Pub Date : 2022-07-03DOI: 10.2989/1814232X.2022.2104926
JM Eggers, K. Cochrane, W. Sauer
The west coast rock lobster Jasus lalandii fishery is South Africa’s third-most-valuable fishery, although the stock is currently estimated at <2% of its pristine biomass. Recent ecologically necessary reductions in the total allowable catch (TAC) had negative economic impacts on stakeholders; however, these have not been quantified as current research into the socio-economic aspects of this fishery is limited. This study explored trends in the net seasonal income and employment opportunities of the fishery in the seasons 2016/17–2018/19 for its different sectors and representative individuals, by analysing records from the government authority and data collected from stakeholders in this fishery through interviews (n = 30) and surveys (n = 19). The results indicate that though the fishery was profitable over the three seasons, with the estimated contribution to gross national income ranging from R453 185 000 (US$33 302 714) in 2018/19 to R564 721 000 (US$41 499 039) in 2017/18, the decreasing quotas had a disproportionate negative effect on some of the representative individuals examined within the different sectors. These worrying economic trends for the different stakeholders indicate that, for effective resource recovery and equitable distribution of fishing opportunities, the socio-economic context of the fishery must be studied more extensively and must be included more directly in management decisions.
{"title":"Estimating the economic income and social contributions derived from the South African west coast rock lobster fishery","authors":"JM Eggers, K. Cochrane, W. Sauer","doi":"10.2989/1814232X.2022.2104926","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2104926","url":null,"abstract":"The west coast rock lobster Jasus lalandii fishery is South Africa’s third-most-valuable fishery, although the stock is currently estimated at <2% of its pristine biomass. Recent ecologically necessary reductions in the total allowable catch (TAC) had negative economic impacts on stakeholders; however, these have not been quantified as current research into the socio-economic aspects of this fishery is limited. This study explored trends in the net seasonal income and employment opportunities of the fishery in the seasons 2016/17–2018/19 for its different sectors and representative individuals, by analysing records from the government authority and data collected from stakeholders in this fishery through interviews (n = 30) and surveys (n = 19). The results indicate that though the fishery was profitable over the three seasons, with the estimated contribution to gross national income ranging from R453 185 000 (US$33 302 714) in 2018/19 to R564 721 000 (US$41 499 039) in 2017/18, the decreasing quotas had a disproportionate negative effect on some of the representative individuals examined within the different sectors. These worrying economic trends for the different stakeholders indicate that, for effective resource recovery and equitable distribution of fishing opportunities, the socio-economic context of the fishery must be studied more extensively and must be included more directly in management decisions.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48704127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2047782
B. Mann, J. Maggs, S. Porter, W. Dalton
Monitoring marine protected areas (MPAs) is critical for evaluating their effectiveness and for improving management. In this study, a single-camera baited remote underwater video system (mono-BRUVS) was deployed quarterly at four sites (10–30-m depths) to quantify the reef fish communities in protected (no-take) and adjacent exploited areas of the Pondoland MPA on the east coast of South Africa (Indian Ocean). To assess size (biomass) of the fish communities, we used 10 years of research linefishing data (2006–2016) from the same areas. Univariate and multivariate analyses were used to compare abundance and biomass of the fish communities between protected and exploited areas. Significant differences were detected between fish communities in protected and exploited areas based on their abundance and biomass. These differences are primarily ascribed to linefishing and the removal of larger, predatory species such as yellowbelly rockcod Epinephelus marginatus, Scotsman Polysteganus praeorbitalis and black musselcracker Cymatoceps nasutus in the adjacent exploited areas. Removal of such predators may have caused trophic cascading or prey release, resulting in very different fish communities. These results highlight the importance of investigating the entire fish community and not only target fishery species when evaluating MPA effectiveness.
