Browsing by Author "Attwood, Colin"

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    A baited remote underwater video survey of the Goukamma Marine Protected Area's ichthyofauna and a subsequent community structure comparison with the Betty's Bay, Stilbaai, and Tsitsikamma Marine Protected Areas
    (2020) Dando, Jackson Willy; Attwood, Colin
    The Goukamma Marine Protected Area (GMPA) along the South African south coast has been in existence since 1990. The MPA encompasses 40.2 km2 of subtidal ocean, 76% of which is made up of sandy substrata and the remainder of which is made of rocky reefs. The imbalance in protected habitat type ratios prompted a proposal for an extension of the MPA's seaward boundary, referred to as the new no-take zone (NNTZ), and a restructuring of its eastern boundary, referred to as the new exploited zone (NEZ). The proposed boundary changes would increase the amount of protected reef by 53% and the overall size of the MPA by 38%. Goukamma has been surveyed using controlled angling surveys (CAS) and underwater visual census (UVC) but has yet to be surveyed using baited remote underwater video (BRUV). I collected and analysed mono-BRUV data over five years to determine patterns in fish community structure in Goukamma and compare it to the pre-existing CAS and UVC data. BRUVs are less invasive and more robust than the other two survey methods and have the potential to become the predominant method of surveying ichthyofaunal communities in South Africa. This work is therefore also intended as a baseline BRUV survey. BRUVs were deployed in Goukamma from 2013 to 2017. The survey produced 328 successful deployment records between 5-41.5 m across reef and sand sites. Date, site coordinates, depth, habitat type, protection zone were used as variables to explain patterns in the fish community data. Fish abundances were recorded using the MaxN metric. MaxN counts were recorded at the instance when the highest number of individuals of each species were present in a single video frame. The deployment records were converted into a single data frame and analysed using the RStudio integrated design environment. Ariids, scyliorhinids, serranids, sparids, and triakids were the most well represented ichthyofaunal families in Goukamma. Boopsoidea inornata, Cheimerius nufar, Chrysoblephus laticeps, Galeichthys feliceps, Mustelus mustelus, Pachymetopon aeneum, Poroderma africanum, Poroderma pantherinum, and Spondyliosoma emarginatum were the most frequently observed species throughout the MPA. Habitat type was identified as the primary determinant of diversity and abundance in the GMPA using multifactor analysis of variance (ANOVA) tests (species richness: F = 191.155, P < 0.001; relative abundance: F = 96.111, P < 0.001) and Wil coxon signed rank tests (Shannon-Wiener: W = 21 102, P < 0.001; Simpson: W = 18 553, P = 4.85x10-10). The reef sites supported a higher species richness and abundance than sandy sites throughout the MPA (Tukey: q = -4.41, P < 0.001 and q = -2.12, P < 0.001, respectively). Diversity and abundance were correlated with each protection zone's predominant habitat type. Exploited zones had significantly higher diversity and abundance than protected zones as a result of the imbalance in Goukamma's protected habitat type ratio (species richness: F = 27.740, P = 7.65x10-16; abundance: F = 10.438, P = 1.51x10-6 ; Shannon-Wiener: W = 17 314, P = 4.58x10-6 ; Simpson: W = 15 896, P = 3.42x10-3 ). The NNTZ had significantly higher species richness and abundance than the NEZ (Tukey: q = 3.07, P < 0.001 and Tukey: q = 1.48, P < 0.001, respectively). The proposed changes will therefore substantially boost diversity and abundance of protected fishes in Goukamma. BRUV samples in Goukamma recorded an overall higher species richness and abundance of sparids, chondrichthyans, and other reef-associated species than CAS and UVC samples. Over 90% more chondrichthyans were recorded in the BRUV samples than by the other two methods. BRUVs are therefore considered to be a suitable replacement for CAS and UVC surveys for the monitoring of South Africa's shallow subtidal ichthyofauna. BRUV data from Betty's Bay, Stilbaai, and Tsitsikamma were available for comparison with the Goukamma data, allowing for an extensive analysis of the south coast's ichthyofaunal communities. A combined data frame of 466 successful BRUV deployments from the four study areas was created. Multi-factor ANOVA tests indicated that location (F = 27.1, P = 1.00x103 ), depth zone (F = 17.4, P = 1.00x103 ), protection status (F = 23.1, P = 1.00x103 ), and habitat type (F = 91.8, P = 1.00x103 ) were all significant in determining community structure among the study areas. Reef sites had higher species richness and abundance than sand sites and species richness and abundance decreased from east to west along the south coast according to subtropical subtraction. However, the presence of an additional habitat type in Betty's Bay, namely kelp forests, resulted in it having a higher species richness and abundance than Stilbaai to the east. Betty's Bay's community structure was the least similar to the other three study areas as a result of the localised kelp forests in and around the MPA. These kelp forests shifted Betty's Bay's community structure away from the sparid-dominance observed in Stilbaai, Goukamma, and Tsitsikamma and towards a carangid- and scyliorhinid-dominance. However, cold-water associated sparids such as Pterogymnus laniarius were more abundant in Betty's Bay than the other study areas. Almost 80% of the species recorded among the study areas were represented in two or more of the four MPAs, indicating a good degree of redundancy of protection along the south coast within the depth ranges sampled. These data suggest that the Cape south coast is adequately protected from the perspective of fish representation. Review of the De Hoop, Sardinia Bay, and Bird Island MPAs should be conducted to further examine complementarity and redundancy of protection along South Africa's south coast.
