Human-wildlife interactions on the tidal flats of the Bijagós archipelago: does shellfishing affect migratory shorebirds?

The Bijagós archipelago in West Africa is home to an ethnic group with a
rich cultural heritage that is tightly linked to nature. The Bijagós
people have a shared cultural identity, but across islands, there are
different resource management regimes stemming from island-specific
context with regards to socio-political organization and strength of
cultural heritage. Across the archipelago, bivalves harvested manually
from the mudflats are an important part of the Bijagós people’s diet,
economy, and culture. Thousands of migratory shorebirds share the use of
these mudflats during their non-breeding season, consuming macrobenthos
such as crustaceans and bivalves, including those harvested by local
people. At the end of their stay in the Bijagós, shorebirds need to fuel
for their migratory flight in order to return to their breeding areas,
being particularly important during this period that they have access to
undisturbed feeding areas with suitable food resources. In this study, we
start by exploring shellfishing patterns across different management
regimes, then assess seasonal variation in the direct impact of
shellfishing on shorebirds (through competition for resources and space),
and finally quantify the indirect impact of sediment disturbance due to
shellfishing upon shorebird prey availability. Results indicate that
bivalve resources are better managed in areas with formal protection,
while traditional management based on cultural beliefs results in poorer
stock conditions. Interestingly, across islands shellfishing activity is
concentrated in mid-winter, decreasing towards shorebirds’ fuelling
period, when they benefit the most from reduced disturbance on the
mudflats. No direct competition for resources was detected, as collected
bivalves were significantly larger than those consumed by shorebirds,
regardless of the season. Indirect impacts caused by sediment disturbance
during shellfishing were also mostly absent, causing only a small
reduction on shorebirds prey density, but with no effect on the available
biomass.