{"title":"Monitoring the effects of spatial protection on the reef fish communities of the Pondoland Marine Protected Area, Eastern Cape Province, South Africa","authors":"B. Mann, J. Maggs, S. Porter, W. Dalton","doi":"10.2989/1814232X.2022.2047782","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2047782","url":null,"abstract":"Monitoring marine protected areas (MPAs) is critical for evaluating their effectiveness and for improving management. In this study, a single-camera baited remote underwater video system (mono-BRUVS) was deployed quarterly at four sites (10–30-m depths) to quantify the reef fish communities in protected (no-take) and adjacent exploited areas of the Pondoland MPA on the east coast of South Africa (Indian Ocean). To assess size (biomass) of the fish communities, we used 10 years of research linefishing data (2006–2016) from the same areas. Univariate and multivariate analyses were used to compare abundance and biomass of the fish communities between protected and exploited areas. Significant differences were detected between fish communities in protected and exploited areas based on their abundance and biomass. These differences are primarily ascribed to linefishing and the removal of larger, predatory species such as yellowbelly rockcod Epinephelus marginatus, Scotsman Polysteganus praeorbitalis and black musselcracker Cymatoceps nasutus in the adjacent exploited areas. Removal of such predators may have caused trophic cascading or prey release, resulting in very different fish communities. These results highlight the importance of investigating the entire fish community and not only target fishery species when evaluating MPA effectiveness.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45143224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2066722
M. Soondur, R. Boojhawon, R. Lowe, D. Kaullysing, B. Casareto, Y. Suzuki, R. Bhagooli
This study aimed to test the effects of rainfall-driven nutrient loading on the microphytoplankton dynamics in the shallow water at Trou aux Biches lagoon on the northwest coast of Mauritius. Changes in density, diversity and estimated productivity of microphytoplankton were monitored in three zones—coast, lagoon and reef—during two rainfall periods of 4 and 3 days’ duration, respectively, in March–April 2017. The average nutrient loading from terrestrial runoff was 15.5% and the salinity decreased by 2.5%. Following the two rainfall events, a 3-fold increase in total microphytoplankton density (TMPD), with a dominance of diatoms, was noted within a week at the coast and lagoon, while it remained relatively unchanged at the reef. These changes in microphytoplankton densities were concomitant with adequate levels of silicate (>2 µM) and high nitrate:silicate ratios (2.84–6.93). During this study, the numbers of genera of diatoms, dinoflagellates and cyanobacteria observed were 28, 12 and 3, respectively. The Shannon–Wiener, equitability and evenness indices showed high diversity values for diatoms and cyanobacteria prior to the rainfall events and for dinoflagellates after the events. The chlorophyll a content, relative electron transport rate, and estimated productivity of microphytoplankton increased during and after the rainy periods. TMPD and chlorophyll a were correlated significantly and positively with nutrients, salinity and temperature. Toxic algal species such as the dinoflagellates Alexandrium, Dinophysis and Tripos were recorded, although not in bloom densities. These findings indicate that rainfall-driven nutrient loading led to an increase in microphytoplankton density and estimated productivity, and a change in its diversity.
