Small-scale fisheries (SSF) account for much of the global fish catch, but data to assess them often do not exist, impeding assessments of their historical dynamics and status. Here, we propose an approach to assess 'data-less' SSF using local knowledge to produce data, life history theory to describe their historical multispecies dynamics, and length-based reference points to evaluate stock status. We demonstrate use of this approach in three data-less SSFs of the Congo Basin. Fishers' recalls of past fishing events indicated fish catch declined by 65–80% over the last half-century. Declines in and depletion of many historically important species reduced the diversity of exploited species, making the species composition of the catch more homogenous in recent years. Length-at-catch of 11 of the 12 most important species were below their respective lengths-at-maturity and optimal lengths (obtained from Fishbase) in recent years, indicating overfishing. The most overfished species were large-bodied and found in the Congo mainstem. These results show the approach can suitably assess data-less SSF. Fishers' knowledge produced data at a fraction of the cost and effort of collecting fisheries landings data. Historical and current data on fish catch, length-at-catch, and species diversity can inform management and restoration efforts to curb shifting baselines of these fisheries. Classification of stock status allows prioritizing management efforts. The approach is easy to apply and generates intuitive results, having potential to complement the toolkits of researchers and managers working in SSF and engage stakeholders in decision-making processes.
Rapids, falls, and cascades might act as barriers for freshwater species, determining the species community up-and downstream of barriers. However, they affect community composition not only by acting as barriers but also by their influence on environmental gradients. Moreover, the directional dispersal of species along the watercourse might determine community composition. A suitable system to study these differential effects is the Congo River, the world's second largest river by discharge. The small 'Upper Congo Rapids' ecoregion features several rapids known as barrier for fish. The Wagenia Cataract at the town of Kisangani constitutes the strongest drop of the Congo River and several studies have emphasized its role as barrier for fish distribution. Alternative explanations for this pattern, however, are rarely evaluated. Though mollusks represent a vital component of the macrozoobenthos, with distribution patterns and underlying drivers often distinct from that of fishes, virtually no field surveys of the Congo River have been reported for decades. We collected and determined mollusks of 51 stations, recorded environmental conditions, and generated proxies for directional species dispersal and an indirect barrier effect. Those variables were subjected to distance-based redundancy analyses and variation partitioning in order to test whether the mollusk community compositions are better explained by an individual or combined influence of the direct and indirect effect of the cataract barrier, environmental conditions, and downstreamdirected dispersal. Our survey showed an exclusive upstream/downstream distribution for just four out of the 19 species, suggesting a limited barrier effect. We revealed no direct influence of the barrier itself on community composition but of substrate type. However, we found an indirect effect of the barrier through replacing spatially structured communities upstream of the cataract with more uniform ones downstream. Downstream-directed dispersal explained the highest fraction of variation in mollusk communities. Thus, environmental factors, the indirect cataract effect, and downstream-directed spatial proxies model mollusk community composition in concert. These results support previous studies showing a multi-factorial imprint on communities. However, a large fraction of variation community composition remained unexplained, potentially due to flood plain dynamics that (re-)shape mollusk communities constantly and a high temporal turnover, evidenced by the comparison with historical surveys. This is likely caused by the growth of Kisangani and resulting human activities. A monitoring system could allow better assessments of these impacts on communities and the conservation status of endemic species in the Wagenia Cataract.
853175676 REMERCIEMENTSNous pensons au projet REAFOR pour sa subvention, à l'Université de Namur/ Belgique. Mots clés : Habitats, diversité, Mormyridae, distribution spatiale, rivières Yoko et Biaro. BYANIKIRO et al. / Int. J. Biol. Chem. Sci. 11(3): 967-999, 2017 968 Characterization and ecology of stands of Mormyrids in the Reserve of Yoko (Kisangani, DR. Congo) R. M. ABSTRACTStudy on the Mormyridae stands in two forest rivers Yoko and Biaro near Kisangani, aimed at characterizing and studying the ecology of the Mormyridae one family of bio-indicator that can be used in conservation and monitoring. It was conducted from September 2008 to August 2009, using gillnets, longlines and traditional traps for the harvest of fish. The characterization of Habitat was made according to a morphology follow -up from specifying transverse profiles every 50 m for each of the 8 selected stations. 214 specimens of fish belonging to 7 species and 4 genera were harvested. Stomatorhinus corneti species is the most represented with 144 specimens either 67.3%, followed by Petrocephalus microphtalmus with 50 individuals or 23.4%. The highest taxonomicrichness was observed in stations Yoko 4 (6 species) and Biaro 3 (5 species) and high diversity and equitability indices. The AFC show that there are net links between environmental variables: width, depth, dissolved oxygen, current speed of water, vegetation, nature of the substrate (Sandy -clayey, stony, gravelly, etc.) and that S. corneti and P. microphtalamus species are strongly linked to the stations Yoko 2 and 3, Biaro 1, 2 and 4 in positive correlation between these variables and axes I and II. This undoubtedly shows that fish communities are distributed based on a complex set of interrelationships between different abioc and biotic variables that describe the environment among others the substrate (mineral or vegetable), depth, oxygen dissolved, etc.
