Search results for: A. K. Whitfield

Items from 1 to 16 out of 16 results

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River flow, zooplankton and dominant zooplanktivorous fish dynamics in a warm‐temperate South African estuary

N. Mbandzi, R. J. Wasserman, S. H. P. Deyzel, N. G. Vine, more

Journal of Fish Biology > 92 > 6 > 1747 - 1767

The possible links between river flow, zooplankton abundance and the responses of zooplanktivorous fishes to physico‐chemical and food resource changes are assessed. To this end, the seasonal abundance, distribution and diet of the estuarine round‐herring Gilchristella aestuaria and Cape silverside Atherina breviceps were studied in the Kariega Estuary. Spatio‐temporal differences were determined...

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Biomass and productivity of fishes in estuaries: a South African case study

A. K. Whitfield

Journal of Fish Biology > 89 > 4 > 1917 - 1930

Estuaries are well known for their role as nutrient and detrital sinks that stimulate high levels of both primary and secondary production which, in turn, support a large biomass of fishes per unit area. This study reviews available information on coastal fish biomasses (g m⁻² wet mass) and productivity (g m⁻² wet mass year⁻¹) in order to place South African data on these topics into a global perspective...

article

Tidal amplitude and fish abundance in the mouth region of a small estuary

A. Becker, A. K. Whitfield, P. D. Cowley, V. J. Cole, more

Journal of Fish Biology > 89 > 3 > 1851 - 1856

Using an acoustic underwater camera (Dual Frequency IDentification SONar, DIDSON), the abundance and direction of movement of fishes > 80 mm total length (L_T) in the mouth of a small South African estuary during spring and neap tidal cycles were observed. While the sizes of fishes recorded were consistent across both tide cycles, the number of fishes passing the camera was significantly greater...

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Trophic Dynamics of the Cape Stumpnose (Rhabdosargus holubi, Sparidae) Across Three Adjacent Aquatic Habitats

L. Carassou, A. K. Whitfield, L. Bergamino, S. Moyo, more

Estuaries and Coasts > 2016 > 39 > 4 > 1221-1233

Migratory fish species are major vectors of connectivity among aquatic habitats. In this study, conventional stomach contents and stable isotope methods (δ¹³C and δ¹⁵N) were combined to understand how fish of different sizes feed across contrasting aquatic habitats. The Cape stumpnose Rhabdosargus holubi (Sparidae, Perciformes) was selected as an abundant estuarine-dependent species in the permanently...

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Why are there so few freshwater fish species in most estuaries?

A. K. Whitfield

Journal of Fish Biology > 86 > 4 > 1227 - 1250

The freshwater fish assemblage in most estuaries is not as species rich as the marine assemblage in the same systems. Coupled with this differential richness is an apparent inability by most freshwater fish species to penetrate estuarine zones that are mesohaline (salinity: 5·0–17·9), polyhaline (salinity: 18·0–29·9) or euhaline (salinity: 30·0–39·9). The reason why mesohaline waters are avoided by...

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Fish trophic structure in estuaries, with particular emphasis on estuarine typology and zoogeography

T. D. Harrison, A. K. Whitfield

Journal of Fish Biology > 81 > 6 > 2005 - 2029

A comparative analysis of the fish trophic structure was undertaken on some 190 South African estuaries spanning three zoogeographic regions and incorporating three broad estuarine types. Fish biomass trophic guild compositions and biomass trophic spectrum profiles were analysed using multivariate statistical techniques and included both inter‐regional (zoogeographic) and intra‐regional (estuarine...

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Effects of altered estuarine submerged macrophyte bed cover on the omnivorous Cape stumpnose Rhabdosargus holubi

J. N. Sheppard, A. K. Whitfield, P. D. Cowley, J. M. Hill

Journal of Fish Biology > 80 > 3 > 705 - 712

The ecological importance of submerged macrophyte beds to fishes within estuaries was investigated through the example of the ubiquitous Cape stumpnose Rhabdosargus holubi, an omnivorous, vegetation and estuary‐dependent species, using stable‐isotope techniques and long‐term abundance (catch‐per‐unit‐effort) data from the East Kleinemonde Estuary, South Africa. Outputs from a Bayesian mixing model...

article

A global review of the cosmopolitan flathead mullet Mugil cephalus Linnaeus 1758 (Teleostei: Mugilidae), with emphasis on the biology, genetics, ecology and fisheries aspects of this apparent species complex

A. K. Whitfield, J. Panfili, J.-D. Durand

Reviews in Fish Biology and Fisheries > 2012 > 22 > 3 > 641-681

This study reviews published information on Mugil cephalus from around the world, with recent genetic studies indicating that the flathead mullet may indeed be a species complex. Disciplines that are covered range from the taxonomy, genetics and systematics, through a variety of biological and ecological attributes, to biomarker and fisheries studies. The eurytopic nature of M. cephalus is emphasized,...

