Sierra Leone River Research Articles

Butterfly Assemblages of Two Wetlands: Response of Biodiversity to Different Environmental Stressors in Sierra Leone

In a bid to enhance the integrity and health of selected network of ecosystems and effectively manage them in Sierra Leone, a baseline assessment of butterfly diversity of two wetland ecosystems Mamunta Mayosso Wildlife Santuary (MMWS) and Sierra Leone River Estuary (SLRE) affected by different environmental stressors was undertaken as part of the Sierra Leone Wetland Conservation Project (SLWCP). We hypothesised that different environmental stressors affect butterfly communities in wetlands in Sierra Leone and the higher the stress the lower the butterfly diversity in an area. Sampling was conducted via field identification by wing patterns, flight mode, direct counts along transects and charaxes trapping. A total of 2300 individuals representing 95 species of butterflies were recorded. Though butterflies were evenly distributed at both sites, MMWS recorded the highest richness and abundance of butterflies during both seasons. This observation is reported to be because of high environmental stressors such as mining, agriculture and pollution from factories in the SLRE. The results further show that MMWS is made up of a mosaic of different vegetation patches that support higher diversity of butterfly species. This study also reveals that anthropogenic activities have a negative impact on butterfly diversity.

Landsat-Derived Estimates of Mangrove Extents in the Sierra Leone Coastal Landscape Complex during 1990-2016.

This study provides the first assessment of decadal changes in mangrove extents in Sierra Leone. While significant advances have been made in mangrove mapping using remote sensing, no study has documented long-term changes in mangrove extents in Sierra Leone—one of the most vulnerable countries in West Africa. Such understanding is critical for devising regional management strategies that can support local livelihoods. We utilize multi-date Landsat data and cloud computational techniques to quantify spatiotemporal changes in land cover, with focus on mangrove ecosystems, for 1990–2016 along the coast of Sierra Leone. We specifically focus on four estuaries—Scarcies, Sierra Leone, Yawri Bay, and Sherbro. We relied on the k-means approach for an unsupervised classification, and validated the classified map from 2016 using ground truth data collected from Sentinel-2 and high-resolution images and during field research (accuracy: 95%). Our findings indicate that the Scarcies river estuary witnessed the greatest mangrove loss since 1990 (45%), while the Sierra Leone river estuary experienced mangrove gain over the last 26 years (22%). Overall, the Sierra Leone coast lost 25% of its mangroves between 1990 and 2016, with the lowest coverage in 2000, during the period of civil war (1991–2002). However, natural mangrove dynamics, as supported by field observations, indicate the potential for regeneration and sustainability under carefully constructed management strategies.

Satellite Remote Sensing of Archaeological Vegetation Signatures in Coastal West Africa

This article discusses how archaeological sites in Sierra Leone, and by extension much of West Africa, can be identified through vegetation patterns (vegetation signatures) detectable in very high-resolution (VHR) multispectral satellite imagery. Settlement sites typically have a differing pattern of vegetation from the surrounding landscape, including concentrations of very large trees with sociocultural and historical significance: cotton (Ceiba pentandra) and baobab (Adansonia digitata). These features are conspicuous elements of the landscape both from the ground and in aerial imagery. Two complementary methods of using VHR multispectral satellite imagery are discussed in this paper: visual interpretation and semi-automated subpixel classification. These techniques are aiding ongoing archaeological survey of the Sierra Leone River Estuary. The impact of recently renewed industrial activity at a site of probable archaeological significance is also assessed through visually interpreted VHR satellite imagery.

