T. A. Mussa, Saleh A.S Yahya, Jose J Castro, L. Chauka
The growth parameters of Lethrinus harak were studied in Zanzibar water from 308 samples collected between June 2019 to May 2020 at Unguja Ukuu and Mkokotoni landing sites. The annulus count indicated that the majority of fishes captured were of three and four years old and very few were five, six, and seven years of age with a mean length of 17.69 cm, 21.04 cm, 24.18 cm, 25.86 cm, and 28.15, respectively. The number of rings was counted on the whole otolith and the growth rings were revealed to be formed annually, with the opaque margins generated from December to February and the hyaline ones during the rest of the year. The growth parameters were estimated as L∞=34.22cm, K=0.25 year-1, and t0=0.00. The total mortality (Z) was estimated as 0.68 year-1 and natural mortality (M) was estimated using Pauly's equation, as 0.65 per year-1 and fishing mortality (F) was 0.03 year-1, which gives an exploitation rate (E) of 0.04 year-1. Although these values indicate the species to be underexploited, the absence of older individuals 15 years and smaller below three years might have affected our findings.
{"title":"Age, growth and mortality characteristics of the Thumbprint Emperor (Lethrinus harak) in Zanzibar","authors":"T. A. Mussa, Saleh A.S Yahya, Jose J Castro, L. Chauka","doi":"10.4314/wiojms.v23i1.2","DOIUrl":"https://doi.org/10.4314/wiojms.v23i1.2","url":null,"abstract":"The growth parameters of Lethrinus harak were studied in Zanzibar water from 308 samples collected between June 2019 to May 2020 at Unguja Ukuu and Mkokotoni landing sites. The annulus count indicated that the majority of fishes captured were of three and four years old and very few were five, six, and seven years of age with a mean length of 17.69 cm, 21.04 cm, 24.18 cm, 25.86 cm, and 28.15, respectively. The number of rings was counted on the whole otolith and the growth rings were revealed to be formed annually, with the opaque margins generated from December to February and the hyaline ones during the rest of the year. The growth parameters were estimated as L∞=34.22cm, K=0.25 year-1, and t0=0.00. The total mortality (Z) was estimated as 0.68 year-1 and natural mortality (M) was estimated using Pauly's equation, as 0.65 per year-1 and fishing mortality (F) was 0.03 year-1, which gives an exploitation rate (E) of 0.04 year-1. Although these values indicate the species to be underexploited, the absence of older individuals 15 years and smaller below three years might have affected our findings.","PeriodicalId":510876,"journal":{"name":"Western Indian Ocean Journal of Marine Science","volume":"28 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140248879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The inability to acclimatise, feed and grow Nile tilapia (Oreochromis niloticus) in full seawater salinity has been a major obstacle to farming in marine waters. We investigated the salinity tolerance of O. niloticus and growth responses to different feeds and culture systems. Fish were first acclimatised to different salinities in laboratory aquaria, and the survival and growth performance in sea water were then assessed in aquaria, cages and ponds. Acclimatization to seawater salinity (5 – 30) took place at a rate of 5 every 9 days. Fish were stocked at densities of 5 fish/20 L in aquaria, 5 fish/m2 in cages and 3 fish/m2 in ponds. Replicates of 5, 3 and 3 were performed in aquaria, cages and ponds, respectively. Fish were fed on commercial (1 and 2) and locally formulated (30 % crude protein) diets. Mortality rates were higher in aquaria, when fish were introduced to salinities between 5 and 30 over 24 hours. Gradual salinity adjustments attained a stable survival rate of 78 % at salinities above 30. Aquarium experiments indicated significant negative correlation between salinity and survival (p < 0.001, r = 0.387) and daily growth rates varied with diet (0.01 – 0.05 g/day). Acclimatized fish showed minimal mortality in ponds and cages. Daily growth rates varied with diet and culture system; 0.54 - 2.48 g/day in cages and 1.1 - 2.5 g/day in ponds. Fish fed on commercial feed 2 showed significant growth rates for all culture methods (p < 0.05). O. niloticus could be fully acclimatised to seawater and attained promising growth rates when subjected to different commercial diets indicating potential of farming the species in marine waters.
