Not just a migration problem: Metapopulations, habitat shifts, and gene flow are also important for fishway science and management

Abstract

Worldwide, fishways are increasingly criticized for failing to meet conservation goals. We argue that this is largely due to the dominance of diadromous species of the Northern Hemisphere (e.g., Salmonidae) in the research that underpins the concepts and methods of fishway science and management. With highly diverse life histories, swimming abilities and spatial ecologies, most freshwater fish species do not conform to the stereotype imposed by this framework. This is leading to a global proliferation of fishways that are often unsuitable for native species. The vast majority of fish populations do not undertake extensive migrations between clearly separated critical habitats, yet the movement of individuals and the genetic information they carry is critically important for population viability. We briefly review some of the latest advances in spatial ecological modelling for dendritic networks to better define what it means to achieve effective fish passage at a barrier. Through a combination of critical habitat assessment and the modelling of metapopulations, climate change‐driven habitat shifts, and adaptive gene flow, we recommend a conceptual and methodological framework for fishway target‐setting and monitoring suitable for a wide range of species. In the process, we raise a number of issues that should contribute to the ongoing debate about fish passage research and the design and monitoring of fishways.

Bidirectional connectivity via fish ladders in a large Neotropical river

“…Migrating animals occupy different habitats to complete segments of their lifecycle (Dingle & Drake, ; Godinho & Kynard, ). In impounded rivers, migrating fish must find, enter, and pass through artificial fishways, crossing the reservoir in route to their breeding grounds, and eventually backtrack their return downstream (Kraabøl et al, ; Wilkes, Webb, et al, ). This spatial–temporal connectivity is a key ecological requirement that environmental managers need to provide in artificially fragmented systems (Auffret, Plue, & Cousins, ).…”

Living in an amphidromous world: Perspectives on the management of fish passage from an island nation

“…Wilkes, Webb, et al () have recently emphasized the need to incorporate a consideration of spatial ecological processes in the research and management of fish passage, and this is particularly relevant for amphidromous species. Recognizing the existence of regional larval pools and source–sink population dynamics within amphidromous populations is critical to the spatial planning of fish‐passage management and to broader conservation efforts.…”

“…In contrast to many salmonids, most amphidromous species do not appear to undertake directed return migrations to natal streams, and thus conservation efforts and barrier mitigation should also consider broader regional meta‐population dynamics (sensu Wilkes, Webb, et al, ). For example, Hickford and Schiel () demonstrated the existence of source–sink population dynamics in Galaxias maculatus populations on the west coast of New Zealand owing to limitations on the availability of spawning habitat in some streams.…”

“…Consequently, considerable effort has been invested in understanding the science of fish passage with a view to mitigating the impacts of instream structures on migratory fish communities, particularly for iconic species such as salmonids in the temperate northern hemisphere (Birnie‐Gauvin, Franklin, Wilkes, & Aarestrup, ; Katopodis & Williams, ; Silva et al, ). The focus on developing solutions and strategies for fish passage of anadromous salmonids has, however, failed to appreciate the differences in migratory behaviour and abilities exhibited by amphidromous species when compared with anadromous species (Birnie‐Gauvin et al, ; Wilkes, Webb, et al, ).…”

Integrating multiple aquatic values: Perspectives and a collaborative future for river science

“…This is in part due to prevailing methodologies being based heavily on northern hemisphere species, such as Salmonidae, leading to the construction and monitoring of fishways often being unsuitable for the native species they are constructed to assist. Wilkes et al (2019) review recent advances in spatial ecology of stream networks to better define what effective fish passage may look like to meet the range of requirements for impacted fish species, including non‐diadromous species (e.g., gene flow, access to critical feeding, and reproductive habitats). Wilkes et al (2019) set out a conceptual and methodological framework for setting targets for assessing fishway success so they can better meet the different movement requirements for a greater proportion the species requiring fish passage in river corridors.…”