types and prey sizes.
Open Access
Measurements of the branchial sieve of sardine (Sardinops sagax ocellatus) from the west and south coasts of southern Africa
(2010) Idris, Izwandy; Moloney, Coleen L; Van der Lingen, Carl D
Branchial sieves of southern African sardine (Sardinops sagax ocellatus) were collected from three geographical regions along the southern African coast: Namibia, the south coast and the west coast of South Africa. Sardine from Namibia represented the northern Benguela upwelling ecosystem while sardine from the west and south coasts of South Africa represented the southern Benguela upwelling ecosystem. Morphometric measurements (gill arch length and gill raker spacing) and counts (number of gill rakers) of branchial sieves on the left side of the first gill arch were taken to determine whether the sardine from these regions have different branchial sieve structures.
Open Access
Meristic and morphometric variation among sardine Sardinops sagax around the coast of southern Africa
(2009) Wessels, Grea; Moloney, Coleen L; Van der Lingen, Carl D
Meristic counts and morphometric measurements were made on previously frozen sardine Sardinops sagax to determine whether there is a difference in the shape of sardine from different areas around southern Africa. Because freezing influences body size, eight different freezing periods were examined to determine the effects of freezing duration on the caudal length, weight and 21 morphometric measurements of sardine collected from commercial catches at Gans Bay and Saldanha Bay, South Africa. The relative weight loss of sardine ranged between 0.86 and 2.49% and the relative loss in caudal length ranged between 1.57 and 2.54%. Most of the morphometric measurements showed small changes with increasing freezing period and, if they decreased, the decrease was gradual. Samples for the morphometric study were frozen between 12 and 17 weeks before analysis. Independent sample t-tests between these freezing periods confirmed that there was no change in the morphometric measurements over this five week period. In total, 35 samples were collected from three main regions: Namibia, the South African west coast and the South African south and east coast.
Open Access
Modelling the effects of spatio-temporal spawning variability on the transport and retention success of sardine (Sardinops sagax) eggs and larvae around South Africa
(2018) McGrath, Alice; Moloney, Coleen L; Van der Lingen, Carl D; Hermes, Juliet C; Roy, Claude
The transport and retention of sardine (Sardinops sagax) eggs on the west and south coasts of South Africa were investigated using a Lagrangrian, particle tracking, individual-based model (IBM), coupled with two 3-D hydrodynamic Regional Ocean Modeling System (ROMS) model configurations of different generations. The same IBM is coupled with PLUME, an older ROMS model configuration used in a previous sardine IBM for the southern Benguela, as well as BENGSAFE, a more recent, better resolved ROMS model configuration. Results from the two runs were compared to see if and how the underlying ocean model affects modelled retention and transport. An updated IBM, extended spatially and temporally to better represent sardine spawning and recruitment, was then coupled with the BENGSAFE model configuration, and assessed. The effects of spawning area, and month, year and depth of particle release, were investigated for each coupled 3D-IBM simulation using linear models. The portion of particles transported from the south coast to the west coast was a focus throughout, as this is of great importance to the management of the sardine fishery. In all simulations, three main systems were identified depending on where particles were released and recruited. Two of these systems were retention-based: particles released on the west coast and retained in the west coast recruitment area (WC-WC), and particles released on the south coast and retained in the south coast recruitment area (SC-SC). The other system is transport-based and represents particles released on the south coast and transported by ocean dynamics to recruit in the west coast recruitment area. Results were similar for the west coast when either hydro- dynamic model configuration was used; depth of release proved to be important in this system with its effect varying depending where on the west coast particles were released. Differences occurred on the south coast, with more transport to the west coast and more offshore loss in the higher resolved BENGSAFE IBM than the PLUME IBM. The difference was attributed to the positioning of the PLUME model's boundary in close proximity to the Agulhas Current, and the conditions at this boundary not properly resolving the current. The initial BENGSAFE IBM was spatially restricted to match the PLUME IBM, and therefore south coast spawning and recruitment was not fully represented. Therefore, the BENGSAFE IBM was spatially extended on the south coast and run for a longer time period. Similar results were obtained in the extended BENGSAFE IBM and the initial BENGSAFE IBM. However south coast retention increased and the average percentage of particles transported to the west coast decreased slightly. Spawning area proved to be an important determinant of retention and transport success in all recruitment systems, and the further east a particle was spawned the less likely it was to be transported to the west coast, and the more likely it was to be retained on the south coast. Transport to the west coast was most successful in late winter; a significant monthly effect on transport success was present. Correlations between standardised anomalies for stock assessment model estimated recruitment and IBM modelled retention/transport for the west and south coast were not significant, highlighting that retention and transport are not the only determinants of recruitment success. The extended BENGSAFE IBM can act as a base level to which extra layers of biological complexities can be added, such as horizontal and vertical egg distribution matching observations, incorporating gonadosomatic index (GSI) values, diurnal vertical migration and buoyancy.
