Consequences of connectivity alteration on riverine fish assemblages: potential opportunities to overcome constraints in applying conventional monitoring designs

Abstract

Patterns of connectivity are critical to structuring both spatial and temporal variation in the composition of species populations and assemblages. Water resource development has an important impact on longitudinal connectivity in rivers, and disrupts natural patterns of dispersal of individuals between segments of the river network. Consequently, artificial barriers alter the structure, size and distribution of species populations leading to impacts on aquatic biodiversity.Quantitative assessment of the ecological effects of connectivity alteration is necessary to develop effective conservation plans to manage the impacts of anthropogenic fragmentation. Connectivity alteration is a complex environmental disturbance because the potential scale of impact is dependent on the spatial scale at which biota undergo life‐history processes such as spawning and recruitment. Few river networks have single migration barriers, meaning that multiple points of fragmentation are present and have potentially interacting effects. Therefore, conventional ‘control–impact’ approaches to impact assessment may be inappropriate or confounded. Furthermore, monitoring patterns of fish population or assemblage structure moving through fish passage facilities alone creates a mismatch between the spatial scale of impact and assessment of water resource development.This paper uses a case study in subtropical Australia to highlight three potential approaches to increasing inference of the impact of fragmentation by barriers on riverine fish. Thorough understanding of life‐history and dispersal ecology of fish is necessary to understand and predict the consequences of fragmentation, and comparing patterns of distribution among species with different migration requirements can identify sources of fragmentation. Monitoring patterns in fish assemblages at both the barrier and river network scale increases the strength of inference of the effects of connectivity alteration and management. Experimental removal of artificial barriers would assist in determining the effect of fragmentation by restoring connectivity. Such approaches would improve predictions of connectivity management and underlying drivers of aquatic biodiversity. Copyright © 2013 John Wiley & Sons, Ltd.

The Effects of DAM Removal on River Colonization by Sea Lamprey Petromyzon Marinus

“…When the barrier that is planned to be removed is also associated with socio‐economic activities, its social acceptance is often challenging (Hart and Poff, ; Lejon et al ., ). To improve this social acceptance, the ecological effects of barrier removal should therefore be quantified and communicated (Kibler et al ., ; Rolls et al ., ). However, to date, long‐term studies providing such information are still scarce (Bernhardt et al ., ; Roni et al ., ).…”

Upstream recolonization by freshwater mussels (Unionoida: Hyriidae) following installation of a fishway

“…Longitudinal connectivity within rivers is essential to the ecology of fish and other taxa, and integral to ecosystem functioning (Dudgeon et al, ). Instream barriers such as dams and weirs impair animal movements and are a major cause of decreased species abundance and diversity in freshwater ecosystems (Rolls, Ellison, Faggotter, & Roberts, ). The removal of barriers is increasingly undertaken in many countries as a part of stream restoration projects; however, removal is not always possible where the function of the barrier is still required (Gangloff, ).…”

Modified tide gate management for enhancing instream habitat for native fish upstream of the saline limit

“…Fragmentation and disconnection of habitats as a result of water resource development is a key factor in the loss of biodiversity of freshwater ecosystems (Dudgeon et al, 2006;Rolls et al, 2013). Disconnections in rivers are particularly damaging because the dendritic structure of river networks restricts dispersal potential, with important consequences for population persistence (Fagan, 2002).…”