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Disputation: Mathew Ogalo Silas


Date: Friday 22 April 2022

Time: 13.00 – 17.00

Location: Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20 and Zoomlink you can find below

Patterns of small-scale coastal fisheries and local fisheries management in Tanzania - adaptation to a changing climate

Zoom link for the dissertation you can find here.



Coastal habitats like mangroves, seagrass meadows, coral reefs, and adjacent offshore waters constitute an important part of the tropical coastal seascape. They provide conducive environmental conditions for fish and other marine animals, which serve as food and income for coastal communities around the world. Despite the beneficial  ecosystem services generated, these habitats are under immense pressure from anthropogenic and climate change impacts that destroy habitats and reduce their capacity to support fisheries. This leaves coastal communities in a challenging situation, where people need to adapt to changing fish stocks. This thesis aimed to understand the past, current, and future patterns of small-scale fisheries in Tanzania and how fishing communities can respond to human activities and climate change. The thesis assesses and integrates fish catch data (from 2013 and 2014) and fishers’ perceptions. Archived fish landing data from 1950 to 2016 were used to understand the role of coastal marine ecosystems for small-scale fisheries and to investigate how local fishers adapt to environmental changes and fishing pressure.
To address the goals of the thesis, Paper I investigated seasonal (gear-based) patterns of fish catch in coastal marine habitats. Paper II explored the influence of environmental conditions and monsoon seasons on fish catch. Papers III and IV examined the effects of climate change on small-scale fisheries, and Paper IV also addressed the response of fishing villages to a declining catch trend in the country. The findings show that the coastal seascape (from nearshore to offshore waters) is vital in sustaining fish stocks, while the productivity of coastal habitats varies with seasons. The highest catch rates were observed in the offshore environment during the northeast monsoon season (Paper I,which is characterised by weak winds and high sea surface temperature. In contrast, the catches of important target species, such as tuna and prawn, were found high in nearshore habitats during the rougher southeast monsoon season (Paper II), which is characterised by strong winds and low sea surface temperature. The fishers’ perceptions revealed similar patterns of high catches of tuna and prawn during  the southeast monsoon season in nearshore waters (Paper II). This emphasises the relevance of incorporating fishers’ perceptions into research to better understand the complex dynamics of small-scale fisheries. A comparative assessment of climate change impacts on long-term fisheries productivity of two target stocks showed clear species-specific effects of climate change. For instance, pelagic mackerel (Rastrelliger kanagurta) was found sensitive to increased precipitation, as a lowered salinity may negatively affect the maturing phase (Paper III). Demersal prawn, on the other hand, was positively related to increased sea surface temperature (Paper III). Importantly, the findings of Paper IV show that most small-scale fishers will continue to fish despite declining catches. This suggests a need of building adaptive capacity among local coastal communities, which could serve as alternative coping mechanisms to the impacts
of climate change and other stressors (Paper IV).

In conclusion, this thesis shows how shallow-water habitats and adjacent offshore waters in the coastal seascape, environmental conditions and seasonal weather patterns, and stressors such as climate change and fishing, play essential roles in determining fish catch patterns and the behaviour of fishers in the western Indian Ocean region. The findings of the thesis demonstrate the benefits of integrating fish catch records and local knowledge facilitating applied research and coastal resource management.