Open Access
Multidisciplinary investigation into stock structure of small pelagic fishes in southern Africa
(2014) Hampton, Shannon; Moloney, Coleen; Bloomer, Paulette; Van der Lingen, Carl D
Three abundant small pelagic fish species co-occur in the Benguela upwelling ecosystem off southern Africa: sardine (Sardinops sagax), anchovy (Engraulis encrasicolus) and round herring (Etrumeus whiteheadi). It is hypothesised that populations of these species have a complex structure that reflects the complexity of their varying habitats. On the basis of the locality and timing of spawning, and morphological, meristic and parasite studies, it has been proposed that there are separate stocks of sardine in South African waters west and east of Cape Agulhas. Consequently, new operational procedures for managing the fishery are based on the premise of two such stocks, termed the west and south coast stocks respectively. In this study, it is hypothesized that the factors causing purported stock differences in sardine should also apply to anchovy and redeye. Three different approaches were used to further test the multi-stock hypothesis for sardine in southern Africa and to provide new information for understanding possible stock differences in anchovy and round herring. The population structure of sardine was investigated through studies on samples taken from the Cape west and south coasts as well as from Namibia and KwaZulu-Natal. Two dimensionless otolith shape indices, otolith elemental signatures, seven microsatellite loci and the mitochondrial DNA marker, ND2, were used to supplement existing information on sardine. Otolith shape, while influenced by fish length and season of capture, distinguished the east coast samples from those taken elsewhere, while the otolith elemental signatures indicated differentiation among sites on a small scale and between samples taken from the west and south coast for certain elements. Both genetic indicators showed high levels of genetic diversity and variation among individuals. There were some genetic differences among sites within a single year, but overall the results suggest that the South African sardine population is well mixed, with weak evidence of genetic patchiness that is not temporally stable. This genetic pattern is evidence of sweepstake recruitment. For anchovy, two spawning locations have been identified in South African waters, but there have been no previous investigations into stock structure. The current study aimed to apply different methods to anchovy samples to determine their usefulness for differentiating population structure,. An analysis of otolith shape revealed that it was primarily influenced by the length of the fish, with no differentiation among sites, whereas an investigation into genetic differentiation using five microsatellite markers revealed high levels of genetic diversity and differentiation among sites. Since there were relatively few samples for a study of this sort, further work is recommended to investigate stock structure in South African anchovy. For round herring, only otolith shape was analysed to test for stock structure. Otolith shape was found to be primarily related to the length of the fish (as in anchovy) and sex, but no significant difference was found between coasts. There were different magnitudes of variability in the results for the three species using different methods. It is likely that the complex, variable environment causes complex patterns of mixing and micro-structuring within all three species, linked to their different niches.
