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Identification of critical life-stage habitats is key to successful conservation efforts. Juveniles of some species show great flexibility in habitat use while other species rely heavily on a restricted number of juvenile habitats for protection and food. Considering the rapid degradation of coastal marine habitats worldwide, it is important to evaluate which species are more susceptible to loss of juvenile nursery habitats and how this differs across large biogeographic regions. Here we used a meta-analysis approach to investigate habitat use by juvenile reef fish species in tropical coastal ecosystems across the globe. Densities of juvenile fish species were compared among mangrove, seagrass and coral reef habitats. In the Caribbean, the majority of species showed significantly higher juvenile densities in mangroves as compared to seagrass beds and coral reefs, while for the Indo-Pacific region seagrass beds harbored the highest overall densities. Further analysis indicated that differences in tidal amplitude, irrespective of biogeographic region, appeared to be the major driver for this phenomenon. In addition, juvenile reef fish use of mangroves increased with increasing water salinity. In the Caribbean, species of specific families (e.g. Lutjanidae, Haemulidae) showed a higher reliance on mangroves or seagrass beds as juvenile habitats than other species, whereas in the Indo-Pacific family-specific trends of juvenile habitat utilization were less apparent. The findings of this study highlight the importance of incorporating region-specific tidal inundation regimes into marine spatial conservation planning and ecosystem based management. Furthermore, the significant role of water salinity and tidal access as drivers of mangrove fish habitat use implies that changes in seawater level and rainfall due to climate change may have important effects on how juvenile reef fish use nearshore seascapes in the future.

Astudy was conducted to determine fish yields from flood depended ponds in Rufiji floodplain, Tanzania. Eight ponds were constructed during dry season in two sites besides two floodplain lakes, Ruwe and Uba. These ponds were self-stocked with different fish species from the lakes. More than eight species were trapped andOreochromis urolepis, Labeo congoro and Clariasspecies were considered as good candidates for aquaculture. Other small fish species were harvested immediately after flood recession and the three key species were cultured for the maximum of seven months. However, other species in small quantities were remained in the ponds for the whole period of experiment. Water quality parameters were monitored throughout the study period. The relationships between water quality variables and flooding events were determined using canonical correspondence analysis (CCA). Other parameters included in the relationships were fish density, manure and number of species trapped and cultured. Dissolved oxygen and pH decreased with time in both sites. Fish yields were influenced by some water quality, flooding episode and other management variables. Chlorophyll-awas the only environmental variable that showed a significant correlation with fish yield (P< 0.01). Fish density and number of species trapped showed a significant effect on the fish yield (P

Coastal ecosystems are energetically connected through passive transport of nutrients but also by migrations of motile organisms. Mangroves are highly productive tropical ecosystems that replenish offshore populations of many species, but we know little about the degree to which this production is fuelled by prey from mangroves, especially in the cases in which mangroves are only accessible at high tide. Different results have been obtained on the importance of mangroves as feeding habitats, confounded by differences in species composition, seascape configuration, and methodology. In the present study, we took a more holistic approach by exploring reliance by fishes on mangroves as a feeding habitat at multiple ecological levels: from individuals to species to communities in mangrove ecosystems from across the globe, using a stable isotope approach. A two end-member mixing model showed a wide range (12–72%) in degree of reliance on mangrove food sources by fishes from different studies across the globe. However, analyzed at the levels of individual fish and species, reliance was low (for example

The abalone, Haliotis tuberculata, is a gastropod mollusc of commercial importance in Europe with considerable potential for aquaculture. A wild population of H. tuberculata from Guernsey, Channel Islands was compared to two hatchery populations; one an F1 stock produced by a hatchery in Guernsey, the other an F3 stock cultured at the Shellfish Research Laboratory (SRL) at Carna, Ireland. The F1 and SRL stocks were each derived from the Guernsey wild population and reproductively isolated from this population for one and three generations, respectively. The three populations were screened for allozyme variation at three polymorphic loci, Gpi, Pgm and Mdh, using starch-gel electrophoresis. When compared with the wild population, both the F1 and SRL samples were very similar in terms of mean effective number of alleles per locus and levels of heterozygosity. However, the SRL stock did show a reduced number of rare alleles when compared to the F1 and Guernsey samples but without showing any evidence of inbreeding or reduction in levels of heterozygosity. Effective population size was calculated from direct census (Ne) and temporal changes in allelic frequencies ( N k ). Ne was estimated to be 48 and 54.5 for SRL and F1, respectively, whereas calculated N k was 21.4 and 23.9, respectively.