'A Less Favourable Specimen': The Abolitionist Response to Self-Emancipated Slaves in Sierra Leone, 1793–1808

'A Less Favourable Specimen':The Abolitionist Response to Self-Emancipated Slaves in Sierra Leone, 1793-1808 Cassandra Pybus (bio) When on 23 February 1807 the bill to abolish the slave trade passed the house of commons, William Wilberforce was exultant. 'Well, Henry', he playfully demanded of his cousin and close colleague Henry Thornton, 'what shall we abolish next?' To which Thornton replied, 'The Lottery, I think.'1 This scene of pious self-congratulation has been replayed over and over in the literature on abolition, yet rarely has it been questioned for what it reveals of the moral ambivalence of these two evangelical heavyweights. This exchange was not simply a rare moment of jocularity; the lottery was the institution most likely to galvanize the abolitionist zeal of the Clapham Sect, whereas the terrible institution of slavery was simply not on their agenda.2 The very next day Wilberforce spoke forcefully against a bill for the gradual abolition of slavery, arguing that slaves must first be trained for freedom. He reiterated the view that he had articulated in the Commons in 1804 that enslaved Africans were not 'fit to receive freedom', and so it would be 'madness to attempt to give it to them'.3 Wilberforce spoke with conviction as a result of his experience as a director of the Sierra Leone Company, which had established a settlement for freed slaves on the west coast of Africa. Henry Thornton was the company chairman and several fellow evangelical abolitionists also served as directors. It is in their response to the emancipated slaves of Sierra Leone that their ambivalence toward enslaved Africans can most clearly be seen.4 A settlement for runaway slaves had been the brainchild of Granville Sharp, champion of James Somerset and the Zong case.5 A passionate anti-slavery advocate, [End Page 97] Sharp was one of the founders of the anti-slavery committee in 1787, which became, rather to his dismay, the Society for Effecting the Abolition of the Slave Trade (or London Committee).6 Into the creation of a 'Province of Freedom' he poured all his deepest convictions about humanity and justice among people of all races. Even though the people to be settled there were mostly illiterate and had suffered the demoralizing experience of slavery, Sharp believe they would be as capable of self-government as any. His plan for governance allowed all males over 16 a vote in the common council where power would reside. Households were divided into tens, called tithings, each of which would elect a tithingman, while every 100 households would choose a hundredor. Each person over 16, regardless of sex, was entitled to a one-acre town lot and a small farm, but overall the land was the responsibility of the community as a whole, with a majority vote to dispose of it. As he conceived it, the 'Province of Freedom' should be quite independent, where the settlers could make any laws not inconsistent with Britain's, hold their own courts and elect their own leaders.7 It was the Committee for the Relief of the Black Poor, under the chairmanship of Henry Thornton, which put Sharp's plan into action. In May 1787 it hastily settled some 340 black refugees from North America on land at the mouth of the Sierra Leone River, which had been 'purchased' from a local chief of the Koya Temne.8 However this settlement did not turn out as Sharp had envisaged. It was an unmitigated disaster.9 When early in 1791 a rescue mission arrived in Sierra Leone, it found only 46 survivors who had been driven out of the settlement by the local chief and were clinging to life on a swampy island in the river mouth. Sharp's anguished appeals for government assistance fell on deaf ears, so he then turned to his abolitionist friends to provide a stable economic base for his 'poor little ill-thriven swarthy daughter, the unfortunate colony of Sierra Leone'. The new plan was to establish a trading enterprise in Sierra Leone that would be an alternative to the abhorrent slave trade, as well as a base for spreading christianity throughout the heathen continent. He recruited Thornton, together...

