Small Estuarine and Non-Estuarine Mangrove Ecosystems of Tanzania: Overlooked Coastal Habitats?

This research article was published in Estuaries: A Lifeline of Ecosystem Services in the Western Indian Ocean, 2016.Small estuaries and non-estuarine habitats harboring mangroves are very important ecosystems which provide important ecosystem goods and services; such as provision of ecological niches for juvenile fishes and invertebrates, enhances fisheries, and in biodiversity conservation. Similar to large estuaries, they are highly perturbed which threatens their existence. This chapter uses beach seine, underwater visual census, and stable isotope data to discuss the importance of and threats to small estuaries and non-estuarine mangroves found in Dar es Salaam, Bagamoyo and Zanzibar, Tanzania. For example, mangroves of Kunduchi (Dar es Salaam) and Mbegani (Bagamoyo) which harbour predominantly higher densities of juveniles (≤10 cm) of two economically important species—Lutjanus fulviflamma and Lethrinus harak—than adjacent coral reefs. Evidence suggests further that the Kunduchi mangroves replenish fish populations on adjacent coral reefs; where over 90% and 29% of adult L. fulviflamma and L. harak individuals, respectively, have been identified to have lived in the mangroves as juveniles. In terms of habitat utilization by different size classes of fish, five of the 13 species (Lethrinus lentjan, L. variegatus, Pelates quadrilineatus, Siganus sutor and Sphyraena barracuda) found in Chwaka Bay (Zanzibar) were found as small-sized individuals in shallow and turbid mangrove areas with large juveniles and sub-adults in adjacent seagrass beds. The non-estuarine mangroves of Kunduchi and those of Mtoni estuary (Dar es Salaam) are subjected to pollution from urban activities. For example, stable isotope data of fishes indicate elevated levels of nitrogen in these mangroves with highest levels (δ15N = 15.2 ± 0.2) recorded in Mtoni estuary. In view of their importance and threats they face, these ecosystems require attention similar to large estuaries. If the current degradation rate of these ‘overlooked’ but equally important ecosystems continues, they may be declared ‘functionally disappeared’ in a few decades

Seasonal and spatial variation of surface current in the Pemba Channel, Tanzania

This research article published by PLOS ONE, 2019The surface current speeds within the Pemba channel were examined using 24 years of drifter data received from the Global Drifter Program. This study aimed to uncover varying surface current in the Pemba Channel in different seasons. The results revealed the Pemba Channel experiences relatively higher median surface current speeds during the southeast (SE) monsoon season compared to the northeast (NE) and inter-monsoon (IN) periods. The strongest current speeds were confined in waters deeper than 200 meters between ~39.4°E and 39.7°E. These results prove that surface currents from the drifters can be used to uncover the patterns of surface circulation even in areas where in-situ measurements are scarce

Small Estuarine and Non-Estuarine Mangrove Ecosystems of Tanzania: Overlooked Coastal Habitats?

This research article published by Springer Nature Switzerland AG., 2016Small estuaries and non-estuarine habitats harboring mangroves are very important ecosystems which provide important ecosystem goods and services; such as provision of ecological niches for juvenile fishes and invertebrates, enhances fisheries, and in biodiversity conservation. Similar to large estuaries, they are highly perturbed which threatens their existence. This chapter uses beach seine, underwater visual census, and stable isotope data to discuss the importance of and threats to small estuaries and non-estuarine mangroves found in Dar es Salaam, Bagamoyo and Zanzibar, Tanzania. For example, mangroves of Kunduchi (Dar es Salaam) and Mbegani (Bagamoyo) which harbour predominantly higher densities of juveniles (≤10 cm) of two economically important species—Lutjanus fulviflamma and Lethrinus harak—than adjacent coral reefs. Evidence suggests further that the Kunduchi mangroves replenish fish populations on adjacent coral reefs; where over 90% and 29% of adult L. fulviflamma and L. harak individuals, respectively, have been identified to have lived in the mangroves as juveniles. In terms of habitat utilization by different size classes of fish, five of the 13 species (Lethrinus lentjan, L. variegatus, Pelates quadrilineatus, Siganus sutor and Sphyraena barracuda) found in Chwaka Bay (Zanzibar) were found as small-sized individuals in shallow and turbid mangrove areas with large juveniles and sub-adults in adjacent seagrass beds. The non-estuarine mangroves of Kunduchi and those of Mtoni estuary (Dar es Salaam) are subjected to pollution from urban activities. For example, stable isotope data of fishes indicate elevated levels of nitrogen in these mangroves with highest levels (δ15N = 15.2 ± 0.2) recorded in Mtoni estuary. In view of their importance and threats they face, these ecosystems require attention similar to large estuaries. If the current degradation rate of these ‘overlooked’ but equally important ecosystems continues, they may be declared ‘functionally disappeared’ in a few decades