The effects of size grading and stocking density on the growth of juvenile European abalone, Haliotis tuberculata L. (Gastropoda: Haliotidae) were assessed in the hatchery. Animals were held in cages deployed in a flowtray with recirculating seawater maintained at 18 ± 2 °C, and fed ad libitum on the red alga Palmaria palmata (L.) Kuntze. In the grading experiment juvenile abalone were divided into four populations consisting of small (mean ± s.e; initial shell length = 15.3 ± 0.15 mm; n = 35), medium (initial shell length = 19.6 ± 0.16 mm; n = 35), large (initial shell length = 23.8 ± 0.17 mm; n = 35) and an ungraded control group (16.8 ± 0.41 mm; n = 35). Rearing was carried out over a period of 226 days, after which it could be concluded that an advantage in overall growth performance had been gained by grading the animals. There was evidence that growth of small abalone improved in the absence of larger conspecifics. In the stocking density experiment with two size grades and three stocking densities, a decreasing exponential relationship was found between growth (body weight and shell length) and stocking density, with a substantial amount of growth occurring at all densities. Final total biomass for both grades of abalone increased with density. For the smaller grade biomass gain increased as density increased. However, for the larger grade biomass gain declined at higher density. Overall mean survival (± s.e) was 98.3 ± 0.4% and was not influenced by density. It is suggested that the choice of stocking density is essentially a trade-off between maximum growth, optimal biomass gain, and economic considerations which may dictate densities that would result in a net reduction in overall production costs.

The age and growth of the cottid fish Clinocottus globiceps Girard from tidepools at Helby Island, British Columbia, Canada were investigated with the aid of whole saccular otoliths (sagittae); ages were validated by marginal increment analysis. Four hundred and twenty five specimens were examined from 214 females and 211 males. Marginal increment analysis on specimens with one to three opaque zones suggested an annual ring deposition in sagittae during the late autumn and spring months. The C. globiceps population was composed of individuals from less than 1 year to 5 years of age for fish measuring between 5–120 mm standard length. Growth was faster for younger than for older age groups. Lengths-at-age data were fitted to the Gompertz growth model, and estimates of the model parameters L0, G and g were 26.7 mm 1.58 and 0.30 for pooled cohorts, respectively. The highest levels of growth occurred during late spring and early summer, when water temperatures were at maximum and food was most abundant. The lowest levels of growth occurred during the autumn and winter months.

Mangroves function as important shelter and feeding habitats for marine fauna, but the degree to which mangrove-derived carbon contributes to local food webs has long been debated. In this study, stable isotope analysis was used as a technique to elucidate the role of mangrove carbon in the diets of the macroinvertebrate and fish fauna of an intertidal fringing mangrove forest and adjacent intertidal/subtidal mudflats in a macrotidal Tanzanian estuary. The expectation was that sessile species and those with low motility depend to a larger extent on local carbon sources than highly motile species. A clear distinction in δ13C was present between primary producers from mangrove and mudflat habitats. Macroinvertebrates revealed a gradient in their δ13C where Sesarma crabs were the only species that directly utilised mangrove carbon by feeding on mangrove leaves/detritus. Uca crabs and the gastropod Littoraria scabra showed a higher dependence on microphytobenthos from the mangrove substratum. Among the fish fauna, the amphibious mudskipper was the only species to which the mangroves were accessible during low tide. Consequently this was the only fish species for which it was clear that it fed in the mangrove habitat, most commonly on mangrove-associated Uca crabs. All other species of sessile as well as motile macroinvertebrates and fish from the mangrove and mudflat habitat showed a high degree of utilisation of mudflat carbon. Overall, mangrove carbon thus contributed little to the mangrove and mudflat food webs, despite the high tidal amplitude and the resulting potential for exchange of carbon and fauna in the estuary studied here. Utilisation of mangrove carbon appears to depend more on the ecology of the species in consideration (e.g., species-specific use of zones within the mangrove habitat) than on their potential motility or tolerance to exposure during low tide.

