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Bacterial larvicides

The Government of the United Republic of Tanzania through Commission for Science and Technology (COSTECH) under “KILIMO KWANZA” initiative

The penaeid prawn fishery of Tanzanian coastal waters occurs within three main fishing grounds referred to as zone 1, 2 and 3. The three zones are connected to major estuaries of Ruvu, Rufiji and Matandu rivers, respectively. The genetic connectivity of Fenneropenaeus indicus population in those areas had not been previously studied. The population study was performed to test the hypothesis that only a single population exists in the area, utilizing the mitochondrial DNA (mtDNA) sequence data. There were 89 sequences of F. indicus used in the analysis. Results indicated that there were 36 haplotypes and the mean haplotype diversity (h) was relatively moderate when there was a low level of nucleotide diversity ( π ). The F S T values ranged from −0.00798 to 0.00918 indicating the absence of differentiations between localities. The Tajima’s D and Fu’s Fs statistic showed the presence of recent expansion of the population. An analysis of molecular variation (AMOVA) indicated a higher variation within a population than among populations. The study established that the populations existing in the three prawn fishing grounds were a panmictic population. Thus, the reconsideration of the geographical distribution of the fishing grounds (Zones 1–3) and extension of closed season management strategy to the artisanal fishers are recommended. Further study is recommended using nuclear markers to infer population structure in the coastal waters of Tanzania.

Abundance and distribution of short-lived species like Octopus cyanea depends on favorable environmental conditions, which are essential for growth and successful recruitment. However, the influence of environmental variables on the abundance and distribution of O. cyanea remains unknown, particularly in the Western Indian Ocean (WIO) region, despite its importance as a fishery resource. This study investigated the role of environmental variables (sea surface temperature [SST], chlorophyll-a [Chl-a], rainfall and wind) on the abundance and temporal distribution of O. cyanea around Mafia Island in Tanzania for a period of 60 months (2013–2017). Octopus catch data were obtained from TANPESCA fish processing factory, while environmental data were obtained from the National Aeronautics and Space Administration - NASA satellite (SST and Chl-a) and the Tanzania Meteorological Agency - TMA (rainfall and wind). The results for the O. cyanea CPUE showed two peaks, between March and October, suggesting successful recruitment and stable environmental conditions during these periods. The additive effect of wind speed and Chl-a with a 4-month lag, was the best model for predicting the abundance and temporal distribution of O. cyanea around Mafia Island followed by the additive effect of SST, wind and Chl-a. Temperature influences octopus growth, while strong wind facilitates the mixing of water, which brings the bottom nutrient rich water to the euphotic zone for increased photosynthesis. In conclusion, the abundance and temporal distribution of O. cyanea are influenced by the additive effect of wind, Chl-a and SST with time-lagged effect of four months. This study recommends seasonal closure of the octopus fishery between April and July and reopening in March and October for sustainable harvesting of this valuable resource.

The present study used mitochondrial DNA control region to investigate the genetic stock structure and phylogenetic relationship of 38 samples of Narrow-barred Spanish mackerel Scomberomorus commerson (Lacepede, 1800) from two sites (Dar es Salaam and Pangani) located along the northern Tanzanian coastal waters. The study revealed that the Narrow-barred Spanish mackerel were characterized by high levels of mitochondrial DNA genetic diversity, at both haplotypes and nucleotide levels which is indicative of a large population size. The Analysis of Molecular Variance (AMOVA) test gave a significantly low F S T value ( F S T = 0 .0011), suggestive of a lack of genetic differentiation between the fish populations of the two investigated sites ( p = 0 . 925 ). Furthermore, AMOVA analysis showed that 99.50% of the total molecular variance was distributed within the populations, while only 0.5% was distributed between the populations. The Median-Joining network revealed a star-like median network, suggesting that the collected samples had similar evolutionary history and characterized by a recent historical population expansion. The present study recommends a single stock model for management of Narrow-barred Spanish mackerel in the northern coastal waters of Tanzania. However, due to the migratory nature of the species, a co-management initiative between coastal states within the Western Indian Ocean (WIO) region along with further studies focused on acquiring detailed information on the genetic stock structure covering the entire area is being recommended.

Shirati Bay is among the important breeding and nursery sites for major fish species in Lake Victoria. Weekly samplings were conducted to assess the temporal patterns in phytoplankton, zooplankton and fish composition, abundance and biomass in relation to prevailing water quality parameters. The study also determined the influences of plankton dynamics and water quality on the fish catch composition and biomass. It was hypothesized that temporal patterns in the composition, abundance and biomass in the plankton in the bay are controlled by water quality parameters that, in turn, affect the composition and biomass of fish catches. The phytoplankton comprised mainly cyanophytes and bacillariophytes, while the zooplankton were dominated by copepods. The heavy rain season exhibited a significantly higher plankton abundance and biomass than the dry season. The plankton abundances in both seasons exhibited significant positive correlations with water temperature and transparency. The phytoplankton community was controlled by calanoid and cyclopoid species. At higher trophic levels, Lates niloticus juveniles, Oreochromis niloticus juveniles and haplochromines controlled Cladocera and Cyclopoid copepods, while Tilapia rendalli juveniles controlled the Rotifera. This study revealed that Cyanophyta and Bacillariophyta are the dominant phytoplankton, whereas cyclopoids dominate the zooplankton species in the bay. These dominant plankton groups are partly controlled by rainfall, water temperature and transparency. Fish biomass, zooplankton and phytoplankton exhibit a typical predator–prey inverse relationship. Thus, evaluation of the plankton composition, abundance and biomass should be mandatory during fisheries stock assessments to effectively manage the fishery resources in the bay.

