https://commons.ru.ac.za/vital/access/manager/Index ${session.getAttribute("locale")} 5 https://commons.ru.ac.za/vital/access/manager/Repository/vital:896 Wed 12 Oct 2022 12:46:11 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1607 Wed 12 Oct 2022 12:09:17 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2855 Wed 12 Oct 2022 11:54:43 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2979 Wed 12 Oct 2022 09:55:06 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3026 Tue 15 Aug 2023 16:06:20 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3503 Tue 06 Jul 2021 09:29:41 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:45834 Thu 27 Jan 2022 16:08:28 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3123 Thu 26 Jan 2023 10:30:16 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:969 Thu 15 Jul 2021 20:55:37 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4973 Thu 13 May 2021 11:24:21 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5327 Thu 13 May 2021 10:27:05 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3784 Thu 13 May 2021 09:24:14 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5725 Thu 13 May 2021 08:49:43 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:767 Thu 13 May 2021 08:33:18 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5498 Thu 13 May 2021 08:22:08 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1128 Thu 13 May 2021 08:17:57 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5653 2 cm; chaetognaths, medusae, ctenophores and mysids), with particular emphasis on the chaetognaths Eukrohnia hamata and Sagitta gazellae, were investigated during three surveys conducted in late austral summer (April/May) of 2001, 2004 and 2005 in the Polar Frontal Zone in the vicinity of the Prince Edward Islands (46º45’S, 37º50’E), Southern Ocean. The 2001 survey formed part of the Marion Offshore Variability Ecosystem Study (MOVES II), while the 2004 and 2005 surveys formed part of the Dynamics of Eddy Impacts on Marion’s Ecosystem study (DEIMEC III and IV respectively). Macrozooplankton samples were collected using WP-2, RMT-8 and Bongo nets. Results of the hydrographic survey indicated that the region of investigation, the Polar Frontal Zone (PFZ), is an area of high mesoscale variability. During the 2004 survey the Antarctic Polar Front (APF) and the Subantarctic Front (SAF) merged to form an intense frontal feature with subsurface temperature and salinity ranging from 8.5-7.5ºC and 34.15-33.88, respectively. A cyclonic cold core eddy, believed to have been spawned from the APF, was observed during the 2005 survey. Macrozooplankton abundance and biomass ranged from 0 to 43.731 ind. m⁻³, and from 0 to 41.55 mg wwt m⁻³ respectively, during the three surveys. Among the carnivorous macrozooplankton, chaetognaths (Eukrohnia hamata and Sagitta gazellae) were most prominent, contributing up to 85% of the total biomass during all three surveys. Elevated biomass values were found near and within the frontal feature during the 2004 survey, and also along the eddy edge during the 2005 survey. However, hierarchical cluster analysis did not reveal the presence of distinct zooplankton groupings associated with the various water masses encountered during the surveys and this is probably due to the high mesoscale variability in oceanographic conditions that are characteristic of the PFZ. The total average predation impact of the selected carnivorous macrozooplankton during the 2001, 2004 and 2005 surveys accounted for 4.93 ± 6.76%, 0.55 ± 0.51% and 4.88 ± 4.45 of the mesozooplankton standing stock, respectively. S. gazellae had the highest consumption rate in all three surveys, consuming up to 800 g Dwt 1000m⁻³d⁻¹ during the study. Of the two chaetognaths, E. hamata dominated the chaetognath standing stock. The combined abundance and biomass values of E. hamata and S. gazellae ranged from 0 to 43.73 ind. m⁻³ and from 0 to 41.551 mg wwt m⁻³ respectively, during the three surveys. Inter-annual variability in the chaetognath densities was apparent. Highest abundances and biomasses tended to be associated with specific water masses, confirming the existence of a relationship between zooplankton community structure and hydrographic conditions. Generally, about 90% of the chaetognaths contained no food in their guts. S. gazellae consumed a wider variety of prey. Oil droplets occurred in the guts of ≈ 51% of E. hamata. Cannibalism was low in both species, but greater in S. gazellae than E. hamata. During the three surveys, the feeding rate values of E. hamata and S. gazellae went up to 0.48 and 2.099 prey d⁻¹ respectively. S. gazellae also had a greater predation impact on the mesozooplankton standing stock than E. hamata. The mean predation impact of the chaetognaths combined was 0.31 ± 0.291%, 0.52 ± 0.28% and 0.53 ± 0.56% of the mesozooplankton standing stock during the 2001, 2004 and 2005 surveys, respectively. During all three surveys, the majority of individuals (≈ 76%) of the chaetognaths were at stage I maturity, suggesting that during the time of study the chaetognaths were not reproducing. In both species a significant difference (log-linear analysis, p < 0.05) in maturities between the years investigated was observed. In general, there were no differences in lengths and maturities between the different water masses encountered during the surveys. The lengths of E. hamata and S. gazellae ranged from 5 to 24 mm and from 9.4 to 63.6 mm, respectively.]]