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.

Citation:

Title: Fish assemblage response to removal of a low‐head dam in the lower reach of a tropical island river
Authors: Johann J. Cancel Villamil, Sean A. Locke
Journal: Freshwater Biology
Year: 2022