This study explored the yield and economic benefits of African sharptooth catfish, Clarias gariepinus, and Nile tilapia, Oreochromis niloticus polyculture, reared in earthen ponds for 270 days integrated with Chinese cabbage, Brassica rapa chinensis, farmed for 45 days to small-scale farmers in Tanzania. An integrated aquaculture–agriculture (IAA) system involving fishes and vegetables resulted in three and 2.5 times higher net yield than the culture of fishes alone and farming of non-integrated vegetables respectively. Vegetables irrigated with pond water resulted in 1.8 times higher net and annual yields than those irrigated with stream water. The practice of fish–vegetable integration and growing of vegetables irrigated with pond water produced 14 and 13 times higher net annual yield, respectively, than the culture of fishes alone. The integrated system produced 20 and 150 times more net returns compared with vegetables irrigated with pond and stream water respectively. Integrating fishes with vegetables resulted in significantly higher annual net cash flow than the farming of fishes and vegetables separately. The study revealed that integrating fishes with B. rapa chinensis increases yields, income and food production to small-scale farmers. Thus, small-scale farmers can adopt IAA technology to meet the increasing demand of fish and vegetables, stabilize their incomes and diversify food production, consequently improving food security. These benefits will be realized by providing proper training in IAA technology and management skills to small-scale farmers.

The present on-farm study assessed the effect of different stocking densities on growth, production, and financial benefits of African sharptooth catfish (Clarias gariepinus) in earthen ponds for 180 days. Low stocking density (LSD), medium stocking density (MSD), and high stocking density (HSD) of 3, 6, and 9 fish m−2, respectively, were tested. C. gariepinus stocked at LSD and MSD showed significantly higher weight gain, specific growth rate, and final mean weight than those cultured at HSD (P

Understanding the 'value' of nursery habitats is increasingly perceived as essential to conservation management of marine ecosystems globally. Yet, most work on this topic has assumed that population dynamics are temporally and spatially static, which clearly oversimplifies some highly complex and integral ecological processes. We used size-frequency data of fish species from mangrove and seagrass habitats collected at various locations over a >2 yr period to explore demographic structure and variability along with potential factors (such as growth, food abundance, and relative predation risk) that might encourage such variability. While demo - graphics were skewed predominantly towards juveniles, older fish (up to 13 yr) were regularly observed in some mangroves or seagrass beds, indicating relatively complex population demo- graphics. Juvenile habitats varied substantially in both prey abundance and relative predation risk — an effect that appeared to give rise to habitat-specific differences in somatic growth rates and fish densities. Fish population size structure was further related to position within the sea- scape, suggesting complex spatial dynamics in the production of fish biomass. Our results demon- strate that effectively appraising juvenile habitats will be a more convoluted process than previ- ously thought, as greater integration is needed between basic ecological processes (e.g. predation risk and food availability) and population demography. Whereas current approaches often iden- tify and manage single, complete nursery habitats based on those that contribute most individuals to adult populations, our study shows that a more dynamic and spatially-explicit management approach is needed, as nurseries have divergent benefits for separate life stages, species, and locations.

Macroinvertebrates and physicochemical parameters were assessed at 15 sites along five rivers in Kilimanjaro region, Tanzania, with the aim of understanding their ecological status and setting a base to the development of a biological index for tropical regions. Investigated rivers that occur within Pangani basin include Karanga, Rau, Lumbanga, Sere, and Umbwe. Sampling sites were categorized according to the level of water and habitat quality as follows: reference or least impacted (4 sites), moderately impacted (5 sites), and highly impacted (6 sites) sites. A total of 12,527 macroinvertebrates belonging to 13 orders and 48 families were recorded. The highest total abundance of 4,110 individuals per m2 was found in Karanga river, while Umbwe river had the lowest with 1,203 individuals per m2. Chironomidae was the most abundant family (2,588 individuals per m2) and the least were Hydridae and Thiaridae, each having 5 individuals per m2. High numbers of taxa were noted among the orders: Ephemeroptera (8), Odonata (8), Diptera (7), and Trichoptera (6). In conclusion, orders with greater diversity of macroinvertebrate families offer a wide range of tolerance to pollution and, thus can potentially be used to develop a biomonitoring index for evaluating pollution in tropical African rivers.

On-farm fish production experiments were conducted for 240 days to investigate the effect of stocking density on growth, yield and economic benefits of Nile tilapia (Oreochromis niloticus) in monoculture and polyculture with African sharptooth catfish (Clarias gariepinus). Low stocking density (LSD), medium stocking density (MSD) and high stocking density (HSD) of 30 000, 60 000 and 90 000 fish ha−1 respectively, were tested. O. niloticus cultured in polyculture attained significantly higher mean weight gain than those cultured in monoculture. O. niloticus and C. gariepinus raised together in polyculture attained significantly higher net annual yield than O. niloticus cultured alone in monoculture. Profitability analysis using partial enterprise budgets revealed that polyculture is a more profitable system than monoculture. The highest growth, yield and economic benefits were achieved at HSD and MSD than at LSD with no significant difference between HSD and MSD. Results demonstrate that farmers can achieve the highest net yield and economic benefits by culturing O. niloticus and C. gariepinus in polyculture at HSD and MSD, preferably MSD for economic reasons.

Management of fisheries in the Lake Victoria Basin is faced with a multitude of natural and anthropogenic pressures such as over-fishing, eutrophication, declining water levels, soil erosion, sedimentation, water hyacinth infestation and encroachment into fish breeding and spawning areas. The idea of establishing a trust fund, which would contribute to the sustainable management of the lake fisheries and conservation of the lake’s ecosystem, was first conceived during Phase I of the Lake Victoria Environmental Management Project (LVEMP I). This occurred by commissioning a consultancy to study the feasibility of establishing a Fish Levy Trust Fund. The Fund was intended to improve the livelihoods of fishing communities and sustainable management of the fisheries resources through enhanced revenue collection and disposal for essential monitoring, management and effective enforcement. Through a lengthy process of consultations and stakeholder engagement during Phase I (1997–2005) and Phase II (2009–2017) of LVEMP, the Lake Victoria Fisheries Trust Fund (LVFTF) was finally established in 2016 as a way of developing a sustainable funding mechanism to conserve biological diversity and ensure socio-economic welfare of communities that depend on the lake for their livelihood. This chapter therefore presents the chronology of events that led to the establishment of LVFTF, and describes the rationale, organizational structure and functions of the Fund.