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    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.
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    An intensive study of movement and population dynamics in Triakis megalopterus in the De Hoop Marine Protected Area, South Africa
    (2024) Wagstaff, Samantha; Attwood, Colin
    Coastal dwelling sharks are particularly at risk of decline due to the predicted rapid change in their environment and high incidences of accidental bycatch. Effective protection typically includes managing the fishing mortality and providing marine protected areas (MPAs) as refugia. To this effect, estimating natural mortality rates and home range size is vital. Triakis megalopterus, a commonly caught, endemic coastal shark of South Africa provides an excellent opportunity for this assessment. Mark-recapture data of 924 T. megalopterus caught at two sites in the De Hoop MPA from 1996 to 2020, a no-take reserve, were used to estimate home range size and natural mortality rates. Displacement frequencies were modelled to estimate home range size and space use within the MPA. Natural mortality rates for both sexes were estimated using two methods, one based on length data, combined with pre-established growth models, and another using the probability of recapture. Triakis megalopterus at De Hoop MPA displays a high level of philopatry. Individuals show consistent small movements over periods up to thirteen years. Multiple recaptures of the same sharks indicate frequent and repeated use of home ranges in the order of 1.0 km of coastline. The best fit model suggests a high degree of central tendency in space use. Skewed sex ratios towards females could be due to sex-specific longevity or mortality. The population had low mean natural mortality rates of 0.099/yr [95% C.I. 0.088/yr to 0.112/yr] for males and 0.072/yr [95% C.I. 0.062/yr to 0.082/yr] for females as estimated from the length data. These rates were close to published findings in other studies, which used models fitted to environmental and life-history data. Survivorship estimates for T. megalopterus based on tag-recapture probabilities were lower than expected compared to length-derived natural mortality rates, but still suggest a low natural mortality rate. The difference is likely caused by deflated length-based mortality estimation, caused by the high number of large female capture lengths, tag loss and predation. In conclusion, the small movements, philopatric tendencies, sex-specific movements, and rates, and small home range of T. megalopterus suggests that populations are highly susceptible to fishing and individuals are unlikely to radiate far and replenish diminished locations.
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    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.
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    Aspects of the early life history and a per-recruit assessment of white stumpnose Rhabdosargus globiceps (Pisces: Sparidae) in Saldanha Bay with recommendations for future research and monitoring
    (2011) Arendse, Clement J; Attwood, Colin
    This study focuses on several aspects of the life history of R. globiceps, and includes a study of juvenile habitat, a hatch date analysis, methods to increase precision of age estimates obtained from reading otoliths and a per-recruit assessment.
