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O'Donoghue S.H.,University of KwaZulu - Natal | Drapeau L.,Paris West University Nanterre La Defense | Peddemors V.M.,KwaZulu Natal Sharks Board
African Journal of Marine Science | Year: 2010

The annual movement of South African sardine Sardinops sagax up the east coast of South Africa, known as the 'sardine run', was investigated using data from aerial surveys for the period 1988-2005 and compared with remotely sensed sea surface temperature (SST) and chlorophyll a data. Sardine sighting rates were highest within the Waterfall Bluff Bight off the Eastern Cape Coast, where conditions appeared to be most favourable. Sardine and predator sightings decreased significantly northwards of Mdoni on the KwaZulu-Natal (KZN) coast, whereas the proportion of nearshore sightings increased. The causal mechanism for this inshore concentration is suggested to be the influx of warm Agulhas Current water from the Durban Eddy that forces sardine shoreward. Cape gannet Morus capensis, common dolphin Delphinus capensis and sardine distributions were associated, and there was an association between SST and sardine and predator distributions. There was a marked increase in bottlenose dolphin Tursiops aduncus sightings upon commencement of the sardine run, with these dolphins being considered to be a 'migratory' stock that enters KZN waters every winter. © NISC (Pty) Ltd. Source

O'Donoghue S.H.,University of KwaZulu - Natal | Drapeau L.,Paris West University Nanterre La Defense | Dudley S.F.J.,KwaZulu Natal Sharks Board | Dudley S.F.J.,University of KwaZulu - Natal | Peddemors V.M.,University of KwaZulu - Natal
African Journal of Marine Science | Year: 2010

The nearshore presence of sardine Sardinops sagax on the KwaZulu-Natal (KZN) coast was investigated using sightings data collected by the KZN Sharks Board from 1997 to 2007. The spatio-temporal distribution of sardine was described in relation to that of their predators and to environmental conditions, and subjected to generalised linear model (GLM) and generalised additive model (GAM) analyses. Variables describing spatio-temporal conditions performed best in the models (r2 = 0.52) with seasonal effects, specifically June and July, making the greatest contribution towards sardine presence. The contribution of the years 2003, 2006 and 2007, and the KZN North Coast, was significantly lower. The predator variables were highly significant (r2 = 0.48) with Cape gannets Morus capensis, followed by the sharks/gamefish and common dolphins Delphinus capensis, being most closely associated with sardine presence. Environmental variables were not as influential in the GLM models (r2 = 0.23), but some variables were useful in describing conditions favouring sardine presence, namely calm current conditions, light north-westerly land breezes and stable atmospheric conditions. Increasing sea surface temperature (SST), moderate north to south currents, large swells and turbid water had a negative impact upon sardine presence. North-easterly and north-westerly winds and north to south currents had a cooling effect upon nearshore SSTs, whereas south-easterly winds and increasing air temperatures caused nearshore warming. Results are discussed in the context of developing an understanding of the mechanisms that govern fine-scale movements of sardine shoals during the KZN sardine run, with a view to predicting such movements. © NISC (Pty) Ltd. Source

Plon S.,South African Institute For Aquatic Biodiversity | Albrecht K.H.,Bremen University of Applied Sciences | Cliff G.,KwaZulu Natal Sharks Board | Froneman P.W.,Rhodes University
Journal of Cetacean Research and Management | Year: 2012