The dwindling catch from Lake Victoria has caused an insufficient fish supply to the population of the Lake Victoria basin, Tanzania. The decrease in catch rates and demand for fish has created room for fish farming practices at both small and commercial scales in the Lake Basin. This chapter provides a result-oriented status of aquaculture research and development efforts made by the government and Non-Governmental Organizations (NGOs) in the Lake Basin from the colonial era to the present. The chapter also highlights strengths, weaknesses, opportunities and challenges (SWOCs) to aquaculture development in the basin. Results show that the basin has a high potential for fish farming development due to suitable characteristics for fish farming. Fishponds are the common culture system used in fish farming in the basin. The ponds are stocked with either Nile tilapia Oreochromis niloticus or African sharptooth catfish, Clarias gariepinus, reared in monoculture or polyculture. A system of integrated aquaculture-agriculture (IAA) farming is also practised in some areas of the basin. The yield from the lake basin has increased with time due to improved pond management techniques. However, more room is available for further increase pending the adoption of technology and improved extension services. Fish farming could help to reduce fishing pressure on capture fisheries in the main lake and contribute significantly to the conservation of the lake’s biodiversity. Ultimately, fish farming will generate income for the people, which is in line with the government’s efforts to alleviate poverty in the country.

Time 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.

Plankton and macroinvertebrates are used as biodiversity indicators on account of their sensitivity to changes in aquatic ecosystems. This chapter assesses the changes in the diversity, abundance and distribution of plankton and macroinvertebrates in the inshore and offshore areas of Lake Victoria, selected satellite lakes and rivers within the lake basin. Samples for both plankton and macroinvertebrates were collected during dry and wet seasons between 2000 and 2006. The results indicated that cyanobacteria were most diverse in both seasons. Microcystis spp., Planktolyngbya spp. and Anabaena spp. were the most dominant cyanophyte species at the sampled sites. The dominant phytoplankton (cyanobacteria) are less digestible and provide poor quality food for the fish; that may have contributed to the reduction or loss of planktivorous haplochromines and tilapiines that once flourished in Lake Victoria. Zooplankton community composition in the lake is dominated by rotifers and cyclopoid copepods, in both inshore and offshore areas. The dominance of cyclopoid copepods is important in the production and sustainability of small fishes and larvae that utilize these organisms as a food base. Macroinvertebrate abundance has shifted from an oligochaete and insect dominated community in 1984 to a community dominated by molluscs. The occurrence of a relatively high abundance of low-oxygen tolerant macroinvertebrate taxa at inshore and offshore stations is an indication of deteriorating water quality water quality conditions due to eutrophication and pollution processes. There is a need for a reduction in nutrient loads and pollutant inputs into the lake in order to ensure the ecosystem health.

Life history traits like growth, reproduction, food and mortality are principal factors in the survival of the fish. This chapter examines the life history indicators of three commercial fish species in Lake Victoria, namely Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus) and the cyprinid known as ‘Dagaa’ (Rastrineobola argentea). The size at first maturity for Nile perch has been declining due to stress in the population caused by heavy exploitation, changes in food availability and deteriorating water quality parameters, particularly dissolved oxygen concentration. The fish exhibits ontogenic shifts in food. R. argentea has an offshore surface dwelling behaviour with about 68% found distributed in waters of more than 40 m depth. Its size at first maturity varies from place to place. R. argentea breeds throughout the year but with distinct peaks during the rainy season. An increase in fecundity has been observed in Nile tilapia and it is considered a mechanism to compensate for the intensive fishing pressure in the lake. Studies indicate an increase in size and growth parameters for Nile tilapia despite the heavy fishing pressure as a result of increased demand in local and foreign markets. The success of the species could be due to the ability of the species to expand their niche. It has diversified its food to include Caridina nilotica, chironomids, chaoborids, molluscs and bottom detrital matter. An ecosystem approach guided by a precautionary principle is required in order to manage the fishery resources in Lake Victoria and to ensure their sustainability.

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.

This chapter traces the history and trends in fisheries research for the Tanzanian part of Lake Victoria and its basin back to the late nineteenth century when the haplochromine species were scientifically identified for the first time. Past studies in the early to mid-twentieth century were mainly designed to address issues related to the introduced species and the abundant haplochromines. Subsequent studies in the late twentieth to early twenty-first centuries integrated multiple disciplines such as fish biology, ecology, biodiversity, limnology, socio-economics and aquaculture. In the late 1990s and early 2000s, lake-wide research projects played a key role in further understanding of the lake-basin flora, fauna and related fisheries. Over the last half century, Lake Victoria has undergone dramatic ecosystem changes, partly driven by the introduction of the predatory Nile perch and the non-indigenous tilapiine species in the 1950s and early 1960s. The profound ecosystem transformation of the lake has also been attributed to cultural eutrophication, climatic variability and over-fishing. In the mid-1950s, the lake had a diverse fish fauna, which was thought to comprise about 29 genera and more than 650 species, with the haplochromines forming about 80% of the demersal fish stocks. Later discoveries in the early 1970s to the late 1990s confirmed that the haplochromine group alone consisted of over 500 endemic species. The introduction of the Nile perch was meant to utilize the abundant haplochromines that were considered commercially unimportant, and to extend fishing operations from the inshore to deeper offshore waters.