{"title":"Salinity tolerance of Nile tilapia (Oreochromis niloticus) to seawater and growth responses to different feeds and culture systems","authors":"D. Mirera, Douglas Okemwa","doi":"10.4314/wiojms.v22i2.6","DOIUrl":"https://doi.org/10.4314/wiojms.v22i2.6","url":null,"abstract":"The inability to acclimatise, feed and grow Nile tilapia (Oreochromis niloticus) in full seawater salinity has been a major obstacle to farming in marine waters. We investigated the salinity tolerance of O. niloticus and growth responses to different feeds and culture systems. Fish were first acclimatised to different salinities in laboratory aquaria, and the survival and growth performance in sea water were then assessed in aquaria, cages and ponds. Acclimatization to seawater salinity (5 – 30) took place at a rate of 5 every 9 days. Fish were stocked at densities of 5 fish/20 L in aquaria, 5 fish/m2 in cages and 3 fish/m2 in ponds. Replicates of 5, 3 and 3 were performed in aquaria, cages and ponds, respectively. Fish were fed on commercial (1 and 2) and locally formulated (30 % crude protein) diets. Mortality rates were higher in aquaria, when fish were introduced to salinities between 5 and 30 over 24 hours. Gradual salinity adjustments attained a stable survival rate of 78 % at salinities above 30. Aquarium experiments indicated significant negative correlation between salinity and survival (p < 0.001, r = 0.387) and daily growth rates varied with diet (0.01 – 0.05 g/day). Acclimatized fish showed minimal mortality in ponds and cages. Daily growth rates varied with diet and culture system; 0.54 - 2.48 g/day in cages and 1.1 - 2.5 g/day in ponds. Fish fed on commercial feed 2 showed significant growth rates for all culture methods (p < 0.05). O. niloticus could be fully acclimatised to seawater and attained promising growth rates when subjected to different commercial diets indicating potential of farming the species in marine waters.","PeriodicalId":510876,"journal":{"name":"Western Indian Ocean Journal of Marine Science","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139217564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Japhet K. Tembo, C. Kihia, Nzula Kitaka, Gordon C. O'Brien, Céline Hanzen, E. Mbaru, Kariuki C. Wanjiru
Biotic interactions such as competition and predation are important ecological drivers of population structure. Interactions among higher trophic level fish can contribute to further population declines in species, such as eels, made vulnerable by overexploitation or environmental change. Furthermore, trophic interactions may further predispose eel populations to collapse, but this is poorly understood, particularly along the Western Indian Ocean (WIO) rivers. This study evaluated stomach contents of fish captured with glass and commercial fyke nets in the Athi and Ramisi Rivers, which discharge into the WIO. Stomach contents were examined using dissecting microscope to establish diet composition. Eels primarily consumed assorted fish (43 %), and crustaceans (36 %); such as penaeid shrimp (14%) and prawns (13%) and crab (9%), thus belonged to a higher trophic level (TL) of 3.47 than native (2.98) or introduced (2.8) sympatric fish species. Diet breadth of eels was significantly lower (0.20) than for sympatric fish species (0.27), attributed to higher diet specialization. The TL of carnivorous fish (3.19) and their diet compared well with those of eels, even though diet preference differed significantly among fish types. Consequently, eels ranked as vulnerable by the IUCN are further threatened by previously undescribed competition from carnivorous fish.
{"title":"Diet and trophic interactions between catadromous eels and sympatric fish in Kenyan east flowing river systems","authors":"Japhet K. Tembo, C. Kihia, Nzula Kitaka, Gordon C. O'Brien, Céline Hanzen, E. Mbaru, Kariuki C. Wanjiru","doi":"10.4314/wiojms.v22i2.7","DOIUrl":"https://doi.org/10.4314/wiojms.v22i2.7","url":null,"abstract":"Biotic interactions such as competition and predation are important ecological drivers of population structure. Interactions among higher trophic level fish can contribute to further population declines in species, such as eels, made vulnerable by overexploitation or environmental change. Furthermore, trophic interactions may further predispose eel populations to collapse, but this is poorly understood, particularly along the Western Indian Ocean (WIO) rivers. This study evaluated stomach contents of fish captured with glass and commercial fyke nets in the Athi and Ramisi Rivers, which discharge into the WIO. Stomach contents were examined using dissecting microscope to establish diet composition. Eels primarily consumed assorted fish (43 %), and crustaceans (36 %); such as penaeid shrimp (14%) and prawns (13%) and crab (9%), thus belonged to a higher trophic level (TL) of 3.47 than native (2.98) or introduced (2.8) sympatric fish species. Diet breadth of eels was significantly lower (0.20) than for sympatric fish species (0.27), attributed to higher diet specialization. The TL of carnivorous fish (3.19) and their diet compared well with those of eels, even though diet preference differed significantly among fish types. Consequently, eels ranked as vulnerable by the IUCN are further threatened by previously undescribed competition from carnivorous fish.","PeriodicalId":510876,"journal":{"name":"Western Indian Ocean Journal of Marine Science","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139226049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The octopus fishery in Zanzibar is an essential activity of coastal communities. To assist with developing fisheries management plans, baseline information on the feeding of Octopus cyanea (Gray, 1849) was collected in relation to sex and maturity stages. The feeding habits and diet composition of 543 O. cyanea were studied over a period of 12 months at Paje, Kizimkazi, Chwaka Bay and Nungwi. Samples at each site were collected on two days per month during spring tide. Digestive tract contents revealed that O. cyanea preyed on 36 species of crustaceans, molluscs and fishes, with crabs a major prey item. The number of prey species in a single stomach ranged from one to six. O. cyanea in Zanzibar is therefore a generalist predator with a mixed diet. The octopus gonadosomatic index (GSI) indicated a peak breeding season in June to October, which correlated with low prey consumption. Mature octopuses ingested a small amount of food from mainly small sessile prey. Females consumed less food than males of similar maturity stages, suggesting that they ate less or had higher digestion rates. The information is useful for developing fisheries management plans for the octopus fishery in Zanzibar.