本研究旨在测试降雨驱动的营养物质负荷对毛里求斯西北海岸Trou aux Biches泻湖浅水中微型浮游生物动力学的影响。在2017年3月至4月的两次降雨期间，分别监测了海岸、泻湖和珊瑚礁三个区域的浮游生物密度、多样性和估计生产力的变化。陆地径流的平均营养负荷为15.5%，盐度下降了2.5%。在两次降雨事件之后，海岸和泻湖的总浮游生物密度（TMPD）在一周内增加了3倍，其中硅藻占主导地位，而珊瑚礁的密度相对保持不变。这些微小浮游生物密度的变化伴随着充足的硅酸盐水平（>2µM）和高的硝酸盐与硅酸盐比例（2.84-6.93）。在这项研究中，观察到的硅藻、甲藻和蓝细菌的属数分别为28、12和3。Shannon–Wiener等稳定性和均匀度指数显示，在降雨事件之前，硅藻和蓝藻的多样性值很高，而在降雨事件之后，甲藻的多样性也很高。雨季前后，浮游植物叶绿素a含量、相对电子传输速率和估计生产力都有所增加。TMPD和叶绿素a与营养物质、盐度和温度呈正相关。有毒藻类物种，如亚历山大藻（Alexandrium）、恐龙藻（Dinophysis）和三角藻（Tripos），虽然没有开花密度，但都有记录。这些发现表明，降雨驱动的营养负荷导致浮游生物密度和估计生产力的增加，以及其多样性的变化。
{"title":"Rainfall-driven nutrient loading affects coastal phytoplankton in the southwestern Indian Ocean: a lagoon at Mauritius Island","authors":"M. Soondur, R. Boojhawon, R. Lowe, D. Kaullysing, B. Casareto, Y. Suzuki, R. Bhagooli","doi":"10.2989/1814232X.2022.2066722","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2066722","url":null,"abstract":"This study aimed to test the effects of rainfall-driven nutrient loading on the microphytoplankton dynamics in the shallow water at Trou aux Biches lagoon on the northwest coast of Mauritius. Changes in density, diversity and estimated productivity of microphytoplankton were monitored in three zones—coast, lagoon and reef—during two rainfall periods of 4 and 3 days’ duration, respectively, in March–April 2017. The average nutrient loading from terrestrial runoff was 15.5% and the salinity decreased by 2.5%. Following the two rainfall events, a 3-fold increase in total microphytoplankton density (TMPD), with a dominance of diatoms, was noted within a week at the coast and lagoon, while it remained relatively unchanged at the reef. These changes in microphytoplankton densities were concomitant with adequate levels of silicate (>2 µM) and high nitrate:silicate ratios (2.84–6.93). During this study, the numbers of genera of diatoms, dinoflagellates and cyanobacteria observed were 28, 12 and 3, respectively. The Shannon–Wiener, equitability and evenness indices showed high diversity values for diatoms and cyanobacteria prior to the rainfall events and for dinoflagellates after the events. The chlorophyll a content, relative electron transport rate, and estimated productivity of microphytoplankton increased during and after the rainy periods. TMPD and chlorophyll a were correlated significantly and positively with nutrients, salinity and temperature. Toxic algal species such as the dinoflagellates Alexandrium, Dinophysis and Tripos were recorded, although not in bloom densities. These findings indicate that rainfall-driven nutrient loading led to an increase in microphytoplankton density and estimated productivity, and a change in its diversity.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48112367","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2075937
MJ Wilcox, J. Landschoff, C. Griffiths
The recently described amphipod Sunamphitoe roberta lives only on the kelp Ecklonia maxima, where it excavates slit-like burrows along the distal margins of thicker primary fronds. Oval chambers along the bases of these slits may represent feeding areas. As burrowing proceeds, the damage progressively erodes back the frond margins, giving them characteristic attenuated and irregular profiles, and probably impacting secondary frond survival and growth, and hence kelp productivity. A kelp forest in False Bay, South Africa, was surveyed to determine what proportion of kelp was infected as well as which individuals were selected as hosts. Forty kelp heads were also dissected to ascertain numbers of amphipods per host and their size composition, and to document details of burrow structure. Of 305 adult kelps inspected, 117 (38.4%) showed visible amphipod damage. Rate of infestation was not correlated with stipe length but was positively correlated with head circumference and negatively correlated with the proportion of secondary fronds remaining. The 40 kelp heads dissected contained 786 S. roberta specimens. These comprised 154 adults (>8 mm), including 33 ovigerous females, and 632 juveniles (<8 mm). The number of amphipods per host ranged from 1 to 112 (mean 19.7 [SD 25.1]). Size distribution was bimodal, and the largest individual measured 20 mm.
