Doctor of Philosophy (PhD)


Oceanography and Coastal Sciences

Document Type



Commercial and recreational fisheries are a valuable resource to millions of people around the world. Developing countries are particularly dependent on the revenue provided by locally harvested fish with total exports from these nations valued at $80 billion USD. For Tanzania, fisheries provide not only a source of revenue but an important source of protein with an estimated 25 to 30kg of fish consumed per person every year. There is no doubt that high fisheries production is critical to the well-being of millions of livelihoods along the Tanzanian coast. An important but poorly understood driver of fisheries production is the availability and use of suitable habitat for fish species at different life stages. Additionally, the lack of alternative livelihood options in the country has led many citizens to make ends meet by aggressively exploiting local habitats including mangrove cutting for building materials, drag net use on seagrass habitats, and indiscriminate gill net use in coral reefs to catch as many fish as possible. An assessment of how fisheries species use seascape habitats may lead to a better understanding of what is needed to conserve Tanzanian fisheries.

The objective of my dissertation is to identify and quantify the linkages that exist between coastal Tanzanian habitats and fish communities using stable isotope-based approaches. Chapter 1 provides the necessary background information and rationale for this dissertation. Chapter 2 examines the habitat-use of three commercially important fish species in a mangrove-seagrass gradient using bulk stable isotopes, mixing models, and hypervolume habitat niche metrics. In Chapter 3, I assessed the trophic structure and energetic pathways present within seagrass fish communities and quantified the biomagnification of total mercury (Hg) up the food web to important fisheries species. Lastly, for Chapter 4, I determined if there is any evidence supporting the notion that mangrove habitats subsidize carbon to fish and invertebrate communities in adjacent habitats. Results from this research support the general paradigm that there is plasticity in habitat use by fishes which varies with life stage, species, and individual.



Committee Chair

Polito, Michael J.

Available for download on Saturday, July 06, 2024