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An assessment of the size structure, distribution and behaviour of fish populations within a temporarily closed estuary using dual frequency identification sonar (DIDSON)

A. Becker, A. K. Whitfield, P. D. Cowley, J. Järnegren, more

Journal of Fish Biology > 79 > 3 > 761 - 775

The fish populations within the East Kleinemonde Estuary, South Africa, were studied using Dual frequency IDentification SONar (DIDSON) during March 2010 which allowed for direct comparisons of the abundance, distribution and behaviour of a wide size range of fishes along the length of the system. Small schooling fishes <100 mm in total length (L_T) were most abundant while larger size classes 100–300...

article

A weight‐of‐evidence approach to determine estuarine fish health using indicators from multiple levels of biological organization

N. Richardson, A. K. Gordon, W. J. Muller, A. K. Whitfield

Aquatic Conservation: Marine and Freshwater Ecosystems > 21 > 5 > 423 - 432

A prototype Estuarine Fish Health Index (EFHI) using biological indicators from multiple levels of biological organization is described. Three test estuaries of similar size and morphology but with different development pressures were sampled for this purpose.The EFHI integrates the well established Estuarine Fish Community Index (EFCI) developed for South African estuaries, which uses fish community...

article

The status of fish conservation in South African estuaries

A. K. Whitfield, P. D. Cowley

Journal of Fish Biology > 76 > 9 > 2067 - 2089

Estuary‐dependent fish species are defined as those taxa whose populations would be adversely affected by the loss of estuarine habitats. Of the 155 species regularly recorded in South African estuaries, only 32 (21%) are completely dependent on these systems, but this figure increases to 103 species (66%) if partially dependent taxa are included in the analysis. The conservation of fishes in estuaries...

article

Biomass and production estimates of a fish community in a small South African estuary

P. D. Cowley, A. K. Whitfield

Journal of Fish Biology > 2002 > 61 > Supplement A > 74-89

The fish community of the small (17.5ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant (n c. 750000) but due to their small size contributed only 11.7% to the total biomass. The total annual productivity of all fishes in the estuary (n...

article

Fishes as indicators of environmental and ecological changes within estuaries: a review of progress and some suggestions for the future

A. K. Whitfield, M. Elliott

Journal of Fish Biology > 2002 > 61 > Supplement A > 229-250

Estuarine habitats, and the fish assemblages associated with them, are potentially impacted upon by many anthropogenic influences which can have a direct influence on the food resources, distribution, diversity, breeding, abundance, growth, survival and behaviour of both resident and migrant fish species. The direct and indirect coupling between ichthyofaunal communities and human impacts on estuaries...

article

The distribution of littoral fish associated with eelgrass Zostera capensis beds in the Kariega Estuary, a southern African system with a reversed salinity gradient

L. D. Ter Morshuizen, A. K. Whitfield

Oceanographic Literature Review > 1995 > 42 > 7 > 562-563

Eelgrass Zostera capensis has expanded its distribution in the Kariega Estuary mainly in response to the reduced salinity gradient in that system. Seine-net sampling showed that Atherina breviceps, Rhabdosargus holubi, Glossogobius callidus and Mugilidae were the most common fish taxa in the Zostera beds. Fish species richness was maximum in the lower reaches, but highest densities occurred in the...

article

An estuary-association classification for the fishes of southern Africa

A. K. Whitfield

Oceanographic Literature Review > 1995 > 42 > 6 > 486

Five major categories of fishes which utilize southern African estuaries are described. A separate analysis for subtropical, warm-temperate and cool-temperate southern African estuaries is also presented. Altogether, 50 families of fishes are associated with estuaries on the subcontinent, of which 47 are primarily marine, two are derived from freshwater environments, and one is represented by catadromous...

article

A comparison of the ichthyofaunas in two permanently open eastern Cape estuaries

A. K. Whitfield, A. W. Paterson, A. H. Bok, H. M. Kok

Oceanographic Literature Review > 1995 > 42 > 5 > 391-392

The Kowie and Great Fish estuaries are situated less than 30 km apart, yet they differ considerably in terms of riverine inflow, turbidity, food resources and habitat availability. A greater ichthyofaunal richness (R) was recorded in the Kowie estuary and this is attributed to the wider range of habitats and greater degree of marine influence in this system. In contrast, all three sampling gears...

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