{"title":"Prevalence, population structure and burrow morphology of the kelp-boring amphipod Sunamphitoe roberta","authors":"MJ Wilcox, J. Landschoff, C. Griffiths","doi":"10.2989/1814232X.2022.2075937","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2075937","url":null,"abstract":"The recently described amphipod Sunamphitoe roberta lives only on the kelp Ecklonia maxima, where it excavates slit-like burrows along the distal margins of thicker primary fronds. Oval chambers along the bases of these slits may represent feeding areas. As burrowing proceeds, the damage progressively erodes back the frond margins, giving them characteristic attenuated and irregular profiles, and probably impacting secondary frond survival and growth, and hence kelp productivity. A kelp forest in False Bay, South Africa, was surveyed to determine what proportion of kelp was infected as well as which individuals were selected as hosts. Forty kelp heads were also dissected to ascertain numbers of amphipods per host and their size composition, and to document details of burrow structure. Of 305 adult kelps inspected, 117 (38.4%) showed visible amphipod damage. Rate of infestation was not correlated with stipe length but was positively correlated with head circumference and negatively correlated with the proportion of secondary fronds remaining. The 40 kelp heads dissected contained 786 S. roberta specimens. These comprised 154 adults (>8 mm), including 33 ovigerous females, and 632 juveniles (<8 mm). The number of amphipods per host ranged from 1 to 112 (mean 19.7 [SD 25.1]). Size distribution was bimodal, and the largest individual measured 20 mm.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44850876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2064548
B. Mann, R. Daly, G. Jordaan, W. Dalton, S. Fennessy
Movement behaviour of the endemic epinephelid Mycteroperca andersoni (formerly allocated to genus Epinephelus) along the east coast of southern Africa was investigated using both conventional dart tagging and passive acoustic telemetry. Results from both methods showed that this species is likely to be a temporary resident on shallow inshore reefs; fish showed high site fidelity and occupied relatively small home ranges for periods seldom exceeding 12 months, whereafter they appeared to undertake ranging-type movements. Adults >400 mm total length were more mobile than juveniles, and the distance moved increased with both fish size and time at liberty. Adults south of Durban, South Africa, moved farther in a northerly direction than those north of Durban, confirming that spawning likely takes place north of Durban. No direct evidence of a spawning migration was found, but anecdotal reports that they form spawning aggregations suggests that migrations for this purpose are likely to occur. The current species-specific linefish regulations and the recently expanded marine protected area network along the east coast of South Africa are believed to be adequate to ensure the future sustainable use of this species. However, improved enforcement of regulations is required, and identification of spawning aggregation sites should be a research priority.
{"title":"Movement behaviour of catface rockcod Mycteroperca (Epinephelus) andersoni (Epinephelidae) off the eastern seaboard of southern Africa","authors":"B. Mann, R. Daly, G. Jordaan, W. Dalton, S. Fennessy","doi":"10.2989/1814232X.2022.2064548","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2064548","url":null,"abstract":"Movement behaviour of the endemic epinephelid Mycteroperca andersoni (formerly allocated to genus Epinephelus) along the east coast of southern Africa was investigated using both conventional dart tagging and passive acoustic telemetry. Results from both methods showed that this species is likely to be a temporary resident on shallow inshore reefs; fish showed high site fidelity and occupied relatively small home ranges for periods seldom exceeding 12 months, whereafter they appeared to undertake ranging-type movements. Adults >400 mm total length were more mobile than juveniles, and the distance moved increased with both fish size and time at liberty. Adults south of Durban, South Africa, moved farther in a northerly direction than those north of Durban, confirming that spawning likely takes place north of Durban. No direct evidence of a spawning migration was found, but anecdotal reports that they form spawning aggregations suggests that migrations for this purpose are likely to occur. The current species-specific linefish regulations and the recently expanded marine protected area network along the east coast of South Africa are believed to be adequate to ensure the future sustainable use of this species. However, improved enforcement of regulations is required, and identification of spawning aggregation sites should be a research priority.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46621865","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2075936
