Barriers to longitudinal river connectivity: review of impacts, study methods and management for Iberian fish conservation

Abstract

Barriers to longitudinal river connectivity: review of impacts, study methods and management for Iberian fish conservationRiver connectivity is essential for the correct functioning of freshwater ecosystems at all scales. However, it has not received the necessary attention by researchers, managers and policymakers until recent years. In this review, we recap the state of knowledge in river connectivity and its applications to conservation. We describe the particular characteristics of river connectivity and summarise the effects of its interruption in different freshwater ecosystem elements. We then focus on the effects of the lack of segment connectivity in fish species and review the different methods developed to study it. The application of connectivity in freshwater fish conservation areas is also reviewed, which highlights the lack of studies on this subject. Finally, connectivity restoration is studied. The review addresses these topics in a general way and then focus on the Iberian Peninsula. The Iberian Peninsula is an interesting place to study river connectivity because it has one of the highest numbers of dams per square kilometre and a large number of endemic and endangered freshwater fish species. Despite the high number of fish species affected by water extraction and damming, river connectivity and its effect in Iberian freshwater fish populations have not been well studied. A small number of studies analyse the effect of small dams in nearby fish communities, but large-scale impact assessments are scarce. More connectivity analyses are needed to improve freshwater ecosystem conservation strategies. We conclude addressing some gaps in the knowledge of fragmentation and research opportunities in river connectivity and conservation

The role of connectivity in conservation planning for species with obligatory interactions: Prospects for future climate scenarios

“…It is widely recognized that even small barriers can significantly limit the movement of individuals in rivers and streams and increase the risk of extinction (Crook et al., 2015; Hermoso, Clavero, & Filipe, 2021; Hermoso, Vasconcelos, et al., 2021; Herrera‐R et al., 2020; Radinger et al., 2018; Zarfl et al., 2019). Accordingly, fish, and by association, mussels, are strongly impacted by instream artificial barriers, as evidenced by reported extinctions and steep population declines (Benson et al., 2018; Branco et al., 2017; Pires et al., 2021; Rodeles et al., 2020), despite the implementation of mitigation strategies (e.g., fish ladders) that are often inefficient (Hermoso et al., 2018).…”

“…In freshwater ecosystems, the hierarchical linear structure of river networks limits the dispersal pathways between current and future suitable habitats, which significantly hurdles climate-driven shifts in species distributions (Crook et al, 2015;Herrera-R et al, 2020;Rodeles et al, 2020). For species with limited dispersal ability, escaping climate change is even more challenging (Archambault et al, 2018;Årevall et al, 2018;Urban et al, 2013).…”

“…Gains can only be taken into account if mussels are able to reach the new areas, which is highly dependent on the ability of fish hosts to transport glochidia and release juveniles at suitable locations. Like most European water bodies, Iberian rivers are highly fragmented by artificial barriers (Belletti et al., 2020; EEA, 2018), which has a significant impact on the movement of fish species within the river network (Branco et al., 2017; Gibson‐Reinemer et al., 2017; Rodeles et al., 2020). Specifically, the location and type of artificial barriers within the river network in relation to the current presence of species will play an important role in determining which future habitats are colonizable and which are not (Radinger et al., 2017).…”

“…Freshwater biodiversity is particularly vulnerable to climate change, which will undoubtedly exacerbate the current rates of decline (Dudgeon, 2020; Reid et al., 2019; Su et al., 2021; WWF, 2022). In freshwater ecosystems, the hierarchical linear structure of river networks limits the dispersal pathways between current and future suitable habitats, which significantly hurdles climate‐driven shifts in species distributions (Crook et al., 2015; Hermoso & Filipe, 2021; Herrera‐R et al., 2020; Rodeles et al., 2020). For species with limited dispersal ability, escaping climate change is even more challenging (Archambault et al., 2018; Årevall et al., 2018; Urban et al., 2013).…”

The past and current distribution of native and non-native fish in the Kowie River catchment, Makhanda, Eastern Cape

“…Similarly, MacRae and Jackson (2001) demonstrated that in small lakes ( 50 ha) in central Ontario, the presence of the non-native predatory Smallmouth Bass Micropterus dolomieu drives small cyprinids to predominantly utilise complex and specific habitats whereas, in lakes without Smallmouth Bass the cyprinids inhabited a more diverse range of habitats. As such, the presence of non-native species in river systems may alter the behaviour of the native biota (Cox and Lima, 2006;Woodford et al, 2017), and current evidence suggests that the impacts of such invasions are more prominent in freshwater ecosystems that are already modified or degraded by humans (Chapman et al, 2020;Rodeles et al, 2020).…”