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    An assessment of the long-term changes in chondrichthyan abundance on the inshore trawl grounds of the Agulhas Bank, South Africa
    (2013) Mussgnug,Robert Sebastian; Attwood, Colin
    Trawl fisheries have been operating in South African waters for roughly 110 years. In contrast to other trawl fisheries, the South African fishery was opened by government-funded scientific trawl surveys beginning in 1898. Detailed records of survey trawls undertaken immediately prior to and during the beginning of commercial trawling activity provided a rare opportunity to examine longterm changes in fish abundance. This dissertation focuses on the chondrichthyans, which are believed to be the group of fishes most at risk from intense exploitation. Despite some problems associated with changes in taxonomy and the efficiency of gear, this analysis was able to compare two distinct periods at three taxonomic levels: The periods were taken to represent baseline values prior to the opening of trawl fisheries and contemporary data, separated by roughly 80 years of intense, trawling activity. Three historically important trawl grounds were identified as having sufficient samples from each period. Between the surveys, trawl velocity did not deviate much from contemporary trawl velocities, although all surveys were found to have a significantly different velocity. In respect to the catch composition, significant changes were found in the relative abundance of the total catch composition, as a general shift from large, long-lived species towards smaller species was found. This applied both for teleosts as well as chondrichthyans, with the entire chondrichthyan catch composition showing a decrease, with the exception of Callorhinchus capensis, which increased significantly. Changes in chondrichthyan swept-area density were found to follow those trends found in the relative abundance: An increase was found in Callorhinchus capensis, whereas all other species decreased. All chondrichthyans were classed in low productivity categories and were assigned a high risk factor to overfishing. Reasons for the declines in the chondrichthyan assemblage were low fecundity, slow maturation and the inability due to these factors to adapt to an environment altered by trawling. Only in the case of Callorhinchus capensis were secondary effects of trawling such as the removal of competitor species likely to have caused the increase in relative abundance and swept area density as well as Callorhinchus capensis having a relatively high fecundity among chondrichthyans. In general, chondrichthyan decreases exceeded those of teleosts, and this work provides broad empirical support for the hypothesis that the low fecundity and slow growth of chondrichthyan species places this group at higher risk than teleosts.
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    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.
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    Baited remote underwater video survey of macro-invertebrate distribution and abundance across False Bay, South Africa
    (2014) Carr, Isabelle; Attwood, Colin
    Assessing invertebrate species diversity and distribution based on environmental predictors is essential for conservation planning. South Africa need to understand ecological patterns to better plan for species conservation. South Africa’s unique coastline requires additional protection, but the design of areas is reliant on evidence based research. South Africa has a distinctive marine environment and is host to tropical, subtropical and temperate invertebrate species. False Bay in the Western Cape province of South Africa is a biodiversity hotspot with high species richness due to the overlap of two bioregions. This project reports on the first comprehensive camera survey of False Bay’s invertebrate population and assesses diversity across more habitat types and a greater depth range than previous dredge studies. 154 sites were sampled across summer and winter, reef and sand and three depth categories: shallow (5-15 m), intermediate (16-30 m) and deep (31-50 m). A total of 67 species from 8 phyla were recorded in this study. Winter samples showed a greater diversity than those sampled in summer (p=0.004). Intermediate depths (Shannon-H=1.184) and reef substrate (Shannon-H=1.403) support a greater diversity of invertebrate species. Habitat emerged as the most significant predictor of species distribution in the bay (p=0.01). Depth (p=0.01) and season (p=0.03) were also of influence, but to a lesser extent. Reef sites were separated from sand sites by the presence of Jasus lalandii and Comanthus wahlbergi on the former and Bullia laevissima, Marthasterias glacialis and Ovalipes trimaculates on the latter. Reef species J. lalandii and Tropiometra carinata and sand species B. laevissima and M. glacialis had the greatest contribution to dissimilarity between winter and summer samples. Complex granite reefs should be a main priority in invertebrate conservation as they host the greatest species diversity and abundance of all habitats sampled. BRUVs have provided a non-invasive, non-destructive method of sampling invertebrate species on all habitat types and are recommended for use in future studies of invertebrate species composition.
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    Baited remote underwater video survey of reef fish in the Stilbaai marine protected area, with an assessment of monitoring requirements
    (2012) De Vos, Lauren; Attwood, Colin; Götz, Albrecht
    Long-term monitoring of changes in species abundance and community composition within marine protected areas (MPAs) is essential to assess whether conservation goals are being reached. The costs, logistics and sampling biases inherent to traditional monitoring methods limit sustainable monitoring in all MPAs along the South African coastline. Baited remote underwater video (BRUV) technology offers non-extractive monitoring with lower labour and cost requirements, whilst eliminating inter-observer variability and increasing statistical power. Species richness and relative abundance were assessed employing BRUV technology in the Stilbaai MPA in the Western Cape, South Africa. ... [The] result corroborated findings from traditional underwater visual census (UVC) and controlled angling surveys, confirming BRUV technology as a sound monitoring tool.