D. Roos, J. Taconet, C. Gentil, B. Brisset, H. Evano, Y. Aumond, J. Huet, C. Lepetit, R. Boymond-Morales, T. Rungassamy, R. Elleboode, K. Mahé
Body length–weight (L–W) relationships of 123 fish species (122 Actinopterygii and 1 Elasmobranchii) were studied from 10 218 individuals caught around Réunion Island from 2000 to 2021. All species, except for 4 with a very small number of individuals and limited length range, showed a significant relationship between total length and total weight. For 52 species, the data showed the body becoming more elongated (i.e. b < 3.0) over their lifespan, while for 63 species the individuals became thicker (i.e. b > 3.0); only 4 species had a b-value equal to 3.0, signifying isometric growth. Of 72 species for which macroscopic observation allowed identification of sex, there was sexual dimorphism for only 9 species (12.5%), with a significant difference between the slopes of the length–weight relationships. Temporal effects were also investigated, using the annual component of time of capture for 75 species and the seasonal component for 73 species. A temporal effect was significant for 27 species (36.0%) when the sampling year was taken into account, and for 14 species (19.2%) when the sampling quarter (season) was taken into account. Finally, among 120 species tested, the relationship between total length and standard length was significant, and among 114 species the relationship between total weight and gutted (eviscerated) weight was significant.
{"title":"Variation of the relationships between lengths and weights applied to 123 fish species observed at Réunion Island (Indian Ocean)","authors":"D. Roos, J. Taconet, C. Gentil, B. Brisset, H. Evano, Y. Aumond, J. Huet, C. Lepetit, R. Boymond-Morales, T. Rungassamy, R. Elleboode, K. Mahé","doi":"10.2989/1814232X.2022.2075936","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2075936","url":null,"abstract":"Body length–weight (L–W) relationships of 123 fish species (122 Actinopterygii and 1 Elasmobranchii) were studied from 10 218 individuals caught around Réunion Island from 2000 to 2021. All species, except for 4 with a very small number of individuals and limited length range, showed a significant relationship between total length and total weight. For 52 species, the data showed the body becoming more elongated (i.e. b < 3.0) over their lifespan, while for 63 species the individuals became thicker (i.e. b > 3.0); only 4 species had a b-value equal to 3.0, signifying isometric growth. Of 72 species for which macroscopic observation allowed identification of sex, there was sexual dimorphism for only 9 species (12.5%), with a significant difference between the slopes of the length–weight relationships. Temporal effects were also investigated, using the annual component of time of capture for 75 species and the seasonal component for 73 species. A temporal effect was significant for 27 species (36.0%) when the sampling year was taken into account, and for 14 species (19.2%) when the sampling quarter (season) was taken into account. Finally, among 120 species tested, the relationship between total length and standard length was significant, and among 114 species the relationship between total weight and gutted (eviscerated) weight was significant.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48420116","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2055643
NN Gabriel, C. Chikwililwa, GM Liswaniso, S. Louw, A. Namwoonde
The anaesthetic effectiveness of separate and combined eucalyptus Eucalyptus globulus and oregano Origanum vulgare essential oils (EO) were investigated in silver kob Argyrosomus inodorus and were compared with clove oil Eugenia caryophyllata. Argyrosomus inodorus adults (595.61 [SE 11.82] g) were exposed to three concentrations of oregano EO (OEO: 25, 50 and 100 µl l−1), eucalyptus EO (EEO: 300, 500 and 600 µl l−1), and their mixtures (12.5 µl l−1 OEO to 150 µl l−1 EEO; 12.5 µl l−1 OEO to 300 µl l−1 EEO; 25 µl l−1 OEO to 150 µl l−1 EEO), with each fish treated as a replicate. Fish were also exposed to 40 µl l−1 of clove oil (CEO), which acted as a control. The two EOs and their mixtures proved to possess anaesthetic capacity in A. inodorus. Anaesthesia induction time (seconds) decreased with increased concentrations, whereas the inverse was reported for the recovery response. Only OEO qualified as an ideal anaesthetic agent for A. inodorus, especially 25 and 50 µl l−1, as the anaesthesia induction times with these concentrations were less than 180 s and recovery was within 300 s. It seems that EEO could achieve greater anaesthetic effectiveness only at a higher concentration (600 µl l−1) or when mixed with OEO (at 25 µl l−1 OEO to 150 µl l−1 EEO). This study introduces oregano as a promising anaesthetic in A. inodorus compared with clove oil and EEO. However, further evaluations are deemed necessary.