What Merchants Did: London Traders in the British Atlantic

London-the political, financial, and commercial heart of the British empirehas suffered an odd fate in the historiography of the eighteenth-century Atlantic. More colonial trade circulated through London than all other English ports combined during the first three quarters of the century. Yet despite its precedence in the imperial economy, the breadth and complexity of London's Atlantic commerce has failed to receive extended examination. Surveys concerned with British overseas trade accord prominence to the metropolis, and fine studies exist of individual merchants and particular branches of commerce. No published work on Georgian London, however, equals the scholarship on trade through Glasgow or Bristol, cities for which port books and firm records survive in greater quantity.1 For historians of early America, the deficiency is serious. In the absence of a view from London, those seeking a broad perspective on the operation of Britain's commercial empire find themselves with peripheries and no core. David Hancock helps fill the void with an intensive inquiry into the work of twenty-three loosely affiliated merchants active in the five decades before the close of the American Revolution. Six owned and operated a slaving fort on Bance Island in the Sierra Leone river from 1748 to 1784; the remaining seventeen represent all known partners in the other ventures conducted by the six principals-Augustus Boyd, John Boyd, Alexander Grant, John Mill, Richard Oswald, and John Sargent. The associates, as Hancock terms this group, represent the increasingly diverse origins of the London mercantile community. They hailed from the provinces, a majority from Scotland and Ireland, and labored, at first, outside the chartered companies and at the perimeter of established trading networks. In Hancock's words, they were marginal men, opportunistic in seizing new prospects for profit, prepared to direct multiple enterprises on a global scale in ways that integrated

Benthic-pelagic coupling and export of organic carbon from a tropical Atlantic continental shelf—Sierra Leone

An approximate carbon budget for the Sierra Leone River Estuary and adjacent inner continental shelf indicates that phytoplankton production is balanced by grazers only in the wet season estuary; on the continental shelf, and in the dry season estuary, phytoplankton production exceeds demand of consumer populations by 70–90%. Regional production is dominated by the dry season estuary where diatom blooms support large population of the phytophagous clupeid fish Ethmalosa fimbriata. It is suggested that as well as what is used in bacterial respiration, not quantified in the study, important amounts of inshore organic carbon production are available for export, or burial, or both, either in inshore mudbanks or at the shelf edge by slumping. This carbon budget for a tropical continental shelf having neither coral-reefs nor coastal upwelling appears to correspond with what is emerging as a generic distinction between shelves and open ocean ecosystems: surplus production on shelves, balance between producers and consumers in the open ocean.

Observations on some population parameters of exploited stocks of Senilia senilis (=Arca senilis) in Sierra Leone

The West African cockle Senilia senilis (L.) (=Arca senilis L., 1758) from some estuaries and muddy shores of Sierra Leone was studied from September, 1973 to February, 1975. Quantitative samples were obtained along transects using quadrats and sieves; some random hand-picked collections were also made. The length, number of rings and the maximum width of the inter-ring bands along the outer convex surface of the right valve were recorded from samples of ≥25 specimens. All the cockle beds examined were exploited and had stocks with a mean density of ≤9 large (>10 mm) cockles/m2, and at River No. 2 estuary at peak spatfall, of 130 seed cockles/m2. Spat settlement began in November-December after the rainy season, reached a peak in January-February and continued to the early part of the following rainy season (May-June). Seed cockles were absent from August to October. In the length-frequency distributions, modes were clear and associated with certain shell-ring numbers. Rings on shells were formed once a year, during July to September, the period of maximum rainfall, and they were successfully used in ageing the cockles. The first ring was formed at a mean age of 7 months and the subsequent ones annually. The growth period of the inter-ring bands, considered to extend from August to the following July (s. senilis growth year), may actually be of only 10 months duration. Sublittoral cockles from No. 2 estuary showed a higher growth rate than those from the levels exposed at low tide and subjected to greater exploitation. Cockles from the Sierra Leone River Estuary showed even greater growth. s. senilis grows slowly and lives long (up to 8 to 9 years), and its von Bertalanffy parameters are: River No. 2 estuary cockles →k=0.27 to 0.31 and L ∞=99 mm; Sierra Leone River Estuary cockles →k=0.22 and L ∞=145 mm. At No. 2 estuary, cockles enter the fishery at 22 to 25 mm (14 to 15 months old) and exploitation is heavy, resulting in the stocks being dominated by a few young year-classes.

