Time filter

Source Type

Cape Town, South Africa

Vorsatz L.D.,University of the Western Cape | van der Lingen C.D.,Branch Fisheries Management | van der Lingen C.D.,University of Cape Town | Gibbons M.J.,University of the Western Cape
African Journal of Marine Science | Year: 2015

Stomach content analyses and measurements of gillraker morphology were used to assess the diet and feeding ecology of the East Coast redeye round herring Etrumeus wongratanai and provide data for comparisons with other small pelagic fishes off South Africa. Samples were collected by jigging from a kayak off Scottburgh, KwaZulu-Natal (KZN), over the period July 2013–May 2014. In total, 66 stomachs (containing 4 407 prey items) and 66 gill arches were examined. Stomach content analyses indicated that East Coast redeye round herring, at the time of sampling, fed on large (1 500–2 500 µm) particles, with ∼2 500 µm particles making the greatest contribution to dietary carbon. The species feeds on larger particles than do anchovy Engraulis encrasicolus and sardine Sardinops sagax, but on particles of a similar size to those consumed by West Coast redeye round herring Etrumeus whiteheadi. There were significant differences in mean gillraker gaps between East Coast redeye round herring and both sardine and anchovy, but not between East Coast and West Coast redeye round herring. The differences in gillraker gaps between East Coast redeye round herring, sardine and anchovy are indicative of resource partitioning through differential feeding, based on zooplankton size. The data suggest that there is no resource partitioning between East and West coast redeye round herring, indicating that competition is likely to occur between them. However, such competition is minimised by limited spatial overlap between these two species. © 2015 NISC (Pty) Ltd.

Pitcher G.C.,Branch Fisheries Management | Pitcher G.C.,University of Cape Town | Krock B.,Alfred Wegener Institute for Polar and Marine Research | Cembella A.D.,Alfred Wegener Institute for Polar and Marine Research
African Journal of Marine Science | Year: 2011

Diarrhetic shellfish poisoning (DSP) poses a significant threat to the safe consumption of shellfish in the southern Benguela ecosystem. The accumulation of DSP toxins was investigated in two cultivated bivalve species, the Pacific oyster Crassostrea gigas and the mussel Choromytilus meridionalis, suspended from a mooring located off Lambert's Bay on the west coast of South Africa. The dinoflagellate Dinophysis acuminata, a known source of polyether toxins associated with DSP, was common through most of the study period. The toxin composition of the dinoflagellate was dominated by okadaic acid (OA) (91%), with lesser quantities of the dinophysistoxin DTX-1 (6.5%) and pectenotoxin PTX-2 (2.4%), and traces of PTX-2sa and PTX-11. The mean cell toxin quota of D. acuminata was 7.8 pg OA cell -1. The toxin profile in shellfish was characterised by a notably higher relative content of DTX-1. The study showed the average concentration of DSP toxins in the mussels to exceed that in the oysters by approximately 20-fold. The results indicate a need to establish species-specific sampling frequencies in shellfish safety monitoring programmes. © NISC (Pty) Ltd.

Smith M.E.,University of Cape Town | Pitcher G.C.,Branch Fisheries Management | Pitcher G.C.,University of Cape Town
African Journal of Marine Science | Year: 2015

The efficacy of ocean colour remote sensing in assessing the variability of phytoplankton biomass within Saldanha Bay is examined. Satellite estimates of chlorophyll a (Chl a) were obtained using the maximum peak-height (MPH) algorithm on full-resolution (300 m) data from the Medium Resolution Imaging Spectrometer (MERIS). Subsurface Chl a maxima often occur within Saldanha Bay below the mean detection depth of the satellite (1.5 m) during periods of thermal stratification. Consequently, the MPH product was poorly correlated to in situ data from 4 m depth (r2 and average relative percentage difference [RPD] of 0.094 and 53% respectively); however, the coefficient of determination was much improved if limited to in situ data collected under conditions of mixing (r2 and RPD of 0.869 and 89%, respectively). Composites of monthly MPH Chl a data reveal mean concentrations consistent with in situ seasonal trends of phytoplankton biomass, confirming the capability of the MPH algorithm to qualitatively resolve surface Chl a distribution within the bay. © 2015 NISC (Pty) Ltd.

de Moor C.L.,University of Cape Town | Johnston S.J.,University of Cape Town | Brandao A.,University of Cape Town | Rademeyer R.A.,University of Cape Town | And 3 more authors.
African Journal of Marine Science | Year: 2015

The waters off South Africa's coastline boast a rich mix of commercially fished species. Quantitative assessments of these marine resources have developed from simple methods first applied in the 1970s, to models that encompass a wide range of methodologies. The more valuable resources have undergone regular assessments in recent decades, with frequencies closely related to the management approach employed for each fishery. Many of these assessments form the operating models used to simulation-test candidate management procedures. This paper provides a comprehensive review of the assessments of 11 of the most important fisheries resources in South Africa. Some assessments use simple biomass dynamics models, whereas others are a hybrid of age- and length-based models, each designed to model the specific characteristics of the resource and fishery concerned. Many of the assessments have been disaggregated by species/stock and/or area as related multispecies/stock/ distribution hypotheses have arisen. This paper explores the similarities and differences in the data available and the methods applied. The review indicates that, whereas the status of three of these resources cannot be estimated reliably at present, the status of six resources is considered to be reasonable to good, whereas that of abalone Haliotis midae and West Coast rock lobster Jasus lalandii remains poor. © 2015 NISC (Pty) Ltd.

Cohen L.A.,University of Cape Town | Pichegru L.,Nelson Mandela Metropolitan University | Gremillet D.,CNRS Center of Evolutionary and Functional Ecology | Coetzee J.,Branch Fisheries Management | And 2 more authors.
Marine Ecology Progress Series | Year: 2014

Seabirds respond to environmental changes by adjusting their breeding and foraging strategies, but this behavioural flexibility has limits. Cape gannets Morus capensis breeding in the southern Benguela on Malgas Island off South Africa's west coast have experienced large fluctuations in natural prey availability over the past decade, linked to environmental change and localised overfishing. When small pelagic fish are unavailable, breeding gannets increase their consumption of low-quality fishery discards (primarily hake Merluccius spp.). To investigate the limits of foraging flexibility of breeding gannets facing variable prey availability, we monitored foraging behaviour, nest attendance, adult body condition and chick growth between 2002 and 2012, along with diet composition and prey abundance (through annual hydroacoustic assessments) during the birds' breeding season. The combined biomass of sardine Sardinops sagax and anchovy Engraulis encrasicolus within the Malgas gannet colony's foraging range varied tenfold across the study period and was positively correlated with the proportion of these high quality fish in the gannets' diet (17 to 90%). Foraging effort increased and nest attendance decreased with decreasing sardine/anchovy consumption. Adult body condition was negatively impacted by increases in hake in the diet. Chick growth was lowest when low sardine and anchovy composition was coupled with an increase in adult foraging effort, suggesting a limit to behavioural compensation for food shortages. This long-term study demonstrates the consequences of variable prey levels for Cape gannet behaviour and fitness. These results highlight the need for detailed investigations of seabird-fishery interactions, and the necessity to limit fishing within Cape gannet foraging ranges during years of low natural prey abundance. © 2014 Inter-Research.

Discover hidden collaborations