https://commons.ru.ac.za/vital/access/manager/Index en-us 5 https://commons.ru.ac.za/vital/access/manager/Repository/vital:5450 Wed 12 May 2021 20:17:57 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2966 Wed 12 May 2021 19:51:41 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4203 Wed 12 May 2021 19:42:47 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4095 Wed 12 May 2021 19:10:05 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5799 Wed 12 May 2021 17:59:09 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3899 Wed 12 May 2021 17:09:38 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2103 Thu 13 May 2021 07:06:35 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5212 Thu 13 May 2021 06:33:38 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5354 70%) throughout the estuary, with two distinct groups being identified on the basis of substratum type. The sampling stations near the mouth with a sandy substratum were distinguished from all other sampling sites in the estuary. The dominant estuarine-spawning species were represented by all life-history stages, suggesting that they bred successfully in the estuary. This group was numerically and gravimetrically dominated by the two zooplanktivorous shoaling species Gilchristella aestuaria and Atherina breviceps with density extrapolated population size estimates of 420 973 and 198 275 individuals, and biomass estimates of 1.6 and 0.6 g m⁻² respectively. The total population size of all estuarine-spawning species with a mean biomass 00.4 g m⁻² was estimated at 754 217 individuals. Population size estimates of the marine-spawning species were calculated using data obtained from three independent mark-recapture experiments. The assumptions for the mark-recapture analyses were adequately met and it was concluded that the techniques provided reliable estimates of population size. However, estimates obtained from density extrapolation revealed enormous variability and were considered to be unreliable. The total population size was estimated at 63 342, 18 592 and 13 5 192 during the three mark-recapture experiments respectively. The numerically dominant species during all three experiments was Rhabdosargus holubi. Biomass production of the marine-spawning species was evaluated over a 123 day census period when population sizes and estimates of growth rates were known. Productivity for all fishes with a standing stock of 26.2 g m⁻² was calculated at 4.5 g m⁻² month01 Rhabdosargus holubi accounted for more than 75% of the total marine fish productivity. This study draws attention to the success of Rhabdosargus holubi in the East Kleinemonde estuary, which is ascribed to aspects of its biology. These include an extended breeding season, the ability to recruit into the estuary under adverse open mouth conditions and its omnivorous food habits. The dominance of this migratory species suggests that it plays an important role in the transfer of energy to the coastal marine environment when the mouth of the East Kleinemonde estuary opens. Predation by birds and a dominant piscivorous fish (Lichia amia) was quantitatively assessed over a period of two years. Monthly food consumption by all piscivorous birds revealed large temporal variability, ranging from 32 to 466 kg month-I An unusual invasion of Cape cormorants during the winter of 1994 accounted for large scale mortality (2246 kg of fish) over a relatively short period. The predatory impact of this episodic event was reflected in the findings of the fish mark-recapture experiments, which revealed a 70% reduction in the total population of marine-spawning fishes (above a certain minimum size) in the estuary subsequent to this invasion. Monthly food consumption by the Lichia amia population in the estuary was calculated at 68 and 58 kg month-I for two distinct time periods when the population size was known. These findings suggest that this species is the top piscivorous predator in the East Kleinemonde estuary. Finally, the findings of this study highlight the temporal variability of fish populations within a single estuary. It is suggested that predation and estuary mouth conditions are the main factors influencing the abundance (and its variability) of individual species in the East Kleinemonde estuary.]]> Thu 13 May 2021 06:28:19 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4396 Thu 13 May 2021 06:27:12 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5365 Thu 13 May 2021 06:25:53 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2836 Thu 13 May 2021 04:03:09 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5342 Thu 13 May 2021 03:31:37 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3900 Thu 13 May 2021 01:07:11 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4866 Thu 13 May 2021 00:01:43 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4551 Thu 07 Jul 2022 16:08:45 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4032 Fri 05 Jul 2024 09:51:13 SAST ]]>