The fishery of Lake Victoria is dominated by four major commercial species; the introduced Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus), native dagaa (Rastrineobola argentea), and haplochromines. Information on the status of these major fish species is limited because there have been few studies on the exact nature of the stock distribution of the species. As such, it has been difficult to trace the trends and fluctuations in abundance, population structure and composition, which are important in planning fisheries management measures. This chapter provides the current status of the fisheries of these four species by reviewing different trends in biomass, catch rates, catch per unit effort and biological indicators using both fisheries dependent and independent data. The results showed that stock abundance fluctuated over the years, with Nile perch and Nile tilapia abundance considerably reduced mainly due to increased fishing pressure, while dagaa and haplochromines increased over time. Seasonality in environmental factors greatly influenced the distribution and abundance of the species, especially Nile perch. Therefore, concerted efforts are needed to avert a declining trend of Nile perch and Nile tilapia so that their fisheries continue to provide benefits sustainably.

Lake Victoria fishery resources are of great socio-economic, nutritional and food security significance to over 30 million people in the region, and to the international community. The proliferation of Nile perch in the 1990s increased the dynamics in the fisheries sector as people moved from the hinterlands to the Lake region to engage in Nile perch processing. This has also attracted global and domestic concerns and as a result, has revolutionized fish quality assurance practices around Lake Victoria. Consequently, there was a need to enforce quality assurance measures and increase public awareness on fish quality assurance issues in accordance with the relevant national laws and regulations. To conform to the export market standards, the government adopted the Hazard Analysis Critical Control Point (HACCP) programme, and implemented the Good Manufacturing Practices (GMP), Good Hygiene Practices (GHP) and Good Laboratory Practices (GLP) measures. It facilitated a mechanism that ensured the overall improvement of the quality assurance chain such as instituting traceability chains, the construction of and equipping the national fish laboratory and conducting regular monitoring and analysis of microbiological and chemical parameters in fish, water and sediments. Fishers and other stakeholders were trained in sanitation and hygiene to ensure that the fish and fishery products are of the highest quality and safe for human consumption. This resulted into an increase in fish exports and significant reduction of Nile perch post-harvest losses, as can be evidenced from the national fishery statistics for the period 1986–2011. As a result, customers are satisfied with compliance in fish quality control and safety assurance measures or programmes in place.

There 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.

The management of the fisheries of Lake Victoria has had several successes and failures. These failures were either due to inadequate awareness of the fishing communities on the proposed protocols, and/or little attention paid by the government during the colonial period on the importance of lake fisheries. After independence of the riparian states, each country developed her own approach, but based on the findings of research and recommendations from Lake Victoria Fisheries Organization (LVFO). Lately, through the LVFO and especially under the Lake Victroria Environmental Management Project (LVEMP), more concrete and harmonised fisheries management programmes have been developed. In Tanzania, the evolution of the management of fisheries can be divided into four major historical periods: The pre-colonial period, the colonial period, the state-owned economy period (1961–1985) and the liberalised economy period (after 1986). This chapter summarises all the events that took place during these four major periods. It also discusses the results and proposes the way forward. In particular, the chapter emphasises the threats to the lake fisheries resources and other aquatic living organisms arising from effluent discharges from towns and the agricultural areas surrounding the lake. The different effective management organs such as BMUs (developed under LVEMP I and incorporated into Fisheries Act of 2003) have been mentioned as the products of LVEMP I. Finally, the chapter makes three recommendations related to future management of the lake.

The research conducted on Lake Victoria fisheries over the last few years has revealed a dominance of three commercial species, namely, the Nile perch (Lates niloticus), the Nile tilapia (Oreochromis niloticus) and the silver cyprinid, Rastrineobola argentea (“Dagaa”). Human activities in the lake basin have led to eutrophication, which has altered fish habitats and fish food, consequently affecting the diversity of fish resources of Lake Victoria. The challenges facing the management of Lake Victoria fisheries call for more research into the role of the quality of water in the observed lake-wide ecosystem changes. There is need to have a well-resourced lake-wide monitoring system for collecting limnochemical, ecological, biological, catch and effort data in order to have a scientific basis for an evaluation of the effect of management practices on the exploitation of the fisheries resources.

Most coastal marine organisms have a dispersive oceanic larval stage, during which they must be able to distinguish and respond to relevant environmental cues when settling into their first benthic habitat. Chemical stimuli emanating from settlement habitats and being dis- persed by water plumes could enable long-distance navigation by larval reef fish, but we know lit- tle about the cues responsible and their interactive effects. In the present study, we tested this by conducting several ex situ choice experiments in which the response of the coral reef fish Lutjanus fulviflamma towards different chemical cues from coastal habitats was tested close to their settle- ment stage. Fish preferred seagrass habitat water over that from coral reef and mangrove habitats. Furthermore, fish were attracted to chemical cues from their own species (conspecifics) and other fish species, as well as vegetation of 4 different seagrass species, when offered in isolation (i.e. soaked in neutral water), but a strong response remained only towards cues from conspecifics and seagrass leaves when these cues were mixed with seagrass habitat water that naturally contains other cues. Hierarchical effects were observed as fish preferred chemical cues from seagrass leaves over those from conspecifics when both were offered at the same time. The importance of visual habitat cues only overruled that of chemical cues when it concerned preferred cues (i.e. seagrass as opposed to mangrove cues). Our findings indicate that pelagic fish and settlers possess the ability to use multiple reliable chemical cues to locate suitable early life stage habitats, although the importance of these cues is context-dependent. Nevertheless, this flexibility in choice behavior is probably an adaptive strategy to enhance fitness by increasing successful ori- entation towards preferred settlement habitats.

