Supporting tables and figures for Cancel Villamil JJ, Locke SA (2022) - Fish assemblage response to removal of a low‐head dam in the lower reach of a tropical island river, Freshwater Biology

Table S1 summarizes studies of the effects of dams on freshwater fish
assemblages Table S2 provides results of fishing in 39 samples in three
rivers in Puerto Rico in 2017-2019. See 2, below.  Figure S1
shows the relationship between fish species richness and time spent
electrofishing in these samples. Abstract of article: 1. Dams are often
removed from rivers to restore habitat connectivity for biota such as
fish. Removal of inland dams is well studied in temperate mainland rivers
but this approach has been little studied in fish assemblages in islands,
tropic systems, or for dams near the mouth of the river. In Puerto Rico,
one of the most intensively dammed territories in the world, all native
river fishes migrate between fresh water and the sea, and previous work
shows these movements are impeded or blocked by dams. 2. Fish assemblages
were compared before and after removal of the Cambalache dam, a porous,
low-head structure near the mouth of the Río Grande de Arecibo, as well as
in two other rivers in Western Puerto Rico, one with a similarly sized and
positioned dam, and one reference river without artificial barriers. Fish
were sampled using backpack electrofishing on 39 occasions during
2017-2019, including seven samples collected after removal of the
Cambalache dam, at between four and six sites per river. 3. Fish
assemblages upstream from dams were poorer in species, and species
richness showed a marginal tendency (P=0.0515) to increase upstream of the
Cambalache dam three months after its removal. The two small lowland dams
studied herein limited the upstream extent of marine species, which
recolonized upstream sites of the Río Grande de Arecibo after removal of
the Cambalache dam. An estimate of relative density (catch per unit
effort) of common native freshwater species was higher above these two
dams, and decreased at upstream sites after removal of the Cambalache dam.
The estimated relative density of a native freshwater species that is of
conservation concern, the American eel (Anguilla rostrata), was reduced
above dams, and increased upstream of the former Cambalache dam after its
removal.  4. In extensive surveys conducted previously in Puerto
Rico, sampling was concentrated higher in the watershed, and native fishes
were more common and abundant below than above dams. The present work was
conducted near the river mouth, and opposite results were observed. These
contrasting results suggest that the effects of dams (or dam removal) on
fish assemblages vary along the river gradient, although data from other
systems are needed to confirm this. 5. The present results suggest
low-head dam removal to be a viable method of restoring connectivity in
fish assemblages in lower reaches of rivers in Puerto Rico and,
potentially, other tropical islands. Removal of dams near the mouth of the
river appears to be of particular benefit to marine fish species that use
lower river reaches.