The diversity and abundance of seagrass and associated macrofauna were studied in transects with and without seaweed farms at Chwaka Bay and Jambiani, in the East Coast of Zanzibar. Eight seagrass species, namely Cymodocea rotundata, Cymodocea serrulata, Thalassia hemprichii,Thalassodendron ciliatum, Syringodium isoetifolium, Halodule uninervis, Halophila ovalis and Enhalus acoroides were recorded in the transects. The mean total biomass of seagrass at Chwaka Bay ranged from 142.4 ± 70.71 to 1652 ± 772.7 g dw/m2 and 212.9 ± 146.2 to 1829 ± 1692 gdw/m2 in station with and without seaweed farms, respectively. At Jambiani, the mean total biomass ranged from 880.4 ± 336.8 to 3467 ± 549.9 and 203.4 ± 102.4 to 3810 ± 2770 g dw/m2 in station with and without seaweed farms, respectively. The overall total biomass of seagrasswas significantly lower (KW = 108.7, p < 0.0001) in station with seaweed farms than in stations without seaweed farms. A total of 93 macrofauna species representing 60 families were encountered and the mean density ranged from 910 to 6990 individuals/m2 at Chwaka Bay andJambiani in stations with and without seaweed farms respectively. The most common macrofauna species were Codakia punctata, Meropesta nicobarica, Echinometra mathaei, Pinna muricata and Clibanarius emystemus. It was shown that the macrofauna abundance and diversity was higher in stations without seaweed farms than in the stations with seaweed farms, which could be due to activities associated with seaweed farming which contributed to the loss of diversity and biomass of flora and macrofauna of the seagrass meadows.

An assessment of the status of Lates stappersii (Boulenger, 1914) stock in the lift-net fishery in Lake Tanganyika, Kigoma area, was carried out from January to December 2003. Results indicated that breeding is seasonal with peaks in February, July-August and December, and so was catch composition, with peaks in March, May and July–August that followed the abundance of its prey, Stolothrissa tanganicae . Catch per unit effort was similar between wet and dry seasons and peaked synchronously at all study sites probably as an indication of its abundance during those months; but also it could mean that the fishes were caught from the same general area. The unselective nature of the lift-net, a common fishing gear in the lake, could be exerting pressure on the pelagic resource, that leads to local over-fishing if not controlled. There is need to institute minimum fish size and mesh size limits and licensing, on a lake-wide basis, as fisheries management measures to safeguard against overexploitation of this highly variable and mobile yet important pelagic fish resource. Tanzania Journal of Science Vol. 32 (2) 2006: pp. 1-12

Contains fulltext : 36476.pdf (Publisher’s version ) (Closed access) Spatial and temporal variation in the fish community structure were studied in a tropical non-estuarine embayment in Chwaka Bay, Zanzibar (Tanzania). Fish samples were collected bi-monthly (at each spring low tide) for 1 year (November 2001–October 2002) from a range of bay habitats ranging from mangroves deep inside the bay to seagrass beds close to the mouth of the bay. Additionally, environmental variables were examined to determine their relationship with the fish community structure. Being a non-estuarine embayment, the environmental variables as well as the fish community structure in each habitat remained relatively constant for most part of the year; however, a marked decline was observed during the rainy period (April–May). Significant variations in fish community variables (density, biomass and species richness) and in water temperature and salinity were observed during the rainy season in all habitats, with larger changes in the mangrove and mud/sand flats habitats than in the seagrass beds. Seasonal variations in water clarity and dissolved oxygen were not significant, though. Many species disappeared from the mangrove and mud/sand flats habitats during the rainy season and those which persisted showed a remarkable decrease in density. Moreover, the results indicate that mangroves were the preferred settling habitats for Gerres filamentosus, Gerres oyena, Lethrinus lentjan and Monodactylus argenteus, especially during the dry period (December–February) before the rainy season. This observation is contrary to what has been reported from some other tropical regions where greater abundance and species richness was observed during the rainy season. A significant relationship was found between density of fish and temperature, salinity and turbidity. Since salinity was the most conspicuously changing environmental variable with seasons, we propose that salinity, alone or in combination with low visibility and temperature, was probably the most important environmental factor structuring the fish assemblage in the mangrove and mud/sand flats habitats, particularly during the rainy season.