Ontogenetic niche shifts are taxonomically and ecologically widespread across the globe. Consequently, identifying the ecological mechanics that promote these shifts at diverse scales is central to an improved understanding of ecosystems generally. We evaluated multiple potential drivers of ontogenetic niche shifts (predation, growth, maturation, diet shifts, and food availability) for three fish species between connected coral reef and nearshore habitats. In all cases, neither diet compositional change nor sexual maturity functioned as apparent triggers for emigration from juvenile to adult habitats. Rather, the fitness advantages conferred on reef inhabitants (that is, enhanced growth rates) were primarily related to high prey availability on reefs. However, there exists a clear trade-off to this benefit as survival rates for small fishes were significantly reduced on reefs, thereby revealing the potential value of (and rationale behind high juvenile abundances in) nearshore habitat as predation refugia. We ultimately conclude that predation risk functions as the primary early life stage inhibitor of ontogenetic niche shifts towards more profitable adult habitats in these systems. Furthermore, this study provides a case study for how complex, meta-dynamic populations and ecosystems might be better understood through the elucidation of simple ecological trade-offs.

Results of estimation of target strength (TS) of physoclistous Nile perch using in situ TS measurements and deformed cylinder model (DCM) at 70 and 120 kHz are presented. The results of the two methods are compared with those from cage experiments conducted between 1999 and 2000. Cage experiments that assumed the 20 Log(L) relationship (TS = 20 Log(TL) − 66.55) provided a good fit only over the length range of 18–38 cm total length, but overestimated the length of large fish (>60 cm TL). The DCM which lead towards a 30 Log(L) provides more accurate conversion over the full length range of single targets. An in situ study that made no assumptions about the shape, structure or orientation of the fish provided a close fit of acoustically estimated length frequency distributions to net hauls with the equations: TS 70 = 32.11 Log ( TL ) − 86.97 at 70 kHz and TS 120 = 30.15 Log ( TL ) − 84.14 at 120 kHz It is suggested that using this approach can provide valid TS to length relationships for acoustic surveys on species for which little information exists and there is little opportunity for direct observation of behavioural aspects that are known to affect TS such as tilt angle and vertical migration.

For seven years, village-based recorders monitored fish catches and water levels in seven floodplain-associated lakes of the Lower Rufiji, Tanzania. The lakes differ in the number of days and volume of inflows from the river, and thus provide a natural experiment to explore the links between catch composition, income per hour of fishing (IPHF) and hydrological connectivity, and to analyse the response of the users. The fishers adapt their fishing mode and equipment to achieve a rather constant IPHF of between 0.2 and 0.8 US$/fisher/hour. In situations of low connectivity, during a series of drought years, the less well-connected lakes lost many species and became a virtual monoculture of Oreochromis urolepis. Only in one extreme case was average fish size significantly reduced, indicating a high fishing pressure. Catch was therefore highly resilient to shifts toward illegal, non-selective and active fishing techniques. Fish diversity and lake productivity were quickly re-established when the larg...

Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management.

Pelagic larvae of various coral reef fish species are known to be active swimmers that can carefully select preferred microhabitat during settlement. Fish larvae may use visual, environmental, or chemical cues to orient and settle in shallow-water habitats such as coral reefs, mangroves, and seagrass beds. In the present study, we investigated in dual-choice laboratory experiments the visual attraction of recent settlers of a reef fish (Lutjanus fulviflamma) towards different microhabitats, conspecifics, and heterospecifics, and the interactive effects among these cues. Fish preferred seagrass and coral above mangrove roots. Fish were more attracted towards a combination of conspecifics or heterospecifics and seagrass microhabitats than to seagrass microhabitats alone, but showed a significantly stronger preference for conspecifics than for heterospecifics when placed in preferred seagrass or non-preferred mangrove microhabitats. However, the preference for conspecifics disappeared when choice was given between conspecifics placed in non-preferred mangrove microhabitat versus heterospecifics placed in preferred seagrass micro habitat. A multiple choice experiment further showed that recent settlers preferred conspecifics of equal or about 1 cm larger body size, but not of 2 or 3 cm larger body size. The higher attraction towards the combination of seagrass microhabitats and conspecifics/heterospecifics shows an additive effect of the latter, which could be explained by the fact that presence of resident fish in preferred habitat may indicate favorable conditions in the field and may offer an increased safety through schooling. However, (1) attraction towards conspecifics of (nearly) similar body size and not larger, (2) stronger attraction towards conspecifics in a non-preferred than in a preferred microhabitat, and (3) equal attraction towards conspecifics in non-preferred microhabitat vs. heterospecifics in preferred microhabitat all indicate that the importance of schooling with conspecifics is highly context-dependent. This may have significant effects on the habitat selection and distribution of early-stage fish (and thus also on consecutive life stages) in coastal habitats. Our findings point to the potential ecological significance of various visual cues, and their interactive effects, for early juvenile coral reef fishes while settling into shallow-water habitats and/or selecting early post-settlement habitats.

Tropical shallow-water habitats such as mangroves and seagrass beds are widely acknowledged as important juvenile habitats for various coral reef fish species, most of which are commercially important to fisheries. Spatio-temporal variability in ontogenetic habitat use by fish among these tropical coastal ecosystems has rarely been investigated, yet there are sufficient reasons to believe that this plays an important role. In the present study, we test the spatio-temporal variability in patterns of ontogenetic habitat use by some mangrove/seagrass-associated coral reef fishes ( Lethrinus harak , Lethrinus lentjan , Lutjanus fulviflamma and Siganus sutor ). Abundances of these four species were investigated during two years in Tanzanian coastal waters, using underwater visual census in mangrove, seagrass, shallow and deep mudflat, and shallow and deep coral reef habitats. The study covered four distinct seasons of the year and was done at two spatially separated (>40 km) locations. Averaged across locations, seasons and years, juveniles (≤10 cm length) of the four study species had significantly higher relative densities in shallow-water (mangroves and seagrass beds) than in deep-water habitats (deep mudflats or coral reefs), whereas the opposite pattern was found for the adults (>15 cm). These findings suggest a strong and general pattern of ontogenetic habitat shifts from shallow- to deep-water habitats. However, specific habitat-use patterns of juveniles as well as adults differed significantly in time and space. Various species showed subtle to considerable flexibility in juvenile as well as adult habitat use across seasons, years, or at different locations. Furthermore, for some species the data suggest presence of ontogenetic habitat shifts at one location but lack thereof at the other location. In summary, ontogenetic habitat use needs to be considered at various spatial and temporal scales for the interpretation of habitat utilization by fish during different life stages. This is important for conservation and management of these habitats, as essential habitats or seasons may be ignored or over-emphasized with respect to their importance for fish during different parts of their life cycle.