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    Biodiversity patterns in False Bay: an assessment using underwater cameras
    (2021) De Vos, Lauren; Attwood, Colin; Bernard, Anthony; Götz, Albrecht
    Understanding how marine biodiversity is distributed, and what drives these patterns, relies on good descriptions of marine ecosystems. This information should inform the protection of biodiversity and guide its management. Relationships between marine landscapes and biodiversity therefore need to be described at scales that are useful to regional management. Simultaneous sampling of marine biodiversity and the seafloor is challenging, so baseline ecosystem descriptions are often mismatched in their abiotic and biotic components. Cameras can sample the seafloor and its associated biodiversity concurrently, with good coverage and at low cost. These are important considerations for sustainable monitoring to inform conservation management in resource-limited regions. Terrestrial landscape characterisations cannot simply be translated to the ocean because interpreting remote ocean terrain assessments in a manner relevant to ecological analysis is complicated by depth, circulation, light attenuation, and other oceanographic variables. The integration of some of these concepts into rapid marine biodiversity assessments therefore needs ground-truthing where they are applied in new regions, to advance sustainability in long-term marine monitoring. This thesis investigated the relationship between landscape composition and benthic marine biodiversity in False Bay, South Africa using novel methods that extended biodiversity sampling across more depths and habitats than any single, previous survey of the bay. This study's approach piloted sampling and interpreting the marine landscape and biodiversity over matching spatial and temporal scales. The coverage, repeatability and ecosystem-level scale applied to this study make it a useful basis to develop monitoring protocols that are appropriate to conservation management at relevant regional scales. New insights for the region include a) a new description of the seafloor using classifications that explain the variation in epibenthic megafauna and ichthyofauna communities, b) a quantitative account of the epibenthic megafauna on the eastern reefs where species diversity was highest, and c) the synthesis of seafloor descriptions with the epibenthic megafauna and ichthyofauna to describe nine regions of False Bay, relative to two previous descriptions of "grounds". Photographs and multibeam bathymetry characterised the seafloor on eight transects across the bay and were ground-truthed by grab samples repeated at representative sites. Two new classifications were applied to describe the seafloor. Horizontal seafloor heterogeneity was highest in the east, and reef was distributed along the eastern and western margins. The Collaborative and Automated Tools for Analysis of Marine Imagery (CATAMI) scheme captured accurate broad-scale descriptions of the physical landscape when applied to photographs. Grabs are still needed to provide fine-scale particle size data on soft sediments where most invertebrate diversity is likely infauna. However, CATAMI abstracts fine-scale sediment variation into simpler groupings more useful for rapid ecosystem assessment. Photographic sampling is repeatable, which is useful for long-term ecosystem monitoring. Photographs taken using a jump camera rig assessed the epibenthic megafauna across habitats and along depth gradients. Rényi diversity showed that species diversity increased in shallow waters up to 40 m, reaching a peak between 30 and 40 m, before decreasing with increasing depth. Species diversity was highest in the east, where seafloor heterogeneity was also highest. This result is interesting because eastern False Bay falls mostly outside the current marine protected area (MPA) network and has been relatively under-represented in previous surveys. The jump camera documents ecosystem-level biodiversity patterns and processes, and the random point count method in Coral Point Count (CPCe) is useful to assess community composition and cover on reefs. The relative abundance and distribution of ichthyofauna were assessed using baited remote underwater video systems (BRUVs). Fifty-seven fish species from 30 families were recorded between 4 and 84 m. Rényi diversity showed that species richness was similar for reef and sand overall, but the Shannon-Wiener diversity index (H') was significantly higher on reef sites than on sand sites (t = 1.972, p < 0.0001). Species richness for the whole bay was similar in winter and summer, which indicates that the same species are likely present year-round; however, the Shannon-Wiener diversity index was significantly higher in winter (t = 1.973, p < 0.013) and evenness was greater in winter at the level of the site. These findings highlight the difficulty in protecting sufficient sand habitat to encompass the patchy distribution of sand-associated species and highlight seasonal differences in optimal visibility for future camera monitoring surveys by conservation management. There are clear patterns in the marine biodiversity of False Bay, at various scales, that can be detected using novel methods for the region. The study's approach to classifying both the landscape and its associated biodiversity creates a framework for future ecosystem threat assessment that can be applied elsewhere, especially along the South African coastline.
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    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.