Habitat utilisation by juveniles of 13 commercially important fish species was studied in five habitats located in Chwaka Bay, Zanzibar: mangrove creeks, mangrove channel, sand/mud flats, a seagrass area close to man- groves, and a seagrass area far from mangroves. Fish samples were collected from each habitat using a seine net, and fish abundance and size were measured to determine habitat utilisation. The seagrass beds near to mangroves showed the most diverse fish assemblage of all habitats, possibly because it functions as a corridor between the mangroves and deeper parts of the embayment. Juveniles of Cheilio inermis, Hipposcarus harid, Leptoscarus vaigiensis ,a ndScolopsis ghanam inhabited seagrass beds only. Juveniles of Gerres filamentosus and Monodactylus argenteus were mainly found in the mangrove habitats. Lethrinus variegatus, Pelates quadrilineatus and Siganus sutor were found in more than two habitats, with highest abundances in seagrass beds. Juveniles of Gerres oyena, Lethrinus lentjan, Lutjanus fulviflamma and Sphyraena barracuda were the most generalist species and were found in all studied embayment habitats. Visual census surveys supported the seine net data showing that most fishes in the embayment habitats were juveniles or sub- adults. In terms of habitat utilisation by different size classes, five of the 13 species (Lethrinus lentjan, L. variegatus, P. quadrilineatus, Siganus sutor and Sphyraena barracuda) were found as small-sized individuals in shallow and tur- bid mangrove areas, whereas large-sized individuals were observed in deeper and less turbid seagrass beds. A possible explanation for this pattern could be an ontogenetic shift in habitat utilisation, although this could not be proven. The patterns observed in the present study show a high similarity to those observed in marine embayments in the Caribbean, indicating that similar mechanisms are at work which make these systems attractive juvenile habitats.

Keywords: Portunid crabs, production, species diversity, habitat preference Production, habitat preference and distribution of the blue swimming crab, Portunus pelagicus and the diversity of portunid crabs were studied along the Dar es Salaam coastline, Tanzania. Samples were obtained from beach seine nettings and basket traps. The samples from basket traps were used in habitat preference studies only. The production of Portunus pelagicus was assessed in terms of catch rate and biomass, and the biomass and contribution of recruits to the stock estimated using the Leslie method. Seasonal variations in catch rate were found, with peaks between December and May. The highest catch rate was recorded at Msasani Bay (2.24 kg/haul/100-m net), and the lowest at Mzinga Creek (1.08 kg/haul/100-m net). The harvestable biomass for Dar es Salaam coast on average was 34.5 tonnes/year, while the contribution of recruitment to the biomass was about 20.2 tonnes/year. Portunus pelagicus was the most abundant portunid in all the sites, comprising between 39.1 and 81.5% of the catches at Mzinga Creek and Kunduchi respectively. Charybdis anisodon, Scylla serrata and Portunus sanguinolentus were also found in various proportions at the sites. Generally there was a significant difference in species diversity between sites, with P. pelagicus showing a high preference for the sub-littoral shallow waters. For rational exploitation of this crab, management measures based on the estimated harvestable biomass and the size at first maturity are recommended. Western Indian Ocean Journal of Marine Science Vol.2(1) 2003: 75-84

