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Abstract 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 that these movements are impeded or blocked by dams.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 four to six sites per river.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 3 months after its removal. The two small lowland dams studied herein limited the upstream extent of marine species, which recolonised 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.In extensive surveys conducted previously in Puerto Rico, sampling was concentrated higher in the catchment, 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.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.
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Protection gaps in Amazon floodplains will increase with climate change: Insight from the world's largest scaled freshwater fish
Abstract The Amazon floodplains represent important surfaces of highly valuable ecosystems, yet they remain neglected from protected areas. Although the efficiency of the protected area network of the Amazon basin may be jeopardized by climate change, floodplains are exposed to important consequences of climate change but are omitted from species distribution models and protection gap analyses.The present and future (2070) distribution of the giant bony‐tongue fishArapaimaspp. (Arapaimidae) was modelled accounting for climate and habitat requirements, and with a consideration of dam presence (already existing and planned constructions) and hydroperiod (high‐ and low‐water stages). The amount of suitable environment that falls inside and outside the current network of protected areas was quantified to identify spatial conservation gaps.We predict that climate change will cause a decline in environmental suitability by 16.6% during the high‐water stage, and by 19.4% during the low‐water stage. About 70% of the suitable environments ofArapaimaspp. remain currently unprotected. The gap is higher by 0.7% during the low‐water stage. The lack of protection is likely to increase by 5% with future climate change effects. Both existing and projected dam constructions may hamper population flows between the central, Bolivian and Peruvian parts of the basin.We highlight protection gaps mostly in the south‐western part of the basin and recommend the extension of the current network of protected areas in the floodplains of the upper Ucayali, Juruà and Purus rivers and their tributaries. This study has shown the importance of integrating hydroperiod and dispersal barriers in forecasting the distribution of freshwater fish species, and stresses the urgent need to integrate floodplains within the protected area networks.
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- Award ID(s):
- 1852113
- PAR ID:
- 10369627
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Aquatic Conservation: Marine and Freshwater Ecosystems
- Volume:
- 32
- Issue:
- 11
- ISSN:
- 1052-7613
- Page Range / eLocation ID:
- p. 1830-1841
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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