Fisheries Statistics for Lake Victoria, Tanzania

This research article published by Springer Nature Switzerland AG., 2017Time series fisheries statistics data mainly from Frame Surveys, Catch Assessment Surveys and Fisheries Annual Statistics Reports for Lake Victoria from 1967–2016 were collected from the Fisheries Development Division in Tanzania. These surveys and reports comprised relevant information and data on fish catches and fishing effort. The data were analysed and used to describe variations and trends in the number of fishers, number of fishing crafts, fish weight, catch per boat, total number of gillnets, beach seines, longline hooks, outboard and inboard engines. Frame Survey results showed an increasing trend in the number of fishers and fishing crafts, with the highest number of fishers and fishing crafts being 109,397 and 31,773, respectively in 2016. Longline hooks increased from 2,200,901 in 2000 to 8,163,119 hooks in 2016. In general, the catch per unit effort (CPUE) for all species was high at 39 mt/boat/year in 1967 and decreased to 8 mt/boat/year in 2014. However, CPUE for Lates niloticus has increased since the late 1980s, with the highest CPUE of 19.22 mt/boat/year being recorded in 1995, and from 2000 it decreased gradually to 7 mt/boat/year in 2014. As the fisheries statistics show an increase in fishing pressure over the years, it is evident that there is a sign of overfishing. For that matter, effective fisheries management is needed for the three riparian states to safeguard the sustainable use of fishery resources in the lake and to provide data that can be used in the evaluation of the fisheries objectives

The decline in phytoplankton biomass and prawn catches in the Rufiji-Mafia Channel, Tanzania

This research article published by African Journals OnlineThe world’s oceans have seen significant declines in phytoplankton-the primary food source in the marine environment. This decline in primary producers is likely to impact the food chain and functions of most coastal and marine ecosystems. Despite being one of the most productive marine fishing grounds in the Western Indian Ocean (WIO) region, the information about phytoplankton biomass in the Rufiji-Mafia Channel is poor. This study aimed to narrow this information gap by assessing phytoplankton biomass in the Channel and its association with the decline of the prawn fishery. We combined in-situ measurement and ocean colour satellite data to determine and assess trends in phytoplankton biomass and sea surface temperature between 2002 and 2014. These trends were related to a declining prawn fishery in the Channel. While phytoplankton displayed a significant declining trend during the southwest monsoon, sea surface temperature showed an insignificant increasing trend. Phytoplankton declined at the rate of 1.2 percent per year (tau = 1.2, z = 3.52, p = 0.004) between 2002 and 2014. This declining trend in Chl-a matches well with the decreasing trend in the prawn fishery (tau = 0.57, z = 3.39, p = 0.0006) and the insignificant increasing trend in sea surface temperature (tau = 0.02, z = 0.43, p = 0.66). This study provides quantitative evidence of trends in chlorophyll and SST and the link with trends in the prawn fishery, which increases our understanding of the changes in marine primary productivity in the coastal waters of Tanzania

Environmental Changes in the Tanzanian Part of Lake Victoria

This research article published by Springer Nature Switzerland AG.,Lake Victoria is known for its explosive speciation and recent time hybridization, which is highly mediated by deterioration of water quality. This chapter summarizes the knowledge on change of water quality and environment of southern part of Lake Victoria, Tanzania. It analyses rainfall, air temperature and water quality data spanning 30 years (1985 to 2015). It also investigates changes in physical-chemical data sampled during and after the Lake Victoria Environmental Management Project I (LVEMP I). The chapter reviews some of the significant water quality changes that have occurred for the past 50 years. The results indicate no significant changes in annual rainfall variability. Nevertheless, trends of air temperature showed no clear patterns for Mwanza and Musoma, but trends of minimum and maximum air temperature in Bukoba increased significantly at annual rates of 0.19 °C and 0.14 °C, respectively. Water level in Lake Victoria has also declined significantly at an annual rate of about 5.5 cm from 1965 to 2004. These findings suggest that lake levels are determined by evapotranspiration rather than rainfall. It was also found that anthropogenic stressors are more important in explaining nutrients loading while thermal stratification explains hypoxia and reduction in water mixing. It is concluded that the current blooms of harmful algae and excess biomass in Lake Victoria will continue unabated unless nutrient loading, anoxia and high rates of denitrification are curbed. Appropriate measures to improve land use management should therefore be taken, while deliberate dumping of industrial, municipal and agricultural wastes into the lake should be controlled

