The inter-regional comparison shows that similar habitats are exploited along the Swahili coast, although to different degrees. The general pattern indicates that samples from offshore islands have higher representations of fish from coral/rocky habitats. Shanga shows a heavier reliance on fish from estuary habitats than on coral species. This is not surprising given that these offshore islands are surrounded by extensive coral reefs, whereas Shanga lies on an island within an estuarine bay. Furthermore, the taxa exploited from these habitats overlap but are not the same in all samples, possibly as a result of different fishing strategies. The identification of fish taxa to genus or species level, whenever possible, is essential to understanding the dynamic interaction between fishers and the aquatic habitats they exploit. The results of the habitat analysis reveal the complexity and variability of past aquatic subsistence strategies along the Swahili coastline and offer a framework for understanding the interrelated role of cultural and environmental effects on aquatic adaptations.
Our analysis of changing habitat use throughout the phases at Shanga indicates that open sea species were exploited only in the second millennium. Similarly, Horton and Mudida (1993, 679) deduced that offshore fishing developed at Shanga after the 12th century. This trend is visible in samples that were included in a regional analysis: all the sites with offshore taxa – Shanga, Chwaka, Mduuni, Mtambwe Mkuu, Ras Mkumbuu, Tumbatu, and Songo Mnara – have evidence of occupation beyond the 12th century (Quintana Morales 2013a). Furthermore, samples dated to before the 12th century, Fukuchani and Unguja Ukuu, do not include offshore species. However, not all samples dated after the 12th century have open-sea fish species (i.e. Vumba Kuu, Kaliwa, and Kizimkazi). The later settlements without offshore fishing have smaller numbers of domesticated animal remains than those with offshore specimens (Quintana Morales 2013a). Furthermore, in two samples that were compared chronologically (Shanga and Chwaka), the number of domesticates increases at the same time that offshore fishing becomes more prevalent on the coast (Quintana Morales 2013a; 2013b).
One possible explanation is that there is a link between having the capital/position needed to manage or obtain livestock and having the ability to invest in more expensive equipment to engage in offshore fishing. Historical accounts describe the use of livestock as important ritual food used in feasting (e.g. Hollis 1900) and as gifts to visitors (e.g. Freeman-Grenville 1962, 57), showing that these were not just markers of high status but cultural tools through which status was created and reinforced (Fleisher 2010). Ethnographic and ethno-archaeological research on the coast indicates that higher socioeconomic classes have more access to domesticated animals and invest in the larger boats required for offshore fishing (Quintana Morales 2013a; Nakamura 2011). Thus, the conditions associated with high consumption of domesticated animals (people with higher prestige and socioeconomic power) also favour the investment in offshore fishing. The faunal sample from Vumba Kuu presents an interesting case because it has a high number of cattle remains (>50% of identified mammal remains) and no evidence of offshore fishing (Quintana Morales 2013a). However, excavations at Vumba Kuu have yielded relatively small quantities of imported ceramics and there is little evidence of coral-stone architecture (Wynne-Jones 2010). These material characteristics are often associated with high levels of socio-economic status. Thus, the link between evidence of high socio-economic power and offshore fishing holds.
A growing coastal population may have provided an alternative or additional pressure to expand the range of exploited aquatic habitats by going farther from the shoreline and targeting larger-bodied fish. At Shanga, for example, the size of the settlement grew from 5 to 15 ha during its occupation (Horton 1996), which indicates a growing population. While both an increasing population and a developing socio-economic hierarchy provide plausible explanations, the timing of these shifting subsistence strategies around the beginning of the second millennium could be associated with a wider set of changes evident across the region, including changes in the location and structure of settlements and technological and architectural developments, that point to an increasingly maritime outlook (Fleisher et al. forthcoming).