The response of otters to environmental changes imposed by the construction of large dams

Abstract

The number of dams is progressively increasing, but nonetheless there are few examples of long‐term studies involving otters and these structures. This study assessed how Eurasian otter Lutra lutra responded over time to environmental changes imposed by the construction of a large reservoir, the Alqueva Dam (250 km2, SE Portugal). Otter distribution was monitored over four phases (pre‐deforestation/flooding, deforestation, flooding, and post‐flooding) from 2000 to 2006 in both the flooded and surrounding areas. During each phase, presence was assessed at two resolutions: 25 km2 (76 survey sites in wet and dry seasons) and 1 km2 (39 survey sites, every three months). In addition, otter spraints were collected at eight survey sites in 2000 (pre‐dam) and 2006 (post‐dam) to assess and compare otter diet with prey availability. Otters were widespread before dam construction (>82.4% positive cells), decreased during deforestation (68.5%), and particularly during the flooding phase (33.3%), recovered during the post‐flooding phase, although not at the level recorded before dam construction (61.5–83.3%). Otter diet was dominated by fish and American crayfish Procambarus clarkii during the pre‐deforestation/flooding phase (56.7% fish, 35.3% crayfish) and at the end of the post‐flooding phase (60.7% fish, 33.2% crayfish). Species richness of fish prey decreased with flooding (16 to 8), as did the ratio of native/non‐native fish species (1.7 to 0.3). Changes in the availability of the main ecological requirements of otter were similar to the changes in the observed otter distribution in the flooded area throughout the impact phases, and decreased during deforestation and flooding with some recovery in the post‐flooding phase. The results emphasize the importance of long‐term monitoring studies that include several post‐impact phases, to evaluate species response to impacts. This will allow better planning of mitigation and compensation measures. Copyright © 2013 John Wiley & Sons, Ltd.

Otter occupancy in the Cape Peninsula: Estimating the probability of river habitat use by Cape clawless otters, Aonyx capensis, across a gradient of human influence

“…For example, the neotropical otter, Lontra longicaudis , has been found to occupy human‐altered habitat in the form of polders in parts of their range (Carillo‐Rubio & Lafon, ; Sepúlveda, Bartheld, Monsalve, Gómez, & Medina‐Vogel, ). Similarly, Eurasian otters, Lutra lutra, inhabit coastal urban centres, including Cork in Ireland (White et al, ), and make use of artificial water bodies such as reservoirs in Portugal (Pedroso, Marques, & Santos‐Reis, ; Pedroso, Sales‐Luís, & Santos‐Reis, ). Small‐clawed otters, Aonyx cinereus , are just as likely to inhabit coffee and tea plantations as they are to inhabit protected areas in the Western Ghats, India (Prakash et al, ); and North American river otters, Lontra canadensis, have recently returned to the now highly urbanized San Francisco Bay in California, USA (Bouley, Isadore, & Carroll, ).…”

The Eurasian otter Lutra lutra (Linnaeus, 1758) in Portugal

“…As a result, otters were found to be frequent in most Portuguese rivers, although, lacking a standardised monitoring protocol, data were mostly scattered over space and time (Ferrand-Almeida, 1980;Macdonald & Mason, 1982;Santos-Reis, 1983;Simões-Graça & Ferrand-Almeida, 1983;Trindade, 1987Trindade, , 1989Trindade, , 1991Beja, 1989a, b). Basto et al, 2011), large dams (Pedroso, 1997(Pedroso, , 2012Pedroso & Santos-Reis, 2006, 2009Pedroso et al, 2007;Sales-Luís et al, 2007;Santos et al, 2008;Pedroso, 2012;Pedroso et al, 2013), estuaries (Campos, 1993;Trigo, 1994;Trindade, 1996;Freitas et al, 2007;SalesLuís et al, 2009;Sales-Luís, 2011) and sea coast environments (Beja, 1989a;Beja, 1992;Gomes, 1998;Pedrosa, 2000;Cerqueira, 2005).…”

“…Gomes et al, 1989;Beja,1989aBeja, ,1991Beja, ,1995aBeja, ,b,1996aFlorêncio, 1993Florêncio, , 1994Trigo, 1994;Gomes, 1998;Farinha, 1995;Sousa, 1995;Chambel, 1997a,b;Pedroso, 1997;Azinheira, 1998;Freitas, 1999;Lopes, 1999;Matos, 1999;Silva, 1999;Pedrosa, 2000;Barrinha, 2002;Magalhães et al, 2002;Trindade, 2002;Garcia, 2005;Novais, 2005;Pedroso & Santos-Reis, 2006;Freitas et al, 2007;Marques et al, 2007;Sales-Luís et al, 2007;Marques, 2010;Basto et al, 2011;Pedroso et al, 2013). Hence the otter diet in the different Portuguese aquatic habitats is currently well known.…”

“…Particularly, several studies showed that otters use both large Santos et al, 2008;Pedroso, 2012;Pedroso et al, 2013) and small reservoirs (Basto et al, 2011), mainly as foraging grounds (Pedroso and Santos-Reis, 2006;Sales-Luis et al, 2007;Basto et al, 2011). In large reservoirs, the fish community is strongly dominated by non-native species that are largely available to otters throughout the year and, accordingly, represent the bulk of otter diet (Pedroso, 2012).…”

High foraging efficiency of Eurasian otters in a shallow Iberian reservoir

“…Surprisingly, otters are now increasingly using reservoirs (and many other human-made habitats) eating mostly exotic invasive species in them, as reported by many Iberian studies (Pedroso and Santos-Reis 2006, Sales-Luis et al 2007, Ruiz-Olmo and Jiménez 2008, Basto et al 2011, Pedroso et al 2013. Some authors have hypothesized that reservoirs are low-quality habitats for otters (Pedroso et al 2013), that are mostly used when native fish become scarce in rivers or that otters only use reservoirs due to density-dependent dispersal from saturated river populations (Pedroso and Santos-Reis 2006, Ruiz-Olmo and Jiménez 2008, Basto et al 2011.…”