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    Biology of Albacore tuna (Thunnus alalunga, Bonnaterre 1788) off the South West Coast of South Africa
    (2013) Norman, Stewart James; Attwood, Colin; Marsac, Francis
    Albacore tuna (Thunnus alalunga) is a highly migratory species found in all of the worlds oceans. The origin of albacore south of Africa is in question. This species constituted 85% of catches of the South African commercial tuna fishing fleet from 2000-2009 and is an important species in supporting a large boat-based recreational fishery. Albacore were sampled at angling competitions, which offer a repeatable and cheap source of tuna, in the Western Cape of South Africa during 2012 and 2013. 119 Samples were used to determine a length-weight relationship and to provide conversion ratios of various body measurements to fork length when total length was not available. Visual examination of testes and ovaries indicated that albacore are not spawning off the coast of South Africa.A comparison between the ease of using sectioned sagittal otoliths and first dorsal spines indicated that otoliths were more precise for estimating the age of albacore. Von Bertalanffy growth parameters were estimated from 51 fish, ranging from 2-9 years old (L∞=1100.07 mm; K=0.238 y-1; t₀=-2.14). Stomach content analysis indicated that the mesopelagic squid Lycoteuthis lorigera is the most important prey item for South African albacore. δ13C and δ15N stable isotope analysis of albacore and yellowfin tuna (T. albacares) muscle tissue showed that they feed on prey that may depend on different primary producers but that the two species of tuna share the same niche in the southern Benguela food web. Trophic levels of 3.8 and 3.76 were assigned to albacore and yellowfin tuna respectively.
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    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.
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    Coral bleaching responses in Sodwana Bay, South Africa
    (2013) Harikishun, Ameil; Attwood, Colin; Sink, Kerry J
    This study assessed the bleaching response (BR) of coral colonies within the central reef complex in Sodwana Bay, South Africa. Bleach surveys were conducted at 16 sites on 8 reefs over the period of 2007 to 2013. A total of 12 858 coral colonies from 30 taxa were randomly sampled and colonies were placed into 7 categories of bleaching response. This allowed for the calculation of taxon-specific BR as a weighted percentage of coral cover bleached. Continuous temperature records from a permanent temperature gauge on Two Mile Reef were used to assess thermal stress over this period. The percentage of coral colonies that bleached in 2007, 2008, 2011, 2012 and 2013 were 37.4%, 17.4%, 23.8%, 33.6% and 38.8% respectively. A binomial GLM model framework was used to separate the effects of year, reef and taxon on the bleaching response. Due to inconsistent sampling of sites over time, only data from the seven sites on Two Mile Reef (TMR) and the two sites on Nine Mile Reef (NMR) were included in the model. A total of 6758 coral colonies from the nine most abundantly sampled taxa were used in the assessment of bleaching response for TMR and NMR over the sample period. Taxon was shown to explain most of the variability in the bleaching response of TMR and NMR over time (40.9%). The standardized reef bleaching response of TMR and NMR indicated the same temporal trends with a range of 5% to 28% of live coral surface bleached. Standardized reef-specific BR showed periods of high (2007, 2012 and 2013) and low (2008 and 2011) bleaching response. Low BR in 2008 and 2011 did not correspond to thermal stress (≥27.5°C) suggesting that local upwelling buffered the effects of thermal stress experienced. Standardized taxon-specific bleaching response for TMR and NMR displayed large variability over time and ranged from 2.5% to 45% of live coral surface bleached, with Montipora being the most susceptible and Galaxea and Playgyra being the least. Mean site-specific BR averaged over all years, including all sites, found that Coscinaraea, Montipora, Astreopora and Anomastrea were the most susceptible taxa. This study and other recent studies draw attention to a trend of either episodic or an increasing frequency and intensity of bleaching in southern African reefs.