Cette étude de la biologie d’un Mormyridae peu connu, Stomatorhinus corneti Boulanger, 1899, a été réalisée dans les rivières forestières Yoko et Biaro du bassin du Congo, région de Kisangani. Diverses techniques de pêche ont permis de récolter 144 spécimens de S. corneti. L’analyse des contenus stomacaux (135 estomacs) a permis d’identifier 19 catégories de proies appartenant aux groupes : débris animaux, débris végétaux, insectes, crustacés, œufs et nymphes d’insectes. Le coefficient intestinal (LI-/LS) moyen calculé pour les spécimens de S. corneti est de 0,56 ; ce qui nous permet de classer cette espèce parmi les invertivores. Le régime alimentaire général de cette espèce, exprimé en pourcentage d’occurrence corrigé, montre que les individus des deux sexes utilisent les mêmes types de proie en proportions semblables. L’espèce S. corneti se reproduit en avril et en septembre. La taille de première maturité est de 80 mm de longueur totale. Le nombre moyen d’ovocytes est de 538 pour une longueur totale de 80 mm en moyenne et pour un poids moyen des gonades de 0,8 g. La taille des ovocytes varie de 0,4 à 1,5 mm de diamètre.
La présente étude sur l’écologie et la répartition des Siluriformes entreprise de septembre 2008 à août 2009, a pour but de caractériser et de déterminer les facteurs responsables de la distribution spatio-temporelle des Siluriformes dans les rivières Yoko et Biaro dans la Réserve forestière de Yoko. Des filets maillants, palangres et nasses traditionnelles ont été utilisés pour capturer les poissons. Ainsi, 572 silures au total, repartis en 15 espèces appartenant à 9 genres et 6 familles ont été récoltés. Les Clariidae et Claroteidae sont les plus diversifiées avec respectivement : 5 et 4 espèces chacune. L’indice de diversité de Shannon varie de 1,54 à 0,40 ; tandis que, celui de Simpson oscille entre 0,75 et 0,18 et l’équitabilité entre 0,86 et 0,29. Ce qui indique une biodiversité élevée mais dont l’équilibre et la structure varient selon les stations. L’Analyse en Composantes Principales (ACP), l’Analyse Factorielle des Correspondances (AFC) et l’Analyse Canonique des Correspondances (ACC) montrent qu’il existe, d’une part, des liens entre les stations Yoko 1, 2, 3 et 4 et Biaro 3 et d’autre part, entre les espèces Schilbe marmoratus, Clarias (Anguilloclarias) ebriensis, Schilbenigrita, Clarias buthupogon, Clarias pachynema et Parauchenoglanis punctatus, du fait de la corrélation positive qui existe entre les paramètres abiotiques et la végétation ripicole. De même, Schilbe grenfelli ; Anaspidoglanis macrostoma et Chrysichthys (Melanodactylus) dageti sont respectivement liées aux stations Biaro 1, 2 et 4, du fait de la corrélation positive existant avec les variables végétation ripicole, température de l’eau élevée (avoisinant 24°C), vitesse de l’eau moyennement faible (variant entre 0,29 et 0,37 m/s) d’une part et d’autre part, du fait de plus grande profondeur de l’eau (0,67 m), plus grande largeur de rivière (17,9 m) et oxygène dissous légèrement déficitaire. Et enfin, du fait de la nature des substrats (sablonneux, caillouteux, rocheux garni de pierres, feuilles mortes, bois morts et débris végétaux). Ceci atteste, que les variables environnementales (abiotiques et biotiques) agissent ensemble dans la répartition spatiale des peuplements des Siluriformes. This paper on the ecology and distribution of Siluriformes, undertaken from September 2008 to August 2009, focuses on characterizing and determining the factors responsible for the spatio-temporal distribution of Siluriformes in the Yoko and Biaro rivers in the Yoko Forest Reserve. Gillnets, longlines, and traditional traps were used to catch the fish. 572 catfish in total, divided into 15 species, belonging to 9 genera and 6 families were collected. The Clariidae and Claroteidae are the most diversified with 5 and 4 species each respectively. Shannon's diversity index varies from 1.54 to 0.40, while that of Simpson oscillates between 0.75 and 0.18 and the equitability between 0.86 and 0.29. This indicates a high biodiversity but their balance and structure varies according to the stations. Principal Component Analysis (PCA), Factorial Correspondence Analysis (FCA), and Canonical Correspondence Analysis (CCA) show that there are, on the one hand, links between stations Yoko 1, 2, 3 and 4 and Biaro 3 and, on the other hand, between the species Schilbe marmoratus, Clarias (Anguilloclarias) ebriensis, Schilbe nigrita, Clarias buthupogon, Clarias pachynema and Parauchenoglanis punctatus. This is due to a positive correlation that exists between the abiotic parameters and the riparian vegetation. Likewise, Schilbe grenfelli, Anaspidoglanis macrostoma, and Chrysichthys (Melanodactylus) dageti are respectively linked to Biaro stations 1, 2, and 4. This also is due to the positive correlation existing with the variables riparian vegetation, high water temperature (around 24°C), and speed of moderately low water (varying between 0.29 and 0.37 m/s) on the one hand. On the other hand, it is due to greater water depth (0.67 m), greater river width (17.9 m), slightly lower dissolved oxygen, and finally because of the nature of the substrates (sandy, stony, rocky topped with stones, dead leaves, dead wood and plant debris). This shows that the environmental variables (abiotic and biotic) act together in the spatial distribution of Siluriformes populations.
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