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

Abstract

1. Amphidromy is a form of migratory life history typified by the reproduction of fish in freshwater environments, the early downstream dispersal of post-hatch larvae to marine environments, and the return of small-bodied young juveniles to freshwater environments for growth to adulthood. Island freshwater fish communities are frequently dominated by fish species with amphidromous life histories.2. Amphidromous life cycles leave fish communities highly susceptible to habitat modification and disruptions to connectivity across marine and freshwater environments. This means that managing waterway connectivity is fundamental to their conservation; however, the unique and often geographically restricted amphidromous communities that characterize many small island nations have received little consideration in the development of strategies for the management of fish passage.3. The ecology and locomotory capabilities of amphidromous species are often poorly studied, partly because their small size at migratory life stages renders current state-of-the-art in situ biotelemetry methods unsuitable. The small size of fish also means that seemingly small obstructions can severely impede migrations. 4. The steps necessary to advance the management of fish passage for island fish communities are: curating and maintaining barrier inventories; evaluating barrier permeability; developing effective barrier mitigation options; and prioritizing restoration and conservation efforts. 5. New methods for understanding the ecology and locomotory capabilities and behaviour of amphidromous fishes are required to advance the management of fish passage for island fish communities. Fish passage solutions that imitate natural streams, such as those promoted in new guidelines in New Zealand, may be the most effective way of improving waterway connectivity; however, integrated approaches to freshwater fish conservation that account for meta-population dynamics, in combination with the management of fish passage, are necessary to optimize conservation outcomes for amphidromous species.

Water infrastructure and the migrations of amphidromous species: impacts and research requirements

“…Juvenile amphidromous species are often considered the most vulnerable life stage to impeded migrations, and as a result, a relatively large amount of research attention has been focussed on the upstream migrations of juveniles relative to larvae or adults heading downstream (Franklin and Gee 2019). Dams and other barriers, such as perched culverts, evidently alter the fish communities upstream in areas where amphidromous species are prevalent.…”

Mountains‐to‐the‐sea conservation: An island perspective

“…Franklin and Gee () emphasize the vulnerability of amphidromous fish species to passage disruption from instream barriers. Access is required in both upstream and downstream directions at key times of year for these fish to complete their life‐cycles, making fish passage a key conservation concern for island states such as New Zealand where amphidromous species dominate.…”

“…New Zealand's marine fauna and flora have a high level of endemism (over 50%), with 6,740 of 12,820 described species classified as endemic (Gordon, Beaumont, MacDiarmid, Robertson, & Ahyong, ). The level of endemism is much higher for native freshwater fish at around 90% of species (Franklin & Gee, ). Furthermore, many seabirds and migratory shorebirds, and some marine mammals (e.g.…”

A comparison of passage efficiency for native and exotic fish species over an artificial baffled ramp

“…Disruptions to connectivity (Franklin & Gee, 2019; Harris et al ., 2016; Wilkes et al ., 2018) and pressures from exotic species (Habit et al ., 2010; McDowall, 2006; Morgan et al ., 2004) are frequently cited as key threats to freshwater fish communities of the temperate Southern Hemisphere. These communities are characterised by a high level of genetic diversity and endemism ( e.g ., Morgan et al ., 2016; Waters & Wallis, 2001; Zemlak et al ., 2008), giving them high‐conservation value.…”

“…These communities are characterised by a high level of genetic diversity and endemism ( e.g ., Morgan et al ., 2016; Waters & Wallis, 2001; Zemlak et al ., 2008), giving them high‐conservation value. Many of these species are also small‐bodied and relatively weak swimming, meaning that seemingly small obstructions in waterways can impede migrations (Franklin & Gee, 2019; Mallen‐Cooper & Brand, 2007). Resolving the dichotomy between re‐establishing native fish migration pathways and managing the impacts and spread of exotic species is, therefore, a critical challenge for sustaining these fish communities.…”