{"title":"The effects of eucalyptus Eucalyptus globulus and oregano Origanum vulgare essential oils on anaesthesia response in a Namibian marine species, silver kob Argyrosomus inodorus","authors":"NN Gabriel, C. Chikwililwa, GM Liswaniso, S. Louw, A. Namwoonde","doi":"10.2989/1814232X.2022.2055643","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2055643","url":null,"abstract":"The anaesthetic effectiveness of separate and combined eucalyptus Eucalyptus globulus and oregano Origanum vulgare essential oils (EO) were investigated in silver kob Argyrosomus inodorus and were compared with clove oil Eugenia caryophyllata. Argyrosomus inodorus adults (595.61 [SE 11.82] g) were exposed to three concentrations of oregano EO (OEO: 25, 50 and 100 µl l−1), eucalyptus EO (EEO: 300, 500 and 600 µl l−1), and their mixtures (12.5 µl l−1 OEO to 150 µl l−1 EEO; 12.5 µl l−1 OEO to 300 µl l−1 EEO; 25 µl l−1 OEO to 150 µl l−1 EEO), with each fish treated as a replicate. Fish were also exposed to 40 µl l−1 of clove oil (CEO), which acted as a control. The two EOs and their mixtures proved to possess anaesthetic capacity in A. inodorus. Anaesthesia induction time (seconds) decreased with increased concentrations, whereas the inverse was reported for the recovery response. Only OEO qualified as an ideal anaesthetic agent for A. inodorus, especially 25 and 50 µl l−1, as the anaesthesia induction times with these concentrations were less than 180 s and recovery was within 300 s. It seems that EEO could achieve greater anaesthetic effectiveness only at a higher concentration (600 µl l−1) or when mixed with OEO (at 25 µl l−1 OEO to 150 µl l−1 EEO). This study introduces oregano as a promising anaesthetic in A. inodorus compared with clove oil and EEO. However, further evaluations are deemed necessary.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41951523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2080268
K. Ortega-Cisneros, E. Weigum, R. Chalmers, S. Grusd, A. Lombard, L. Shannon
The Ecopath with Ecosim (EwE) modelling framework was used to develop a model of Algoa Bay and test the ecosystem impacts of the implementation of the Addo Elephant National Park Marine Protected Area (MPA). The Ecopath model included 37 functional groups ranging from phytoplankton to top predators and was fitted to 12 and 14 time-series of biomass and landings, respectively, from 2010 to 2019 (calibration period), using Ecosim. Two scenarios representing different degrees of fisheries closures in the MPA were explored through a 30% and a 100% reduction in fishing effort. Temporal simulations were run until 2059. The fitting procedure identified the best-fit model as the one including the effects of fishing, the six most-sensitive predator–prey interactions, and environmental forcing (primary production anomaly on small phytoplankton). Overall, the predicted biomass and catch time-series reasonably reproduced the observed time-series for 2010–2019, with the biomass of sardine Sardinops sagax, round herring Etrumeus whiteheadi, and African penguins Spheniscus demersus showing the best fits to data. Both MPA scenarios resulted in higher total biomass compared with the baseline by the end of the simulation and decreased catches due to less fishing effort. The most profound biomass increases under the MPA scenarios were observed in apex and pelagic elasmobranchs, yellowtail Seriola lalandi and African penguins. Future research is needed to improve the more-uncertain model parameters and include other key sectors in Algoa Bay, such as shipping. However, this model provides a good foundation for future work including the application of spatially explicit modelling of the bay using Ecospace.