Spatial and seasonal variations of fish assemblage composition were studied in three non-estuarine mangrove creeks of Zanzibar (Tanzania). Fish were collected monthly for one year at three sites (l ...

Spatial and seasonal variations in density of the striped mullet Mugil cephalus were investigated in four mangrove creeks in Zanzibar (Tanzania) during a one-year cycle. Fish were collected monthly ...

The effect of different sewage concentrations (0, 20, 60 and 100%), vegetation (Bare, Avicennia marina or Rhizophora mucronata) and immersion periods (immersion/emersion period of 12/12 h or 3/3 days just for 100%) conditions were studied for 6 months on survival and growth rates of Terebralia palustris (Linnaeus, 1767). Gastropods' activity and ecosystem engineering preformed at bare and A. marina planted cells and 3 sewage conditions (0, 20 and 60%) were determined. Survival rates were higher than 70% in all treatments. Growth rate decreased significantly with increasing sewage concentrations (mainly at unplanted conditions) and longer immersion periods. A complete shift (from immersion to emersion periods) and a significant decrease in mobility and consequently its engineer potential, due to sewage contamination, lead to a 3-4 fold decrease in the amount of sediment disturbed. Sewage contamination, primary producers' abundance and environmental conditions may have influenced the gastropods survival, growth and its ecosystem engineering potential.

Fish assemblages in Tanzanian mangrove creek systems influenced by solar salt farm constructions

The pelagic fishery of Lake Tanganyika provides employment to about 1 million consumers and protein to many more people living around the lake. It is mainly based on three commercially important fish species namely two clupeids Stolothrissa tanganicae and Limnothrissa miodon commonly known as “dagaa” and a perch Lates stappersii. A declining trend of the perch both in its composition and abundance in the pelagic fish landings is partly tied to local over-fishing and climate change. There are three important periods in the exploitation process identified as: (1) a traditional fishery period, the pre-1975 period marked by low catches of Lates spp. and a dominance of clupeids; (2) an industrial fishery period (1975–1978) marked by high catches of Lates stappersii and high total landings; and (3) an artisanal fishery period (post 1984) with relatively low catches and high dominance of clupeids especially Stolothrissa tanganicae. Population growth and refugee influx from the politically volatile Burundi and Democratic Republic of Congo both caused high fish protein demand, particularly for dried clupeids. Also changes in the rural economy caused by drought in the area are resulting into high exploitation pressure on the pelagic resources. Concerted efforts to prevent/reduce exploitation pressure on the pelagic fish resources should take into action a lake wide management strategy where by management issues in all the riparian countries should be harmonized. More effort should be geared towards preventing the use of beach seines and small meshed nets subsequently ensuring a sustainable utilization of the pelagic fish resources.

This study was conducted to assess the reproductive biology and early breeding behaviour of female Oreochromis niloticus reared in monoculture and polyculture with Clarias gariepinus in earthen ponds for 8 months. Results revealed no significant difference in length at first maturity (L50) between females reared in monoculture and polyculture systems. Similarly, no significant differences were detected in absolute fecundity, relative fecundity, gonado-somatic index and condition factor between the two culture systems. The absolute fecundity was more strongly correlated with total length and body weight than with ovary weight. The study concluded that early breeding of O. niloticus in captivity is not affected by the culture systems used. Therefore, O. niloticus production in either system can be improved only through proper pond management techniques.

Limnological studies were conducted in three alkaline lakes (Lake Big Momela, Manyara and Embagai) with the aim of investigating the cause of mass mortality of the Lesser Flamingos in Lake Manyara and Lake Big Momela during July–August 2004. High concentrations, up to 150 million filaments per liter of the potentially toxic planktonic cyanobacterium Arthrospira fusiformis were found in surface scum of Lake Big Momela where Lesser Flamingos were dying at a rate of between 15 and 50 individuals per day during the study period. Gut content analyses indicated that A. fusiformis was the main food item in moribund flamingos. Mouse bioassay suggested that the crude microalgal extract dominated by A. fusiformis was toxic with all mice close to death becoming lethargic, with loss of balance, uncoordinated movements, intermittent tremors, dyspnoea with gasping followed by respiratory arrest. This observation gives circumstantial evidence that A. fusiformis at such high concentrations was toxic to the Lesser Flamingo in Lake Big Momela.