> Thu 13 May 2021 08:13:35 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3776 Thu 13 May 2021 08:08:56 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:761 Thu 13 May 2021 08:08:15 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3448 Thu 13 May 2021 08:07:48 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3483 Thu 13 May 2021 08:07:42 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1018 Thu 13 May 2021 08:03:44 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4183 Thu 13 May 2021 07:33:33 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3423 Thu 13 May 2021 07:19:38 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3435 Thu 13 May 2021 07:19:29 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6036 Thu 13 May 2021 07:14:05 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1452 Thu 13 May 2021 07:05:04 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5735 Thu 13 May 2021 07:03:09 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5310 1.8 m TL) displayed philopatric behaviour for specific parts of their ranges, including gestating and parturition areas. Significant differences were observed in the percentage of recaptures between the different tag types, tagging programs, individual taggers and capture methods used to tag sharks. The annual tag retention rate for juvenile sharks, 94.19% (95% C.I. = 80.68% - 100.00%) was significantly higher than for adult sharks, estimated at 29.00% (95% C.I. = 6.76% - 64.39%). Tag reporting rates, from fishermen varied both spatially and temporally from 0.28 (95% C.I. = 0.00 – 0.63) to 0.77 (95% C.I. = 0.56 – 0.97). Associated tag wound damage and biofouling growth indicated that B-type tags were a suitable tag type for use on C. taurus, whereas C-type tags were not. The CJS bias-adjusted estimate for juvenile survival was 0.456 (95% C.I. = 0.367 – 0.516) and for adult sharks, 0.865 (95% C.I. = 0.795 – 0.915). From 1984 to 2004 the mean bias-adjusted population size for juvenile sharks was estimated at 3506 (95% C.I. = 2433 – 4350) and for adult sharks, 5899 (95% C.I. = 7216 – 11904). Trends in abundance over the 20-year study period indicated a stable, healthy population.]]> Thu 13 May 2021 07:00:36 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1173 Thu 13 May 2021 06:59:24 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1724 Thu 13 May 2021 06:59:19 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5696 0.05 in all cases). A key feature of the two investigations was the virtual absence of juveniles (total length < 15 mm) among the amphipod population, supporting the suggestion that they exhibit strong seasonal patterns in reproduction. Gut content analysis during both years indicated that for both the male and female amphipods’, copepods were the most prevalent prey species found in stomachs, followed by chaetognaths and pteropods. Results of electivity studies indicate that T. gaudichaudii is an opportunistic predator, generally feeding on the most abundant mesozooplankton prey. Results of in vitro incubations indicated that the total daily feeding rate of T. gaudichaudii during 2004 ranged from 11.45 to 20.90 ind. m⁻³ d⁻¹, which corresponds to between 0.12 and 1.64% of the total mesozooplankton standing stock. In 2005, the feeding rate ranged between 0.1 and 1.73% of the total mesozooplankton standing stock. The low predation impact of T. gaudichaudii during this study can be related to their low abundances and high interannual variability throughout the region of investigation.]]> Thu 13 May 2021 06:57:14 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5144 Thu 13 May 2021 06:54:06 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2375 Thu 13 May 2021 06:50:14 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4737 Thu 13 May 2021 06:43:13 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3707 Thu 13 May 2021 06:39:19 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3157 Thu 13 May 2021 06:34:54 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5417 Thu 13 May 2021 06:30:47 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3752 Thu 13 May 2021 06:26:12 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2363 Thu 13 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