Ecopath with Ecosim (EwE)建模框架用于开发Algoa湾模型，并测试实施阿多大象国家公园海洋保护区(MPA)对生态系统的影响。Ecopath模型包括从浮游植物到顶级捕食者的37个功能基团，并使用Ecosim分别拟合了2010年至2019年(校准期)的12个和14个生物量和登陆时间序列。通过减少30%和100%的捕捞量，研究了两种不同程度的海洋保护区渔业关闭情景。时间模拟一直持续到2059年。拟合过程确定了最优拟合模型，即包括捕捞效应、六种最敏感的捕食者-猎物相互作用和环境强迫(小型浮游植物的初级生产异常)。总体而言，预测的生物量和捕获量时间序列较好地再现了2010-2019年的观测时间序列，其中沙丁鱼、圆鲱鱼、白头鱼和非洲企鹅的生物量与数据最吻合。在模拟结束时，两种MPA情景的总生物量都高于基线，而由于捕捞努力减少，渔获量减少。海洋保护区情景下生物量增幅最大的是顶、中上层板鳃、黄尾和非洲企鹅。未来的研究需要改进更不确定的模型参数，并包括Algoa湾的其他关键部门，如航运。然而，该模型为未来的工作提供了良好的基础，包括使用Ecospace对海湾进行空间显式建模的应用。
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Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2066723
A. Towner, Rga Watson, A. Kock, Y. Papastamatiou, M. Sturup, E. Gennari, K. Baker, T. Booth, M. Dicken, W. Chivell, S. Elwen, T. Kaschke, D. Edwards, M. Smale
Risk-induced fear effects exerted by top predators are pervasive in terrestrial and marine systems, with lasting impacts on ecosystem structure and function. The loss of top predators can disrupt ecosystems and trigger trophic cascades, but the introduction of novel apex predators into ecosystems is not well understood. We documented the emigration of white sharks Carcharodon carcharias in response to the presence of a pair of killer whales, Orcinus orca, at a large white shark aggregation site in South Africa. Between February and June in 2017, five white shark carcasses washed up on beaches in Gansbaai, Western Cape Province, four of which had their livers removed. Sightings per unit effort (sea days) and telemetry data demonstrated that white sharks emigrated from Gansbaai following these predation events, and in response to further sightings of this pair and other killer whale pods in the vicinity. Tagging data demonstrated the immediate departure of white sharks from Gansbaai, and some sharks were subsequently moving east. Contrary to expected and well-documented patterns of white shark occurrence at this site, their sightings dropped throughout the following 2.5 years; change-point analysis on both datasets confirmed these departures coincided with killer whale presence and shark carcasses washing out. These findings suggest that white sharks respond rapidly to risk from a novel predator, and that their absence triggered the emergence of another predator, the bronze whaler Carcharhinus brachyurus. Predator–prey interactions between white sharks, other coastal sharks, and killer whales are increasing in South Africa and are expected to have pronounced impacts on the ecosystem.