Co-management of Lake Victoria Fisheries

This research article published by Springer Nature Switzerland AG., 2017There have been concerns about the declining fish catches and fisheries ecosystem health for a number of fisheries including Lake Victoria. Consequently, a co-management system has been introduced as a means of, among others, reversing the declining catches. It is hypothesized that non-involvement of fishers in the management of the lake’s fisheries is a major reason for the ever-decreasing catches. This chapter discusses this particular management regime and its application in the lake’s fisheries. The analysis is based on data collected by the Fisheries Division since co-management was introduced in the lake in 1998. The chapter traces the lake’s fishery management since the pre-colonial to the post-colonial period. It presents the aim and rationale for managing the lake’s fishery, the structure of the management and roles of governors. It also analyses trends in illegal fishing practices as well as enforcement performance. The argument here is that co-management has helped in bringing on board fishers and this has enabled laws and regulations to be implemented in a much better way than they were under a central-command system. The chapter subsequently concludes that the involvement of fishing communities in the management of fisheries has created a forum for the exchange of ideas, knowledge and experience on the resources. This strategy has made the communities understand the importance of compliance to the law and regulations and effective management measures

Small Scale Fisheries Management: Lessons from Cockle Harvesters in Nicaragua and Tanzania

This research article published by Taylor & Francis Online, 2010The role of women in gleaning fisheries tends to be underestimated and poorly documented although they play an important role in coastal food security and income generation. This article describes two initiatives for co-management of women dominated cockle (Anadara spp.) fisheries implemented in Zanzibar Island of Tanzania and in Nicaragua that were based on a Fiji model. In each case, significant progress was made at the pilot scale but required adaptation to the community and national context. The Nicaragua case resulted in increasing densities of cockles inside and outside small scale no-take zones in a small estuary after a two-year period of implementation. In Zanzibar, out of several no-take sites established on reef flats, only one showed similar results. Other sites’ poor performance is likely due to poor site selection, small size, and non-compliance. Varying degrees of poaching affected both locations and continues to be an issue. In Zanzibar, local and national government played highly supporting roles whereas in Nicaragua, local government was supportive but national government continues to exhibit top-down decision-making, while still evaluating the alternative co-management approach. In both cases, university extension initiatives were influential in building community capacity for management and playing an advocacy role with national government. Both locations are poised for scaling up to more geographic sites as well as fostering policy change that can lead to more integrated and ecosystem-scale approaches to sustainable fisheries management

Ecological Changes in the Zambezi River Basin

This research article was published in Council for the Development of Social Science Research in Africa, 2021.Africa faces a plethora of challenges and chief among these is a change in the climate (Zakaria and Maharjan 2014) which is one of the key factors affecting the ecology and hydrology of its river basins (Kusangaya et al. 2014). Beilfuss (2012) proposed that Africa’s arid regions are highly vulnerable to climate change with the Zambezi River Basin (ZRB) being particularly at risk (Kling et al. 2014). After the Nile and Niger rivers, the ZRB is the next most trans-boundary river basin in Africa as it serves eight African countries. Consequently, water resource development planning is crucial, since any changes in climate will impact the hydrological cycle and the amount of water retained in hydrological systems (Beilfuss 2012) of which only up to 3 per cent is readily available as usable and shared freshwater. Like some Sub-Saharan countries, which have experienced up to 0.5 C increases in temperature (Hendrix and Glaser 2007), the Zambezi River Basin is also facing changes in climate (Ndhlovu 2013). A recent study by Kling et al.(2014) reported rises in temperature and more variable precipitation in the basin since the 1980s. Such historical climatic changes, and those projected towards the mid-century (2050), are of concern with serious social and economic implications to local communities (Mubaya et al. 2012). The Intergovernmental Panel on Climate Change (IPCC) projected a global decadal temperature rise of 0.2 C (IPCC 2007). However, regional climat

Caudal fin as a proxy for dorsal muscle for nutrient enrichment monitoring using stable isotope analysis: the case of Gerres filamentosus and G. oyena from mangrove creeks of Tanzania

This research article was published in Western Indian Ocean Journal of Marine Science, Volume 21, Issue 2, 2022.The use of fish dorsal muscles in stable isotope studies, which is an invasive method that results in fish deaths, limits their applicability for rare and endangered fish species, as well as when large sample sizes and replicates are required, prompting research into feasible non-lethal sampling methods. The possibility of employing fin clippings (a non invasive approach) was investigated as a proxy for dorsal muscle in nutrient pollution monitoring studies using two common mangrove fish species, namely Gerres filamentosus and G. oyena, which are known to spend their early life stages primarily within mangroves. The dorsal muscles and caudal fin tissues of fish from the mangrove creeks of Kunduchi and Mbegani, Tanzania, were examined for 13C and 15N signatures. Dorsal muscles from Kunduchi (mean SD: 13C = -16.8 ± 2.86, 15N = 9.34±1.15) were more enriched than from Mbegani (mean SD: 13C = -18.60 ± 2.11, 15N = 7.27±1.09), and this enrichment was consistent across the two studied species. Caudal fins indicated similar enrichment trends. Fin tissue stable isotope values explained between 62 % and 87 % of dorsal muscle 13C and between 89 % and 98 % of dorsal muscle 15N variability. These findings support the use of fin-clipping as a non-lethal proxy for stable isotope analysis of the studied species for nutrient enrichment, and additional research into non-lethal sampling methods is recommended