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    Diet of albacore (Thunnus alalunga) and yellowfin tuna (Thunnus albacares) off the south-west coast of South Africa
    (2022) Allie, Mogammad Ighsaan; Attwood, Colin
    Considering the magnitude of albacore and yellowfin biomass, these two economically vital tuna species apply a considerable amount of predation pressure on prey communities off the South African coast. Nevertheless, little is known about their respective diets in this upwelling region. Fish Aggregating Devices (FADs), otherwise used globally, are banned in South Africa therefore giving us a unique opportunity to examine the natural diet of the tuna surrounding our shores. Sixty-one stomachs were sampled from recreational fishing competitions in May 2016 and 2018 off the south-west coast of South Africa to investigate the diets of albacore and yellowfin tuna. The fork length (mm) and wet weight (g) of the fish were recorded. The importance of each prey in the diet was estimated by the Index of Relative Importance (IRI). Each sample specimen was cut open, had its entire stomach carefully removed and frozen for later dissection and analysis. Prey items were initially grouped into fish, cephalopods and crustaceans and later identified to the lowest possible taxonomic level, counted, and weighed. The difference in diet between the species was investigated and modelled by Analysis of Similarity (ANOSIM), Non-Metric Multidimensional Scale (NMDS) and Principal Component Analysis (PCA). The feeding strategy was determined by Costello's Diagram. The 43 albacore and 18 yellowfin tunas ranged in fork length from 740 to 959 mm and 803 to 1720 mm, respectively. The most important prey class based on IRI in the diet of albacore was crustaceans (6162.01), followed by cephalopods (3672.47). For yellowfin the highest IRI was cephalopods (6269.39) followed by fish (3977.53) and unlike the diets of yellowfin in other parts of the world, crustaceans were numerically a very low prey item making up just 15.84% of the diet. Yellowfin, the larger of the two tuna species consume larger prey items and are more opportunistic than albacore, showing a greater vertical feeding range, by diving deep for cephalopods and surface feeding on offal from hake trawlers. Intra-species variations for both tuna proved to be smaller than the difference between the two species, with no substantial changes in either diet based on fish size. Unlike diets of tuna species in other parts of the world, the data suggest that southern African albacore and yellowfin were less dependent on fish (possibly due to the lack of FADs in the case of yellowfin), but more likely due to the higher availability of crustaceans and cephalopods at the upwelling front. The magnitude of the role of cephalopods in the Benguela ecosystem is likely to be underestimated.
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    The diet, reproductive biology age and growth of yellowtail, Seriola lalandi, in South Africa
    (2014) Dunn, Kieron; Attwood, Colin; Jarre, Astrid; Kerwath, Sven
    Yellowtail, Seriola lalandi, is an important line-caught fish in South African waters, yet little information is available on their life-history. This study aims to add information on the diet and feeding habits, reproductive biology and the age and growth of yellowtail in South Africa. The diet of 62 yellowtail caught in the Western Cape of South Africa between 2011 and 2012 was investigated. Fish sampled by line and speargun ranged from 488 to 916 mm fork length (FL). Prey items were removed from stomachs, sorted, counted and weighed in order to calculate the percentage number (% N), percentage weight (% W), frequency of occurrence (% F) and index of relative importance (% IRI). Of the 62 stomachs examined 11 (17.7 %) were empty, 16 (26.0 %) contained only unidentifiable remains and 47 (82.5 %) contained identifiable remains. Prey items covered 18 species belonging to five classes: bony fishes, crustaceans, cephalopods, polychaetes and bivalves. Small pelagic fish were the dominant prey type, followed by crustaceans. The remaining taxa were of negligible importance. Some dietary differences were observed between sample areas. Most notable was the increased importance of crustaceans at Dassen Island on the West Coast compared to the sites at Robben Island, False Bay and Struisbaai. The reproductive characteristics of yellowtail were documented from fish collected from 1974 to 2012. Samples were collected from Cape Infanta on the South Coast to Lamberts Bay on the West Coast of South Africa. Histological validation of macroscopic staging criteria revealed that active and developing ovaries are commonly staged incorrectly. A protracted spawning season from November to February with peak spawning in December and January was deduced from GSI values. No hydrated eggs were observed. Females matured at 550 mm FL (95 % CI = 532 - 570 mm) and males matured at 585 mm FL (95 % CI = 555 - 619 mm). The age and growth characteristics of yellowtail in South African waters were determined from readings of whole sagittal otoliths collected from 1974 to 2012. Whole otoliths were considerably easier to read than sectioned otoliths. A total of 524 whole otoliths were taken from fish ranging from 430 to 1080 mm FL, of which 141 (27 %) were discarded and 384 (73%) were readable. Agreement between all three readers was 13 % (n = 50) and between any two was 71 % (n = 274). Maximum ages for male and female yellowtail were 7 and 8 years respectively. Age at 50 % maturity (A50) for males it was 2.3 years while females matured (A50) at 3.6 years. Von Bertalanffy growth parameters did not differ between males and females (P > 0.05). A statistical penalty was used to keep the estimated growth parameters within biological limits and produced a von Bertalanffy growth equation with an L∞ and K of1064 mm and 0.17 y-1 respectively. The growth performance index (φ) of yellowtail in South African waters was found to be 3.51. This is high for the family Carangidae but on par with other species in the genus Seriola. The life history characteristics for yellowtail in South African waters closely resemble those of other yellowtail populations. The diet of yellowtail in South African waters represents that of a robust generalist feeder that is not reliant on specific prey for its survival. The age, growth and reproductive characteristics of yellowtail in South African waters indicate that they are a fast growing and relatively early maturing species. These life-history characteristics indicate that the stock is resilient in relation to other line-fish species, but the large proportion (41%) of fish caught below the 50 % size at maturity suggests that a revision of the minimum size limit should be considered.
