Aquatic Connectivity on a Fish's Scale: Measuring Dispersal in Retropinna Semoni from Inland Australian River Systems

Abstract

Ecological theory and research has shown a critical link between in-stream connectivity and the ecological persistence of aquatic fauna with particular emphasis on taxa with higher commercial or recreational value such as fishes. However, limited information exists on both the dispersal levels and behaviour of fish that have no obvious economic or conservation values. The biological connectivity (or isolation) of individuals/populations across heterogeneous spatio-temporal dimensions occurs primarily via the processes of movement and dispersal. The movement of individuals affects current patterns of population dynamics over an ecological timescale whilst dispersal ultimately shapes the level of gene flow among populations and contributes to the processes that shape population dynamics over an evolutionary timescale. Despite the temporal differences in scale, both the ecological and evolutionary outcomes of connectivity are governed by the ability of individuals to freely move or disperse through all axes of space and time. This very ability for individual connectivity relies on factors both intrinsic and extrinsic to the species. In an attempt to better understand the fundamental population dynamics of aquatic fauna in the natural environment, it is vital to design and apply methodologies that can accurately estimate in-stream levels of connectivity. By utilising such techniques researchers can then determine the underlying biological principles that shape the patterns of distribution and abundance for a given species and use these key biological indicators to contribute to the information required in the long term protection and management of an often undervalued resource. The focus of the study was to estimate levels of connectivity in a model species, the ubiquitous Australian smelt (Retropinna semoni), both on an ecological and an evolutionary timescale across contrasting drainage systems from inland rivers of Australia. Contrasting patterns of connectivity from different drainage systems allowed inferences to be drawn on the effects that extrinsic factors, such as flow regimes and stream architecture, have had on population dynamics. Additionally, utilising a temporal approach provided information on the changes that have occurred to population dynamics on a small scale from annual changes in local hydrological conditions and longer term changes resulting from human induced impacts, and finally the effects that may have shaped the structure of a species over evolutionary timescales...