Contains fulltext : 35162.pdf (Publisher’s version ) (Closed access) The relative importance of bay habitats, consisting of mangrove creeks and channel, seagrass beds, and mud and sand flats, as feeding grounds for a number of fish species was studied in Chwaka Bay, Zanzibar, Tanzania, using gut content analysis and stable isotope analysis of carbon and nitrogen. Gut content analysis revealed that within fish species almost the same food items were consumed regardless of the different habitats in which they were caught. Crustaceans (mainly copepods, crabs and shrimps) were the preferred food for most zoobenthivores and omnivores, while fishes and algae were the preferred food for piscivores and herbivores, respectively. The mean d13C values of fishes and food items from the mangrove habitats were significantly depleted to those from the seagrass habitats by 6_9 and 9_7% for fishes and food items, respectively, and to those from the mud and sand flats by 3_5 and 5_8%, respectively. Fishes and food items from the mud and sand flats were significantly depleted as compared to those of the seagrass habitats by 3_4 and 3_9%, for fishes and food, respectively. Similar to other studies done in different geographical locations, the importance of mangrove and seagrass themselves as a primary source of carbon to higher trophic levels is limited. The different bay habitats were all used as feeding grounds by different fish species. Individuals of the species Gerres filamentosus, Gerres oyena, Lethrinus lentjan, Lutjanus fulviflamma, Pelates quadrilineatus and Siganus sutor appeared to show a connectivity with respect to feeding between different habitats by having d13C values which were in-between those of food items from two neighbouring habitats. This connectivity could be a result of either daily tidal migrations or recent ontogenetic migration.

There is paucity of information on the effects of exploitation on reproductive characteristics of blackspot snapper, Lutjanus fulviflamma (Forsskal 1775) in Tanzanian coastal waters. We compared size at first sexual maturity (LM50), sex ratio, fecundity, and breeding season of L. fulviflamma in least fished Mafia Island Marine Park (MIMP) and intensively fished areas (IFA) between May 1999 and April 2001. Fish in MIMP matured at significantly smaller size (female: LM50 = 206.3 mm; male: LM50 = 195.5 mm) than in IFA (female: LM50 = 216.7 mm; male: LM50 =212.1 mm) total body length. Sex ratio was balanced at 1.03 : 1 (female : male) in MIMP, but it was skewed 0.9 : 1 (female : male) in IFA. Size-related differences in sex ratio were observed with males predominating in the smaller sizes and females in the larger sizes. Total fecundity of fish in MIMP was determined at 45,200–430,200 oocytes in females of between 207 and 293 mm total length. Lutjanus fulviflamma in MIMP has a prolonged spawning season lasting from September to March peaking in December. None of the fish from IFA were in breeding state, suggesting recruitment overfishing is an added matter of concern for the long-term sustainability of the fishery at the current exploitation level. Resume Il existe tres peu d'informations sur les effets de l'exploitation sur les caracteristiques de la reproduction de Lutjanus fulviflamma (Forsskal 1775) dans les eaux cotieres de Tanzanie. Nous avons compare la taille au debut de la maturite sexuelle (LM50), le sex-ratio, la fecondite et la saison de reproduction de L. fulviflamma dans le Parc Marin de l'Ile de Mafia (MIMP) ou la peche est moins intense et dans des eaux intensement exploitees (IFA) entre mai 1999 et avril 2001. Les poissons du MIMP deviennent mâtures tout en ayant une longueur totale significativement plus petite (femelles: LM50 = 206,3 mm; mâles: LM50 = 195,5 mm) que dans les IFA (femelles: LM50 = 216,7 mm; mâles: LM50 = 212,1 mm). Le sex-ratio est equilibrea 1,03/1 (femelles/mâles) dans le MIMP, mais il est de 0,9/1 (femelles/mâles) dans les IFA. On a observe des differences du sex-ratio liees a la taille, avec les mâles qui predominent dans les plus petites tailles et les femelles dans les plus grandes. On a determine la fecondite totale dans le MIMP, entre 45.200–430.000 ovocytes a l'interieur des femelles comprises entre 207 et 293 mm de longueur totale. Dans le MIMP, Lutjanus fulviflamma a une saison de frai prolongee, allant de septembre a mars avec un pic en decembre. Aucun des poissons des IFA n’etait en periode de reproduction, ce qui signifie une sur-peche du potentiel reproducteur, ce qui est un motif d'inquietude pour la durabilitea long terme de la peche a son niveau actuel.

Competitive success within coral reef communities is controlled by various factors. In addition to competitive abilities in direct interactions with a contestant, external influences such as disturbance caused by nutrient input may determine the outcome of antagonistic interactions. We examined the competitive success of corallimorpharians on coral reefs by investigating their distribution patterns within reefs and how well they perform in interference competition with staghorn corals in different environments. Substrate composition and corallimorpharian growth were examined on three reefs in Tanzania under different disturbance regimes using the line-intercept transect and point techniques. A transplant experiment was conducted in which staghorn corals (Acropora formosa) were exposed to the polyps of Rhodactis rhodostoma to establish how competition between corals and corallimorpharians affects their respective distributions. Within reefs corallimorpharians seemed to be more competitive in shallow waters. This could be due to both environmental factors as well as varied competitive abilities depending on surrounding benthos that changed with depth. Reef environment also seemed to influence corallimorpharian growth among reefs as they had the highest densities in the areas with the highest nutrient loads. The transplant experiment revealed that the corallimorpharians had a competitive advantage over the corals, and in comparisons of reefs influenced by different degrees of disturbance, corallimorpharians were most competitive in the area with the highest nutrient content. Hence, stress on coral reefs in the form of raised nutrient loads may favour the competitive success of corallimorpharians.