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    Distribution and community structure of Chaetodontidae (Perciformes) in iSimangaliso Wetland Park with the view to applying the Butterflyfish Indicator Hypothesis in this region of South Africa
    (2014) Noble, Talitha Gaby; Attwood, Colin; Sink, Kerry J
    Coral reefs are globally in a vulnerable state, because of both human impacts and environmental alterations. An understanding of coral reef ecosystems and the ability to detect changes in the reef environment early on are necessary to apply effective conservation. The co-evolution of coral and coral feeding fishes means that some species may exhibit interactions useful for indicating reef health, acting as an early warning system. Chaetodontidae (Perciformes) are one such family, containing coral dependent (obligate corallivore) species. This concept is known as the Butterflyfish Indicator Hypothesis (BIH). Through the collection of baseline data for butterflyfish abundance, diversity and species composition, the possible applicability of the BIH was investigated within Marine Protected Areas (MPA¡¯s) of iSimangaliso Wetland Park, on the north-eastern coast of South Africa. Other factors possibly impacting butterflyfish distribution were also investigated in this region. These factors were level of MPA protection (sanctuary or partially protected), reef rugosity and site effects. 78 transects across 13 dive sites were swum using Underwater Video Census (UVC) for data capture. Reef rugosity displayed no impact on any of the sampled factors, whilst site and protection level did. Protection was the factor with the greatest influence on butterflyfish species richness (df = 77, t = 2.85, p < 0.005), evenness of spread (df = 77, t = 1.79, p < 0.05) and total abundance, as revealed by the General Linear Model (GLM) with the lowest Aikake¡¯s Information Criterion (AIC) (y = ¥âₒ + ¥â©û (protection)). None of the factors altered Chaetodon meyeri distribution significantly, the only observed obligate corallivore, for which low abundances were observed. Differences in total butterflyfish abundance and species diversity appear to be particularly useful in revealing human impacts on coral health. The lack of C. meyeri, likely accounted to low abundances of its preferred coral Acropora (Scleractinia: Acroporidae), suggest that the BIH is not useful in this region.
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    The effects of a marine reserve on galjoen (Dichistius capensis) at Cape Point, South Africa, and implications for the management of the recreational fishery
    (2013) Elston, Chantel; Attwood, Colin
    Marine protected areas (MPAs) are gaining credibility in the scientific community because of their duality as a conservation and fishery management tool, but sometimes the actual effects of an MPA fall short of the expected outcomes. Case-by-case studies are needed to understand what works and what doesn’t and this understanding can then be applied to decision making and adaptive management. The galjoen (Coracinus capensis), a surf zone teleost endemic to South Africa, is a popular fish for recreational shore anglers and as such the population has declined to dangerously low levels. Marine reserves were established around Cape Point to try and counteract this decline. This study aimed to determine whether these reserves are having a positive effect on galjoen mortality, density and size. A controlled shore angling program has been running on the Cape Peninsula since 1986 in which anglers use a standardised fishing technique. The anglers record the length of their fishing trip as well as the fork length of the fish they catch. Two sites located in near proximity to each other, one in a reserve and one in an exploited area, were chosen from the data set to compare. This avoided the conflicting problem of major habitat differences. General linear models (GLMs) were used to isolate the effect of area on the catch per unit effort (CPUE) as well as fork length, and a negative log-likelihood function was used to estimate the mortality rate and sex ratio for each area. CPUE increased significantly from of 1.02 ± 0.81 galjoen.angler-¹.hour-¹ in the exploited area to 1.48 ± 0.85 galjoen.angler-¹.hour-¹ in the protected area and fork length increased significantly from 300.69 ± 34.71mm in the protected area to 329.31 ± 40.19mm in the exploited area. The GLMs revealed that the parameters ‘area’ and ‘year’ significantly affected the variation in CPUE and fork length, and that area had the greatest explanatory power in both cases suggesting that the reserve had a positive effect on the galjoen density and size. The mortality estimate for the protected site, which was taken as natural mortality, was 0.55 year-¹ and the mortality estimate at the exploited site was 1.0 year-¹. Fishing mortality (F) was estimated as 0.45 year-¹ which was considered to be close to FMSY. Increases in CPUE over time in the exploited area led to the hypothesis that the reserve is re-stocking adjacent exploited areas. A reduction in F over time suggested that effort is reduced in the exploited study area, but it is unknown whether this effort has been displaced to another area adjacent the reserve. Because conventional fishery management tools are difficult or impossible to enforce for the galjoen stock and because the reserves appear to be positively affecting the galjoen within the reserve, it is suggested that the reserves are the optimal and most efficient conservation and fishery management tool for the galjoen stock.
