Western Indian Ocean Journal of Marine Science

A decade of the Blue Economy concept in the western Indian Ocean region: research and technology perspectives

Majuto C. Manyilizu — 2023-10-02

The World Bank defines the Blue Economy as “the sustainable use of ocean resources for economic growth, improved livelihoods, and jobs while preserving the health of the ocean ecosystem”. The implementation of Blue Economy concept at global, continental, regional and country levels have had mixed results since its origin in 2012. Here, a systematic review of progress in the western Indian Ocean region is undertaken, focused on research and technology between 2012 and 2021. Apart from applications to ocean modelling, big data and satellite data, the term Blue Economy did not appear as a key term in most publications from the region, suggesting that it is not well understood or researched. Existing studies aligned with three Africa Blue Economy Strategy thematic areas: (1st) fisheries, aquaculture and ecosystem conservation; (3rd) environmental sustainability, climate change and coastal infrastructure; and (5th) policies, institutional and governance. Multi-disciplinary and multi-institutional collaborations focusing on technology are required to boost Blue Economy implementation in the Western Indian Ocean region, including for thematic areas for shipping transportation and trade (2nd) and sustainable energy, extractive minerals, gas, and innovative industries (4th).

Suitability of a superheated steam dryer for drying sardines

Prissillah Antelm — 2023-10-19

The suitability of a superheated steam dryer for drying sardines was investigated. Proximate composition (moisture, crude protein, crude fat, ash, and crude fibre; minerals-calcium, zinc, iron) for fresh, oven dried (OD) at 100 °C, oven dried (OD) at 120 °C and superheated steam dried (SSD) sardines at 120 °C was evaluated and the results reported on a dry matter basis. There were significant differences (p<0.05) in moisture, crude fat, and ash content among fresh and dried samples, but not for crude protein or crude fibre. The crude protein % content of fresh, OD at 100 °C, OD at 120 °C, and SSD, was 78.17, 78.40, 75.77, and 76.05 and crude fibre % was 0.59, 0.12, 0.02, and 0.13, respectively. The SSD sardines had the highest fat content (11.8 %) and the fresh sardines had the lowest (8.1 %). There was a significant difference in calcium content (p<0.05) but not for zinc and iron content. Overall, SSD retained the nutrients of sardines well.

Hydrodynamics of nearshore coastal waters: Implications for marine cage farming in Kenya

David O. Mirera — 2023-10-26

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, 0.89
m/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.

Lessons for ensuring continued community participation in a mangrove blue carbon conservation and restoration project in Madagascar

Lalao A. Ravaoarinorotsihoarana — 2023-11-06

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.

Feeding habits and diet composition of Octopus cyanea (Gray, 1849) in Zanzibar waters, Tanzania

Amini I. Hamad — 2023-11-09

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.

Salinity tolerance of Nile tilapia (Oreochromis niloticus) to seawater and growth responses to different feeds and culture systems

David Oersted Mirera — 2023-11-28

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.

Diet and trophic interactions between catadromous eels and sympatric fish in Kenyan east flowing river systems

Japhet K. Tembo — 2023-11-28

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.

Phthalates in marine sediment, water and the cockle Anadara antiquata on the coast of Tanzania

Sai Ngassa — 2023-12-08

Phthalates are a group of chemicals used as plasticisers, and are easily released into the environment, where they degrade over time. We investigated the concentrations of phthalates in sediments, seawater, and the cockle Anadara antiquata from beaches at Dar es Salaam, Mtwara, Tanga and Zanzibar in Tanzania. A dispersive liquid-liquid microextraction method was used to extract analytes from samples, whereafter they were analysed with a gas chromatograph coupled to a mass spectrophotometer. Concentrations of diisobutyl phthalate (DiBP), dibutyl phthalate (DBP) and Bis(2-ethylhexyl) phthalate (DEHP) were determined. DiBP concentrations were highest at Dar es Salaam (11.5 - 12.4 ng/mL in seawater; 11.5 - 13.6 ng/g dry weight in sediments), compared to the other three sites, where minimum and maximum concentrations in sediments were 3.5 ng/g dw (Mtwara) and 10.7 ng/g dw (Tanga). DBP concentrations were also highest at Dar es Salaam (12.4 - 20.6 ng/mL in seawater; 12.1 - 18.7 ng/g dw in sediments) compared to 2.7 (minimum, Mtwara) and 11.2 ng/g dw (maximum, Tanga). DEHP at Dar es Salaam ranged from un-detected to 12.6 ng/mL in seawater and to 12.6 ng/g dw in sediments. It was further revealed that A. antiquata from Kawe Beach (Dar es Salaam) had higher concentrations of DiBP, DBP, and DEHP compared to other sites. Monitoring of phthalate concentrations will indicate pollution hotspots and trends in the region.