Functional responses of fisheries to hydropower dams in the Amazonian Floodplain of the Madeira River

1. Tropical river fisheries support food security for millions of people
but are increasingly threatened by hydropower development. How dams affect
these fisheries remains poorly known in most regions. Here, we used a
functional traits approach to evaluate the extent to which the composition
of fishery yields in the Madeira River Basin the largest sub-basin in the
Amazon, respond to dam construction. We also explored how dams affected
the monetary value of yields and fishing-based income of the communities.
2. We collected fishing data in 17 locations distributed more than 300 km
across upstream, reservoir, and downstream zones during pre-and post-dam
construction periods. We interviewed 711 fishers from 13 communities to
assess fishing income during pre- and post-dam periods. 3. Catch-per-unit
effort (CPUE) declined significantly, i.e., by 37%, after dam
construction. Multivariate analysis yielded six species clusters according
to trait syndromes related to life history, migration,
swimming-performance/microhabitat-use and economic value that were
associated with the environmental data characteristic of pre- and post-dam
periods. Comparison of CPUE of each cluster indicated that large species
with periodic life-history strategy and regional or long-distance
migratory behavior were most affected by dam construction, with CPUE
declining by, on average, 31%. Declines in yields and shifts in functional
composition of the fishery yields resulted in average decline of 21% in
the monetary of functional clusters and 30% in fishing income. 4.
Synthesis and applications. Our study indicates that the implementation of
the dams and associated changes in environmental conditions affected the
functional composition of yields and reduced catches, negatively affecting
the fishing-based income of the studied communities in the Madeira
River.Whereas catches of all functional clusters declined after the dams,
species possessing large body sizes, traits related to a periodic life
history strategy, either with long-distance or regional migratory
behaviors, and the greatest economic importance appeared to be
particularly vulnerable. These results imply that hydropower expansion
will cause detrimental effects for fisheries and the livelihoods they
sustain. Our results underscore the urgent need for considering
alternative sources of renewable energy (e.g., solar power and in-stream
turbines) to avoid irreversible socio-environmental damages of large dam
projects. In river reaches where dams are already in operation or under
construction, minimizing impacts will require improving operational
protocols to reduce hydrological alterations and developing research and
technology to improve the functionality of fish passages. In these
locations, addressing losses in fishery value and fishing-based income
will also require the implementation of fair compensation measures.
Maintaining fish production requires conserving flow pulses and
free-flowing rivers and tributaries critical for completing life cycles of
fish species with vulnerable traits.