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    Effects of protection and environmental factors on rock lobster, abalone, and giant periwinkle abundances in the Table Mountain National Park Marine Protected Area
    (2022) Gardner, Kathryn; Attwood, Colin; Kock, Alison
    The Table Mountain National Park Marine Protected Area (TMNP-MPA) was established in 2004 to restore and protect the Cape Peninsula's biodiversity, including the populations of exploited macro-invertebrate species. Scientific publications on MPAs support the idea that biodiversity protection is well served by MPAs, particularly no-take MPAs. Focusing on west coast rock lobster, abalone and giant periwinkle, historically the three most important invertebrate resources of the region, this study assesses the effectiveness of spatial regulations in the TMNP-MPA. Three comprehensive peninsula-wide SCUBA surveys were conducted in 2000, 2003 and 2019. Patterns in the abundance of the three species were analyzed using generalized-linear models (GLM) to explore the effects of the TMNP-MPA and no-take zones within, whilst accounting for habitat, depth, species interactions, and the physical protection offered by False Bay. Overall, the rock lobster abundance around the Cape Peninsula decreased since the implementation of the TMNP-MPA, however, to a lesser degree than the dramatic overall decline of the rock lobster population in South Africa over this time. This decrease is possibly due to increased illegal harvesting of adults and juveniles and increased predation from recovering fish populations within TMNP-MPA. However, rock lobster abundance did respond positively to the length of protection in no-take zones, suggesting that the enforcement of no-take zones within the MPA was effective. The beneficial effects of the no-take zones are likely insufficient to compensate for increased harvesting in adjacent areas within the MPA but prevented a greater decline in rock lobster. No change in abalone abundance was detected over the years in the TMNP-MPA or within no-take protected zones. The regional abalone population has declined drastically over a similar period due to poaching. Effective policing has likely prevented the abalone within the MPA from following suit. Giant periwinkle abundance increased since the establishment of TMNP-MPA. However, it is unknown if this pattern reflects the regional giant periwinkle population, so it cannot be determined if the increase is a direct result of the MPA. However, the giant periwinkle abundance had not benefited from the no-take zones, suggesting general harvest restrictions in TMNP-MPA are affording them sufficient protection, or that the greater population is increasing. A combination of environmental factors, such as warmer water temperatures and reduced nutrients, could explain the decreased abundance of rock lobster in False Bay, compared to those along the Peninsula's west coast. Predation by rock lobster could explain the opposite pattern found in both the giant periwinkle and abalone that were more common in False Bay. Expected abundance patterns based on the habitat preferences of each species, associated with water depth, the presence of sand, and kelp and urchin density were found. The creation of the TMNP-MPA, with its many and varied no-take and harvest zones provided an excellent opportunity to test the effectiveness of no-take spatial protection in a complex marine community and in the vicinity of a heavily exploited coastal zone near a metropolitan setting. This is especially valuable for macro-invertebrates, which are not commonly the focus of MPA studies in South Africa. This study supports the use of MPAs as a protection measure for overexploited macro-invertebrates. The extent of the success of this protection is evident by way of comparison with the magnitude of declines elsewhere. As both rock lobster and abalone fisheries are heavily plagued by poaching, the impact of no-take zones and the enhanced policing brought by the TMNP-MPA as a whole, likely helped to buffer the declines of rock lobster and abalone, respectively.
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    Empirical evaluation of the effectiveness of South Africa's marine protected area network in representing fish communities
    (2011) Fernández, Sofía Solano; Attwood, Colin
    In this study, fish community structure as sampled by shore angling, trawling, boat-based line-fishing and seine netting was compared across the EEZ of South Africa, including sites in designated MPAs. Multivariate statistics were used to assess the extent to which MPAs represent the full range of fish communities in South African waters. Results show there is an increase in fish diversity from west to east along the South African coast.