Natural diet and feeding habits of blackspot snapper, Lutjanus fulviflamma (Forsskal 1775) were investigated in Mafia Island Marine Park (MIMP) and intensively fished areas (IFA) between May 1999 and April 2001. An index of relative importance (IRI) was used to assess the food preference for L. fulviflamma. Feeding habits were studied with respect to sex and size of the predator, seasons and feeding periodicity. Of 4642 L. fulviflamma specimens sampled, 46% had empty stomachs. Brachyurans were the main prey of L. fulviflamma accounting for 48% IRI. Benthic invertebrates dominated by other crustaceans, gastropods, bivalves, cephalopods and polychaetes and demersal teleosts made up the remainder of the diet. Female and male L. fulviflamma were not effectively segregated by trophic dimension in the study areas. Specimens in the 90–120 mm total length (TL) fed exclusively on crustaceans, with shrimps accounting for 40% IRI. Lutjanus fulviflamma in the 270–300 mm TL preferred fish prey accounting for 50% IRI. The diet of fish species showed clear spatial differences, which were dependent on size distributions. Lutjanus fulviflamma fed mostly but not exclusively at night peaking at dusk and dawn. The results clearly demonstrate that L. fulviflamma is an opportunistic forager, which exhibits both diel and ontogenetic feeding habits. Resume On a etudie, entre mai 1999 et avril 2001, les habitudes alimentaires de la daurade a taches noires, Lutjanus fulviflamma (Forsskal 1775) dans le Parc Marin de l'Ile de Mafia (MIMP) et dans des zones intensement pechees (IFA). On a utilise un index d'importance relative (IRI) pour evaluer les preferences alimentaires du poisson. On a etudie ses habitudes alimentaires en tenant compte du sexe et de la taille du predateur, des saisons, et de la periodicite de la prise d'aliments. Sur les 4642 specimens de L. fulviflamma recueillis, 46% avaient l'estomac vide. Les Brachyures etaient leurs proies principales, avec un IRI de 48%. Les invertebres benthiques domines par d'autres crustaces, des gasteropodes, des bivalves, des cephalopodes et des polychetes ainsi que les poissons de fond composent le reste du regime. Le mâle et la femelle de L. fulviflamma ne se distinguaient pas nettement au point de vue trophique dans les zones etudiees. Les specimens compris entre 90 et 120 mm de longueur totale (TL) se nourrissaient exclusivement de crustaces, ou les crevettes comptaient pour un IRI de 40%. Les L. fulviflamma de 270 a 300 mm de TL preferaient les proies poissons, comptant pour un IRI de 50%. Le regime compose de poissons montrait des differences spatiales nettes, qui dependaient de la distribution par taille. Lutjanus fulviflamma se nourrissait principalement mais pas exclusivement pendant la nuit, avec des pics au crepuscule et a l'aube. Les resultats montrent clairement que L. fulviflamma est un mangeur opportuniste, qui affiche des habitudes alimentaires nycthemerales et ontogenetiques.

The benefits of marine protected areas (MPAs) to fish productivity remain debated, and comprehensive research projects have been suggested to assess MPA function. This study evaluated MPA performance in a developing country in the context of local needs. We compared density and size of the blackspot snapper, Lutjanus fulviflamma (Forsskal 1775), in Mafia Island Marine Park (MIMP), Tanzania, with adjacent intensively fished areas (IFA) using underwater visual censuses (a total of 105, 50-m transects) as well as investigating the catches in the local fishery. The target species was over four times more numerous, its biomass six to ten times higher and individual sizes on an average 37% larger on reefs in MIMP compared to the IFA. Fish numbers and biomass were negatively correlated with fishing intensity and positively correlated with hard coral cover and structural complexity. This study supports predictions that MPAs can play a key role in the conservation of habitats and management of a fishery. It is suggested that for the purpose of management, it is possible to evaluate MPA performance with limited resources by focusing on key information.

The aim of this work was to determine the abundance of crabs inmangrove communities along a latitudinal gradient along the eastern coastof Africa from 4°S to 32°S. Surveys were made atMombasa (Kenya), Zanzibar (Tanzania), Maputo (Mozambique) and in theTranskei (South Africa). Crabs were estimated at three designated levelsin the mangroves by visual census using a common protocol, and numberswere converted to biomass.Even after standardising the selection of sites and methods of censusthere was still extensive variability in the data, emphasising the complexheterogeneity of mangrove ecosystems. Lunar phase (full versus new moonsprings) did not have a consistent effect on results, but shore height hadseveral effects. Total crab biomass was similar in the two lower shore strataexamined, but about twice as high at the top-Avicennia level. Theratio of grapsid biomass:ocypodid biomass also changed with height: fromnear unity in the lower mangrove, to 0.14 in the middle strata, but to 15at the top.There was no consistent latitudinal trend in total crab numbers, but totalcrab biomass increased from north to south. In addition there was aconsistent and marked change in the grapsid biomass:ocypodid biomassratio: this swung from 0.65 at Mombasa to 6.8 in the Transkei. This hasimplications for the transfer of primary production through the food chain. Grapsids are important macrophagous feeders on the leaves and other partsof mangroves, whereas ocypodids are microphagous deposit feeders.

The overall performance of an aquaculture system is partly determined by its water quality parameters. Poor water quality stresses and adversely affects fish growth causing low production, profit and product quality. Diurnal dynamics of water quality parameters were investigated in Nile tilapia (Oreochromis niloticus) monoculture and polyculture with Clarias gariepinus in earthen ponds. Dissolved oxygen, temperature and pH were measured and monitored for 24 h. Water samples for nutrient analysis were collected from the middle of ponds in triplicate at about 30–35 cm below the water surface using a plastic bottle. Nitrite–nitrogen (NO2–N), nitrate–nitrogen (NO3–N), unionised ammonia (NH3–N), soluble reactive phosphorus and free carbon dioxide were analysed following standard methods and procedures. The results show that dissolved oxygen concentrations during the past midnight and pre-dawn hours were significantly lower than the levels in the morning and afternoon hours (ANOVA, F = 45.709, P 0.05). Fish yield was relatively higher in polyculture (45.74 ± 0.44 tons/ha) than monoculture (30.77 ± 0.54 tons/ha). During fish farming, optimum fish growth and hence economic benefits can be accrued by devoting some efforts on monitoring the fish pond water at regular intervals. This quality assurance process will ensure that fish farmers produce fish with maximum growth and yield without polluting pond water and the surrounding environment.