Browsing by Author "Groeneveld, Johan C."

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    Estuarize-WIO: A socio-ecological assessment of small-scale fisheries in estuaries of the Western Indian Ocean
    (Western Indian Ocean Journal of Marine Science, 2021-12-23) Groeneveld, Johan C.; Hoguane, Antonio M.; Kuguru, Baraka; Mackay, Fiona; Munga, Cosmas; Santos, Jorge
    Estuaries provide unique ecosystem goods and services and have been focal points for human settlement and resource use throughout recorded history. In the Western Indian Ocean (WIO) region, the effects of human population growth, rapid economic development and climate change on estuaries threaten their ecological functioning and the sustainability of estuary-dependent livelihoods. Governance systems are ill-equipped to deal with the mounting challenges. Longterm datasets that describe estuary-scale trends are scarce, and socio-ecological interactions that support sustainable use of resources are incompletely understood. To address these gaps, the Estuarize-WIO project (2016-2019) compiled datasets on biophysical, ecological, socioeconomic and fisheries aspects of selected estuaries in Mozambique (Bons Sinais), Tanzania (Ruvu) and Kenya (Tana), analysed trends per estuary, and used a socio-ecological systems (SES) framework to integrate information from multiple sources at local and regional levels. The introductory paper of this Special Issue of the Western Indian Ocean Journal of Marine Science provides regional context and reviews the relevant literature available for WIO estuaries. In succeeding papers, estuarine circulation is inferred from hydrological measurements, seasonal and decadal trends in land cover and land use are investigated using remote sensing images, household surveys are used to investigate socio-economic circumstances and resource use, and long-term catch survey data and field samples are used to describe small-scale fisheries. In the synthesis paper, a SES framework is constructed to investigate linkages and feedback loops in individual estuaries. A regionally comparative analysis accross the WIO region was conducted, and recommendations were made for future research and governance. The methodological approach developed for Estuarize-WIO is well-suited to research of data poor systems with limited accessibility and research infrastructure.
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    Small-Scale Fisheries of the Tana Estuary in Kenya
    (Western Indian Ocean Journal of Marine Science, 2021-12-23) Manyenze, Fatma; Munga, Cosmas N.; Mwatete, Chrisestom; Mwamlavya, Hamadi; Groeneveld, Johan C.
    The role of small-scale fisheries in maintaining socio-ecological systems (SES) in the Western Indian Ocean is well-documented, yet few studies have addressed estuarine fisheries in the region. Small-scale fisheries in the Tana Estuary in Kenya are described in this paper, accounting for location along a salinity gradient, seasonality, gear types used, species composition and relative abundance of landings. Monthly shore-based sampling was undertaken at four locations in 2017 – Ungwana Bay near the estuary mouth, lower and mid-estuary, and upper estuary at Ozi village, ⁓10 km upstream. Fishing gear comprised of seine nets, gillnets, hook-and-line and traditional gear such as self-made traps, sticks and spears operated from the shore (foot fishers), dugout canoes, dhows and fibreglass boats with outboard engines. A total of 12,840 fish and crustacean specimens belonging to 89 species in 45 families were sampled. Landings were dominated by catfishes Arius africanus (31 %) and Clarias gariepinus (21 %), small pelagic fishes Pellona ditchela (10 %) and several sardine species (⁓5 %), croaker Otolithes ruber (10 %), eel catfish Plotosus limbatus (6 %), mullet Mugil cephalus (4 %) and Nile tilapia Oreochromis niloticus (4 %). Multivariate analyses (nMDS and ANOSIM) found that fishing gear (p < 0.05) and location (p = 0.001) significantly influenced catch composition, but season (p = 0.146) was not significant. Traps were used in the upper and mid estuary only and were selective for three catfish species. Seine nets (54 species) and gillnets (40 species) were least selective and used at all four locations. Rarefaction curves indicated that species diversity was higher at the bay and lower estuary than the mid and upper estuary, and that diversity was highest for canoe-gillnet and canoe-encircling net combinations. Catch rates (avg. of 2.3 to 8.4 kg.fisher-1.day-1) depended on gear type and was highest for monofilament gillnets. Catches comprised a broad size range of multiple species, but on average, seine nets selected smaller individuals than traps, gillnets and long lines. The high complexity and organization of the fishery at an estuary-scale makes it a good example of a relatively intact SES suitable for regional comparative analyses.