桑给巴尔的章鱼渔业是沿海社区的一项重要活动。为了协助制定渔业管理计划，我们收集了有关章鱼（Octopus cyanea，Gray，1849 年）摄食与性别和成熟阶段的基线信息。在 Paje、Kizimkazi、Chwaka Bay 和 Nungwi，对 543 只 O. cyanea 的摄食习惯和食物组成进行了为期 12 个月的研究。每个地点的样本都是在春潮期间每月两天采集的。消化道内容物显示，O. cyanea捕食了 36 种甲壳类、软体动物和鱼类，其中螃蟹是主要的猎物。一个胃中的猎物种类从 1 种到 6 种不等。因此，桑给巴尔的 O. cyanea 是一种混合食物的食肉动物。章鱼性腺指数（GSI）表明，章鱼的繁殖旺季在 6 月至 10 月，这与猎物消耗量低有关。成熟章鱼主要从小型无梗猎物中摄取少量食物。雌性章鱼消耗的食物少于成熟阶段相似的雄性章鱼，这表明它们吃得更少或消化率更高。这些信息有助于制定桑给巴尔章鱼渔业管理计划。
{"title":"Feeding habits and diet composition of Octopus cyanea (Gray, 1849) in Zanzibar waters, Tanzania","authors":"Amini I. Hamad, Christopher A. Muhando","doi":"10.4314/wiojms.v22i2.5","DOIUrl":"https://doi.org/10.4314/wiojms.v22i2.5","url":null,"abstract":"The octopus fishery in Zanzibar is an essential activity of coastal communities. To assist with developing fisheries management plans, baseline information on the feeding of Octopus cyanea (Gray, 1849) was collected in relation to sex and maturity stages. The feeding habits and diet composition of 543 O. cyanea were studied over a period of 12 months at Paje, Kizimkazi, Chwaka Bay and Nungwi. Samples at each site were collected on two days per month during spring tide. Digestive tract contents revealed that O. cyanea preyed on 36 species of crustaceans, molluscs and fishes, with crabs a major prey item. The number of prey species in a single stomach ranged from one to six. O. cyanea in Zanzibar is therefore a generalist predator with a mixed diet. The octopus gonadosomatic index (GSI) indicated a peak breeding season in June to October, which correlated with low prey consumption. Mature octopuses ingested a small amount of food from mainly small sessile prey. Females consumed less food than males of similar maturity stages, suggesting that they ate less or had higher digestion rates. The information is useful for developing fisheries management plans for the octopus fishery in Zanzibar.","PeriodicalId":510876,"journal":{"name":"Western Indian Ocean Journal of Marine Science","volume":"67 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139282278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lalao A. Ravaoarinorotsihoarana, Jenny Maltby, Leah Glass, Jenny Oates, Cicelin Rakotomahazo, Dolce A. Randrianandrasaziky, Lanto Ranivoarivelo, Thierry Lavitra
Successful conservation projects that restrict or change access to common pool resources require meaningful community participation not only through consultation but also by empowering communities to take a leading role from the early stages of its design. In this study, community participation was assessed in the Tahiry Honko community-led mangrove blue carbon project in southwest Madagascar using the Spectrum of Public Participation tool developed by the International Association for Public Participation. Trends of community participation at village meetings were assessed using the meeting records from 2014 to 2019. Performance in the project activities was assessed based on the indicators of success. It was learned that: (i) careful scheduling of meetings is crucial to avoid community fatigue; (ii) anonymous democratic votes are an effective, inclusive approach to address domination in a group activity and obtain informed consent; (iii) creating a comfortable space for women is vital to promote their participation in decision-making; (iv) voluntary approach with meal compensation is effective to engage all community groups in mangrove replanting; (v) competitive process is crucial to recruit motivated volunteers for mangrove forest patrols; and (vi) dissemination of patrol results is helpful in developing an adaptive strategy in the absence of effective enforcement of rules.
