Modelling the effects of dams on freshwater fish distributions in Hokkaido, Japan

Abstract

1. We examined the effects of habitat fragmentation caused by dams on freshwater fish species using a database of 7848 fish presence/absence surveys, conducted between 1953-2003 in Hokkaido, Japan. 2. A series of generalised linear models showed that for 11 of 41 taxa examined, the probability of occurrence had been influenced either negatively (eight taxa) or positively (three taxa) by the presence of a dam downstream from their habitat. 3. Maps of modelled predictions revealed that dams had had widespread negative impacts on certain taxa, while for other taxa the impact was limited to specific basins. Two of the three taxa whose probability of occurrence was increased in areas above dams have long been transplanted into reservoirs in Japan. 4. For four of the eight taxa whose probability of occurrence was reduced above dams and all three taxa whose probability of occurrence increased above dams, the temporal length of habitat isolation (i.e. the number of years between dam construction and sampling) was also a significant predictor of the probability of occurrence. This pattern indicates that these taxa experienced a gradual rather than an instantaneous population impact as a result of dam construction. 5. The eight taxa whose probability of occurrence was reduced as a consequence of dams all exhibit migratory life cycles. Although migratory taxa are probably more susceptible to the negative effect of dams, we could not detect significant relationships between migration life histories and the effect of fragmentation by dams. 6. These analyses enable stream and fisheries managers to quantify the impacts of habitat fragmentation because of dams for individual species. The spatially explicit nature of our analyses also enables identification of the areas of the impact at broad geographical scales. Using our results, managers can take effective conservation and restoration measures to predict, mitigate or remove the impact of dams. For example, our results can be used to prioritise dams for removal or to predict losses of biodiversity and ecosystem services in advance of dam construction.

Assessing fish assemblages similarity above and below a dam in a Neotropical reservoir with partial blockage

“…River impoundments generally exert negative effects on native fish species, especially on migratory species, disrupting longitudinal connectivity and obstructing migrations routes (Joy and Death, 2001;Fukushima et al, 2007). Furthermore, the accumulation of migratory fishes immediately below dams is well documented (Taylor et al, 2001;Gehrke et al, 2002) and were found in this study, since several species associated to downriver zone are migratory or rheophilic species -e.g., Leporinus copelandii Steindachner, 1875; Pimelodus fur (Lütken, 1874); and Prochilodus lineatus (Valenciennes, 1837).…”

Silver eel downstream migration in fragmented rivers: use of a Bayesian model to track movements triggering and duration★

“…Obstacles to migration, such as dams, are considered to be one of the main threats to those fish species (Limburg and Waldman, 2009). They are also seen as the root cause of some population extinctions or their keeping in confined areas within river catchments (Porcher and Travade, 1992;Kondolf, 1997;Coutant and Whitney, 2000;Larinier, 2001;Fukushima et al, 2007). Obstacles can have a large variety of impacts.…”

Modelling basin-scale distribution of fish occurrence probability for assessment of flow and habitat conditions in rivers

“…there was no river fragmentation or flow regulation, the OP of 28 fish species would increase further compared to the increase in scenario D2, while only two fish species that had higher occurrence probabilities in D2 than D1 would decrease. As mentioned above, river fragmentation limits the migration of diadromous fish and decreases their OP (Fukushima et al 2007, Han et al 2008. Furthermore, the indirect effects of dams, e.g.…”

“…To date, flow regulation and channel fragmentation caused by dam construction have altered the flow regimes of over half of the large river systems in the world (Nilsson et al 2005), resulting in habitat degradation and decline in aquatic species (Poff et al 1997). The effects of dams on freshwater fish distribution have also been reported, particularly for diadromous fishes (Fukushima et al 2007, Nislow et al 2011. Besides flow regimes, water quality and physical habitat conditions, such as catchment area, river width, slope, altitude and riverbed material, are also key factors that affect the distribution and population of fishes.…”