Seasonal Fluctuations and Distribution of Nitrite in a Tropical West African Estuary

VERY little is known about the distribution and seasonal fluctuations of inorganic nitrogen in West African estuaries. I have given1 some preliminary figures based on a series of spot analyses and found that in the Sierra Leone River estuary there are both horizontal and vertical gradients in the concentrations of nitrite, nitrate and ammonia, with the higher values in the upstream direction and with increasing depth. The concentration of nitrite was found to vary from 8 to 4 mgm. nitrogen/m.3, nitrate from 141 to 74 mgm. nitrogen/m.3 and ammonia from 22 to 10 mgm. nitrogen/m.3—samples taken over a period of only 3 months were, however, examined.

Sea-Water as the Primary Source of Sulphate in Tidal Swamp Soils from Sierra Leone

ONE of the main features of the chemical composition of the black glutinous muds of relatively high organic content in the Sierra Leone River Estuary is their high content of sulphide. Work carried out by the Rice Research Station at Rokupr on the Scarcies River, some 30 miles north of the Sierra Leone River estuary, suggests that the principal source of oxidizable sulphur in these estuarine soils is iron disulphide, or possibly some other polysulphide1. The presence of sulphide in marine muds has been ascribed by various authors to a number of causes. It may be produced by the way of bacterial decomposition of organic matter containing sulphur. On the other hand, it is known that certain bacteria in the presence of organic material can reduce sulphates to sulphides; this reaction probably accounts for the presence of ferrous sulphide in marine muds in many parts of the world.

Seasonal and Tidal Fluctuations in the Trawl Catches from the Sierra Leone River Estuary

IN March 1958, a series of fish-marking experiments was initiated for the first time in Sierra Leone territorial waters. Only the demersal species of commercial importance were marked, and the area chosen for the first year's liberations was the trawling ground off Robene Point, some 13 miles from the mouth of the Sierra Leone River estuary. The fish for marking were caught with a 28 ft. or 42 ft. otter trawl towed by a 28 ft. diesel-powered launch. A total of 439 hauls, each of 39 min. duration, was made during the course of the marking experiments.

The Food of the Demersal Fish of a West African Estuary

As part of a project to investigate the relationship between the West African demersal fish and the marine benthic communities, an analysis of the food and feeding intensity of the fish commonly taken in otter-trawls in the Sierra Leone River was undertaken by this Institute in 1952. A quantitative survey of the benthos, and a study of its community structure, is now nearing completion in the same area. The study of the food of demersal fish was confined by practical considerations to the Sierra Leone River, which is convenient to these laboratories and calm enough to be worked at all seasons by the open launches used in the period 1952-55. The term 'Sierra Leone River' is applied to the large and open estuary of the Rokel River; at the mouth, between Cape Sierra Leone and the Bullom Shore, it is almost ten miles wide. Into this estuary flow the effluents of the Rokel River, of several smaller rivers, and of innumerable serpentine creeks draining mangrove flats. There is no bar across the mouth, and the main channel is 10-12 fm deep, so that there is free influx of marine organisms. From May to October, during the rainy season, conditions of lowered salinity extend right to the mouth, while during the dry season there is a considerable inflowing of sea water. The tidal streams are strong, reaching 5 kn on the ebb of springs, and much transport of deposits occurs, so that the nature of the bottom at any one place may change radically over a period of only a few months. Demersal fish, of which the majority are euryhaline, are present in the estuary throughout the year and are much fished from canoes with hand and long-lines.

XXII. Observations on the Griggirrys of the Mandingos. In a Letter from Elliott Arthy, Esq. to William Blizard, Esq. F.R.S, and F.A.S.

I send you inclosed a small specimen of African manuscripst, which I obtained from one of the natives of that quarter of the globe, on a voyage into Sierra Leone River, in the year 1795. Pieces of manuscript of a similar kind are in general use among a tribe of Africans, called Mandingos, who inhabit a part of Africa, situated about one hundred miles to the northward of the British colony at Sierra Leone. They are commonly folded into a smali compass, and inclosed in little leathern cases, to which are fixed leathern thongs, by means of which they are hung, and constantly worn, round either the necks or waists of the Mandingos.