Stable isotopes track the ontogenetic movement of three commercially important fishes along a coastal Tanzanian seascape

Coastal habitats serve a variety of functions for fisheries species including the provision of foraging areas. Numerous studies have demonstrated that fish species shift their habitat preferences as they age, and this paradigm is also common in commercially important species. In this study, the timing and magnitude of ontogenetic movements in 3 coastal fishes (thumbprint emperor Lethrinus harak, crescent perch Terapon jarbua, and dory snapper Lutjanus fulviflamma) was examined in Tanzania. A combination of carbon and nitrogen stable isotope analysis, Bayesian mixing models, and niche metric analysis was used to quantify the ontogenetic timing and magnitude of shifts in each species’ habitat niche. Results from this work identified an ontogenetic shift in the relative importance of mangrove and seagrass habitat use between smaller, younger individuals and larger, older individuals across all 3 species. However, the ontogenetic timing of this shift varied between species, with thumbprint emperor exhibiting the most abrupt shift in habitat use with increasing body size, followed by dory snapper and crescent perch. Management approaches that emphasize the conservation of seascapes are suggested to support sustainable fisheries in coastal Tanzania.