{"title":"Fear at the top: killer whale predation drives white shark absence at South Africa’s largest aggregation site","authors":"A. Towner, Rga Watson, A. Kock, Y. Papastamatiou, M. Sturup, E. Gennari, K. Baker, T. Booth, M. Dicken, W. Chivell, S. Elwen, T. Kaschke, D. Edwards, M. Smale","doi":"10.2989/1814232X.2022.2066723","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2066723","url":null,"abstract":"Risk-induced fear effects exerted by top predators are pervasive in terrestrial and marine systems, with lasting impacts on ecosystem structure and function. The loss of top predators can disrupt ecosystems and trigger trophic cascades, but the introduction of novel apex predators into ecosystems is not well understood. We documented the emigration of white sharks Carcharodon carcharias in response to the presence of a pair of killer whales, Orcinus orca, at a large white shark aggregation site in South Africa. Between February and June in 2017, five white shark carcasses washed up on beaches in Gansbaai, Western Cape Province, four of which had their livers removed. Sightings per unit effort (sea days) and telemetry data demonstrated that white sharks emigrated from Gansbaai following these predation events, and in response to further sightings of this pair and other killer whale pods in the vicinity. Tagging data demonstrated the immediate departure of white sharks from Gansbaai, and some sharks were subsequently moving east. Contrary to expected and well-documented patterns of white shark occurrence at this site, their sightings dropped throughout the following 2.5 years; change-point analysis on both datasets confirmed these departures coincided with killer whale presence and shark carcasses washing out. These findings suggest that white sharks respond rapidly to risk from a novel predator, and that their absence triggered the emergence of another predator, the bronze whaler Carcharhinus brachyurus. Predator–prey interactions between white sharks, other coastal sharks, and killer whales are increasing in South Africa and are expected to have pronounced impacts on the ecosystem.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45499213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-02DOI: 10.2989/1814232X.2022.2042383
Ecv Butler, A. Childs, Mks Smith, R. Foster, W. Potts
Knowledge of the location and timing of spawning events is critical for fisheries management. As is the case for many southern African fishes, the spotted grunter Pomadasys commersonnii was historically thought to reproduce in the coastal waters off KwaZulu-Natal Province (KZN), South Africa, with subsequent egg and larval dispersal towards the Eastern Cape (EC) and Western Cape (WC) provinces facilitated by the Agulhas Current. More recently, year-round residency within areas of the EC and the observation of reproductively mature individuals in certain WC estuaries has provided some support for spawning events southwest of KZN. This study reports empirical evidence of active spawning in the sheltered marine section of the Knysna estuarine bay, WC. Observations of spawning behaviour were noted during large aggregations of adult fish over shallow sandbanks in February 2017. A single male and female were collected, and their reproductive organs were macroscopically staged as ‘spawning.’ Gonad histological examination verified active spawning of the female via the presence of hydrated oocytes, migratory nucleus oocytes and post-ovulatory follicles. Future research should focus on the identification and conservation of critical spawning events and investigate the potential role of large marine-dominated estuarine systems in the life history of this and other marine estuarine-dependent species. Lastly, the results of this study contribute towards a knowledge base that challenges the traditional theory of northeastward spawning migrations as the sole life-history strategy for numerous South African fishery species.
{"title":"Spawning observations of Pomadasys commersonnii in the marine section of the Knysna estuarine bay, Western Cape, South Africa","authors":"Ecv Butler, A. Childs, Mks Smith, R. Foster, W. Potts","doi":"10.2989/1814232X.2022.2042383","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2042383","url":null,"abstract":"Knowledge of the location and timing of spawning events is critical for fisheries management. As is the case for many southern African fishes, the spotted grunter Pomadasys commersonnii was historically thought to reproduce in the coastal waters off KwaZulu-Natal Province (KZN), South Africa, with subsequent egg and larval dispersal towards the Eastern Cape (EC) and Western Cape (WC) provinces facilitated by the Agulhas Current. More recently, year-round residency within areas of the EC and the observation of reproductively mature individuals in certain WC estuaries has provided some support for spawning events southwest of KZN. This study reports empirical evidence of active spawning in the sheltered marine section of the Knysna estuarine bay, WC. Observations of spawning behaviour were noted during large aggregations of adult fish over shallow sandbanks in February 2017. A single male and female were collected, and their reproductive organs were macroscopically staged as ‘spawning.’ Gonad histological examination verified active spawning of the female via the presence of hydrated oocytes, migratory nucleus oocytes and post-ovulatory follicles. Future research should focus on the identification and conservation of critical spawning events and investigate the potential role of large marine-dominated estuarine systems in the life history of this and other marine estuarine-dependent species. Lastly, the results of this study contribute towards a knowledge base that challenges the traditional theory of northeastward spawning migrations as the sole life-history strategy for numerous South African fishery species.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42741998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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