Preliminary results for the artisanal fisheries of Octopus cyanea Gray (1849) in Tanzania are provided for the period April 2000 until June 2001. A total of 2546 individual catches and 15473 specimens were analyzed from 3 sites located at Tanga, Mafia Island, and Mtwara. Size range, average weight and catch per unit effort (CPUE) were all significantly lower at Tanga and Mtwara compared to Mafia indicating that the former sites may be overfished. Abundance of smaller individuals was higher at Tanga and Mtwara, but overall biomass was lower. Octopi at each site exhibited allometric growth as indicated by analyses of the length-weight relationships. Females become sexually mature at a minimum weight of 600 g while for males the minimum weight was 320 g. Higher numbers of mature individuals were found in June of both years and correlate with peaks in the gonosomatic index. Recruitment peaked a few months after brooding periods. Sex ratios indicate females may be more prone to capture during brooding periods. Reasons for differences between sites are discussed.

Keywords: penaeid prawns, species composition, abundance, reproduction, Tanzania The coastal waters of Bagamoyo in Tanzania, constitute an important penaeid prawn trawling ground. Despite the high economic value attached to this resource, the biological information necessary for its sustainable exploitation is scanty and fragmented. The present study was therefore designed to investigate the species composition, population abundance and reproduction of the penaeid prawns in Bagamoyo coastal and nearshore waters. Samples were obtained monthly for a period of one year from inshore waters adjacent to the Ruvu Estuary while additional samples were bought at the beach from artisanal fishermen. In the laboratory, samples were identified to the species level. Four penaeid species, Fenneropenaeus indicus (formerly known as Penaeus indicus [Farfante and Kensley, 1997]), Penaeus monodon, P. japonicus , and Metapenaeus monoceros were found in the Ruvu Estuary and nearshore waters. Fenneropenaeus indicus was the most abundant, and more so during the rainy season than the dry season. The sex ratio in F. indicus was found to vary significantly from the theoretical 1:1 ratio while that of P. monodon did not vary significantly from 1:1. The average size at first maturity was different within sexes. For F. indicus males and females carapace length was 3.4 and 3.9 cm respectively. For P. monodon it was 3.58 and 4.3 cm for males and females respectively. Fecundity ranged from 40,000 to 222,000 eggs for F. indicus and 72,000 to 314,000 eggs for P. monodon . Fecundity increased with prawn size, suggesting that much of the available energy in larger prawns is devoted to egg production rather than growth. Western Indian Ocean Journal of Marine Sciences Vol.2(2) 2003: 117-126

A one year study was carried out at Kunduchi Creek, Dar es Salaam, to determine spat settlement using the three different substrates (clutches): coconut shells, asbestos and cockle shells, set at three different depths, 0.5 m, 1 m, and 1.5 m. The experiment was set up at three different sites within the creek. There were no significant differences among treatments (sites, depths, clutches). However, spat settlement exhibited seasonal differences, with peak spatfall recorded during the long rains (April to May). There were significant differences in the number of spat between the upper and lower surfaces of the substrates, with more spat preferring the underside. It was concluded that the Kunduchi Creek is a potential site for oyster farming. However, since the area is heavily used by artisanal fisherfolk, any future plans to establish mariculture operations would have to take into consideration potential conflicts with other user groups. Tanzania Journal of Science Volume 27A (Special Issue) 2001, pp. 65-78

Finding effective solutions to manage marine resources is high on political and conservation agendas worldwide. This is made more urgent by the rate of increase in the human population and concomitant resource pressures in coastal areas. This paper links empirical socio-economic data about perceptions of marine resource health to the breaking of marine management rules, using fisheries as a case study. The relationship between perceived rule-breaking (non-compliance with regulations controlling fishing) and perceived health of inshore marine environments was investigated through face-to-face interviews with 299 heads of households in three Tanzanian coastal communities in November and December 2011. Awareness of rules controlling fishing activity was high among all respondents. Fishers were able to describe more specific rules controlling fishing practices than non-fishers (t = 3.5, df = 297, p