{"title":"Lessons for ensuring continued community participation in a mangrove blue carbon conservation and restoration project in Madagascar","authors":"Lalao A. Ravaoarinorotsihoarana, Jenny Maltby, Leah Glass, Jenny Oates, Cicelin Rakotomahazo, Dolce A. Randrianandrasaziky, Lanto Ranivoarivelo, Thierry Lavitra","doi":"10.4314/wiojms.v22i2.4","DOIUrl":"https://doi.org/10.4314/wiojms.v22i2.4","url":null,"abstract":"Successful conservation projects that restrict or change access to common pool resources require meaningful community participation not only through consultation but also by empowering communities to take a leading role from the early stages of its design. In this study, community participation was assessed in the Tahiry Honko community-led mangrove blue carbon project in southwest Madagascar using the Spectrum of Public Participation tool developed by the International Association for Public Participation. Trends of community participation at village meetings were assessed using the meeting records from 2014 to 2019. Performance in the project activities was assessed based on the indicators of success. It was learned that: (i) careful scheduling of meetings is crucial to avoid community fatigue; (ii) anonymous democratic votes are an effective, inclusive approach to address domination in a group activity and obtain informed consent; (iii) creating a comfortable space for women is vital to promote their participation in decision-making; (iv) voluntary approach with meal compensation is effective to engage all community groups in mangrove replanting; (v) competitive process is crucial to recruit motivated volunteers for mangrove forest patrols; and (vi) dissemination of patrol results is helpful in developing an adaptive strategy in the absence of effective enforcement of rules.","PeriodicalId":510876,"journal":{"name":"Western Indian Ocean Journal of Marine Science","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139288533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hydrodynamic characteristics are important considerations in the design of cages used for fish farming in nearshore marine environments. The hydrodynamics of sites in mangrove creeks and comparatively open water channels in Kilifi and Kwale Counties in Kenya were sampled across tidal cycles and seasons using an Acoustic Wave and Current Profiler (AWAC). Water temperature ranged between 25.9 °C and 33.0 °C, and was lower in deeper areas with larger tidal heights than in shallower areas with smaller tidal heights. The water column height ranged between 9.68 - 14.69 m at Kijiweni, 1.16 - 6.7 m at Kibokoni and Tsunza, and 0.72 - 2.57 m at Dabaso. Maximum current speeds were 0.83 - 0.87 m/s at Kijiweni, 1.1 m/s at Kibokoni, 0.89m/s Tsunza, and 0.34 m/s at Dabaso. Wave height reached 0.35 and 0.36 m at Kijiweni, 2.7 m at Kibokoni, 1.3 m at Tsunza, and 1.6 m at Dabaso. The considerable difference in hydrodynamic characteristics between the sampling sites indicate that cages for marine fish farming should be designed specifically for local conditions in mangrove creeks and Cages for fish farming therefore require specific design and structural features depending on the local hydrodynamic conditions.
{"title":"Hydrodynamics of nearshore coastal waters: Implications for marine cage farming in Kenya","authors":"D. Mirera, Athman Salim, Joselyne Kendi","doi":"10.4314/wiojms.v22i2.3","DOIUrl":"https://doi.org/10.4314/wiojms.v22i2.3","url":null,"abstract":"Hydrodynamic characteristics are important considerations in the design of cages used for fish farming in nearshore marine environments. The hydrodynamics of sites in mangrove creeks and comparatively open water channels in Kilifi and Kwale Counties in Kenya were sampled across tidal cycles and seasons using an Acoustic Wave and Current Profiler (AWAC). Water temperature ranged between 25.9 °C and 33.0 °C, and was lower in deeper areas with larger tidal heights than in shallower areas with smaller tidal heights. The water column height ranged between 9.68 - 14.69 m at Kijiweni, 1.16 - 6.7 m at Kibokoni and Tsunza, and 0.72 - 2.57 m at Dabaso. Maximum current speeds were 0.83 - 0.87 m/s at Kijiweni, 1.1 m/s at Kibokoni, 0.89m/s Tsunza, and 0.34 m/s at Dabaso. Wave height reached 0.35 and 0.36 m at Kijiweni, 2.7 m at Kibokoni, 1.3 m at Tsunza, and 1.6 m at Dabaso. The considerable difference in hydrodynamic characteristics between the sampling sites indicate that cages for marine fish farming should be designed specifically for local conditions in mangrove creeks and Cages for fish farming therefore require specific design and structural features depending on the local hydrodynamic conditions.","PeriodicalId":510876,"journal":{"name":"Western Indian Ocean Journal of Marine Science","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139313417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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