Open Access
The occurrence of a testicular coccidian Eimeria sardinae (Thélohan, 1820) (Reichenow, 1921) in southern Africa sardine Sardinops sagax (Jenyns, 1842)
(2013) Ssempa, Nurudean Norman; Reed, Cecile C; Van der Lingen, Carl D
A total of 553 male southern African sardine Sardinops sagaxcollected between 2010 and 2012 from around southern Africa, including from the northern Benguela off Namibia and from the South African west, south and east coasts, were examined for the occurrence of a testicular coccidian Eimeria sardinae to assess its potential use as a "biological tag" in order to differentiate between hypothesized discrete sardine stocks within the region. Sardine from Namibia and from the South African east coast showed no infection by E. sardinae, whereas fish from the South African west and south coasts were infected. Average prevalence infection values of 48.9 ± 6.3 and 48.1 ± 9.7% were recorded for sardine from the west and south coasts. Average infection intensity of 49.5 ± 15.8 oocysts per sample was recorded for the west coast and 69.8 ± 33.5 oocysts per sample for the south coat sardine. There was no significance difference in E. sardinae infection (t=0.08; p=0.94) in S. sagax from the South African west coast and south coast. These results provide some support for the hypothesis of multiple sardine stocks off southern Africa and hence are important for fisheries management. The intensity of infection had a significant (Analysis of Variance-NOVA, p<0.05) negative effect on the gonadosomatic index values of infected fish from both the west and south coasts. There was a declining trend in condition factor values with increasing intensity of infection category, however no significant effect was observed. The marked negative effect of infection intensity on GSI, with heavy infection possibly leading to parasitic castration, has potentially important implications for sardine population dynamics and requires futher research.
Open Access
Parasite assemblages of Cape horse mackerel (Trachurus capensis Castelnau, 1861) from the northern and southern Benguela
(2013) Le Roux, Jessica Louise; Reed, Cecile C; Van der Lingen, Carl D
A survey of parasites infecting Cape horse mackerel, Trachurus capensis Castelnau, 1861, from both the southern and northern Benguela ecosystems was conducted to test the hypothesis of discrete stocks in each subsystem. One hundred and twenty five T. capensis of two size classes were collected off the coasts of South Africa and Namibia and their bodies and organs were examined for parasitic infections. Differences in parasite assemblages between smaller and larger T. capensis within each subsystem, between T. capensis of each size class from the two subsystems, and between larger fish collected in different seasons within the southern Benguela, were assessed. A total of twenty-nine parasite species were found infecting T. capensis. Ten of these were identified to species level (Ceratomyxa australis, Davisia donecae, Ectenurus lepidus, Gastrocotyle trachuri, Goussia cruciata, Lernanthropus trachuri, Nybelinia lingualis, Rhadinorhynchus cadenati, Scolex pleronectis and Tergestia laticollis), three to genus level (Anisakis sp., Caligus sp. and Kudoa sp.). Significant spatial differences in T. capensis parasites were observed, with larger fish differing in infection intensity and abundance of Anisakis sp. and infection intensity of L. trachuri. Significant spatial variation in parasites was also observed in smaller fish, which differed in Anisakis sp. abundance, L. trachuri infection intensity and abundance, G. trachuri abundance and G. cruciata infection intensity and abundance. Significant fish size effects on T. capensis parasites were also observed in both subsystems. Anisakis sp. infection intensity and abundance and G. cruciata abundance differed significantly between larger and smaller fish from the southern Benguela. Larger and smaller fish from the northern Benguela differed in G. cruciata infection intensity and abundance, G. trachuri abundance and L. trachuri abundance. No seasonal differences in parasites of larger T. capensis from the southern Benguela were observed. By using a discriminant function analysis parasite abundance data correctly assigned 92% of larger fish and 96% of smaller fish to their respective southern and northern Benguela sub-populations or stocks. These results show that analyses of parasites can be used to infer population structure and support the hypothesis of distinct T. capensis stocks in the northern and southern Benguela subsystems.