Mangroves and seagrass beds have long been perceived as important nurseries for many fish species. While there is growing evidence from the Western Atlantic that mangrove habitats are intricately connected to coral reefs through ontogenetic fish migrations, there is an ongoing debate of the value of these coastal ecosystems in the Indo-Pacific. The present study used natural tags, viz. otolith stable carbon and oxygen isotopes, to investigate for the first time the degree to which multiple tropical juvenile habitats subsidize coral reef fish populations in the Indo Pacific (Tanzania). Otoliths of three reef fish species (Lethrinus harak, L. lentjan and Lutjanus fulviflamma) were collected in mangrove, seagrass and coral reef habitats and analyzed for stable isotope ratios in the juvenile and adult otolith zones. δ(13)C signatures were significantly depleted in the juvenile compared to the adult zones, indicative of different habitat use through ontogeny. Maximum likelihood analysis identified that 82% of adult reef L. harak had resided in either mangrove (29%) or seagrass (53%) or reef (18%) habitats as juveniles. Of adult L. fulviflamma caught from offshore reefs, 99% had passed through mangroves habitats as juveniles. In contrast, L. lentjan adults originated predominantly from coral reefs (65-72%) as opposed to inshore vegetated habitats (28-35%). This study presents conclusive evidence for a nursery role of Indo-Pacific mangrove habitats for reef fish populations. It shows that intertidal habitats that are only temporarily available can form an important juvenile habitat for some species, and that reef fish populations are often replenished by multiple coastal habitats. Maintaining connectivity between inshore vegetated habitats and coral reefs, and conserving habitat mosaics rather than single nursery habitats, is a major priority for the sustainability of various Indo Pacific fish populations.

Prolific breeding and production of high percentage of recruits are main problems in mixed-sex Nile tilapia (Oreochromis niloticus) culture in earthen ponds. The current study assessed the efficiency of different sizes of African sharptooth catfish (Clarias gariepinus) in controlling recruitment in mixed-sex Nile tilapia cultured in tanks and its effect on growth performance, percentage survival and yield. Three treatments consisting of triplicate ponds stocked with mixed-sex Nile tilapia in monoculture and in polyculture with large (62.50 ± 3.26 g) and small (40.00 ± 2.68 g) African sharptooth catfish were fed on a 297.50 g kg−1 crude protein diet for 126 days. Results showed that, the number of recruits was significantly lower in larger African sharptooth catfish predator than smaller ones and monoculture of Nile tilapia. Polyculture with larger African sharptooth catfish resulted in significantly higher growth performance of Nile tilapia. Large African sharptooth catfish in polyculture reduced the amount of small, low-value recruits, while the yield of large and high value Nile tilapia was increased. This study revealed that fish farmers can reduce prolific breeding, obtain higher growth performance and produce larger size of marketable Nile tilapia by predominantly stocking ponds with large African sharptooth catfish predator of at least 60 g.

Unaffordability of commercial feeds to semi-intensive Nile tilapia, Oreochromis niloticus farmers has led to reliance on supplemental feeding and fertilization for nutrition of their fish without a scientific basis. This study compared the growth, survival, condition factor and yield performance of O. niloticus fed on mixed ingredients (MI) and rice bran alone (RB) diets reared in fertilized earthen ponds in small scale farmers’ ponds. The study also determined phytoplankton composition, biomass and abundance in the experimental ponds. Quadruplicate ponds were stocked with O. niloticus and African sharptooth catfish, Clarias gariepinus at a stocking ratio of 1:3. The initial mean weights of O. niloticus and C. gariepinus were 14.62 ± 0.61 and 20.34 ± 1.44 g respectively. The fish were fed on MI and RB diets with protein content of 184.74 and 126.06 g kg−1 respectively for 270 days. The results showed that growth performance, survival rate and condition factor of O. niloticus were not affected by either feeding with MI or RB diet (p > 0.05). Moreover, there were no significant differences obtained in phytoplankton biomass and abundance in O. niloticus ponds fed on the two diets (p > 0.05). Furthermore, feeding O. niloticus either on MI or RB diet did not affect the net and gross fish yields (p > 0.05). The study revealed that the use of either MI or RB diet does not significantly affect the performance of O. niloticus cultured in semi-intensive earthen ponds where natural food organisms are an integral part of the culture system. Rice bran could be used for semi-intensive culture of O. niloticus in fertilized ponds to boost the production based on its availability and low cost.