Data from bycaught, but otherwise presumed healthy individuals can contribute important biological data on species of cetaceans that are otherwise lacking. This study utilises data collected from systematic necropsies performed between October 1970 and May 2010 on 142 Indo-Pacific humpback dolphins (Sousa chinensis), 607 Indo-Pacific bottlenose dolphins (Tursiops aduncus), and 640 long-beaked common dolphins (Delphinus capensis) incidentally caught and drowned in the shark nets off KwaZulu-Natal, South Africa. The aim of this analysis was to: (1) determine average absolute and relative organ weights for the three taxa as baseline values for later pathological examinations; and (2) examine potential correlations with the physiology and ecology in the three genera. Body length-weight relationships were described for the three species, indicating that S, chinensis is more robust than T. aduncus, with D. capensis being the smallest species out of the three taxa. Organ weights, as a percentage of total body weight were examined for the three delphinids. Organs examined included heart, lungs and trachea, liver, kidneys, spleen, and testes. Relative heart, liver and kidney weights were significantly larger in the small-bodied, fast-swimming D. capensis, than in the slower, more coastal S. chinensis and T. aduncus, possibly reflecting differences in activity patterns between the three species. Relative lung and trachea weights were not significantly different in the three species. Combined testes weight, as a percentage of total body weight, in combination with information on group size and sexual dimorphism suggested a monogamous or extreme polygynous (harem) mating system in S. chinensis, frequent copulations in T. aduncus, and sperm competition in D. capensis. The results of the present study suggest that the relative sizes of the major organs in the three genera are a reflection of the differing life histories and ecologies of the species examined. Source

Atkins S.,Endangered Wildlife Trust | Atkins S.,University of Witwatersrand | Cliff G.,KwaZulu Natal Sharks Board | Cliff G.,University of KwaZulu - Natal | Pillay N.,University of Witwatersrand
Biological Conservation | Year: 2013

Humpback dolphins (Sousa plumbea) in South Africa are classified as Vulnerable and one quantifiable threat is accidental mortality in the shark nets in KwaZulu-Natal. We investigated the spatial, temporal and life history patterns of this bycatch to guide mitigation strategies to decrease humpback dolphin capture. A total of 203 individuals were caught between 1980 and 2009. We analysed patterns of captures in relation to the area of capture (location) and year and month of retrieval from the nets. We also analysed the distribution of the sex and size (body length) of humpback dolphins. Most catches (61%) occurred at Richards Bay in the northern part of their distribution in South Africa. Annual catch rate fluctuated considerably and there was little seasonality. The sex ratio was male-biased (1.55:1) and in particular skewed towards adolescents (56%) which constituted the majority of the catch. We suggest that mitigation strategies be focused at Richards Bay, throughout the year. Of the existing shark net mitigation strategies, changing fishing gear from nets to baited hooks (drumlines) could be useful to decrease humpback dolphin capture rates. © 2012 Elsevier Ltd. Source

Davidson B.,Saint James School of Medicine | Cliff G.,KwaZulu Natal Sharks Board | Cliff G.,University of KwaZulu - Natal
Fish Physiology and Biochemistry | Year: 2011

Female raggedtooth sharks (Carcharias taurus) migrate from the waters off the eastern Cape past KwaZulu-Natal and up to southern Mozambique and then back on an annual basis. They mate off the KwaZulu-Natal coast, gestate the pups off Mozambique, then deliver same off the eastern Cape. Prior to mating, they hypertrophise their livers and store large amounts of lipid, then towards the end of gestation subsist on this stored lipid as well as using it to feed their pups in utero. Raggedtooth sharks are aplacental, and hepatic lipids provide nutrients to the pups via continued ovulation throughout pregnancy. The fact of the liver hypertrophy was well documented, but whether the nature of the stored lipid or the amount of lipid per Kg of liver changed with season was unknown. Samples from raggedtooth females caught throughout the year were analysed for their lipid and fatty acid contents and significant differences noted between lipid, but not fatty acid, concentration with certain seasons. Liver mass decreased from spring to winter (16.3-9.9 kg) as did lipid concentration (572-326 mg/g). Within the fatty acids, 22:6n3 was ±17%, 20:5n3 ±7%, total n3 ±30% and total n6 ±7%. Also, both total polyunsaturates (±36%) and total monounsaturates (±33%) were greater than the total saturates (±28%). © 2010 Springer Science+Business Media B.V. Source

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